Charging the 12 vdc Battery

[JoeS]

,,,since the DC to DC output does not show any indication of being temperature compensated. It will be much better than what an ICE does though and get you by adequately...

I've seen the 12v system drop to 13.9vdc at warm ambient temperatures and IIRC I've seen 14.4vdc as well. I'd like to put the issue of our 12v dc-dc temperature compensation on the table:

Could some of our cold-weather friends measure the 12v battery voltage at low temperatures with the ignition key ON? When summer comes we can do the high end as well. Might as well use this thread to post our readings for now. With enough data points of temperature vs. voltage we might be able to produce a decent curve.

My reason for asking is to find out what the operating voltage extremes are of our 12v system in case I want to replace our lead-acid battery with lithiums, and the readings will help me determine which chemistry to use.

Edit: removed off-topic remarks

 

[PV1]

According to EVBatMon's IGCT Power tile, my i-MiEV holds 14.2 volts in a fairly broad temperature range (within 50-80 F). With temperatures near freezing, this increases to 14.3-14.4 volts, and during the last cold snap (0-10 F) was up to 14.5 volts.

If you'd like, I can take more detailed measurements using a multi-meter. Pennsylvania can't decide what season it wants to be in, so temperatures are all over the place.

 

[JoeS]

PV1, thanks for that. The only 'true' reading is that measured right at the battery terminals themselves, as I don't know where the car's own sensing points are actually located. I'm more concerned with the very-low-temperature voltages as they might be too high if i use four cells in series: 14.5v/4=3.625 which is still within the usual LiFePO4 upper limit.