The population uses quite a lot of LED rechargeable flashlights with built-in chargers, which often fail. In this article, the authors share their experience in repairing LED flashlights FO-DIK AN-0-005 and Cosmos A618LX.
LED flashlight FO-DIK AN-0-005 ( photo 1) made in Russia contains five LEDs, a battery with an operating voltage of 4...4.5 V and a built-in network charger (charger).
The schematic diagram of the FO-DIK AN-0-005 flashlight charger is shown in Fig.1.
After a short period of use, the flashlight stopped functioning. When disassembling the device, it was discovered that the tracks on the miniature printed circuit board of the flashlight were completely burned out, and the high-voltage diode VD2 ( Fig.1) out of order. Unfortunately, the positional part numbers on the board are not indicated. Therefore, the authors, creating a scheme Fig.1, indicated these numbers on it arbitrarily.
- high-voltage diodes VD1, VD2 type 1N4007 can be replaced by KD105B, V, G or KD209B, V; KD226V, G, D;
- high-voltage capacitor C1 with a rating of 0.68...1.5 µF x 400...630 V;
- resistors, type MLT-0.25, R1 with a nominal value of 560...620 kOhm, R2 - 220...330 Ohm;
- LED HL1 any miniature.
When connected to a 220 V network, the voltage on the battery should be 4.5...5 V, and the HL1 LED should light up.
On Fig.2 shows a diagram of the charger of the Cosmos A618LX flashlight, in which the super-bright LEDs have failed. As can be seen from Fig.2, the diagram of this lantern differs from the diagram Fig.1 only a full-wave rectifier using diodes VD1-VD4. The element values are similar Fig.1.
Having analyzed both circuits, we can conclude that if for some reason the flashlight’s battery fails or its electrodes are unsoldered, then when the charging flashlight is turned on, the 220 V mains voltage will disable all the flashlight’s super-bright LEDs. For this reason, when charging flashlights, it is not recommended to turn on (check) the flashlight being charged.
For safety and the ability to continue active activities in the dark, a person needs artificial lighting. Primitive people pushed back the darkness by setting fire to tree branches, then they came up with a torch and a kerosene stove. And only after the invention of the prototype of a modern battery by the French inventor George Leclanche in 1866, and the incandescent lamp in 1879 by Thomson Edison, did David Meisel have the opportunity to patent the first electric flashlight in 1896.
Since then, nothing has changed in the electrical circuit of new flashlight samples, until in 1923, Russian scientist Oleg Vladimirovich Losev found a connection between luminescence in silicon carbide and the p-n junction, and in 1990, scientists managed to create an LED with greater luminous efficiency, allowing them to replace a light bulb incandescent The use of LEDs instead of incandescent lamps, due to the low energy consumption of LEDs, has made it possible to repeatedly increase the operating time of flashlights with the same capacity of batteries and accumulators, increase the reliability of flashlights and practically remove all restrictions on the area of their use.
The LED rechargeable flashlight that you see in the photograph came to me for repair with a complaint that the Chinese Lentel GL01 flashlight I bought the other day for $3 does not light, although the battery charge indicator is on.
The external inspection of the lantern made a positive impression. High-quality casting of the case, comfortable handle and switch. The plug rods for connecting to a household network for charging the battery are made retractable, eliminating the need to store the power cord.
Attention! When disassembling and repairing the flashlight, if it is connected to the network, you should be careful. Touching exposed parts of a circuit connected to an electrical outlet may result in electric shock.
How to disassemble the Lentel GL01 LED rechargeable flashlight
Although the flashlight was subject to warranty repair, remembering my experiences during the warranty repair of a faulty electric kettle (the kettle was expensive and the heating element in it burned out, so it was not possible to repair it with my own hands), I decided to do the repair myself.
It was easy to disassemble the lantern. It is enough to turn the ring that secures the protective glass a small angle counterclockwise and pull it off, then unscrew several screws. It turned out that the ring is fixed to the body using a bayonet connection.
After removing one of the halves of the flashlight body, access to all its components appeared. On the left in the photo you can see a printed circuit board with LEDs, to which a reflector (light reflector) is attached using three screws. In the center there is a black battery with unknown parameters; there is only a marking of the polarity of the terminals. To the right of the battery there is a printed circuit board for the charger and indication. On the right is a power plug with retractable rods.
Upon closer examination of the LEDs, it turned out that there were black spots or dots on the emitting surfaces of the crystals of all LEDs. It became clear even without checking the LEDs with a multimeter that the flashlight did not light due to their burnout.
There were also blackened areas on the crystals of two LEDs installed as backlight on the battery charging indication board. In LED lamps and strips, one LED usually fails, and acting as a fuse, it protects the others from burning out. And all nine LEDs in the flashlight failed at the same time. The voltage on the battery could not increase to a value that could damage the LEDs. To find out the reason, I had to draw an electrical circuit diagram.
Finding the cause of the flashlight failure
The electrical circuit of the flashlight consists of two functionally complete parts. The part of the circuit located to the left of switch SA1 acts as a charger. And the part of the circuit shown to the right of the switch provides the glow.
The charger works as follows. The voltage from the 220 V household network is supplied to the current-limiting capacitor C1, then to a bridge rectifier assembled on diodes VD1-VD4. From the rectifier, voltage is supplied to the battery terminals. Resistor R1 serves to discharge the capacitor after removing the flashlight plug from the network. This prevents electric shock from capacitor discharge in the event of your hand accidentally touching two pins of the plug at the same time.
LED HL1, connected in series with current-limiting resistor R2 in the opposite direction with the upper right diode of the bridge, as it turns out, always lights up when the plug is inserted into the network, even if the battery is faulty or disconnected from the circuit.
The operating mode switch SA1 is used to connect separate groups of LEDs to the battery. As you can see from the diagram, it turns out that if the flashlight is connected to the network for charging and the switch slide is in position 3 or 4, then the voltage from the battery charger also goes to the LEDs.
If a person turns on the flashlight and discovers that it does not work, and, not knowing that the switch slide must be set to the “off” position, about which nothing is said in the flashlight’s operating instructions, connects the flashlight to the network for charging, then at the expense If there is a voltage surge at the output of the charger, the LEDs will receive a voltage significantly higher than the calculated one. A current that exceeds the permissible current will flow through the LEDs and they will burn out. As an acid battery ages due to sulfation of the lead plates, the battery charge voltage increases, which also leads to LED burnout.
Another circuit solution that surprised me was the parallel connection of seven LEDs, which is unacceptable, since the current-voltage characteristics of even LEDs of the same type are different and therefore the current passing through the LEDs will also not be the same. For this reason, when choosing the value of resistor R4 based on the maximum permissible current flowing through the LEDs, one of them may overload and fail, and this will lead to an overcurrent of parallel-connected LEDs, and they will also burn out.
Rework (modernization) of the electrical circuit of the flashlight
It became obvious that the failure of the flashlight was due to errors made by the developers of its electrical circuit diagram. To repair the flashlight and prevent it from breaking again, you need to redo it, replacing the LEDs and making minor changes to the electrical circuit.
In order for the battery charge indicator to actually signal that it is charging, the HL1 LED must be connected in series with the battery. To light an LED, a current of several milliamps is required, and the current supplied by the charger should be about 100 mA.
To ensure these conditions, it is enough to disconnect the HL1-R2 chain from the circuit in the places indicated by red crosses and install an additional resistor Rd with a nominal value of 47 Ohms and a power of at least 0.5 W in parallel with it. The charge current flowing through Rd will create a voltage drop of about 3 V across it, which will provide the necessary current for the HL1 indicator to light. At the same time, the connection point between HL1 and Rd must be connected to pin 1 of switch SA1. In this simple way, it will be impossible to supply voltage from the charger to the LEDs EL1-EL10 while charging the battery.
