diy solar

diy solar

LiFePO4 heating pad for cold temperatures

I plan to power my heating pads from the bus bar. If the heating pad (with its own thermostat) needs to run, it can. If the heating pad runs during the day during sunny hours it will pick up power from the MPPT. Otherwise, it gets power from the battery bank.
 
I plan to power my heating pads from the bus bar. If the heating pad (with its own thermostat) needs to run, it can. If the heating pad runs during the day during sunny hours it will pick up power from the MPPT. Otherwise, it gets power from the battery bank.
Have you picked out a heating pad?
The orange 3d printer pads seem about the right size for a bottom mount.
The Battleborn are wrap around but probably a little small for the 12v 280AH Prismatics. But maybe I should check on them, $220, mmmm.
 
I have mine waiting to install. I had them custom made by UltraHeat. I provided the dimensions as well as a drawing of the battery in the compression rack so they could see what I needed.

With the battery sitting upright (terminals up), the two pads will cover the long sides of the battery. I chose this method because I knew the short sides were going to be covered up by the compression boards on each end.

20200829_093302.jpg

Picture of the entire kit. One thermostat covers both batteries.

20200829_093158.jpg
 
I'm not going to turn off the trailer. Normal stuff will be off but I plan to leave the BMS active since the solar will be active.
if your concern is mostly centered on when the vehicle is in storage, why not disconnect chargers or disconnect the batteries completely? Lithium doesn't want to be stored full or near full, so if the vehicle is just sitting for months, is there a reason solar has to be active?
I am planning to change the charge profile on the Victron 100/50 so it doesn't result in a 100% SOC. A concern there is that if I'm not bringing the batteries up to a certain level, the BMS won't balance the cells.

If you disconnect everything while in storage, I don't think there is a need to worry about balancing, is there? The batteries should be pretty stable, beyond the minimal self discharge rate, right? The battery should be at mid-SOC for storage so voltage differences will be minimal.
 
If you disconnect everything while in storage, I don't think there is a need to worry about balancing, is there? The batteries should be pretty stable, beyond the minimal self discharge rate, right? The battery should be at mid-SOC for storage so voltage differences will be minimal.

Charging will still be ongoing. I'm at the trailer throughout the winter doing maintenance. There's always something that needs fixing. The trailer is "down" for only about three months as I don't mind camping in the cold. I draw the line at pulling the camper during snowstorms.
 
Was tempted by the Battleborn, so I Amazon Smile'd it.
Suggest checking out the alternatives when one scrolls down.
Lots of choices...
 
I've had some cold temps for a couple of mornings to test my heat pad with external digital thermostat. The pad is like the one Will posted at the bottom of his original post. I used settings a bit lower than the ones the pad comes with. Both mornings of about freezing my batteries were at 50.3° F
I have some ideas about making my own that won't be limited to any predetermined shape or size. Waiting on some parts to show up from China. More to come.
Hay friend, what did you come up with
 
I have mine waiting to install. I had them custom made by UltraHeat. I provided the dimensions as well as a drawing of the battery in the compression rack so they could see what I needed.

With the battery sitting upright (terminals up), the two pads will cover the long sides of the battery. I chose this method because I knew the short sides were going to be covered up by the compression boards on each end.

View attachment 22920

Picture of the entire kit. One thermostat covers both batteries.

View attachment 22921
Jim, have you added these yet? Curious on how it works out for the cold season.
 
HRTKD,
How is the heating pad arranged?
On the batteries bottom?
Any concern the battery weight will crush the heating element?
 
The heating pads will go on each long side of the battery, which means they are on the short sides of the cells.

In the picture below, the pads will fit between the cells and the threaded rod. I planned ahead when I made the compression frame and made sure there was enough room to insert the heating pad. Rigid foam insulation will be placed outside the threaded rods and on top of the battery. The top is going to be challenging with all the wires that are there. I'll probably mount the insulation on top of the compression frame so it doesn't have to touch any wires.

20200902_205309.jpg

Where things get a little fuzzy is the placement of the thermostat/controller. It says to put it away from heat sources. I could put it a couple feet away in the same compartment, but I'm not trying to warm the compartment. I think I'll put it on top of one of the batteries, near where the temperature sensor for the BMS is located.

The pads are rated to consume 1 amp each. My expectation is that the heating will be slow and controlled. On at 35° F, off at 45° F. That seems pretty safe to me.
 
Hmmm, since my battery is still on the boat, a 280Ah just like yours, could you give me some dimensions, please??
 
Hmmm, since my battery is still on the boat, a 280Ah just like yours, could you give me some dimensions, please??

At the time I spec'd out the battery warmer I didn't have my cells yet. I used published dimensions and came up with 11.25" length x 6 13/16" width x 8 1/16" height for a 4s battery. I figured if the cells were a little thicker in the real world, the pads would still fit OK.

My cells are in my RV trailer at the storage lot, so I don't have ready access to them.
 
It says to put it away from heat sources.

That's only in case you use it the classical way in your house (you want to measure the ambient temp, not the heat source temp).

In your case you need to put the sensor where you want the temperature to be stabilised by the heat pads (on top of the cells roughly in the center sounds good).
 
My Fridge (A Vitrifrigo C75L) has a remote heat exchanger. I was toying with the idea of building a well insulated battery box inside the living area with perhaps locating the heat exchanger inside the box thus using the heat to help keep the chill off the batteries? I don't know how effective this would be but I thought it could a handy way of making use of energy that would otherwise be wasted.
The only issue with that is - when the ambient temperature is low your H/E will be giving out the least heat. When ambient temperature is high - you'll get the most heat just when you don't need it. I'm thinking about putting mine under the bottom of the wardrobe and ducting the heat upwards to keep jackets warm.
 
@HRTKD have you considered running a temp switch of some type for the heating pads to turn on below a certain temp? Will they be running full time until you manually disconnect? We only get freezing temps for a month or so here in PNW. I don't plan to use the RV during that time, its sitting. so I could manually disconnect. Id rather not have to pull my batteries each winter season. it is an option.
 
@HRTKD have you considered running a temp switch of some type for the heating pads to turn on below a certain temp? Will they be running full time until you manually disconnect? We only get freezing temps for a month or so here in PNW. I don't plan to use the RV during that time, its sitting. so I could manually disconnect. Id rather not have to pull my batteries each winter season. it is an option.

The heating pads came with a temperature switch. On at 35° F and off at 45° F. I'm going to put in a manual switch so there is no draw (no matter how small) in non-winter seasons.
 
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