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Battery heater questions

100 Proof

"Please Lord, don't let me do something stupid."
Joined
Feb 14, 2021
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206
I've just added 28 Watts worth of heaters to the bottom of my cells. I'm trying to figure out how to complete the configuration and I have a few questions.

For those who have added heaters to your battery banks inside of insulated enclosures, where did you put your temperature probes? Did you put them in the airspace, attached to the top of the battery, attached to the side of the battery, or somewhere else? Why did you put it where you put it?

Do you have any data driven information on how you programmed your controllers? For example, does your programming take into account thermal mass, thermal coasting, etc? What set points did you use to turn your heaters on and off?

Thanks!
 
I didn't get any feedback on my question, so I just experimented myself. I ended up taping the thermocouple halfway up a cell in the middle of my 2S4P pack. I set the controller to 40 degrees F. It basically bounces between 39 and about 43 degrees over a several hour cycle.

For my heater, I used 4 of these 7W polyimide heaters. https://www.amazon.com/gp/product/B07P2RJDPL. I attached them to a .060” aluminum plate I had and covered them with felt and Kapton tape. I covered the other side of the plate with phenolic tape to give the cells something to slide on as they expand and contract in my compression fixture. At only 28 Watts, they heat my cells gently and evenly. Of course, the whole thing is in an insulated box.
 

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Seems reasonable. I have a plan but have not implemented it yet. Mine is going to have to recover from -20C or colder so I have a lot more power than you are using. I have 2 heating circuits. The high power circuit will be controlled by a thermostat in the airspace below the cells. The low power circuit will be controlled by a thermostat in the airspace above the cells. The BMS temperature probe will be located between cells in the top 1/3 in a notch cut into the 1/4" plywood separating the cells.
 
Just a quick follow-up to this post I wrote little over 2 years ago. I'm now on my third winter using the system exactly as described above. It's worked perfectly! I've had no reason to modify it or make any changes. All I do at the end of the heating season is flip the switch off and remove my insulated cover. I suppose I don't even have to do that if I don't want to, but as I'm actively using the travel trailer more in the summer, I remove it just to prevent damage since it is just fragile foam.

Anyway, just a quick update in case anybody was following this post and wanted to know how it turned out. Happy New Year!
 
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