Temperature control of LiFePO4 battery banks?

[fafrd]

Looking at the datasheet for the EVE 280Ah cells, rated capacity is specified at 25C +/-2C, meaning 73.4F to 80.6F.

At -20C / 4F the capacity drops by 30% to 200Ah but the discharge curve also gets very wonky, dropping to 2.65V right out of the gate then slowly rising to 3.0V (probably due to internal heat generated at 1C discharge rate) before dropping to 2.5V after 200Ah (43 minutes at 1C).

4F is pretty cold and I don’t need to worry about those temps here in California, but it is 52F / 11C outside right now and we frequently dip to 40F / 4C over winter, so I’m wondering two things:

1/ has anyone characterized discharge performance of these EVE 280Ah cells at moderately cold temperatures around freezing (0C / 32F)?

2/ since the shape of the discharge curve changes so radically at colder temperatures, is anyone going to the trouble of heating their LiFePO4 cells to maintain 25C?

I’m planning to use my 280Ah bank as the backbone of a DC-coupled solar system for self-consumption, which all pencils out pretty nicely using standard 25C discharge curves.

But if I leave the bank at ambient temps and get a completely different discharge curve at winter temps of 40-50F, system performance will be a problem.

I was originally worried about keeping my LiFePO4 cells cool enough and not overheating during charge or discharge, but now that I’ve understood my maximum discharge rate will be very modest (0.12C) and even my peak charge current of under 0.3C is below standard charge rates of 0.5C and will only be for a maximum of 1-2 hours during the hottest part of the day, I’m getting more concerned about assuring my cells are kept warm enough to deliver the performance I’m counting on.

Anyone else have similar concerns and if so, interested in solutions anyone has thrown together...

 

[snoobler]

My $.02

1/ I haven't seen it.
2/ No way. Too much wasted energy. Better to store them in a temperature controlled environment.

 

[vtx1029]

It’s not very difficult to get some 12v heating pads and a temp controller. If you are really worried about it.

 

[upnorthandpersonal]

2/ since the shape of the discharge curve changes so radically at colder temperatures, is anyone going to the trouble of heating their LiFePO4 cells to maintain 25C?

No, just keeping it above 5C for charging. Don't care if capacity is less at lower temps really.

 

[HRTKD]

No, just keeping it above 5C for charging. Don't care if capacity is less at lower temps really.

Ditto.

My 560Ah of LiFePO4 batteries sit in my trailer all year. In the winter I have the heating pads to keep them from going below 35° F. There are small loads on the batteries during the winter. Small enough that I'm not worried about it. I do camp in cold weather. But when I'm actively camping, the furnace is on and the batteries come up to the temperature inside the trailer.

 

[fafrd]

It’s not very difficult to get some 12v heating pads and a temp controller. If you are really worried about it.

can’t tell if I’m really worried about it yet - that’s why I asked. If most here are happy with the performance they are getting out of their EVE LiFePO4 cells at temps above 5C / 41F, I should be fine at cellar temps here in Northern California.

Throwing together a thermostat-controlled heating pad isn’t that big of a deal but designing a case to both maintain heat when too cold and to vent off heat when too hot is...

I’m not in a big rush and may try running a capacity test with battery placed in a cooler this summer just to understand whether venting heat is something I ever need to worry about.

Knowing whether my use case means I never need to worry about overheating would greatly simplify case design (and would make it easy to add heat control if I ever conclude that would be worthwhile).

 

[HRTKD]

can’t tell if I’m really worried about it yet - that’s why I asked. If most here are happy with the performance they are getting out of their EVE LiFePO4 cells at temps above 5C / 41F, I should be fine at cellar temps here in Northern California.

Throwing together a thermostat-controlled heating pad isn’t that big of a deal but designing a case to both maintain heat when too cold and to vent off heat when too hot is...

I’m not in a big rush and may try running a capacity test with battery placed in a cooler this summer just to understand whether venting heat is something I ever need to worry about.

Knowing whether my use case means I never need to worry about overheating would greatly simplify case design (and would make it easy to add heat control if I ever conclude that would be worthwhile).

Many of us have come around to the realization that the worry is more about ambient heat than heat generated by the batteries themselves. Once I get back into the spring/summer/fall camping season, the insulation is coming off the batteries. I have no plans for cooling the batteries. I may put in a fan or two to cool the compartment where all my components - including the batteries - are located. The batteries aren't the big heat source. Instead, it's the inverter and the solar charge controller that I'll be keeping an eye on.

If you have your batteries in an unvented, closed area - like a cooler - I could see there being a potential for heat buildup.

 

[vtx1029]

I currently have a 12v 560ah battery setup in my trailer, just spend 5 days running off of it and I'm very pleased with the performance of these cells. when I looked at the cells they remained sub 0.01v for cell balance even while pulling 60+ amps. My avg temp was around 55*F, I also let my cells go below freezing but never charge below freezing.

 

[fafrd]

I currently have a 12v 560ah battery setup in my trailer, just spend 5 days running off of it and I'm very pleased with the performance of these cells. when I looked at the cells they remained sub 0.01v for cell balance even while pulling 60+ amps. My avg temp was around 55*F, I also let my cells go below freezing but never charge below freezing.

My cells will be in the cellar at a pretty constant 65F, so I don’t need to worry about freezing temps.

I just checked cell capacity with a little temperature-controlled chamber I threw together and get 100% at 23C (77F).

I’m going to charge again at 65F to check whether I see any significant capacity degradation at expected cellar temps.

If not, I’m good to go. If not I’ll need to decide whether it’s significant enough to do anything about.

I temperature control for beer-making all the time. Rigging up a heatpad to maintain at least 23C (or whatever) and a fan to maintain below 27C (or whatever) is not a big deal - it’s just more complexity and something else that can go wrong.

So I’m hoping my cells charge about as well at 65F (18C) as they do at 77C.