Several years ago I bought a once cheap Turnigy charger for LiPos at Parkflyer, and it went whack after a couple of months.
It was a microchip of Channel 3 that failed. There was no marking except two figures and six outputs. My further search for another chip was unsuccessful, so I put it in a box, and there it had lain all these years.

A month ago I came across a charger board on AliExpress featuring a balancer for charging just one LiPo cell. The board has a USB connector, so I could charge a battery from my PC with 1A current. It cost less than 50 cents and they offered free delivery. So, I decided to try those little things on my failed battery charger. I paid a sum and waited.

As I was waiting for the item to arrive, I studied the charger’s structure. It was all so simple. It was to be powered by a 12V/1A adapter, and there was an impulse voltage converter on the microchip’s input. The converter is configured for a step-down transformer (see the picture). The transformer features three independent secondary windings, each having its own half-way rectifier and a 470 ufd/10 V capacitor. Simply put, each of the three channels was powered independently. Then I tested each capacitor for voltage, and it was 5V – exactly what I wanted.

Here is the little circuit layout that I drew.

Yesterday I received my much longed-for balancers. They arrived pretty soon – after a month. Instead of putting it off till tomorrow I got down to work right away, since I had figured it all out and prepared by the time.

The boards feature USB ports. I extracted them and put aside, as I thought I could use them elsewhere. Here are my little balancers ready for modernization. Each board features two planar LEDs – red and green, which indicate that the battery is charging (red) and fully charged (green).

First, I made a makeshift of the board to get a picture. I powered the boards (the balancers), and to so I removed two wires (+ and -) from each filter capacitor (C1, C2, C3) and soldered them to balancers’ inputs (in) as shown in the drawing.

I connected the charger output wires to the balancers’ outputs (BAT). Then I bridged Boards 1- 2, and Boards 2-3, as shown in the circuit layout.

When I powered the charge from the adapter, the green LEDs went on, because the charger was disconnected.

When I connected the uncharged battery, the red lights went on indicating the charging process. You can see a file on the picture below. I put it on the wires to keep them and the boards steady. Please, disregard that, it’s just a makeshift.
On the whole, it worked well. I had prepared a little box, and it didn’t take much time to put the system into it. I made it within one evening. I cut holes for the LEDs, and they were quite visible, especially when there was no direct sunlight.

I used a piece of ruler to provide a reliable connection between the boards and the box.
When the battery is disconnected, the green lights go on.
When the battery is being charged, the red lights are on

When the battery is fully charged, the green lights are on.

Instead of using a board with a rectifier, like I did, you can use a step-down transformer with several same-type windings. For example, you can use TH-30, TH-36, or similar ones. These transformers feature four 6.3V windings. If you use a 3S charger, there must be three windings; for a 4S charger, use four windings.

Each wiring should be loaded on a separate rectifier (a diode or bridge) and a high-capacity (2200-3300 ufd112V) filter capacitor, as shown in the circuit layout. It does not make a big difference. Put all three rectifiers together and measure the direct-current voltage at the filter capacitors. It will be about 9V, which is too much. Reduce it to 5-5.5V. To do so, include in the circuit of the transformer’s primary wiring (220V) a powerful (300-510 O) wire-wound resistor. It will drain the excess voltage.

I chose not to use a jack, and instead I made a wire ‘tail’ and soldered an N-pin connector to its end. I like it better this way, because I can charge my battery without extracting it from the device. However, I have to be careful not to confuse the polarity. Therefore, I color-mark all connectors: red stands for plus, and black – for minus.

Finally, when I have no choice but to use an iMAX charger, I have to take it out of the device. In fact, I have several chargers for LiPos, including an iMAX, plus two do-it-yourself chargers, which I described in my previous posts. However, when I found these little balancers on AliExpress, I thought I could test them and rebuild the charger, which I did successfully. Thank you, the Chinese!

I have lots of chargers, and my grandson has two RC cars featuring LiPos (including backup ones), so I wouldn’t mind having another charger close at hand.

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Here is the link to the balancer boards on AliExpress:

This is the translated version. You can read the original Russian article here.