To equalize the magnitude of the currents flowing through the LEDs EL3-EL10, it is necessary to exclude resistor R4 from the circuit and connect a separate resistor with a nominal value of 47-56 Ohms in series with each LED.
Electrical diagram after modification
Minor changes made to the circuit increased the information content of the charge indicator of an inexpensive Chinese LED flashlight and greatly increased its reliability. I hope that LED flashlight manufacturers will make changes to the electrical circuits of their products after reading this article.
After modernization, the electrical circuit diagram took the form as in the drawing above. If you need to illuminate the flashlight for a long time and do not require high brightness of its glow, you can additionally install a current-limiting resistor R5, thanks to which the operating time of the flashlight without recharging will double.
LED battery flashlight repair
After disassembly, the first thing you need to do is restore the functionality of the flashlight, and then start upgrading it.
Checking the LEDs with a multimeter confirmed that they were faulty. Therefore, all the LEDs had to be desoldered and the holes freed from solder to install new diodes.
Judging by its appearance, the board was equipped with tube LEDs from the HL-508H series with a diameter of 5 mm. LEDs of type HK5H4U from a linear LED lamp with similar technical characteristics were available. They came in handy for repairing the lantern. When soldering LEDs to the board, you must remember to observe polarity; the anode must be connected to the positive terminal of the battery or battery.
After replacing the LEDs, the PCB was connected to the circuit. The brightness of some LEDs was slightly different from others due to the common current-limiting resistor. To eliminate this drawback, it is necessary to remove resistor R4 and replace it with seven resistors, connected in series with each LED.
To select a resistor that ensures optimal operation of the LED, the dependence of the current flowing through the LED on the value of the series-connected resistance was measured at a voltage of 3.6 V, equal to the voltage of the flashlight battery.
Based on the conditions for using the flashlight (in case of interruptions in the power supply to the apartment), high brightness and illumination range were not required, so the resistor was chosen with a nominal value of 56 Ohms. With such a current-limiting resistor, the LED will operate in light mode, and energy consumption will be economical. If you need to squeeze out maximum brightness from the flashlight, then you should use a resistor, as can be seen from the table, with a nominal value of 33 Ohms and make two modes of operation of the flashlight by turning on another common current-limiting resistor (in the diagram R5) with a nominal value of 5.6 Ohms.
To connect a resistor in series with each LED, you must first prepare the printed circuit board. To do this, you need to cut any one current-carrying path on it, suitable for each LED, and make additional contact pads. The current-carrying paths on the board are protected by a layer of varnish, which must be scraped off with a knife blade to the copper, as in the photograph. Then tin the bare contact pads with solder.
It is better and more convenient to prepare a printed circuit board for mounting resistors and soldering them if the board is mounted on a standard reflector. In this case, the surface of the LED lenses will not be scratched, and it will be more convenient to work.
Connecting the diode board after repair and modernization to the flashlight battery showed that the brightness of all LEDs was sufficient for illumination and the same brightness.
Before I had time to repair the previous lamp, a second one was repaired, with the same fault. I didn’t find any information about the manufacturer or technical specifications on the flashlight body, but judging by the manufacturing style and the cause of the breakdown, the manufacturer is the same, Chinese Lentel.
Based on the date on the flashlight body and on the battery, it was possible to establish that the flashlight was already four years old and, according to its owner, the flashlight worked flawlessly. It is obvious that the flashlight lasted a long time thanks to the warning sign “Do not turn on while charging!” on a hinged lid covering a compartment in which a plug is hidden for connecting the flashlight to the mains for charging the battery.
In this flashlight model, the LEDs are included in the circuit according to the rules; a 33 Ohm resistor is installed in series with each one. The resistor value can be easily recognized by color coding using an online calculator. A check with a multimeter showed that all the LEDs were faulty, and the resistors were also broken.
An analysis of the cause of the failure of the LEDs showed that due to sulfation of the acid battery plates, its internal resistance increased and, as a result, its charging voltage increased several times. During charging, the flashlight was turned on, the current through the LEDs and resistors exceeded the limit, which led to their failure. I had to replace not only the LEDs, but also all the resistors. Based on the above-mentioned operating conditions of the flashlight, resistors with a nominal value of 47 Ohms were chosen for replacement. The resistor value for any type of LED can be calculated using an online calculator.
Redesign of the battery charging mode indication circuit
The flashlight has been repaired, and you can begin making changes to the battery charging indication circuit. To do this, it is necessary to cut the track on the printed circuit board of the charger and indication in such a way that the HL1-R2 chain on the LED side is disconnected from the circuit.
The lead-acid AGM battery was deeply discharged, and an attempt to charge it with a standard charger was unsuccessful. I had to charge the battery using a stationary power supply with a load current limiting function. A voltage of 30 V was applied to the battery, while at the first moment it consumed only a few mA of current. Over time, the current began to increase and after a few hours increased to 100 mA. After fully charging, the battery was installed in the flashlight.
Charging deeply discharged lead-acid AGM batteries with increased voltage as a result of long-term storage allows you to restore their functionality. I have tested the method on AGM batteries more than a dozen times. New batteries that do not want to be charged from standard chargers are restored to almost their original capacity when charged from a constant source at a voltage of 30 V.
The battery was discharged several times by turning on the flashlight in operating mode and charged using a standard charger. The measured charge current was 123 mA, with a voltage at the battery terminals of 6.9 V. Unfortunately, the battery was worn out and was enough to operate the flashlight for 2 hours. That is, the battery capacity was about 0.2 Ah and for long-term operation of the flashlight it is necessary to replace it.
The HL1-R2 chain on the printed circuit board was successfully placed, and it was necessary to cut only one current-carrying path at an angle, as in the photograph. The cutting width must be at least 1 mm. Calculation of the resistor value and testing in practice showed that for stable operation of the battery charging indicator, a 47 Ohm resistor with a power of at least 0.5 W is required.
The photo shows a printed circuit board with a soldered current-limiting resistor. After this modification, the battery charge indicator lights up only if the battery is actually charging.
Modernization of the operating mode switch
To complete the repair and modernization of the lights, it is necessary to resolder the wires at the switch terminals.
In models of flashlights being repaired, a four-position slide-type switch is used to turn on. The middle pin in the photo shown is general. When the switch slide is in the extreme left position, the common terminal is connected to the left terminal of the switch. When moving the switch slide from the extreme left position to one position to the right, its common pin is connected to the second pin and, with further movement of the slide, sequentially to pins 4 and 5.
To the middle common terminal (see photo above) you need to solder a wire coming from the positive terminal of the battery. Thus, it will be possible to connect the battery to a charger or LEDs. To the first pin you can solder the wire coming from the main board with LEDs, to the second you can solder a current-limiting resistor R5 of 5.6 Ohms to be able to switch the flashlight to an energy-saving operating mode. Solder the conductor coming from the charger to the rightmost pin. This will prevent you from turning on the flashlight while the battery is charging.
Repair and modernization
LED rechargeable spotlight "Foton PB-0303"
I received another copy of a series of Chinese-made LED flashlights called the Photon PB-0303 LED spotlight for repair. The flashlight did not respond when the power button was pressed; an attempt to charge the flashlight battery using a charger was unsuccessful.
The flashlight is powerful, expensive, costs about $20. According to the manufacturer, the luminous flux of the flashlight reaches 200 meters, the body is made of impact-resistant ABS plastic, and the kit includes a separate charger and a shoulder strap.
LED flashlight Photon has good maintainability. To gain access to the electrical circuit, simply unscrew the plastic ring holding the protective glass, rotating the ring counterclockwise when looking at the LEDs.
When repairing any electrical appliances, troubleshooting always starts with the power source. Therefore, the first step was to measure the voltage at the terminals of the acid battery using a multimeter turned on in mode. It was 2.3 V, instead of the required 4.4 V. The battery was completely discharged.
