I am building a battery box that will have 16 of the 280ah LiFePo4 batteries a chargery BMS. It will go on the outside of an RV and I was thinking about how to protect it from temperature extremes. Do I want to insulate the box or not? Is ventlation enough or do I need to cool them? I was going to buy some RV tank heater to protect them from the cold along with the BMS cutoff but I had not realy though about them heating up in the summer.
Battery Box Heating/cooling
- Thread starter ndrober
- Start date
Depends.
What are the extremes of temp where you are?
Summer sun or shade?
Will the inside living area of the RV be heated? If so you should only insulate the outside area of the battery box so it can get some indirect heat from inside the RV. Depending on where you live, that may be enough.
I live in the southwest, so it 20 F in the winter and 90F in the summer. I can see swings down to 0F and 120 F, but in those cases the RV will be parked and connected to shore power.
The battery box in below the RV mounted between the frame rails so it will be shaded year round. I was thinking of insulating the box and adding a small fan to pull air through.
BabylonFive
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- Jan 24, 2021
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I'm having some similar concerns over my own first battery box.
When you heavily charge and discharge, your batteries (and conductors) will generate heat, and especially in hot conditions (I'm in Texas) this is a bad thing -- you'd want to ventilate.
When you are camping in a cold condition, near and under freezing, your LiFePO4 batteries will be damaged when charged at that temp; in this situation you want NO ventilation, and instead some heating (heating mat or other), and you'd not want to leak the heat to the outside world and be very inefficient.
These aspects make the battery box design more complicated and interesting. It makes perfect sense when most folks recommend to put the batteries INSIDE. This is where you expend energy to keep conditions moderate anyway, as least while you are using it. Unfortunately there's no such thing as electrically-controlled insulator which can magically go from conductive to insulative -- at least no that i know of.
I had designed a crazy box where the batteries were all surrounded by mineral oil, which could be heated or cooled with a liquid-to-liquid heat exchanger which could run either heated or cooled water into the control side. It would have been super overkill, and if it were the only bit of project I had in front of me it would have been super fun.
Best reasonable way to do it would be some sort of thermostatically-controller forced air cooling, combined with reasonable insulation and a thermostatically-controlled heating pad. When the fan is off, the insulation works ok; when nearing freezing the pad will heat up the batteries to say 38 to 40 degrees F, and when over a certain internal condition the fan would come on and heat the batteries.
As it is, I think I'll just put heating pads under, wood around, and forced air into the box at the edge to run around and over the batteries as described above. I'll put the temp sensor in the middle of the pack. Best I can do, IMHO.
David
P.S. no, i don't care about compression of the batteries, so I could run oil around them if i wanted, or even just pack aluminum sheets between each cell.
When you heavily charge and discharge, your batteries (and conductors) will generate heat, and especially in hot conditions (I'm in Texas) this is a bad thing -- you'd want to ventilate.
When you are camping in a cold condition, near and under freezing, your LiFePO4 batteries will be damaged when charged at that temp; in this situation you want NO ventilation, and instead some heating (heating mat or other), and you'd not want to leak the heat to the outside world and be very inefficient.
These aspects make the battery box design more complicated and interesting. It makes perfect sense when most folks recommend to put the batteries INSIDE. This is where you expend energy to keep conditions moderate anyway, as least while you are using it. Unfortunately there's no such thing as electrically-controlled insulator which can magically go from conductive to insulative -- at least no that i know of.
I had designed a crazy box where the batteries were all surrounded by mineral oil, which could be heated or cooled with a liquid-to-liquid heat exchanger which could run either heated or cooled water into the control side. It would have been super overkill, and if it were the only bit of project I had in front of me it would have been super fun.
Best reasonable way to do it would be some sort of thermostatically-controller forced air cooling, combined with reasonable insulation and a thermostatically-controlled heating pad. When the fan is off, the insulation works ok; when nearing freezing the pad will heat up the batteries to say 38 to 40 degrees F, and when over a certain internal condition the fan would come on and heat the batteries.
As it is, I think I'll just put heating pads under, wood around, and forced air into the box at the edge to run around and over the batteries as described above. I'll put the temp sensor in the middle of the pack. Best I can do, IMHO.
David
P.S. no, i don't care about compression of the batteries, so I could run oil around them if i wanted, or even just pack aluminum sheets between each cell.
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Read up on phase change materials. Coconut palm oil freezes ( solidifies) at 24.5 degrees C. and it has a high latent heat requirement.
Effectively, this means that the batteries temperature will be quite stable in the hot or cold direction at the melting/freezing point temperature.
A whole lot of energy has to be transferred to supply the solid<>liquid phase change, without any change in actual temperature.
There are many other materials too, but as you mentioned oil, there is one that should be readily available.
Kinds of paraffin are chemically inert with metal and can also be tailored to certain phase change temps.
I haven't done this, because I haven't built my bank yet, but I have been giving it some thought.
BabylonFive
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OK, that is interesting.
If the phase-change material had a reasonable latent heat, yet also was a pretty good insulator, then it might be an interesting temperature-driven automatic cooler. The processes of conduction and convection don"t necessarily have to be shared -- by this I mean that a battery inside a metal heat-sink box could be cooled effectively by the liquid phase or by operation at high temps, but it would partly be insulated from very cold temps by freezing in place and stopping convection. I fear the effect isn't extreme in the cooling or insulating phases.
Cool (see what I did there?).
I think mineral oil, or something else chemically and biologically inoffensive, could simply be pumped to a heat sink for high conduction to ambient thus good cooling, and then not pumped during cold for high insulation to ambient allowing self-heat or a small electric heater's heat to stay in the batteries and keep them warm. This all presumes a well insulated box with circulating oil in contact with all the batteries.
Thanks for the info.
David
