There are times in every person’s life when lighting is needed, but there is no electricity. This could be a simple power outage, or the need to repair the wiring in the house, or perhaps a forest hike or something similar.

And, of course, everyone knows that in this case, only an electric flashlight will help out - a compact and at the same time functional device. Now there are many different types of this product on the electrical equipment market. These include regular flashlights with incandescent lamps, and LED flashlights with rechargeable batteries. And there are a great many companies producing these devices - “Dick”, “Lux”, “Cosmos”, etc.

But not many people think about the principle of its operation. Meanwhile, knowing the structure and circuit of an electric flashlight, you can, if necessary, repair it or even assemble it with your own hands. Let's try to figure this out.

The simplest lanterns

Since flashlights are different, it makes sense to start with the simplest thing - with a battery and an incandescent lamp, and also consider its possible malfunctions. The circuit diagram of such a device is elementary.

In fact, there is nothing in it except a battery, a power button and a light bulb. And therefore there are no special problems with it. Here are a few possible minor troubles that may result in the failure of such a flashlight:

• Oxidation of any of the contacts. These could be the contacts of a switch, light bulb or battery. You just need to clean these circuit elements, and the device will work again.
• Burning out of an incandescent lamp - everything is simple here; replacing the light element will solve this problem.
• The batteries are completely discharged - replace the batteries with new ones (or charge them if they are rechargeable).
• Lack of contact or broken wire. If the flashlight is no longer new, then it makes sense to change all the wires. This is not at all difficult to do.

LED flashlight

This type of flashlight has a more powerful luminous flux and at the same time consumes very little energy, which means that the batteries in it will last longer. It's all about the design of the light elements - LEDs do not have an incandescent filament, they do not consume energy on heating, and therefore the efficiency of such devices is 80–85% higher. The role of additional equipment in the form of a converter involving a transistor, resistor and high-frequency transformer is also great.

If the flashlight has a built-in battery, then it also comes with a charger.

The circuit of such a flashlight consists of one or more LEDs, a voltage converter, a switch and a battery. In earlier flashlight models, the amount of power consumed by the LEDs had to match the amount produced by the source.

Now this problem has been solved using a voltage converter (also called a multiplier). Actually, this is the main part that contains the electrical circuit of the flashlight.

If you want to make such a device with your own hands, there will not be any special difficulties. Transistor, resistor and diodes are not a problem. The most difficult part will be winding a high-frequency transformer on a ferrite ring, which is called a blocking generator.

But this can also be dealt with by taking a similar ring from a faulty electronic ballast of an energy-saving lamp. Although, of course, if you don’t want to tinker or don’t have time, then you can find highly efficient converters on sale, such as 8115. With their help, using a transistor and a resistor, it became possible to produce an LED flashlight on a single battery.

The LED flashlight circuit itself is similar to the simplest device, and you shouldn’t dwell on it, because even a child can assemble it.

By the way, when using a voltage converter in the circuit on an old, simple flashlight, powered by a 4.5 volt square battery, which is no longer available for purchase, you can safely install a 1.5 volt battery, i.e. a regular “finger” or “little finger” one. battery. There will be no loss in luminous flux. The main task in this case is to have at least the slightest understanding of radio engineering, literally at the level of knowing what a transistor is, and also to be able to hold a soldering iron in your hands.

Refinement of Chinese lanterns

Sometimes it happens that a purchased flashlight with a battery (which appears to be of good quality) completely fails. And it is not necessarily the buyer’s fault for improper operation, although this also occurs. More often, this is a mistake when assembling a Chinese lantern in pursuit of quantity at the expense of quality.

Of course, in this case it will have to be remade, modernized somehow, because the money has been spent. Now you need to understand how to do this and whether it is possible to compete with the Chinese manufacturer and repair such a device yourself.

Considering the most common option, in which when the device is turned on, the charging indicator lights up, but the flashlight does not charge and does not work, you can notice this.

A common mistake by the manufacturer is that the charge indicator (LED) is connected in parallel with the battery, which should never be allowed. At the same time, the buyer turns on the flashlight, and seeing that it is not lit, again supplies power to the charge. As a result, all LEDs burn out at once.

The fact is that not all manufacturers indicate that such devices cannot be charged with the LEDs turned on, since it will be impossible to repair them, all that remains is to replace them.

So, the modernization task is to connect the charge indicator in series with the battery.

As can be seen from the diagram, this problem is completely solvable.

But if the Chinese installed a 0118 resistor in their product, then the LEDs will have to be changed constantly, because the current supplied to them will be very high, and no matter what light elements are installed, they cannot withstand the load.

LED headlamp

In recent years, such a lighting device has become quite widespread. Indeed, it is very convenient when your hands are free, and the beam of light hits where the person is looking, this is precisely the main advantage of a headlamp. Previously, only miners could boast of this, and even then, to wear it, you needed a helmet, onto which the flashlight was, in fact, attached.

