Keeping batteries cool-low tech

[Bluedog225]

Has anyone taken temp readings inside a styrofoam cooler on a hot day? I’m interested in how temps track. For example, let’s stipulate something like a 100F day and 70F night.

I’d suspect that the temp inside a cooler would be buffered from the outside highs and lows. E.g.: it would be nice if the temp in the cooler remained between 90F and 80F. Filling the voids with fiberglass or similar would add additional insulation.

I’ve seen several experiments to keep batteries cool or warm but wondered if anyone had run this completely passive experiment.

Thanks

 

[sunshine_eggo]

Your scenario would play out nicely (80-90°F) for batteries being stored, but not in use.

Batteries are their own heat source when in operation. When discharging at a low to moderate rate overnight, they are not generating a lot of heat, so they track nicely with ambient; however when they are charging, they can generate heat and meet or exceed ambient and may need ambient as a heat sink. Insulation would interfere with any heat transfer away from a hot battery.

 

[Bluedog225]

Good point. When its 110F, I’m generally not up there. And I would store the batteries for the summer. When using the place, I would open the cooler lid and hook up the solar panels.

 

[sunshine_eggo]

Good point. When its 110F, I’m generally not up there. And I would store the batteries for the summer. When using the place, I would open the cooler lid and hook up the solar panels.

Watts = ((T2 - T1) * A) / ( R / 5.68)

T2 = outside temp, °C
T1 = inside temp, °C
A = area of surface, m^2
R = R value of surface.

Without running the numbers, you can just focus on the R value. Let's say your cooler has an R value of 8. That means it would slow the energy transfer between inside and outside by factor of 8 and would thus slow the temperature change by a factor of 8. This does NOT take into account the battery's thermal mass, which changes temperature at its own rate depending on thermal conductivity, but it will change more slowly due to the fact that the cooler is slowing the energy flow between outside and inside.

EDIT: error in prior formula. "/ 5.68" was added as the SI formula uses RSI rating, not R-value.

 

[Bluedog225]

Thanks. That is a very great answer. I’ll be interested in finding out how the measured numbers look. It will have to wait till next summer to run test.