Power Resistor Heater

Living in a city which temps go from 35c to -35c,Looking at ways to keep the batteries cool/heated. The future14s powerwall will be going into a shed which I'll insulate the cabinet where the batteries are going, looking for feedback on how to heat/cool. How much heat is required to keep it at 5 Celsius.

Here's what I'm thinking for Heating: Based on the chart below as a starting base, I'm going to take 8ft ceilingheight so that's 5ftx10ftx8ft=400cu.ft --> 400/500watts = 0.8watts/cu.ft:





Heated Cabinet will be small I would say 3ft x 6ft x 1ft. So that's 18cuft. 18cu.ft * .8 watts = 14.4 watts to heat this cabinet?

does this make sense?
Was looking at 4 *100watt 10ohm power resistors and hook them up in series and spread them throughout the cabinet for event heat distribution but that's at 90 watts. I will add a micro controller to turn on the resistors when the temperature dips below a threshold.
maths is this correct?:
V=IR 60=I*(40ohm) I=1.5A
power across total circuit=Isquared *R P = (1.5*1.5)(40) P=90Watts or 22.5 watts /resistor
The joys of living in a harsh environment.
Suggestions/opinions?

found some more info: http://www.digikey.fi/Web Export/Supplier Content/Riedon_696/PDF/riedon-an-resistors-as-heaters.pdf

Interesting.
You actually wouldn't need to heat the whole room. That's a lot of thermal area to heat up. You'd only need to heat up the cells themselves. So you could design a unit that has the thermal resistors within the packs to keep the packs within proper temperature range.
You wouldn't need to heat the electronics or the wiring for the most part. Some parts of the electronic board might work better being heated slightly, but most would be fine in cooler air.

The wiring wouldn't need any heating as the cooler the wire, the easier the electrons move. Well, that is, till it gets really super cold. I'm sure you could find a datasheet on copper wire to find it's bottom electrical efficiency in cooler temps.

I personally won't need these as I live in Southern US. It doesn't hardly get below 32F here. Rarely does it get below 40F, even.

Good application for those who live far north, or extreme South (Southern Aussie?)

Hi Jeremy,

what would happen if you would take just a heating gun/heating vent and connect it to a timer and would heat every one /two/tree hours your cabinet? With a vent you even can cool it.
I would say it is an easy and simple way. If you have an converter in this room just plug the device in and that is.

Good luck!
BigBen

Jeremy,

Have you thought about super insulating it? I know that dry ice inside of 2" thick styrofoam cooler lasts for a surprisingly long time.

My first impulse would be to try to create a space around the battery packs that is insulated and has controlled ventilation. When it is cold, you can shut the ventilation and heat it. The more insulation, the less energy it will take to maintain temps. When it is hot, you can provide forced ventilation with cooler air as needed.

-John-

BigBen said:

Hi Jeremy,

what would happen if you would take just a heating gun/heating vent and connect it to a timer and would heat every one /two/tree hours your cabinet? With a vent you even can cool it.
I would say it is an easy and simple way. If you have an converter in this room just plug the device in and that is.

Good luck!
BigBen

Click to expand...

Good Idea, but I think I'd prefer passive heating. if the fan fails on the gun = fire hazard.

The plan is to create a super insulated area with a removable insulate cover. Summertime I wouldn't put the cover on. Even super insulated enclosures will eventually equalize with the outdoor temperature. Some testing in the freezer will be in order. the funny thing is the freezer is only 1/2 the temp I need to test to.