Nowadays, the mounting of such a device is convenient, you can wear it under any circumstances, and you don’t have a rather large and heavy battery hanging on your belt, which, moreover, must be charged once a day. The modern one is much smaller and lighter, and also has very low energy consumption.

So what is such a lantern? And the principle of its operation is no different from LED. The design options are the same - rechargeable or with removable batteries. The number of LEDs varies from 3 to 24 depending on the characteristics of the battery and converter.

In addition, such flashlights usually have 4 glow modes, not just one. These are weak, medium, strong and signal - when the LEDs blink at short intervals.

The modes of the LED headlamp are controlled by a microcontroller. Moreover, if it is available, even a strobe mode is possible. In addition, this does not harm LEDs at all, unlike incandescent lamps, since their service life does not depend on the number of on-off cycles due to the absence of an incandescent filament.

So which flashlight should you choose?

Of course, flashlights can be different in voltage consumption (from 1.5 to 12 V), and with different switches (touch or mechanical), with an audible warning about low battery. This may be the original or its analogues. And it’s not always possible to determine what kind of device is in front of your eyes. After all, until it fails and repairs begin, you cannot see what kind of microcircuit or transistor is in it. It’s probably better to choose the one you like and solve possible problems as they arise.

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:

1. 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.
2. 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%).
3. 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.
4. New devices are installed quickly, with considerable savings in cable costs, which in semiconductors require a smaller diameter.
5. Service life of LED devices: more than 15 years when operating 8 hours a day.
6. Low voltage is used to power LEDs. This makes their installation and operation safer than equipment designed for 220/380 V.
7. Semiconductors have good resistance to vibration, increased mechanical strength, and high temperature characteristics.
8. The color rendering index of semiconductor devices exceeds 80. Without wasting energy or using filters, the devices are able to provide deep and pure colors of light.
9. LED devices are suitable for timers, volume sensors, dimmers (light intensity regulators). LEDs are widely used in programmable equipment with variable lighting intensity.
10. 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.
11. LEDs have a minimum start-up time. Even in frosty weather, the device instantly reaches the color temperature and the specified light level.
12. 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.
13. 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:

1. 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.
2. To indicate the charging process, the VD1 LED is included in the circuit.
3. 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.

Dedicated to all those who have similar LED lights.
A typical problem with the latter is a 4-volt lead-acid (AGM) battery that “suddenly” stops working.
Recently there was a review with a solution to a similar problem. .
I took a slightly different path, it will become clear why later.

First, a little about the lanterns:


Budget flashlights with decent sizes and mediocre characteristics. But they continue to be bought and used. The flashlight contains many super-bright 3-5mm LEDs.




LEDs are usually connected in parallel, through current-limiting resistors.


The heart of the flashlight is a lead-acid battery (AGM) with a capacity of up to 4.5Ah.


A positive point is the unpretentiousness of the battery. Possibility of recharging at any time and operation at subzero temperatures. The last point is not taken into account in my modification, since the operation of the flashlight at significant negative temperatures is not planned.

Looking ahead, I’ll say that it took about 2 hours to remake the lantern.

Open the flashlight and remove the dead battery:

To begin with, I measured the current consumption at a battery voltage of 3.84 V:




Resistors are installed in series with the LEDs to limit the current. Due to the changed voltage of the flashlight, it would be possible to lower the resistance of the resistors, but I did not do this. The brightness has dropped slightly, you can live with this, and it’s time-consuming.
At a voltage of 4.2V, the current exceeded 1 A. This became the starting point in solving the problem. There is no need to use a cheap power bank kit due to the latter’s inability to produce the required current.

The solution was on the surface:
Two board options, one with overdischarge protection, the other without protection:


A little about the boards. The controller is one of the most common TP4056. I used a similar board. Controller documentation. The controller provides a charging current of up to 1 Ampere, so you can roughly calculate the battery charging time.
Which board to use in your flashlight depends on the type of 18650 elements used. If there is overdischarge protection, then the one on the right. Otherwise, you can assign the battery protection function to the board, which it does an excellent job of. The boards differ from each other in the presence of additional parts, such as a DW01 discharge controller and an 8205 power switch (dual field-effect transistor) to disconnect the battery from the load at the right time or protect it from overcharging.

There is a lot of space inside, you can install at least a dozen batteries, but for testing I made do with one.


The latter was removed from an old laptop battery and tested on an IMAX B6 charger:




With a discharge current of 1 Ampere, the residual capacity is 1400 mAh. This is enough for about an hour and a half of continuous operation of the flashlight.

Let's try to connect the battery to the board:




The wires to the battery must be soldered carefully, without overheating the battery. If you are not sure, you can use a battery holder.


It is also advisable to observe the color differentiation of the pants and use wires of different colors to connect the power.

We connect the board via a micro USB cable to the power supply:




The red LED lights up and the charge has started.

Now you need to install the charge controller board in the flashlight. There are no special fastenings, so we make a collective farm using everyone’s favorite superglue.