When connecting the charger, the voltage at the battery terminals did not change, it became obvious that the charger was not working. The flashlight was used until the battery was completely discharged, and then it was not used for a long time, which led to a deep discharge of the battery.
It remains to check the serviceability of the LEDs and other elements. To do this, the reflector was removed, for which six screws were unscrewed. On the printed circuit board there were only three LEDs, a chip (chip) in the form of a droplet, a transistor and a diode.
Five wires went from the board and battery into the handle. In order to understand their connection, it was necessary to disassemble it. To do this, use a Phillips screwdriver to unscrew the two screws inside the flashlight, which were located next to the hole into which the wires went.
To detach the flashlight handle from its body, it must be moved away from the mounting screws. This must be done carefully so as not to tear the wires off the board.
As it turned out, there were no radio-electronic elements in the pen. Two white wires were soldered to the terminals of the flashlight on/off button, and the rest to the connector for connecting the charger. A red wire was soldered to pin 1 of the connector (the numbering is conditional), the other end of which was soldered to the positive input of the printed circuit board. A blue-white conductor was soldered to the second contact, the other end of which was soldered to the negative pad of the printed circuit board. A green wire was soldered to pin 3, the second end of which was soldered to the negative terminal of the battery.
Electrical circuit diagram
Having dealt with the wires hidden in the handle, you can draw an electrical circuit diagram of the Photon flashlight.
From the negative terminal of the battery GB1, voltage is supplied to pin 3 of connector X1 and then from its pin 2 through a blue-white conductor it is supplied to the printed circuit board.
Connector X1 is designed in such a way that when the charger plug is not inserted into it, pins 2 and 3 are connected to each other. When the plug is inserted, pins 2 and 3 are disconnected. This ensures automatic disconnection of the electronic part of the circuit from the charger, eliminating the possibility of accidentally turning on the flashlight while charging the battery.
From the positive terminal of battery GB1, voltage is supplied to D1 (microcircuit-chip) and the emitter of a bipolar transistor type S8550. The CHIP performs only the function of a trigger, allowing a button to turn on or off the glow of EL LEDs (⌀8 mm, glow color - white, power 0.5 W, current consumption 100 mA, voltage drop 3 V.). When you first press the S1 button from the D1 chip, a positive voltage is applied to the base of the transistor Q1, it opens and the supply voltage is supplied to the LEDs EL1-EL3, the flashlight turns on. When you press button S1 again, the transistor closes and the flashlight turns off.
From a technical point of view, such a circuit solution is illiterate, since it increases the cost of the flashlight, reduces its reliability, and in addition, due to the voltage drop at the junction of transistor Q1, up to 20% of the battery capacity is lost. Such a circuit solution is justified if it is possible to adjust the brightness of the light beam. In this model, instead of a button, it was enough to install a mechanical switch.
It was surprising that in the circuit, LEDs EL1-EL3 are connected in parallel to the battery like incandescent light bulbs, without current-limiting elements. As a result, when turned on, a current passes through the LEDs, the magnitude of which is limited only by the internal resistance of the battery and when it is fully charged, the current may exceed the permissible value for the LEDs, which will lead to their failure.
Checking the functionality of the electrical circuit
To check the serviceability of the microcircuit, transistor and LEDs, a 4.4 V DC voltage was applied from an external power source with a current limiting function, maintaining polarity, directly to the power pins of the printed circuit board. The current limit value was set to 0.5 A.
After pressing the power button, the LEDs lit up. After pressing again, they went out. The LEDs and the microcircuit with the transistor turned out to be serviceable. All that remains is to figure out the battery and charger.
Acid battery recovery
Since the 1.7 A acid battery was completely discharged, and the standard charger was faulty, I decided to charge it from a stationary power supply. When connecting the battery for charging to a power supply with a set voltage of 9 V, the charging current was less than 1 mA. The voltage was increased to 30 V - the current increased to 5 mA, and after an hour at this voltage it was already 44 mA. Next, the voltage was reduced to 12 V, the current dropped to 7 mA. After 12 hours of charging the battery at a voltage of 12 V, the current rose to 100 mA, and the battery was charged with this current for 15 hours.
The temperature of the battery case was within normal limits, which indicated that the charging current was not used to generate heat, but to accumulate energy. After charging the battery and finalizing the circuit, which will be discussed below, tests were carried out. The flashlight with a restored battery illuminated continuously for 16 hours, after which the brightness of the beam began to decrease and therefore it was turned off.
Using the method described above, I had to repeatedly restore the functionality of deeply discharged small-sized acid batteries. As practice has shown, only serviceable batteries that have been forgotten for some time can be restored. Acid batteries that have exhausted their service life cannot be restored.
Charger repair
Measuring the voltage value with a multimeter at the contacts of the output connector of the charger showed its absence.
Judging by the sticker pasted on the adapter’s body, it was a power supply that produced an unstabilized DC voltage of 12 V with a maximum load current of 0.5 A. There were no elements in the electrical circuit that limited the amount of charging current, so the question arose: why in Did you use a regular power supply as a charger?
When the adapter was opened, a characteristic smell of burnt electrical wiring appeared, which indicated that the transformer winding had burned out.
A continuity test of the primary winding of the transformer showed that it was broken. After cutting the first layer of tape insulating the primary winding of the transformer, a thermal fuse was discovered, designed for an operating temperature of 130°C. Testing showed that both the primary winding and the thermal fuse were faulty.
Repairing the adapter was not economically feasible, since it was necessary to rewind the primary winding of the transformer and install a new thermal fuse. I replaced it with a similar one that was on hand, with a DC voltage of 9 V. The flexible cord with a connector had to be resoldered from a burnt adapter.
The photo shows a drawing of the electrical circuit of a burnt-out power supply (adapter) of the Photon LED flashlight. The replacement adapter was assembled according to the same scheme, only with an output voltage of 9 V. This voltage is quite sufficient to provide the required battery charging current with a voltage of 4.4 V.
Just for fun, I connected the flashlight to a new power supply and measured the charging current. Its value was 620 mA, and this was at a voltage of 9 V. At a voltage of 12 V, the current was about 900 mA, significantly exceeding the load capacity of the adapter and the recommended battery charging current. For this reason, the primary winding of the transformer burned out due to overheating.
Finalization of the electrical circuit diagram
LED rechargeable flashlight "Photon"
To eliminate circuit violations in order to ensure reliable and long-term operation, changes were made to the flashlight circuit and the printed circuit board was modified.
The photo shows the electrical circuit diagram of the converted Photon LED flashlight. Additional installed radio elements are shown in blue. Resistor R2 limits the battery charging current to 120 mA. To increase the charging current, you need to reduce the resistor value. Resistors R3-R5 limit and equalize the current flowing through the LEDs EL1-EL3 when the flashlight is illuminated. The EL4 LED with a series-connected current-limiting resistor R1 is installed to indicate the battery charging process, since the developers of the flashlight did not take care of this.
To install current-limiting resistors on the board, the printed traces were cut, as shown in the photo. The charge current-limiting resistor R2 was soldered at one end to the contact pad, to which the positive wire coming from the charger had previously been soldered, and the soldered wire was soldered to the second terminal of the resistor. An additional wire (yellow in the photo) was soldered to the same contact pad, intended to connect the battery charging indicator.
Resistor R1 and indicator LED EL4 were placed in the flashlight handle, next to the connector for connecting the charger X1. The LED anode pin was soldered to pin 1 of connector X1, and a current-limiting resistor R1 was soldered to the second pin, the cathode of the LED. A wire (yellow in the photo) was soldered to the second terminal of the resistor, connecting it to the terminal of resistor R2, soldered to the printed circuit board. Resistor R2, for ease of installation, could have been placed in the flashlight handle, but since it heats up when charging, I decided to place it in a freer space.
When finalizing the circuit, MLT type resistors with a power of 0.25 W were used, except for R2, which is designed for 0.5 W. The EL4 LED is suitable for any type and color of light.
