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Battery charging circuit for more than one cell?

Former Member

I was very excited when I heard that Ben Heck was about to make a Video about Battery Charging Circuits, but my hope that he would show us a circuit to charge multiple cells wasn't fulfilled. So, I'm working on a Project that requires a 4s to 5s Lipo Battery and I have no idea how I should work this out. Could anybody help me out on this one? Most confusing for me is that I need an Output Voltage of 18.5V (5s) but to charge I need 4.2V on every Cell. How can this be done?

 

Thanks in Advance for any Help!!

  • Florian,

     

    Please be very careful when charging LiPo's!! Back in the day that NiMH was the 'leading' chemistry, you could easily make charger by making a constant current source. If you had a string of batteries, and one of them would get a lower capacity during use you could 'balance' your pack again by overcharging the pack; the pack would get hot, but no bad things would happen. Please read this on balancing: Balancing Li-Po Battery Packs - How and Why

    Everything Lithium-rechargeable should be handled with care!! Overcharging is not an option as your pack might explode. Cell voltages need to be carefully checked during charging, and the charging algorithm is a bit more complex than NiMH (first constant current, than constant voltage charging).

     

    Now for your solution: you could either try the approaches in this document by Adafruit (PDF): https://learn.adafruit.com/downloads/pdf/multi-cell-lipo-charging.pdf , where each battery gets charged by its own charging circuit, or build your own system (which I advice against if you're not experienced in electronics).

     

    Good luck!

  • in reply to vsluiter

    No offenseto element 14. On adafruit, you get Lipo cells of 2500mah. There are also these chrgers-micro coonneter Lipo chargers. You could make a toogle switch and choose when to give output. connect in series and it will give required voltage. When you input the chrging point, rather than using 4 micro usb cables, use one which can provide 2-2.5 amps and connect it to all of them. The charger let's you choose when to give output via a pin as well as tells you when a cell is low. I'm going to use it my self in a future project andconnect in parellel rather than series.

  • in reply to vsluiter

    : I know of the dangers of the LiPo-Cells,thats why I am asking you for help here. I use them a lot on other projects, but always that way that I was unplugging them and put them on a dedicated LiPo-charger.

    Now I'm planning something like Ben's mobile gamingstations, but it should be battery powered too.

     

    @royston dsouza: I know of the guide from Adafruit and already read them, but my problem with this setup is, that I can't use the system while charging it. Other than that, it would work for me.

     

    Does anybody have a solution to this problem?

    Isn't there a charger IC available for, lets say 6 Cells wich will balance charge? Like the one Ben used in his charger circuit?

     

    Thank You!

  • in reply to Former Member

    Hi Florian.

     

    I quickly looked at Linear and TI's  website. As far as I can see it will be a two-fold design approach; you'll need a charger that provides enough voltage / current, and you'll need a solution to monitor  each cell's voltage. I think most 'straightforward' designs are built up this way. If you want to go fancy (and / or care about battery life) you could also add cell balancing.

  • in reply to vsluiter

    On adafruit, there are special charger boards that allow you to charge and run at the same time.