custom LI-ion battery pack charging

[manhackman]

I have a similar project to thread658-127532.

First of all, I should let you know I am looking for a cost effective way of doing this, and I have absolutely no exp. with battery charging and circuit design... But I'm handy, have done IC projects from kits.

I would like to make a custom battery pack from surplus LI-ION batteries wired together to produce a greater voltage and Ah. The batteries are 7.2 volts, 2000 mAh, and I'll probably put them in sieries and parallel to get 21.6v 4000 mAh (6 bateries). Then DC-DC converters to get my desired voltages... 12v and 20v
The batteries are quite cheap ($3 can ea.) and I've seen some universal chargers that could charge the individual batteries, but nothing that could handle the whole pack.
Is there a product I could buy? Could I build my own charger relatively easily?or reverse engineer one?

any help/thoughts would be nice!

 

[manhackman]

I found this today

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2393

It should do the trick

 

[felixc]

You saw the number of warnings in the link that you provided. This isn't to say that their product is dangerous, it is related to the fact that reliably charging lithium ion batteries is quite complex, and that given the energy density of such batteries, bad things can happen. At the same time you don't want to start a design just for a qty 1 application. So just be careful to never overcharge your batteries.

 

[pdybeck]

manhackman,

Its not as simple as you may think. Safely and reliably charging Li-Ion batteries is a rather large project to be undertaken. There is a lot to consider with Li-Ion battery packs and charging them. Cell balancing, temperture protection, disharge rates/control, shelf life considerations, slight changes in battery chemistries and how to adapt to that, etc... As others have stated this is something to be approached with care. I am familiar with the complexity involved - not first hand, but pretty close. If you have a large scale project, it would be worth it to consider looking at some products/companies that do it successfully and reliably. If you have a smaller project, just be very careful. Let me know if you have a larger scale project as I could put you in touch with some people.

Pete