This photo shows the charging indicator while the battery is charging. Installing an indicator made it possible not only to monitor the battery charging process, but also to monitor the presence of voltage in the network, the health of the power supply and the reliability of its connection.
How to replace a burnt out CHIP
If suddenly a CHIP - a specialized unmarked microcircuit in a Photon LED flashlight, or a similar one assembled according to a similar circuit - fails, then to restore the flashlight's functionality it can be successfully replaced with a mechanical switch.
To do this, you need to remove the D1 chip from the board, and instead of the Q1 transistor switch, connect an ordinary mechanical switch, as shown in the above electrical diagram. The switch on the flashlight body can be installed instead of the S1 button or in any other suitable place.
Repair with modernization
LED flashlight Keyang KY-9914
Site visitor Marat Purliev from Ashgabat shared in a letter the results of repairing the Keyang KY-9914 LED flashlight. In addition, he provided a photograph, diagrams, a detailed description and agreed to publish the information, for which I express my gratitude to him.
Thank you for the article “Do-it-yourself repair and modernization of Lentel, Photon, Smartbuy Colorado and RED LED lights.”
Using examples of repairs, I repaired and upgraded the Keyang KY-9914 flashlight, in which four of the seven LEDs burned out, and the battery life expired. The LEDs burned out due to the switch being toggled while the battery was charging.
In the modified electrical diagram, changes are highlighted in red. I replaced the faulty acid battery with three used Sanyo Ni-NH 2700 AA batteries connected in series, which were on hand.
After reworking the flashlight, the LED consumption current in two switch positions was 14 and 28 mA, and the battery charging current was 50 mA.
Repair and alteration of LED flashlight
14Led Smartbuy Colorado
The Smartbuy Colorado LED flashlight stopped turning on, although three new AAA batteries were installed.
The waterproof body was made of anodized aluminum alloy and had a length of 12 cm. The flashlight looked stylish and was easy to use.
How to check batteries for suitability in an LED flashlight
Repairing any electrical device begins with checking the power source, therefore, despite the fact that new batteries were installed in the flashlight, repairs should begin with checking them. In the Smartbuy flashlight, the batteries are installed in a special container, in which they are connected in series using jumpers. In order to gain access to the flashlight batteries, you need to disassemble it by rotating the back cover counterclockwise.
Batteries must be installed in the container, observing the polarity indicated on it. The polarity is also indicated on the container, so it must be inserted into the flashlight body with the side on which the “+” sign is marked.
First of all, it is necessary to visually check all contacts of the container. If there are traces of oxides on them, then the contacts must be cleaned to a shine using sandpaper or the oxide must be scraped off with a knife blade. To prevent re-oxidation of the contacts, they can be lubricated with a thin layer of any machine oil.
Next you need to check the suitability of the batteries. To do this, touching the probes of a multimeter turned on in DC voltage measurement mode, you need to measure the voltage at the contacts of the container. Three batteries are connected in series and each of them should produce a voltage of 1.5 V, therefore the voltage at the terminals of the container should be 4.5 V.
If the voltage is less than specified, then it is necessary to check the correct polarity of the batteries in the container and measure the voltage of each of them individually. Perhaps only one of them sat down.
If everything is in order with the batteries, then you need to insert the container into the flashlight body, observing the polarity, screw on the cap and check its functionality. In this case, you need to pay attention to the spring in the cover, through which the supply voltage is transmitted to the flashlight body and from it directly to the LEDs. There should be no traces of corrosion on its end.
How to check if the switch is working properly
If the batteries are good and the contacts are clean, but the LEDs do not light, then you need to check the switch.
The Smartbuy Colorado flashlight has a sealed push-button switch with two fixed positions, closing the wire coming from the positive terminal of the battery container. When you press the switch button for the first time, its contacts close, and when you press it again, they open.
Since the flashlight contains batteries, you can also check the switch using a multimeter turned on in voltmeter mode. To do this, you need to rotate it counterclockwise, if you look at the LEDs, unscrew its front part and put it aside. Next, touch the flashlight body with one multimeter probe, and the second one to the contact, which is located deep in the center of the plastic part shown in the photo.
The voltmeter should show a voltage of 4.5 V. If there is no voltage, press the switch button. If it is working properly, then voltage will appear. Otherwise, the switch needs to be repaired.
Checking the health of the LEDs
If the previous search steps failed to detect a fault, then at the next stage you need to check the reliability of the contacts supplying the supply voltage to the board with LEDs, the reliability of their soldering and serviceability.
A printed circuit board with LEDs sealed into it is fixed in the head of the flashlight using a steel spring-loaded ring, through which the supply voltage from the negative terminal of the battery container is simultaneously supplied to the LEDs along the flashlight body. The photo shows the ring from the side it presses against the printed circuit board.
The retaining ring is fixed quite tightly, and it was only possible to remove it using the device shown in the photo. You can bend such a hook from a steel strip with your own hands.
After removing the retaining ring, the printed circuit board with LEDs, which is shown in the photo, was easily removed from the head of the flashlight. The absence of current-limiting resistors immediately caught my eye; all 14 LEDs were connected in parallel and directly to the batteries via a switch. Connecting LEDs directly to a battery is unacceptable, since the amount of current flowing through the LEDs is limited only by the internal resistance of the batteries and can damage the LEDs. At best, it will greatly reduce their service life.
Since all the LEDs in the flashlight were connected in parallel, it was not possible to check them with a multimeter turned on in resistance measurement mode. Therefore, the printed circuit board was supplied with a DC supply voltage from an external source of 4.5 V with a current limit of 200 mA. All LEDs lit up. It became obvious that the problem with the flashlight was poor contact between the printed circuit board and the retaining ring.
Current consumption of LED flashlight
For fun, I measured the current consumption of LEDs from batteries when they were turned on without a current-limiting resistor.
The current was more than 627 mA. The flashlight is equipped with LEDs of type HL-508H, the operating current of which should not exceed 20 mA. 14 LEDs are connected in parallel, therefore, the total current consumption should not exceed 280 mA. Thus, the current flowing through the LEDs more than doubled the rated current.
Such a forced mode of LED operation is unacceptable, as it leads to overheating of the crystal, and as a result, premature failure of the LEDs. An additional disadvantage is that the batteries drain quickly. They will be enough, if the LEDs do not burn out first, for no more than an hour of operation.
The design of the flashlight did not allow soldering current-limiting resistors in series with each LED, so we had to install one common one for all LEDs. The resistor value had to be determined experimentally. To do this, the flashlight was powered from standard batteries and an ammeter was connected to the gap in the positive wire in series with a 5.1 Ohm resistor. The current was about 200 mA. When installing an 8.2 Ohm resistor, the current consumption was 160 mA, which, as tests showed, is quite sufficient for good lighting at a distance of at least 5 meters. The resistor did not get hot to the touch, so any power will do.
Redesign of the structure
After the study, it became obvious that for reliable and durable operation of the flashlight, it is necessary to additionally install a current-limiting resistor and duplicate the connection of the printed circuit board with the LEDs and the fixing ring with an additional conductor.
If previously it was necessary for the negative bus of the printed circuit board to touch the body of the flashlight, then due to the installation of the resistor, it was necessary to eliminate the contact. To do this, a corner was ground off from the printed circuit board along its entire circumference, from the side of the current-carrying paths, using a needle file.
To prevent the clamping ring from touching the current-carrying tracks when fixing the printed circuit board, four rubber insulators about two millimeters thick were glued onto it with Moment glue, as shown in the photograph. Insulators can be made from any dielectric material, such as plastic or thick cardboard.
The resistor was pre-soldered to the clamping ring, and a piece of wire was soldered to the outermost track of the printed circuit board. An insulating tube was placed over the conductor, and then the wire was soldered to the second terminal of the resistor.
