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On one of the amateur radio sites I saw a circuit for charging portable Ni-Mn and Ni-Cd batteries with an operating voltage of 1.2-1.4 V from a USB port. Using this device, you can charge portable rechargeable batteries with a current of approximately 100 mA. The scheme is simple. To collect it will not be difficult even for a novice radio amateur.

The scheme is simple

Of course, you can buy a ready-made memory. On sale now there are a great many for every taste. But their price is unlikely to satisfy a beginner hobbyist or someone who is able to make a charger with their own hands.
I decided to repeat this scheme, but make a charger to charge two batteries at once. The USB 2.0 output current is 500 mA. So you can safely connect two batteries. The modified scheme looked like this.

Charging Scheme

I also wanted to be able to connect an external 5 V power supply.
The circuit contains a total of eight radio components.

radio elements

The tool will require a minimum set of amateur radio: soldering iron, solder, flux, tester, tweezers, screwdrivers, knife. Before soldering the radio parts, they must be checked for serviceability. For this we need a tester. Resistors are very easy to check. We measure their resistance and compare with the nominal. On how to check the diode and LED there are many articles on the Internet.
For the case I used a plastic case measuring 65 * 45 * 20 mm. The battery compartment was cut out of a Tetris children's toy.


I’ll tell you more about the alteration of the battery compartment. The fact is that initially
the pros and cons of the battery power terminals are set the opposite. But I needed that in the upper part of the compartment there were two insulated positive terminals, and at the bottom one common negative. To do this, I moved the lower plus terminal to the top, and cut the total negative terminal out of tin, soldering the remaining springs.

battery compartment

battery compartment

charger housing

As a flux when soldering springs, I used soldering acid in compliance with all safety rules. The place of soldering must be washed in running water until the traces of acid are completely removed. The wires from the terminals were soldered and passed into the body through the drilled holes.

charger board

The battery compartment was fixed on the case cover with three small screws.
I cut the circuit board out of the old Dandy game console modulator. Deleted all unnecessary parts and tracks of printed wiring. He left only the power socket. I used thick copper wire as new tracks. I drilled holes for ventilation in the bottom cover.


The finished board firmly sat in the case, so I did not begin to fix it.

the charger is ready

After installing all the radio components in their places, we check the correct installation and clean the board from flux.
Now let's deal with the wiring of the power cord and setting the charging current for each battery.
I used a USB cable from an old computer mouse and a piece of power cable with a plug from the Dandy as a power cord.

plug connection

The power cord needs special attention. In no case should you confuse "+" and "-". On my “+” plug, the power is connected to the central pin with a black wire with a white stripe. And the “-” power goes through the black (without a strip) wire to the external contact of the plug. On the USB cable, “+” goes to the red wire and “-” to black. We solder plus with plus and minus with minus. The soldering spots are carefully isolated. Next, we check the cord for a short circuit by connecting the tester in the resistance measurement mode to the plug terminals. The tester should show infinite resistance.Everything needs to be double-checked, no matter what the USB port is burned. If everything is fine, connect our cord to the USB port and check the voltage at the plug. The tester should show 5 volts.


The last setting step is to set the charging current. To do this, we break the circuit of the diode VD1 and the "+" battery. In the gap we connect the tester in the mode of measuring the current turned on to the limit of 200 mA. Plus a tester for the diode, and minus to the battery.


We insert the battery into place, observing the polarity, and apply power. In this case, the LED should light up. It indicates that the battery is connected. Next, by changing the resistance R1, we establish the required charge current. In our case, it is approximately 100 mA. With a decrease in the resistance of the resistor R1, the charging current increases, and with an increase it decreases.

charging current

We do the same for the second battery. After that we twist our body and
The charger is ready to use.
Since different finger batteries have different
capacity, it will take different time to charge these batteries. Batteries
capacity of 1400 mA / h with a voltage of 1.2 V need to be charged using this
circuits are approximately 14 hours, and 700 mAh batteries will need only 7 hours.
I have 2700 mAh batteries. But I did not want to charge them 27 hours from the USB port. Therefore, I made a power socket for an external 5 volt 1A power supply, which I was lying idle.


Here are some more photos of the finished device.





do-it-yourself charger

I painted the stickers with FrontDesigner 3.0. Then printed on a laser printer. Cut out with scissors, pasted the front side onto a thin adhesive tape 20 mm wide. Excessive tape was cut. I used glue stick as glue, having previously lubricated it with the sticker and the place where it is glued. How reliable this is, I don’t know yet.
Now the pros and cons of this scheme.
The plus is that the circuit does not contain scarce and expensive parts and is assembled literally on the knee. There is also the opportunity to power from a USB port, which is important for beginner hams. No need to puzzle where to power the circuit. Despite the fact that the circuit is very simple, this charging method is used in many industrial chargers.
It is also possible to complicate the circuit a little by switching the charging current.


By selecting R1, R3 and R4, you can set the charging current for batteries with different capacities, thereby providing the recommended charging current for this battery, which is usually 0.1C (battery C-capacity).
Now the cons. The biggest one is the lack of stabilization of the charging current. I.e
When the input voltage changes, the charging current will change. Also, with an error in the installation or short circuit of the circuit, there is a high probability of burning the USB port.
come back
Comments (9)
  1. Vladimir
    #1 Vladimir Guests May 28, 2014 10:01
    Can li-ion batteries be charged to them?
  2. Alexander
    #2 Alexander Guests May 18, 2015 21:49
    Good evening! Tell me, does the LED turn off when the battery is charged via USB according to your scheme? Thank.
  3. Alex
    #3 Alex Guests October 18, 2015 22:53
    Quote: Alexander
    Good evening! Tell me, does the LED turn off when the battery is charged via USB according to your scheme? Thank.

    Aleskander, no, nothing goes out, because This is an option for the simplest charger.
  4. E
    #4 E Guests June 10, 2016 10:53 p.m.
    the first thing that caught my eye was the power of the resistor P1 - 0.25W.
    based on the calculation of 5V x 0.1 A = 0.5 W - for a current of 100 mA it should be MORE - you get 1 watt.
    for currents higher - even more.
    But at all I did not understand the essence of all these perversions with a usb port and the probability of burning my mother.
    just BP ATX is taken, and a 3.3V bus, which extends to 10A.
    The LED and resistor can be discarded altogether. leaving only 1n4007 and a resistor, which should initially be tuning type SP3 - 2W.
    unsolder the conclusions and select the necessary charging current for them, which is extremely important for batteries. so we have a stabilized power supply + protection against short circuit + current adjustment for any capacity + the ability to "swing" a dead battery with the same resistor
  5. Stousa
    #5 Stousa Guests December 22, 2016 18:05
    More reliable charger circuit type current stabilizer
  6. Alexander
    #6 Alexander Guests 31 january 2017 19:02
    Is it okay that 1 pin is "+" and 4 "is" on USB?
    Judging by the comments, how many people have already gathered the scheme and no one has noticed.
    It is not clear, the roofing felts are the author of lamers, the roofing felts are so conceived ...
  7. Dmitry Nick.
    #7 Dmitry Nick. Guests August 13, 2017 16:37
    I collected and everything charges well.
  8. Stanislav
    #8 Stanislav Guests May 29, 2018 23:42
    I’m just the owner of the purchased memory, but for safety, far from civilization, you can do it yourself, indeed, there is nothing particularly complicated.
  9. Mik
    #9 Mik Guests December 16, 2018 21:03
    Homemade products have not yet been translated into Russia!
    And to what voltage will the batteries charge? The charging current should match the capacity ... And other parameters ... Not afraid to ruin the batteries?

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