LiPo Battery Charging

Discussion in 'The Projects Forum' started by tyhahn92, Apr 2, 2014.

  1. tyhahn92

    Thread Starter New Member

    Apr 2, 2014
    Hi Everyone,

    First post in the forum after reading for quite a while in school, so I hope this is in the right place. I am working on a LiPo battery charger for a single cell 3.7V battery. I found a schematic online to build (attached below) but I had to make some changes because of the availability of parts at school. I made these changes:

    BC857B were changed to BC560C
    BCP68 changed to 2SC13830R
    BSS138 changed to 2N7000

    After building the circuit with these substitutions, I got an output voltage of 4.6 volts which is about 0.4V too high to be safe for a lithium battery. My question is, can I change the resistor values (which resistors?) to make the output voltage lower? I don't fully understand the principals of the transistors and they are the only parts I have available. I don't have computer modeling available to me at this time so I can't put it into any software at school yet. Thanks so much for any help!
  2. MaxHeadRoom


    Jul 18, 2013
    Charging LiPo batteries require certain requirements to be followed.
  3. tyhahn92

    Thread Starter New Member

    Apr 2, 2014
    That is a very interesting article, thank you. I do believe that the circuit in the original design was supposed to accomplish these goals without a micro controller and the charge current should decrease with as the battery charges. The LED indicator illuminates less as the battery becomes more charged.

    Maybe I am wrong and this transistor design does not accomplish this? Thanks!
  4. IcedFruits

    Active Member

    Jan 15, 2014
    careful, even slight overvoltage/overcharge may cause the lipo cell to go on fire or even explode.

    better to use lipo charger ICs for these.