Best temperature for batteries (LiFePO4)

[CaliSunHarvester]

What is the best temperature for server rack type LiFePO4 batteries? I put mine with the AIO in a dedicated shed that is under a roof overhang on the northern side of the building, it's never in the sun. The AIO insists on indoor installation, so I went overboard with wall thickness etc..: wood framed, insulation, Tyvek on outside over OSB, fully sheetrocked inside.

I built this during rain season and keeping humidity low was a priority for me.

I did not expect that the AIO would generate so much heat. Humidity is under 30% when it rains!
Outside temperature is 7C at night and 17C at day time (today).

Temperature range in the shed


And that's after I added a ventilation in and out (4" pipe with inline blower, 100cfm)

Now the batteries. Their temperature ranges between 28 and 31C (as of today).


I am concerned that in summer these batteries will be closer to 40C!!

Should have made the shed bigger.

What temperature range do other people target?

 

[Skypower]

I feel your pain. You may notice that the air in the shed is cooler near the floor so if possible place the batteries closer to the floor but above any potential water level. Batteries not only store electricity, they store heat. Heat, like the state of charge takes a while to change. If you have access to the tops of your cells (DIY) it’ll help to blow air over them as long as air is COOLER than the cells. The terminals and busses are excellent heat conductors and radiators to pull heat from the core of the cells. When your shed cools down cooler than the cells ( when your inverter isn’t heating it) is the best time to cool them down to get ahead of it. I have a fan to cool them on a timer. The rest of the time there is no air moving around the batteries (stagnant/still) because I don’t want the hot air heating them. It is a good idea to deflect away (barrier/partition) hot air from the inverter and draw the hot air out with a vent fan. Remember that you need to provide an intake for fresh air if your shed is well sealed. Every location is different so look temperature differences, times and airflow to your advantage.
Good luck.

 

[DIYrich]

5-40 c. Under 30c is better. Wouldn't want more than 50c.

Note: you can discharge at lower Temps, but you should not charge below 0c. Hence 5c just to be safe.

 

[Skypower]

On a really hot day the air at head level gets to 45c but my batteries rarely get over 33c because of aforementioned management.

 

[CaliSunHarvester]

Weird, I did not get notifications about these responses. Thought just nobody was worried about temperature.

notice that the air in the shed is cooler near the floor

yes, I did notice that. Especially since my AIO blows warm air out at its bottom, which is like 4' below the ceiling. The batteries are in a stack. Lowest battery always coolest.

I have a fan at the bottom near the battery stack that blows the cool air at the floor upwards.

Remember that you need to provide an intake for fresh air if your shed is well sealed.

Certain times of the day the batteries show a higher temperature than the room temperature (measured near AIO). These would be the best times to cool the batteries.

Also, I expect everything to change as outside temperatures rise. Right now they are below 10C at night and 15 to 20C at day time. Easy to cool with a 4" inlet then.
Yes, I do have a 4" intake near the ceiling on one side and the 4" exit on the opposite side. The exhaust side has a inline fan attached to the ABS pipe that I embedded into the wall. ABS pipe on the inlet as well. I do have 1/4" mesh in front of the ABS, concerned about critters now.