Can you describe why you need to be charging at below freezing temps? The reason I ask is, the simplest solution, if you must charge in below freezing temps; is to place them inside the Transit and keep it above freezing using the engine heating or a space heater..

Some manufacturers now offer LiFePO4 batteries capable of charging at below freezing (LifeBlue & ReLion I think) so no need for heat wraps.

Cold temps will reduce the capacity of the battery too.

I boondock using 2 x 75AH LiFePO4 batteries and as long as the daytime temps reach the restart temp on my BMS (Battery Management System), charging will be allowed. Based on my electrical usage, my batteries will last 2 - 3 full days before needing to be recharged. My battery box is outside (underneath the Transit) and unheated. No issues using them to date. If you are in constant below freezing temps, that's a different story.

I'm currently boondocking so may not be logged into this site that often,

Cheers, Steve

 

The brand I went with has a low temp version with built in heater, but I needed mine to get to the outfitter about 2 weeks before they started shipping the low temp.

With regular lithium I've had no trouble in Denver. Often below freezing for days, but my batteries are inside the wagon and I have no significant power draws when we're not out doing something, in which case van heater or Espar is cranked at some point during the day/night which brings them up to charging temp.

Discharge can happen much colder than charge, so they discharge a bit till the van is warm, then can start charging.

 

We have used seat heating elements and a digital thermostat to warm LiFePO4 batteries. We also insulate batteries with 3M Thinsulate AU4002-5.

Heater: https://www.amazon.com/gp/product/B002U6IL9O
Controller: https://www.amazon.com/gp/product/B011VGAPOC
Thinsulate: https://www.ebay.com/itm/132070330532

All the best,
Hein
DIYvan
541 490 5098

 

We have used seat heating elements and a digital thermostat to warm LiFePO4 batteries. We also insulate batteries with 3M Thinsulate AU4002-5.

Nice! Where do you place the pad and sensor? I was thinking about DIYing this for awhile and pad on the bottom sensor on the top made sense to me but I didn't know how long it would take the batteries to heat-through and didn't want to over-heat them with the pad!

 

We laminate the heating element between two layers of thin minicell foam and set the batteries on it. The thermocouple goes on the side of the battery case near the bottom. We would rather know the temperature there so we don't overheat.

All the best,
Hein
DIYvan
541 490 5098

 

We laminate the heating element between two layers of thin minicell foam and set the batteries on it. The thermocouple goes on the side of the battery case near the bottom. We would rather know the temperature there so we don't overheat.

Makes sense! Maybe the sensor on the bottom of the battery to control the heater and a sensor on the top of the battery to tell when it is above freezing and can be charged! Certainly no reason not to have two relays for a project like this!

 

HEIN thanks for the ideas. I think I will go that route.

So the reason why I think this is important is I am unsure if their is in fact BMS inside the batteries to protect them from charging while frozen. They are Chinese LiFePO4. I do have a Victron BMV 712 that I will install but I believe it is only battery monitoring vs full on management with temperature controls.

Since it will be left unattended in "autonomous" state, I don't want the charge controller to charge batteries if it is below 32 degrees. I suppose I could just leave the diesel heater running but I do not believe it has a thermostat to start the heater up if it reaches 32.

 

I decided to order this:

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because the size fits the LiFeBlue 200Ah perfectly. It comes with the hi/low switch and built in thermostat. So now I’m thinking that I don’t need an extra controller at all. I’ll just select hi or low and let the thermostat take care of overheating. I can monitor battery temp on the LiFeBlue App. We will see if it works!