MMM Voltage-- Is this too much?
 

I was wondering if I could run 8s Li-Ion at 3.2v/cell nominal fully charged. The total voltage would be 25.2v. Is that too much? Also, charging the Li-Ion, should I use the A123 charge or the LiPo charge on my 1210i? Maybe set charge fullness to about 95%? Any ideas? Also, is balancing these cells as important as balancing LiPos? Here are the cells.
http://www.robotmarketplace.com/prod...ld_li-ion.html

The nominal voltage and fully charged voltage are two separate numbers. In this case, the nominal voltage is 3.20v, and the fully charged voltage is 3.65v. Normally LiFePO4 settles down to ~3.45-3.50v after a charge, so 8s LiFePO4 will typically be ~27.6-28.0v when plugged into the ESC. 6s Lipo fully charged is 25.2v, so I think 8s LiFePO4 will be too much for the MMM.

With A123s, balancing isn't so much of an issue. With other less expensive LiFePO4 I'm guessing the quality isn't as good, so balancing might be a bit more necessary.

CC say max 7s A123....

PS use LiFe/A123 mode

They also said there was a 27v rated component on the pcb, so any overvoltage will let out the magic white smoke.

:eyes: I was hoping this would work... :cry:

one way to find out, a $170 experiment :)

A123 are probably the best case as far as lithium chemistries go, and just happen to have max charge voltage at 7s lining up exactly with that 6s lipo, but with a higher nominal. the huge voltage drops these cells experience probably makes up more than the difference though.

When I read Li-Ion I thought you were referring to the 3.6v nominal cells...A123 are 3.3v nominal, so what li-ion's were you looking at that are 3.2v nominal?

Maybe this will help you with your decision.

first minute of a run with 8s1p A123 in a 1:8 buggy/truggy hybrid
http://www.braintrust.at/2007/ds/rc/...un01_graph.gif

The battery pack was fully charged 5 weeks before i did this run. Peak voltage 27.88V, but it usually is higher (28.5V) when the pack comes fresh from the charger. After a minute voltage drops somewhat (25V) but while braking voltage may rise (+1V). After a run with 18-20A discharge on average, the average voltage is 23.8V (a bit lower then 3V per cell).

Seems a bit too risky for me. 7s A123 should be on the safer side.

Yeah. Man, I wish there was a good HV car controller that doesn't cost my life savings to get. Plus with the vehicle I have in mind, mechanical brakes are not an option.