A charger for us nerds...

[Cornelius]

My 3 year old GM 36V, 16Ah battery has been getting a bit lazy lately; I get only 25km out of one charge opposed to around 40km earlier, before the lvd cuts the power. The cell voltages are all within 0.02V of each other; both when fully charged, and after a 25km roundtrip. (Though, measured 1 week after the trip; the bms might have balanced the cells during that week of rest...)

Now, i'm very curious about most things, so I wanted to know why, so I bought an 'iCharger 1010B+':

http://www.jun-si.com/EnProductShow.asp?ID=93

Primary made for the RC market; it's also an excellent charger for us nerds that want to know more, and control more...

It has support for max 10 Lithium cells, and max 10A charge current. It shows you all cell voltages, and have multiple charging schemes and discharging schemes.
3 features made me buy it: 10A charge current, it can run from a 12V car battery, and it can show you each cell's internal resistance. The last feature are what really tells you the most about a cell's condition.

With a bit fiddling, I created an adapter to fit the GM's balance plug into the iCharger, and it showed me what I suspected; all cells had an internal resistance between 15 and 25 milliOhm, except one that measured 54 milliOhm...
(When I say 'cell' here, it means one group of 4 parallel cells inside my 36V/16Ah GM battery...)

So...
Even when cell voltage showed that all cells was equal and well balanced; one cell are probably not capable to deliver its voltage under full load anymore, due to higher internal resistance. So now I know...

Now; i'm working on building a replacement for my gm battery, and I will write a story on that soon. All I will say for now is that it will consist of 24 LiFePo4 cells rated at 3.3V, 10Ah each, giving me a 40V, 20Ah pack.

[csm]

My 3 year old GM 36V, 16Ah battery has been getting a bit lazy lately

you mention it is 3 years old. I presume it is approximately 36 months old? How many charge cycles have you given it? How many miles/kilometers have you put on it at this point?

With a bit fiddling, I created an adapter to fit the GM's balance plug into the iCharger, and it showed me what I suspected; all cells had an internal resistance between 15 and 25 milliOhm, except one that measured 54 milliOhm...
(When I say 'cell' here, it means one group of 4 parallel cells inside my 36V/16Ah GM battery...)

The charger seems like a good tool for battery diagnostics. Do you have a picture of your adapter? Please post. I am interested in doing the same test as you.

Also, I am concerned that you checked the cells in packs of 4. I have read reports that sometimes connections between cells can be faulty. And the possibility that there may be individual sluggish cells within the packs of 4 which may cause an overall reduction of capacity. I am fairly new at lithium pack diagnostics and am eager to learn everything I can. How much did your charger and cable adater materials/supplies cost you?

cell voltage showed that all cells was equal and well balanced

What voltage did you have your charger set to look for in your cell packs of 4, for charging and discharging??

Have you posted any videos and/or pictures of you charging/discharging/diagnostics of your packs? I would like to see them.