BATTERY HEAT

[jerryt253]

New to all of this. For my offgrid cabin, installed a Growatt 3000 connected to a Eg4 24volt battery, powered by 2 - 300 watt solar panels. System is in an unheated outbuilding, not severe weather here in Central Washington state, but temps below freezing. Major concern right now is keeping the battery warm enough to not cut off. Should I be thinking about exchanging for a heated battery, and if so, what brand? Or, perhaps a heating pad? Not sure if my system would keep up with energy needed to power heat for the battery. System does not get a lot of use, as I don't get there too often. Or, better to put inverter in standby and switch battery breaker off when not there? And, if I understand correctly, I need at least a 6000w generator to recharge the battery through the inverter - maybe best using a 24v battery charger run by a generator. Thoughts? Any recommendations for a charger? Thanks for your time. Appreciate any advice as I am on a steep learning curve.

 

[MisterSandals]

Or, better to put inverter in standby and switch battery breaker off when not there?

If you don't need to power anything while away, i'd opt for just disconnecting everything. The self discharge is very low.

 

[OffGridInTheCity]

There hasn't been a lot of hands-on with this, but from all the things I've read, mildly cold temps (15F) won't hurt an inactive lithium-ion battery bank so much if you let it warm up before using it.

So one approach is to keep the batteries in the cabin and off when gone. When you arrive, heat the cabin (wood stove?) and give batteries an hour or 2 to absorb ambient and then you're good to go.

Another is to take the battery bank with you / kept warm in vehicle - and plug in when you arrive. Depends on size of battery bank etc of course. If large battery bank, maybe transport a small battery to help bring the cabin alive and when warmed up then switch over to permanent battery bank.

Similarly is to transport an entire portable power station and plug into cabin distribution box and PV panels that are permanent.

 

[OM617YOTA]

I'm in the Willamette Valley of Oregon, not too far away. 15F is about the coolest we get, ever. I think you could build a heating system that would be completely practical, without much trouble.

I insulated my battery box with two layers of R7.7 foam insulation. Stuck a couple stick-on 24v heaters pads to a chunk of aluminum I had laying around, running directly off my 24v battery voltage. The surface of the heaters were getting warmer than I wanted, easily topping 140F(not the enclosure, just the heaters), so I rewired them in series to increase resistance and drop surface temps of the heaters themselves to something I was comfortable with having in the battery box. The surface of the heaters themselves, not the aluminum heat spreader, and not in contact with the batteries, tops out at around 100F now, and draw ~20w. Used a cheap electric base board heater thermostat to control them. They've thus far kept the batteries at ~67F through all the cold we've had this year, with zero trouble.

I initially added the heater when the batteries were around 42F, and the heater ran solid for a couple days, 20w of heat doesn't generate much delta T in 200lbs of thermal mass. Since getting up to temp, I haven't noticed the heater run at all, and don't notice it kicking on and off. It hasn't used enough power to worry about at all with 1.6kw of solar on it.

If we got down to -40 for weeks, it would need more insulation, but the same basic setup would work.

 

[gotbeans]

didn't see your post before @OM617YOTA it is very similar to what I have going in

Reptile Heating Pad To Keep LFP Batteries Warm?

There has been a few discussions on self heating LFP or using external heaters and it occurred to me I used to have an iguana and used a small pad heater in the tank that actually got very warm and used low watts. So I looked for them on Amazon and they have lots of models big and small and...

diysolarforum.com

These systems work very well and I think it is way easier to keep these batteries warm than people realize. All it needs is a little insulation and very little power. Probably at 12-20 inches of insulation no power would be needed even at 0F / -17C

 

[OM617YOTA]

My heating system kept my batteries at 65F this past weekend, external temp 23F. Not using enough power to notice.