# [EVDL] LiFePO Temperature Compensation?



## EVDL List (Jul 27, 2007)

I'm in my third winter with CALB cells now. What I have found is the the
cells hit the limit voltage set point of the charger at a lower SOC in
winter due to higher internal R. So if it is set so I get a full charge at
cell temperature of 80 F, I would not at a temperature of 50 F. My cells
are mounted on battery heaters which keep them at 65 F in winter, so I don't
see much difference in winter/summer charging or performance. 

My Manzanita charger triggers an internal timer when the limit voltage is
hit, and the pack voltage continues to increase by a few volts as charge
current decreases, so it may behave differently than chargers like the Elcon
which hold at a set limit voltage when in CV mode and run until the current
decreases to some defined magnitude. In that case I would expect charging
would be to about the same SOC but would take longer due to longer CV mode
time, but someone with an Elcon would have to answer that.

There is a similar effect due to charge current level. The pack hits the
charger limit voltage at lower SOC at high charge currents due to higher
voltage drop across the cells. I assume that is why a "fast charge" is
said to give about 80% SOC. 

I don't think any of us diyers know the effect of driving cells to lower
voltage in winter since we have not done controlled life cycle tests. I
would guess Renault knows with data from their test facility described in
"ChargedEVs" magazine, and probably GM and Nissan.

--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/LiFePO-Temperature-Compensation-tp4074473p4076381.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere. Thanks.
|
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev


----------

