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Old 04-25-2010, 12:29 AM   #5 (permalink)
rmay635703
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Quote:
Originally Posted by Ryland View Post
I don't know what the max temp on batteries is, but 80-100F is pretty much ideal according to people at the local EV club,

My understanding is that the heat generated by charging is not that much, that a 300watt heating pad left on for 2-3 hours will get the batteries up to temp on a 20 degree day but that charging them doesn't do that much
Um, actually I disagree with most of the statements above except the heating pad. The statements above need to be qualified a bit, they are only true for specific circumstances.

1. 80-100F being ideal is only the case for the internal battery temperature, not ambient and only WHILE you are driving the car and only if your vision of ideal is for the max capacity and amp draw ability. It is certainly not ideal while charging and DEFINATELY not ideal if the battery is just sitting there with near a full charge as the positive plates die from corrosion at those temperatures. They also wear out faster if charging at that temperature. Also if you are not drawing amps very hard and are not using much of the batteries max capacity having hot will only wear the positive plate out a bit faster.

2. The heat generated by charging is VERY significant, of coarse it depends on if its a flooded, agm, gel and the rate of charge. Needless to say an aggressive charge during winter, especially if you can time the charge to finish just before you are going to leave definitely heats the batteries 10-30 degrees above ambient. I had a timer that would start and finish charging at different rates so my car would just finish the charge when I was going to leave, it would trickle slowly then the main charger would kick in around 2am and the pack would be hot and ready for me to leave to work, it actually would melt the snow off the boxes on some days.

True it wasn't as good as a heater by any stretch but certainly was much better than if the charge was finished 6 hours before and the batteries were cold when leaving than fresh off charge.
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