• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Charging Multi Cell LiPo Batteries via USB

#1
I'm looking for a way to charge a 2 cell LiPo via a USB port... I know there are USB chargers for single cell batteries, but I'm not sure if there are any multicell chargers (or if it's even possible). I'm looking for a cheap/easy way to charge the batteries on my quad while camping/hiking so I thought I'd buy a solar pack capable of charging a tablet (12 watts). If I buy that, all I'd need is a charger...

Help?
 

joshuabardwell

Senior Member
Mentor
#2
The simplest way to do this would be to get a standard balance charger that runs off 12 volts, then use it with a solar system capable of outputting 12 volts. The whole USB thing is an unnecessary complication. Also, I can't find any LiPo balance chargers that run off of 5v or USB--just a couple examples of people asking if it can be done and being told it isn't.

I would suggest something like this, combined with an Accucel 6 or similar.

http://www.amazon.com/dp/B00KIXSXWQ?psc=1

You will also need a separate solar panel that outputs 12 volts to charge the battery pack.
 
Last edited:
#3
Thanks for the help.

It's sad that there aren't any USB chargers (the solar kits are much cheaper than one that puts out 12V) but your ideas definitely give me a starting point.
 

joshuabardwell

Senior Member
Mentor
#4
Thanks for the help. It's sad that there aren't any USB chargers (the solar kits are much cheaper than one that puts out 12V) but your ideas definitely give me a starting point.
Part of the problem may be that the USB spec is not designed for high-wattage output. Phone chargers can go higher, as you pointed out, but that's a pretty specialized situation. So there is not much incentive for a manufacturer to design a high-output LiPo charger that runs off of USB. Meanwhile, 12 volt batteries are cheap as chips and common. Not the best for backpacking, but there you go.

If you are determined to go with a USB system, look into buying a boost converter like this one. Create a cable that has a USB plug on one side and a DC barrel plug on the other side, with the boost converter in the middle. Bob's your uncle.

Do be sure not to over-draw your system. I'm not sure what the effect on current is when doing a boost conversion, but I'm willing to take a stab at it. The boost converter must draw increased current on the input side to get the higher voltage on the output side. The energy has to come from somewhere, right? If I had to guess, I would say the right way to think about it is to use power, which combines the effect of both current and voltage. If you have a 12 watt iPad charger, then 12 watts = 1 amp @ 12 volts. So I would guess that the max you could pull on the output side would be 1 amp, and that doesn't account for conversion losses. Subtract another 10% for conversion losses and you get about 0.9 amps max current available. Since the charger itself is not 100% efficient, the realistic charging rate you might expect to achieve could be something like 0.8 amps.
 
Last edited:
#5
Part of the problem may be that the USB spec is not designed for high-wattage output. Phone chargers can go higher, as you pointed out, but that's a pretty specialized situation. So there is not much incentive for a manufacturer to design a high-output LiPo charger that runs off of USB. Meanwhile, 12 volt batteries are cheap as chips and common. Not the best for backpacking, but there you go.

If you are determined to go with a USB system, look into buying a boost converter like this one. Create a cable that has a USB plug on one side and a DC barrel plug on the other side, with the boost converter in the middle. Bob's your uncle.

Do be sure not to over-draw your system. I'm not sure what the effect on current is when doing a boost conversion, but I'm willing to take a stab at it. The boost converter must draw increased current on the input side to get the higher voltage on the output side. The energy has to come from somewhere, right? If I had to guess, I would say the right way to think about it is to use power, which combines the effect of both current and voltage. If you have a 12 watt iPad charger, then 12 watts = 1 amp @ 12 volts. So I would guess that the max you could pull on the output side would be 1 amp, and that doesn't account for conversion losses. Subtract another 10% for conversion losses and you get about 0.9 amps max current available. Since the charger itself is not 100% efficient, the realistic charging rate you might expect to achieve could be something like 0.8 amps.
I think I'll have to go with a solar setup that has a 12V output until USB Type-C {20V(100W) and 5A - enough to power/charge a laptop} comes out and we get a charger that'll run off it... I'm not sure that doing a boost converter is worth it.

Thanks again.