Lucky?
 

If your lucky there might be some kind of a miniature "pot" switch that you can make minute voltage adjustments with. Then you can just calibrate each charger to the same voltage. I was kind of thinking that you might run into this problem, but we never know until someone tries it out. You are the guinee pig here. Thank you. Anyway hopefully you can find a loop-hole with this setup and get it to work right for your application. Good luck.

Here's a few pics of the inside. I don't see a pot and Brian, what is a IC? :oh:

http://i177.photobucket.com/albums/w...p_charger8.jpg

http://i177.photobucket.com/albums/w...p_charger9.jpg

http://i177.photobucket.com/albums/w...p_charger7.jpg

http://i177.photobucket.com/albums/w...p_charger6.jpg

http://i177.photobucket.com/albums/w...p_charger5.jpg

http://i177.photobucket.com/albums/w..._charger10.jpg

Starting from the cord side, I see what looks to be a bridge rectifier, cap filter, an opto-isolated simple switching power supply, and the IC (labeled U2) is presumably the actual charger IC, but the top has been sanded to prevent identification.

However, I do notice the resistors used are 5% tolerance (gold 4th band). No big deal if they aren't used to "program" cell cutoff voltage or whatever, but if they are being used in the charging part of the circuit, I would have expected to see 1% or 2% tolerance precision resistors (5 bands).

Do you think changing those resistors would make these chargers more precise? If they are part of the charging like you said. It would be easy enough to change those resistors and then charge a few 18650 cells to find out what the end voltage is. I just need to know which resistors to get. Thanks Brian.

I'm not sure. If the part number of the IC wasn't ground off, you could look up the datasheet for it and see what purpose/effect any support components would have.

I can't quite make out the color code to know what the exact resistor value should be, and you shouldn't measure it while in the circuit because other components could affect the reading. But once you figure out the default resistor value (looks to be under 1k), you can replace it with a pot and adjust it until it matches the exact value as found on the color code on the resistor. But again, if it's not part of the charging circuit, it will have little or no effect on the output. It's all a shot in the dark at this point.

I was hoping for something more encouraging but I guess it is what it is. Thanks.

This EV thing is turning into a hobby that is worst than RC! I went 72V 30Ah just two weeks ago and I am having so much fun with it that I already want to go 100V 40Ah.

Do it man. Just be careful with 100V DC and your fingers.

Tell me about it, this 72V battery I made bit me a couple times during the construction. My fault, I was in a hurry trying to get it done and I really shouldn't work like that. 100V 40Ah would be with genuine A123 prismatic cells from A123RC. So I need the money before I worry about the fingers. Maybe next year.