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Old 04-23-2010, 06:15 PM   #1 (permalink)
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Insulate batteries from heat?

This seems like a rather obvious question, but I thought I'd check first. I'm guessing that I need to remove all the insulation around my batteries now that it's unlikely that the temp will get below 40 degrees for the next 6 months or so. I am thinking that the batteries will begin reaching temps too hot with the summer coming, and the insulation might actually damage the batteries. On the other hand, could the insulation keep the batteries from getting too hot if the car is sitting out in the sun all day??

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Old 04-23-2010, 06:34 PM   #2 (permalink)
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...it's a seasonal problem:

1) you want to keep heat IN during the winter.

...but,

2) you want to keep heat OUT out during the summer.
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Old 04-23-2010, 07:45 PM   #3 (permalink)
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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, I would put some reflective insulation on the top to keep the heat off of them but leave an air gap, you can also install a solar panel and either hook it to a fan to blow air around them, or hook it to the vent fan of the car to bring cool air in while it's parked.
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, using them on the other hand will create a bit of heat.
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Old 04-23-2010, 10:26 PM   #4 (permalink)
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I remove my insulation in the warm weather and I usually drop the rear seat and crack the windows open to keep the batteries under 100F. At school my spot is in direct sunlight and cracking the windows help a lot. At home I just pop the trunk open to get the same effect.

I did find that the insulation kept the batteries cooler than the trunk, if they weren't charging. Once on the charger, their temp shot up to over 115F in no time, pumping 12.5 AMPs into them.
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Old 04-25-2010, 12:29 AM   #5 (permalink)
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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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Old 05-13-2010, 05:09 PM   #6 (permalink)
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If you talk strictly Pba batteries. As temperature increases so does capacity but longevity decreases. You should use temperature compensation in your charge voltage profile. This will prevent overcharging in the heat and undercharging in the cold. Over and undercharging are the leading cause of early lead acid battery failure.

Generally speaking if you find the temperature to be comfortable so will a Pba battery. Most ratings are from a temp in the mid 70's (F).

Keep your battery cool and it will last longer. Run it hot and it will shorten the life. If you need performance and not longevity you may enjoy having a hot pack but be sure to monitor the charge voltage and look for the weakest link.

My Solectria has a fairly good insulation around the battery compartments which is bonded and not easily removable. Summer heat build up can be considerable from both driving and charging. When ambient temps are in the 100's it becomes more and more difficult to get the pack back into at least the 80's. Thankfully we have some cool night. I run compartment blowers and reduce charge rate in the summer, charging at the coolest possible time if able. A moderate drive easily raises the temp 5-10 degrees and a recharge another 5-10.

If you can remove insulation easily on all the batteries so they are the same temp I would do so. Your right in that the ambient air wouldn't be able to raise a insulated compartment as quickly but usage will and they aren't going to cool down very fast so a potential death spiral begins if you drive it much.

Stay cool.

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