After simply upgrading the flashlight with your own hands, it began to turn on stably and the light beam illuminated objects well at a distance of more than eight meters. Additionally, the battery life has more than tripled, and the reliability of the LEDs has increased many times over.
An analysis of the causes of failure of repaired Chinese LED lights showed that they all failed due to poorly designed electrical circuits. It remains only to find out whether this was done intentionally in order to save on components and shorten the life of the flashlights (so that more people would buy new ones), or as a result of the illiteracy of the developers. I am inclined to the first assumption.
Repair of LED flashlight RED 110
A flashlight with a built-in acid battery from the Chinese manufacturer RED brand was repaired. The flashlight had two emitters: one with a beam in the form of a narrow beam and one emitting diffused light.
The photo shows the appearance of the RED 110 flashlight. I immediately liked the flashlight. Convenient body shape, two operating modes, a loop for hanging around the neck, a retractable plug for connecting to the mains for charging. In the flashlight, the diffused light LED section was shining, but the narrow beam was not.
To make the repair, we first unscrewed the black ring securing the reflector, and then unscrewed one self-tapping screw in the hinge area. The case easily separated into two halves. All parts were secured with self-tapping screws and were easily removed.
The charger circuit was made according to the classical scheme. From the network, through a current-limiting capacitor with a capacity of 1 μF, voltage was supplied to a rectifier bridge of four diodes and then to the battery terminals. The voltage from the battery to the narrow beam LED was supplied through a 460 Ohm current-limiting resistor.
All parts were mounted on a single-sided printed circuit board. The wires were soldered directly to the contact pads. The appearance of the printed circuit board is shown in the photograph.
10 side light LEDs were connected in parallel. The supply voltage was supplied to them through a common current-limiting resistor 3R3 (3.3 Ohms), although according to the rules, a separate resistor must be installed for each LED.
During an external inspection of the narrow beam LED, no defects were found. When power was supplied through the flashlight switch from the battery, voltage was present at the LED terminals, and it heated up. It became obvious that the crystal was broken, and this was confirmed by a continuity test with a multimeter. The resistance was 46 ohms for any connection of the probes to the LED terminals. The LED was faulty and needed to be replaced.
For ease of operation, the wires were unsoldered from the LED board. After freeing the LED leads from the solder, it turned out that the LED was tightly held by the entire plane of the reverse side on the printed circuit board. To separate it, we had to fix the board in the desktop temples. Next, place the sharp end of the knife at the junction of the LED and the board and lightly hit the knife handle with a hammer. The LED bounced off.
As usual, there were no markings on the LED housing. Therefore, it was necessary to determine its parameters and select a suitable replacement. Based on the overall dimensions of the LED, the battery voltage and the size of the current-limiting resistor, it was determined that a 1 W LED (current 350 mA, voltage drop 3 V) would be suitable for replacement. From the “Reference Table of Parameters of Popular SMD LEDs,” a white LED6000Am1W-A120 LED was selected for repair.
The printed circuit board on which the LED is installed is made of aluminum and at the same time serves to remove heat from the LED. Therefore, when installing it, it is necessary to ensure good thermal contact due to the tight fit of the rear plane of the LED to the printed circuit board. To do this, before sealing, thermal paste was applied to the contact areas of the surfaces, which is used when installing a radiator on a computer processor.
In order to ensure a tight fit of the LED plane to the board, you must first place it on the plane and slightly bend the leads upward so that they deviate from the plane by 0.5 mm. Next, tin the terminals with solder, apply thermal paste and install the LED on the board. Next, press it to the board (it’s convenient to do this with a screwdriver with the bit removed) and warm up the leads with a soldering iron. Next, remove the screwdriver, press it with a knife at the bend of the lead to the board and heat it with a soldering iron. After the solder has hardened, remove the knife. Due to the spring properties of the leads, the LED will be pressed tightly to the board.
When installing the LED, polarity must be observed. True, in this case, if a mistake is made, it will be possible to swap the voltage supply wires. The LED is soldered and you can check its operation and measure the current consumption and voltage drop.
The current flowing through the LED was 250 mA, the voltage drop was 3.2 V. Hence the power consumption (you need to multiply the current by the voltage) was 0.8 W. It was possible to increase the operating current of the LED by decreasing the resistance to 460 Ohms, but I did not do this, since the brightness of the glow was sufficient. But the LED will operate in a lighter mode, heat up less, and the flashlight’s operating time on a single charge will increase.
Testing the heating of the LED after operating for an hour showed effective heat dissipation. It heated up to a temperature of no more than 45°C. Sea trials showed a sufficient illumination range in the dark, more than 30 meters.
Replacing a lead acid battery in an LED flashlight
A failed acid battery in an LED flashlight can be replaced with either a similar acid battery or a lithium-ion (Li-ion) or nickel-metal hydride (Ni-MH) AA or AAA battery.
The Chinese lanterns being repaired were equipped with lead-acid AGM batteries of various sizes without markings with a voltage of 3.6 V. According to calculations, the capacity of these batteries ranges from 1.2 to 2 A×hours.
On sale you can find a similar acid battery from a Russian manufacturer for the 4V 1Ah Delta DT 401 UPS, which has an output voltage of 4 V with a capacity of 1 Ah, costing a couple of dollars. To replace it, simply re-solder the two wires, observing the polarity.
After several years of operation, the Lentel GL01 LED flashlight, the repair of which was described at the beginning of the article, was again brought to me for repair. Diagnostics showed that the acid battery had exhausted its service life.
A Delta DT 401 battery was purchased as a replacement, but it turned out that its geometric dimensions were larger than the faulty one. The standard flashlight battery had dimensions of 21x30x54 mm and was 10 mm higher. I had to modify the flashlight body. Therefore, before buying a new battery, make sure that it will fit into the flashlight body.
The stop in the case was removed and a part of the printed circuit board from which a resistor and one LED had previously been soldered off was cut off with a hacksaw.
After modification, the new battery installed well in the flashlight body and now, I hope, will last for many years.
Replacing a lead acid battery
AA or AAA batteries
If it is not possible to purchase a 4V 1Ah Delta DT 401 battery, then it can be successfully replaced with any three AA or AAA size AA or AAA pen-type batteries, which have a voltage of 1.2 V. For this, it is enough connect three batteries in series, observing polarity, using soldering wires. However, such a replacement is not economically feasible, since the cost of three high-quality AA-size AA batteries may exceed the cost of purchasing a new LED flashlight.
But where is the guarantee that there are no errors in the electrical circuit of the new LED flashlight, and that it will not have to be modified either. Therefore, I believe that replacing the lead battery in a modified flashlight is advisable, as it will ensure reliable operation of the flashlight for several more years. And it will always be a pleasure to use a flashlight that you have repaired and modernized yourself.
Another Chinese lantern has broken. Buying a new one is not a problem, but I would like a proven and trouble-free device. It was decided to assemble a homemade flashlight, fortunately there were many, many batteries, LEDs, and all sorts of SMD powder. So, what I would like to see inside the flashlight:
- High quality LED
- Lens that focuses the beam
- Driver for limiting current via LED
- Controller for automatic battery charging, with indication
- Battery protection circuit
- Capacious battery so that the flashlight can work for about 10 hours
- Turn on/off with a tact button
No sooner said than done. Flashlight diagram:
The circuit does not contain microcontrollers, does not require configuration, and starts working immediately after assembly. Everything works as follows. When battery G1 is connected, circuit C6R8 resets counter DD1 to its original state. Button SB1 is connected to the counting input of the counter DD1 through the anti-bounce circuit C8R11R12. Pressing the button triggers the counter, as a result, a logical 1 appears at the OUT1 pin, and the DA2 LED driver turns on. The driver output current is 350 mA. When you press the button again, a logical 1 appears at the OUT2 output, and through the VD3 diode the counter is reset to its original state, the DA2 LED driver is turned off. The DA1 chip contains a charging circuit; resistor R1 sets the desired charging current. In this circuit, the current is limited to 500 mA, since the USB port is used. When charging, the counter chip DD1 is reset through circuit R10VD4. Thus, the operation of the flashlight is blocked during charging, and nothing interferes with the charging process. Chip DA3 and transistor VT1 form a protection circuit against battery discharge. Power is supplied to the protection controller DA3 through diodes VD1, VD2. This is necessary to raise the protection threshold to 3 volts.