Gluing your fingers at least once is the sacred duty of everyone who has used it.

We make a bracket from a suitable metal plate (an element from a children's metal construction set will do).


In order to avoid short circuits, we use insulating material. I used a piece of heat shrink tubing.

I secured the board by first connecting the wires that previously went to the lead battery:




From the outside it looks like this:


Small defects are visible on the sides of the connector. They are corrected as follows: the hole or crack is filled with baking soda and then 1-2 drops of superglue. The glue sets instantly. After 30 seconds, you can use a file to process the surface.
We secure the battery inside using any available method. I used sealant; some people prefer a glue gun.
The charging connector hole will be covered later with a rubber cap.

We assemble and enable:


Works.
Upd: If you plan to connect several batteries in parallel, then before connecting, in order to avoid damage to the latter, it is necessary to bring all batteries to a single EMF (simple voltage).

Conclusions: Costs in money are approximately 100 rubles and 2 hours of time. I don’t take the battery into account; I used a half-dead one with high internal resistance. I get a working flashlight. The procedures I describe are not a panacea; there are other options for modifying flashlights. I did not display an indication of the charging process/readiness on the case. The blue/red LED glow is visible through the housing.
By the way, the board can have any mini or micro USB connector you like. It all depends on the availability of the necessary cables. Besides everything else, we still have a power supply on hand for charging a lead-acid battery - it will be useful to attach it somewhere.

Pros:
Working light, lighter weight (although this is an insignificant fact). You can charge in any accessible place if you have a USB charger or a computer.
Cons:
The battery is afraid of frost, the brightness is lower (by about 10-15%) compared to the factory version. At the end of the discharge, the brightness drops, noticeably to the eye. To solve this problem, you can install a more capacious (or several) battery.

Flashlight circuit with battery

As a radio mechanic, I am interested in the simplest electronic devices. This time we will talk about a flashlight with a battery.

Here is a diagram of a flashlight with a battery.

The flashlight consists of two parts. In one part there is a battery and a mains charger, and in the other there is a switch and an incandescent lamp. To charge the battery, one part of the flashlight is disconnected from the head (where the lamp and switch are) and connected to a 220V network.

The photo shows an adapter connector that connects the battery and the switch to the incandescent lamp.

The design of such a flashlight is extremely simple. To charge a lead-acid battery G1 with a capacity of 1 A/h (1 ampere-hour) and a voltage of 4V, a circuit with a quenching capacitor C1 is used. Most of the 220V network voltage drops on it. Then the alternating voltage after the quenching capacitor is rectified by a diode bridge using diodes VD1 - VD4 (1N4001).

To smooth out ripples, an electrolytic capacitor C2 is installed after the diode bridge. The load for this entire rectifier is battery G1. If you turn it off, the rectifier output will have a voltage of about 300 volts, although when the battery is connected, the voltage at its output is 4 - 4.5 volts.

It is worth noting that the circuit with a damping (ballast) capacitor is simple, but quite dangerous. The fact is that such a circuit is not galvanically isolated from the 220 volt network. When using a transformer, the circuit becomes more electrically safe, but due to the high cost of this part, a circuit with a quenching capacitor is used.

The VD5 diode is necessary so that when the circuit is disconnected from the network, the battery does not discharge through the rectifier circuit and the indication on the red LED HL1 and resistor R2. But the EL1 incandescent lamp (or a circuit of LEDs) is connected to the battery only through switch SA1. It turns out that the VD5 diode serves as a kind of barrier that passes current to the battery from the mains rectifier, but not back. This is such a simple defense. It is also worth saying that a small part of the rectified voltage is lost on the VD5 diode - due to the voltage drop across the diode when connected directly ( V F). It is somewhere between 0.5 - 0.7 volts.

I would also like to say something about the battery. As stated, it is sealed lead acid (Pb). Consists of two 2 volt cells connected in series. That is, the battery, as they say, consists of 2 cans.

The battery indicates that the maximum charge current is 0.5 amperes. Although for lead Pb batteries it is recommended to limit the charge current to 0.1 of its capacity. Those. for this battery, the best charging current will be 100mA (0.1A).

Typical problems with battery-powered flashlights are:

Failure of mains rectifier elements (diodes, electrolytic capacitor, resistor in the indication circuit);

Malfunction of the switch button (easily repaired by any suitable latching button or rocker switch);

Battery degradation (aging);

Worn contact connectors.

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 rechargeable batteries, 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 lamp with the same malfunction was repaired. 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, and 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 slider 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 slider, 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.

The Photon LED flashlight 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. An EL4 LED with a current-limiting resistor R1 connected in series 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 be 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 functioning of the flashlight 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 through the flashlight body. The photo shows the ring from the side it presses against the printed circuit board.

The retaining ring is fixed quite firmly, and it was possible to remove it only with the help of 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 via a switch directly to the batteries. 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 the HL-508H type, 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 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 modes of operation, 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.

Checking 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 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.