First Real Test DIY Battery Heating

[Rbertalotto]

First real test of DIY battery heaters....Last night it got down to 25 degrees. At sunset the temperature was 40 degrees. The batteries in the travel trailer were at 100%. This morning at dawn, the temperature is 28 degrees and batteries are at 93%......the battery box is at 44 degrees. I have the high and low on the temperature controller set at 35/45......could be set lower, but I wasn't sure how reliable or accurate the temperature controller was. I will set it lower. In the Roof Top Tent system, the battery was at 100% at dusk and at dawn it is at 90%. This system high and low is set at 35/40
Both trailer and truck are using the same controller and heating pad.....Trailer has two 100ah Li batteries in an insulated hard case with 420w solar on roof. The truck has single Li battery in a soft side picnic cooler with 200w solar on the roof.
You can read all about the installation and watch videos of the systems here.... www.rvbprecision.com
Hope this might help someone else traveling the same path.

 

[kbeefy]

Copied you but ordered a 7x24 pad as it will fit my 200aH battery better than the 12". I already received the temp controller you settled on.

Cheers!

 

[Leeds]

Interesting, thanks for the detailed writeup ?

You seem to have chosen a ~70w heater for your battery to heat it up quickly and cycle on and off.

I went a slightly different route with a similar 100ah lifepo4 battery. But instead of a "hot" heater I made a very small heater, roughly 6 watts, also controlled thermostatically.

The "low and slow" crockpot approach allows me to heat the battery to about 10°f above the ambient air temp in the compartment. And it also allows me to run the battery for days and days (and days) if it stays cold.

Of course if the compartment temp gets below 23° and/or the battery temp drops to 32° I also cut off the ability to charge the battery via a bistable relay on a dummied-out temp sensor on the charge controller.

I'm looking forward to logging data through this winter but I'm already very excited by how well it works.

What approach have you taken to the dead-battery freezing-temp-sunrise scenario?

 

[Rbertalotto]

A Quick Test.... Yesterday was no way near ideal conditions for this test, but the results are interesting none the less. Yesterdays daily temperature was in the high 40s.....At 5:30pm I shut down the DIY battery heaters. Ambient temperature was 33.6F.....The battery box internal temperature was 44.2F and the batteries internal temperature was 46.4 (Batteries were being charged throughout the day by 420w of solar...Batteries were at 100% when checked at 5:30PM)......This morning at 7AM....Ambient temperature was 47.3F....Battery box was at 43.5 and batteries internal temperature was 39.2........Interesting! Why did battery internal temperature decrease 5F yet the battery box internal temperature only went down 1F....May be the dramatic rise in outside ambient temperature kept the box warmer than the batteries? Regardless, interesting stuff here......Will perform again when we have much colder weather.

 

[fratermus]

I went a slightly different route with a similar 100ah lifepo4 battery. But instead of a "hot" heater I made a very small heater, roughly 6 watts, also controlled thermostatically.

Similar approach here -- I warm my 100Ah with a 16w pad + temp controller. It holds the setpoint (50F) in the van in freezing weather without issue.