Finding a suitable case turned out to be much more difficult than coming up with a design. The choice fell on a plastic plumbing coupling.
Drilled holes in the plugs.
The board is located in the middle of the pipe and occupies the entire internal area. This eliminates the need for fastening; the board sits inside like a glove.
On one side of the board there are batteries, a USB connector for charging, and a control button.
On the other side there are SMD components and a heatsink for cooling the LED.
The radiator size is somewhat small, but overall there is enough cooling. The current through the LED is only 350 mA.
The board is located between the radiator and batteries.
I installed a CREE XPGWHT-L1-0000-00EE7 LED with a warm white glow on the radiator.
I installed optics R-20XP01-30H, angle 30 degrees.
I screwed the LED and optics to the radiator.
To monitor the battery charging process, I made a light guide from plexiglass.
We insert the insides into the body.
We install plugs. The result is such a brutal flashlight.
Back view.
The indicator glows orange while charging.
When charging is complete, the indicator changes color to green.
One charge lasts for 9 hours. I'm pleased with the result.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| DD1 | Chip | HCF4017 | 1 | To notepad | ||
| DA1 | Charge controller | TP4056 | 1 | To notepad | ||
| DA2 | Chip | AMC7135 | 1 | To notepad | ||
| DA3 | Chip | DW01p | 1 | To notepad | ||
| VT1 | Transistor | FS8205 | 1 | To notepad | ||
| VD1-VD4 | Rectifier diode | LL4148 | 4 | To notepad | ||
| R1 | Resistor | 2.7 kOhm | 1 | To notepad | ||
| R2, R3, R7 | Resistor | 330 Ohm | 3 | To notepad | ||
| R4, R5 | Resistor | 0 ohm | 2 | To notepad | ||
| R6 | Resistor | 100 Ohm | 1 | To notepad | ||
| R9, R10, R12 | Resistor | 1 kOhm | 3 | To notepad | ||
| R8 | Resistor | 10 kOhm | 1 | To notepad | ||
| R11 | Resistor | 20 kOhm | 1 | To notepad | ||
| C1, C5, C6, C7 | Capacitor | 100 nF | 4 | To notepad | ||
| C3, C4 | Capacitor | 10 µF | 2 | To notepad | ||
| C2 | Tantalum capacitor | 47 µF | 1 |
If for some reason it is impossible to use a stationary electrical network, and the household does not have a portable, autonomous lamp, then you can assemble an LED lamp with your own hands.
Advantages of LED lamps
LED lighting elements are displacing conventional incandescent lamps from the market. This is due to a number of advantages of LED technology:
- The emission of light in semiconductors occurs more intensely. They are 8 times brighter than incandescent lamps, and also work better than sodium or energy-saving devices.
- Due to their high efficiency compared to common light bulbs, LEDs can save from 60 to 90% of electricity. LED devices consume less resources than energy-saving devices (by 15-20%).
- The maintenance cost of semiconductors is lower because they have few failures and failures. LEDs are used in difficult operating conditions - for emergency systems, on high-rise architectural objects, in structures with expensive installation, in bridge lighting.
- New devices are installed quickly, with considerable savings in cable costs, which in semiconductors require a smaller diameter.
- Service life of LED devices: more than 15 years when operating 8 hours a day.
- Low voltage is used to power LEDs. This makes their installation and operation safer than equipment designed for 220/380 V.
- Semiconductors have good resistance to vibration, increased mechanical strength, and high temperature characteristics.
- The color rendering index of semiconductor devices exceeds 80. Without wasting energy and using filters, the devices are able to provide deep and pure colors of light.
- LED devices are suitable for timers, volume sensors, dimmers (light intensity regulators). LEDs are widely used in programmable equipment with variable lighting intensity.
- There are no ultraviolet and infrared radiation in diode products, the light is monochromatic, there is no strobing or glare. This allows them to be used in lighting systems of various purposes, sizes and shapes.
- LEDs have a minimum start-up time. Even in frosty weather, the device instantly reaches the color temperature and the specified light level.
- Due to the absence of harmful radiation and heat, semiconductors can be safely used for medical purposes, as well as for lighting rooms with people, animals and plants.
- The devices are recycled after their intended service life without producing environmentally hazardous substances.
LED rechargeable flashlight circuit
Simple circuits with conventional lamps are energy-consuming. They have a weak luminous flux and lead to rapid failure of the lamps. To get rid of these disadvantages, more complex devices are used with batteries instead of batteries and LEDs that replace incandescent lamps.
To improve the performance of the flashlight, additional elements are included in its circuit:
- Charging is carried out from a 220 V network through a rectifier using a smoothing capacitor C1. The circuit is designed to convert some of the electricity into heat and limit the voltage applied to the battery.
- To indicate the charging process, the VD1 LED is included in the circuit.
- LEDs are used as load in the flashlight.
To operate the LEDs in this circuit, 2 AA batteries are used. DFL-OSPW5111P has high light brightness (30 cd). The current required for operation is 80 mA. The device glows white.
A ready-made unit is often used as a voltage stabilizer - the ADP1110 (1111) microcircuit, which belongs to the family of switching regulators capable of operating from power supplies with voltages from 2 to 12 V. The device has stationary outputs 12 V, 5.5 V, 3.3 V .
It is possible to program different operating modes of the microcircuit:
- 200 mA at 5 V if using 12 V input and buck mode;
- 100 mA at 5 V from 3 V output and boost mode.
Power from any type of battery is supplied to a relatively large DC capacitor and from its plates to the ADP1110. For example, “tablets” can be used as an energy source.
To additionally filter the voltage and limit current ripple, the circuit uses an inductor and a Schottky diode. In the latter, due to the metal-conductor transition, a barrier effect occurs. The device is characterized by low forward resistance, increased speed and low junction capacitance.
Required components for assembly
To assemble a flashlight with your own hands you will need:
- copper wires;
- batteries (“tablets”) or accumulator;
- LEDs;
- device for placing a power source;
- soldering iron and solder;
- glue - liquid nails, epoxy resin, superglue (it is better to have a gun for precise application);
- switch;
- details of the voltage stabilizer depending on the circuit (you can use a microcharging module, for example, TP4056; or assemble a circuit from individual elements yourself);
- flashlight body;
- lenses for LED.
How to assemble it yourself?
Assembling an LED flashlight is not difficult if you have minimal skills in working with a soldering iron. For example, you can use an old personal computer motherboard and remove a “pocket” from it to hold the battery. This should be done carefully so as not to damage the surface and contacts.
The body of a small flashlight can be made from a syringe. To do this, use a paint knife to cut off the cone on which the needle is installed and remove the piston.
To avoid overheating of the LED, a radiator must be cut from an aluminum plate to the size of the lens. Using superglue, the lens holder housing is connected to the aluminum heatsink.
Solder the diode contacts with copper wire. As insulation, you can use a thermal casing and a lighter.
The part with the lens and LED should be secured with glue to the body of the syringe.
We connect the LED contacts to the battery contacts and insert them into the structure.
If the charging module board does not fit into the remaining part of the syringe, it can be divided into two parts and connected together with tape. Broken contacts should be soldered with copper wire.
The microswitch must be connected through a resistor to the charging module board. The remaining contacts of the module are connected in accordance with the diagram.
After assembling the flashlight, a micro-USB connector and a switch button should remain on the surface. If the work is done correctly, such a flashlight will work for 10-12 hours on a single charge.
