How much do I need to worry about heat?

[beckkl]

As I wait for 16 cells to arrive, I have been day dreaming about how I will build this battery. I like how @Off-Grid-Garage did it, and plan to take a similar approach. I plan on getting a heat pen, and custom fitting the enclosure with 1 or 2" of foam, as this battery will experience harsh winter weather. My half brained thought at this point would be to custom build a "box" for the cells, out of foam, with a foam lid that would fit nice and tight. The bottom of the box would have heat elements and an aluminum plate. Then in the summer, maybe take the lid off and install some fans in the main enclosure to circulate air.

I know how bad cold temps are, but how worried do I need to be about heat? I do not plan on drawing more than 100A from the pack.

 

[Maast]

Heat ages lifepo4 - the cooler you can keep them the better. Heat above 15C (59F) will begin to somewhat accelerate the aging of your cells but the aging curve doesnt really start climbing quickly until you get above 20C (69F).
Take a look at this research paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6126518/

 

[beckkl]

Yikes! This is going to get interesting. The pole shed this will ultimately be stored in is going to get fairly hot in the summer.

 

[Maast]

I should have said it better though: temperatures below 20C retard normal aging which is what the above study was all about. It doesnt really accelerate until you get above 80F.

If you're going to have it in a outside shed what you can do is bury a 6" diameter plastic pipe in the ground about 18-24 inches deep and 20-50 feet long (depending on just how hot you're talking about) and have that connected to a coleman cooler or heavily insulated plywood box, then have another pipe going to a flat black painted metal chimney stucking 8ish feet in the air in the sunlight. With the cooler lid closed the black metal stack will heat up in the sun and suck air into your long plastic pipe which'll cool down the air and keep the cells cool.

You could get the same effect by having a 12v fan directly connected to a small solar panel sucking/blowing air through the pipe. Or go really energy intensive and have a small air conditioner for the cooler.

You can't let them charge when at freezing either, charging frozen LFP cells destroys them very very quickly. Heating can be provided by a 40 degree snap disk thermostat connected to a heating pad inside the cooler. You can find 12v heating pads fairly easily, and if you're doing 24 or 48v you just put two or four heating pads in series.

 

[Luthj]

You need to look at the average daily temperature to get a feel for this. High mass blocks of cells will lag behind the current temp, cutting the extremes off the high/low peaks.

To a certain extend cool winter temps (say keeping the pack around 40F), will balance out occasional high pack temps. My insulated pack rarely gets more than 4-5F above ambient, even with modest C rates. If needed a vent fan can be added, but that can actually speed heating of the pack if the ambient is high.