Finalization of the finished LED flashlight
In some cases, it is easier to buy an inexpensive ready-made LED flashlight and, with the help of small improvements, make a more advanced model.
For example, in the HG-528 HUAGE device and flashlights similar in circuit design, diodes EL1-EL5 often fail. The problem arises because owners often forget to disconnect semiconductor elements when charging from the mains.
You can modify your flashlight so that it will be impossible to charge unless you change the position of the SA1 switch so as to turn off the LEDs. In addition, the short-lived batteries of these devices can be replaced with more energy-intensive lithium-ion devices from mobile phones. Why are rectifier diodes VD1-VD4 and a filter consisting of capacitance C1 and two resistors R1, R2 removed from the flashlight?
After a small cutting of the plastic parts of the case, a cell phone battery is placed in the vacant space. The latter is connected with a copper wire to the device circuit.
The developers of the Lentel GL01 LED rechargeable flashlight made an error in the electrical circuit, which also leads to failure of the device if it is turned on for charging when the LEDs are not turned off. In addition, 7 diodes are connected in parallel, which causes the unevenness of the current flowing through them during operation of the flashlight due to the different current-voltage characteristics of the semiconductor elements. This leads to frequent burnout of both the LEDs themselves and resistor R4.
If individual resistors (45 - 55 Ohms) are connected in series with each LED, and resistor R4 is removed from the circuit, then the current values will be equalized. To prevent voltage from reaching the LEDs of the charger while charging the battery, you need to connect HL1 (indicator) to the first pin SA1.
How to repair an LED flashlight?
The most common causes of breakdowns of flashlights that use LEDs as lighting devices are:
- LED malfunctions;
- lack of supply voltage in the circuit;
- breakage of the switch;
- failure of the wires that go from the LED to the battery;
- the contacts to which the batteries are connected have oxidized;
- breakdown or burnout of electronic circuit elements.
For example, repairing an LED pen flashlight often involves replacing the KT315 field-effect transistor, which in the circuit is connected in series with one of the windings of the high-frequency transformer T1. LED VD1 is located parallel to the transistor, which is the load of the blocking generator.
The choice by developers of such an element as KT315 is associated with its low cost. Therefore, when repairing a device, instead of the installed conductor device, you can use other types of transistors with a frequency of more than 200 MHz.
If you need to replace the transformer, you will need a wire with a diameter of 0.2 mm.
It is necessary to wind 20 turns for each winding in the case when a ferromagnetic ring is used. In the absence of the latter, a cylinder is suitable, on which you will need to wind windings of 100 turns each.
Repair of the device should begin with an external inspection of the lighting and electronic circuit elements and wires. In the absence of obvious signs of malfunction - burnt parts, broken connections, the presence of plaque and oxides that disrupt normal electrical contact - you will need measuring instruments that can be used to detect failed electronic parts.
Nowadays, power outages have become very frequent, so in amateur radio literature a lot of attention is paid to local power sources. Not very energy-intensive, but very useful during emergency shutdowns, is a compact rechargeable flashlight (AKF), the battery of which uses three sealed nickel-cadmium disk batteries D 0.25. The failure of the ACF for one reason or another causes considerable disappointment. However, if you apply a little ingenuity, understand the design of the flashlight itself and know basic electrical engineering, then it can be repaired, and your little friend will serve you for a long time and reliably.
Circuit design. Design
Let's start, as expected, by studying the instruction manual 2.424.005 R3 Rechargeable flashlight "Electronics V6-05". Inconsistencies begin immediately after a careful comparison of the electrical circuit diagram (Fig. 1) and the design of the flashlight. In the circuit, the plus comes from the battery, and the minus is connected to the HL1 light bulb.
In reality, the coaxial terminal HL1 is permanently connected to the plus of the battery, and the minus is connected through S1 to the threaded socket. Having carefully examined the installation connections, we immediately notice that HL1 is not connected according to the diagram, capacitor C1 is not connected to VD1 and VD2, as shown in Fig. 1, but to the elastic contact of the structure, pressing the minus battery, which is structurally and technologically convenient, since C1, as the largest element, it is quite rigidly mounted with structural elements - one of the pins of the power plug, structurally combined with the ACF housing and the battery spring contact; resistor R2 is not connected in series with capacitor C1, but is soldered with one end to the second pin of the power plug, and the other to the holder. U1. This is also not taken into account in the ACF scheme in . The remaining connections correspond to the diagram shown in Fig. 2.
But if you do not take into account the design and technological advantages, which are quite obvious, then in principle it does not matter how C1 is connected, according to Fig. 1 or Fig. 2. By the way, with a good idea to refine the AKF charger circuit, it was not possible to avoid the use of “extra” elements.
The memory circuit, while maintaining the general algorithm, can be significantly simplified by assembling it according to Fig. 3.
The difference is that elements VD1 and VD2 in the diagram in Fig. 3 perform two functions, which made it possible to reduce the number of elements. Zener diode VD1 for the negative half-wave of the supply voltage on VD1, VD2 serves as a rectifier diode, it is also a source of positive reference voltage for the comparison circuit (CC), the (second) function of which is also performed by VD2. CC works as follows: when the EMF value at the cathode VD2 is less than the voltage at its anode, the normal process of charging the battery occurs. As the battery charges, the EMF value on the battery increases, and when it reaches the voltage at the anode, VD2 will close and the charge will stop. The value of the reference voltage VD1 (stabilization voltage) must be equal to the sum of the voltage drop in the forward direction across VD2 + voltage drop across R3VD3 + battery emf and is selected for a specific charge current and specific elements. The emf of a fully charged disk is 1.35 V.
With this charging scheme, the LED, as an indicator of the battery charge state, lights up brightly at the beginning of the process, as it charges, its brightness decreases, and when it reaches full charge, it goes out. If during operation it is noticed that the product of the charge current and the glow time of VD3 in hours is significantly less than the value of its theoretical capacity, then this does not indicate that the comparator on VD2 is not working correctly, but that one or more disks have insufficient capacity.
terms of Use
Now let's analyze the charge and discharge of the battery. According to specifications (12MO.081.045), the charging time for a completely discharged battery at a voltage of 220 V is 20 hours. The charging current at C1 = 0.5 μF, taking into account the spread in capacity and fluctuations in the supply voltage, is about 25-28 mA, which corresponds to the recommendations, and The recommended discharge current is twice the charging current, i.e. 50
mA. The number of complete charge-discharge cycles is 392. In a real ACF design, the discharge is carried out on a standard 3.5 V x 0.15 A light bulb (with three disks), although it gives an increase in brightness, but also due to an increase in current from the battery in excess of that recommended by the specifications , negatively affects the service life of the battery, so such a replacement is hardly advisable, since in some copies of the disks this can cause increased gas formation, which in turn will lead to an increase in pressure inside the housing and to a deterioration in the internal contact made by the disc spring between the tablet package active substance and the minus part of the body. This also leads to the release of electrolyte through the seal, causing corrosion and associated deterioration of contact both between the disks themselves and between the disks and the metal elements of the AKF structure.
In addition, due to leakage, water evaporates from the electrolyte, resulting in an increase in the internal resistance of the disk and the entire battery. With further operation of such a disk, it completely fails as a result of the conversion of the electrolyte partly into crystalline KOH, partly into potash K2CO3. It is for these reasons that special attention must be paid to charge-discharge issues.
Practical repair
So, one of the three batteries has gone bad. You can assess its condition with an Avometer. To do this (in the appropriate polarity), each disk is briefly short-circuited with the probes of an avometer set to measure direct current within 2-2.5 A.
For good, freshly charged disks, the short-circuit current should be within 2-3 A. When repairing an ACF, two logical options may arise: 1) there are no spare disks; 2) there are spare disks.
In the first case, this solution will be the simplest. Instead of the third, unusable disk, a washer is installed from the copper body of an unusable transistor of the KT802 type, which, moreover, fits well in size into most AKF designs. To make a washer, remove the terminals of the transistor electrodes and clean both ends with a fine file from the coating until copper appears, then they are ground on fine-grained sanding paper laid on a flat plane, after which they are polished to a shine on a piece of felt with an applied layer of GOI paste. All these operations are necessary to reduce the influence of contact resistance on the combustion time. The same applies to the contact ends of the disks, the darkened surfaces of which during operation are desirable to be sanded for the same reasons.
Since removing one disk will lead to a decrease in the brightness of the HL1 glow, a 2.5 V light bulb at 0.15 A is installed in the AKF or, even better, a 2.5 V light bulb at 0.068 A, which, although it has less power, reduces the current discharge makes it possible to bring it closer to that recommended by the specifications, which will have a beneficial effect on the life of the battery disks. Practical disassembly and analysis of correctable causes of disk failure showed that quite often the cause of failure is the destruction of the disc spring. Therefore, do not rush to throw away an unusable disk and, if you are lucky, you can make it work some more. This operation will require sufficient accuracy and certain plumbing skills.
To carry it out, you will need a small bench vice, a ball from a ball bearing with a diameter of about 10 mm and a smooth steel plate 3-4 mm thick. The plate is placed through a 1mm thick electrical cardboard gasket between the jaws and the positive part of the body, and the ball is placed between the second jaw and the negative part of the body, orienting the ball approximately at its center. The electrical cardboard gasket is designed to eliminate short circuits of the disk, and the plate is designed to uniformly distribute the force and prevent deformation of the positive part of the battery case from notching on the jaws of the vice. Their size is obvious. Gradually tighten the vice. Having pressed the ball 1-2 mm, remove the disk from the device and control the short-circuit current. Usually, after one or two clamps, more than half of the charged disks begin to show an increase in short-circuit current up to 2-2.5 A. After a certain stroke, the clamping force increases sharply, which means that the deformable part of the housing rests on the tablet. Further pressing is impractical, since it leads to destruction of the battery. If after the stop the short-circuit current does not increase, then the disk is completely unusable.
In the second case, simply replacing the disk with another one may also not bring the desired result, since fully functional disks have so-called “capacitive” memory.
Due to the fact that when operating in a battery, there is always at least one disk that has less than the capacity value, which is why when it is discharged, the internal resistance sharply increases, which limits the possibility of complete discharge of the remaining disks. It is not advisable to subject such a battery to some recharging to eliminate this phenomenon, since this will not lead to an increase in capacity, but only to failure of the best drives. Therefore, when replacing at least one disk in a battery, it is advisable to subject them all to forced training (give one full charge-discharge cycle) to eliminate the above phenomena. The charge of each disk is carried out in the same ACF, using washers made of transistors instead of two disks.
The discharge is carried out on a resistor with a resistance of 50 Ohms, providing a discharge current of 25 mA (which corresponds to the specifications), until the voltage across it reaches 1 V. After this, the disks are combined into a battery and charged together. Having charged the entire battery, discharge it to the standard HL until the battery reaches 3 V. Under a load of the same HL, check the short-circuit current of each disk discharged to 1 V again.
For disks suitable for operation as part of a battery, the short-circuit current of each disk should be approximately the same. The battery capacity can be considered sufficient for practical use if the discharge time to 3 V is 30-40 minutes.
Details
Fuse.U1. Having observed the evolution of ACF circuitry during repairs for about two decades, it was noticed that in the mid-80s some enterprises began to produce batteries without fuses with a current-limiting resistor of 0.5 W and a resistance of 150-180 Ohms, which is quite justified, since in the event of a breakdown The C1 role. U1 was played by R2 (Fig. 1) or R2 (Fig. 2 and 3), the conductive layer of which evaporated much earlier (than U1 burned at 0.15 A), interrupting the circuit, which is what is required from the fuse. Practice confirms that if a current-limiting resistor with a power of 0.5 W in a real ACF circuit heats up noticeably, then this clearly indicates a significant leakage C1 (which is difficult to determine with an avometer, and also due to changes in its value over time), and it must be replaced .
Capacitor C1 type MBM 0.5 µF at 250 V is the most unreliable element. It is designed for use in DC circuits with the appropriate voltage, and the use of such capacitors in AC networks, when the voltage amplitude in the network can reach 350 V, and taking into account the presence in the network of numerous peaks from inductive loads, as well as the charging time of a completely discharged ACF according to the specifications (about 20 hours), then its reliability as a radio element becomes very low. The most reliable capacitor, which has optimal dimensions that allow it to fit into ACFs of various design sizes, is the capacitor K42U-2 0.22 μF Ch 630 V or even K42U 0.1 μF Ch 630 V. Reducing the charging current to approximately 15-18 mA, at 0.22 μF and up to 8-10 mA at 0.1 μF, practically only causes an increase in its charging time, which is not significant.
LED indicator of charging current VD3. In ACFs that do not have an LED indicator of the charge current, it can be installed by connecting it to the open circuit at point A (Fig. 2).
The LED is connected in parallel with the measuring resistor R3 (Fig. 4), which must be selected when making a new one or reducing C1. With capacitance C1 equal to 0.22 μF instead of 0.5 μF, the brightness of VD3 will decrease, and at 0.1 μF VD3 may not light up at all. Therefore, taking into account the above charge currents, in the first case, resistor R3 must be increased in proportion to the decrease in current, and in the second case, it must be removed completely. In practice, taking into account the fact that working with 220 V is very unsafe, it is better to select the resistance R3 by connecting an adjustable direct current source (RIPS) through a milliammeter to point B (Fig. 3), and controlling the charge current. Instead of R3, a potentiometer with a resistance of 1 kOhm is temporarily connected, turned on by a rheostat to the minimum resistance. By increasing the RIPT voltage, the battery charging current is set to 25 mA.
Without changing the set voltage of the RIPT, connect the milliammeter to the open circuit VD3 at point C and, gradually increasing the resistance of the potentiometer, achieve a current through it of 10 mA, i.e. half of the maximum for AL307. This point is especially important for circuits without a zener diode, in which, at the first moment after switching on when charging C1, the current through VD3 can become large, despite the presence of a current-limiting resistor R1, and can lead to VD3 failure. In steady state, R1 has virtually no effect on the charge current due to its low resistance compared to the reactive (about 9 kOhm) resistance C1. When modifying, VD3 is installed in a hole with a diameter of 5 mm, drilled symmetrically to the parting line in the housing between the supports of the spring contact connected to the coaxial terminal HL1 and the battery positive. The measuring resistor is placed there.
Rectifier diodes
Considering the presence of a current surge during the initial charge of C1, to increase reliability in the AKF rectifier, it is advisable to use any silicon pulse diodes with a reverse voltage of 30 V or more.
Non-standard use of ACF
By making an adapter from the base of an unusable light bulb and the power connector of a radio receiver, the AKF can be used not only as a light source, but also as a source of secondary power supply with a voltage of 3.75 V. At an average volume level (consumption current 20-25 mA), its capacity is quite sufficient for listening to VEF for several hours.
In some cases, in the absence of electricity, the ACF can be recharged from a radio broadcast line. Owners of AKF with an LED indicator can observe the process of dynamic blinking of the LED. VD3 burns especially smoothly from “heavy” rock, so if you don’t like listening, charge the ACF, use the energy for peaceful purposes. The physical meaning of this phenomenon is that reactance decreases with increasing frequency, therefore, at a significantly lower voltage (15-30 V), the pulsed value of the charge current through the indicator is sufficient for it to glow and, naturally, recharge.
Literature:
- Vuzetsky V.N. Charger for a rechargeable flashlight // Radioamator. - 1997. - No. 10. - P. 24.
- Tereshchuk R.M. and others. Semiconductor receiving and amplifying devices: Reference. radio amateur. - Kyiv: Nauk. Dumka, 1988