diy solar

diy solar

LiFePO4 heating pad for cold temperatures

I took a different approach. I built a well insulated box and put a heat pad on one side, but not touching the battery. ( I did not try to wrap the battery. ) This means the temp on the batteries will be more even. When I open the box in the summer, I don't have to unwrap the battery.

I'm constrained on space. A close fitting wrap/pad will work better for me. I'm not ruling out something that heats the general area, but it would be a lot less efficient. Enclosing the batteries with R3 1/2" rigid foam is doable, but I would have no room around the insulation. So there's no room to add any gap between the insulation and the battery.
 
In the summer the wrap will hold in any heat generated by the batteries. It will act like a blanket.
Not much though, a heat pad would have a very low R-value, the insulation around it will be more of a problem there. The insulated box (if you have one) will just need a vent opening in summer
 
In the summer the wrap will hold in any heat generated by the batteries. It will act like a blanket.

I suspect this insulation would be a much much bigger factor than the heating pad. Unless you are in a situation where every degree of temp is important, removing the insulation but leaving the heating pad in place is maybe more than enough.

Under 0.5c especially under 0.33c, battery temps are pretty close to ambient (within a couple degrees) so as I understand (not an expert) there isn't a ton of heat that needs dissipating. A thin heat pad (particularly if its just on one or two sides) seems like it might not be that big of a deal. I suspect good passive or basic active ventilation could maybe make a bigger positive difference than whatever negative the heat pad did.

edit: and to be clear this is all speculative (apart from the data on battery temps compared to ambient temps which comes from a study)
 
I suspect this insulation would be a much much bigger factor than the heating pad. Unless you are in a situation where every degree of temp is important, removing the insulation but leaving the heating pad in place is maybe more than enough.

Under 0.5c especially under 0.33c, battery temps are pretty close to ambient (within a couple degrees) so as I understand (not an expert) there isn't a ton of heat that needs dissipating. A thin heat pad (particularly if its just on one or two sides) seems like it might not be that big of a deal. I suspect good passive or basic active ventilation could maybe make a bigger positive difference than whatever negative the heat pad did.

edit: and to be clear this is all speculative (apart from the data on battery temps compared to ambient temps which comes from a study)

Removing the insulation would be a LOT easier than removing the wrap. Since I have yet to implement/install anything, I can probably make the insulation relatively easy to remove.

I really don't want to fry my batteries. But I don't have any LiFePO4 experience yet.
 
I really don't want to fry my batteries. But I don't have any LiFePO4 experience yet.

Totally understand, there is a lot to consider.

Here is some additional info on temperature vs charge discharge rate and a short excerpt from NordkynDesign:

The gaps between the cells can present an advantage for cooling when thermal management is necessary due to very high currents, but, in marine applications, the currents are modest and the battery cells never seem to get more than a few degrees above ambient temperature.
 
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If the gap between cells helps cooling, it should also help with heating. However, if I've covered the cell gaps with a wrap, it kind of defeats the purpose of the gaps as far as cooling goes. After the wrap is on, only one side of the battery with gaps would still be exposed.

If I were to compress my cells with something other than plywood, something that is non-insulating, then the wrap could go on the sides and the bottom. Here is one way the wrap could be applied, but only if the compressing mechanism is under the wrap.

Battery_With_Wrap.JPG
 
Removing the insulation would be a LOT easier than removing the wrap. Since I have yet to implement/install anything, I can probably make the insulation relatively easy to remove.

I really don't want to fry my batteries. But I don't have any LiFePO4 experience yet.

Jim, in my experience unless your going to be in the extreme temps on either end there really is nothing to worry about.
I'm using passive heating (if you recall from my other thread), batteries are compressed, 5 100ah sitting side x side, thick rubber mat on the bottom of a plywood enclosure that goes up 3/4 of the batteries sides, I have a thin rubber floor mat cut to fit on top of the batteries and at times would place a wool lined carhartt jacket on them when outside ambient temps below 32f (cells always stayed 43f +/-. Even last year before adding the rubber mat they sit on now when in Nov I was in Kansas and the night temps dropped into to mid teens the batteries stayed in the 40f range.
I'm in WY right now and with the hot spell a couple of day ago here are some mics temp recordings. Remember I have 2 remote thermometers, 1 outside the trailer in the shade under a livingroom slide, 1 in the front compartment of the 5th wheel where the the batteries/ inverter/ scc are mounted and then the individual cell temps on all 20 cells themselves.
8/17 16:00 96f ambient, 93f compartment 78-80f cells
18:00 93f ambient, 93f compartment, 80f cells
19:45 90f ambient, 93f compartment, 82f cells
8/18 06:00 72f ambient, 82f compartment, 80f cells
20:15 85f ambient, 92f compartment, 82f cells
8/19 05:45 68f ambient, 82f compartment, 78f cells
This morning 07:00 68f ambient, 78f compartment, 73f cells

For your build I would make a box with the foam (rubber on the bottom, foam sides) try it out. Seeing your CO and using it for hunting in the late season as a hunting camp.

After 4.5 years of using these in all temps the cells are normally always cooler than the ambient temp outside during the summer and cells temps are 40-45f even on the coldest nights into the teens. There are always loads on the pack from 2-8ah during the night, 175-200a during the day at various SOC.
 
Jim, in my experience unless your going to be in the extreme temps on either end there really is nothing to worry about.
I'm using passive heating (if you recall from my other thread), batteries are compressed, 5 100ah sitting side x side, thick rubber mat on the bottom of a plywood enclosure that goes up 3/4 of the batteries sides, I have a thin rubber floor mat cut to fit on top of the batteries and at times would place a wool lined carhartt jacket on them when outside ambient temps below 32f (cells always stayed 43f +/-. Even last year before adding the rubber mat they sit on now when in Nov I was in Kansas and the night temps dropped into to mid teens the batteries stayed in the 40f range.
I'm in WY right now and with the hot spell a couple of day ago here are some mics temp recordings. Remember I have 2 remote thermometers, 1 outside the trailer in the shade under a livingroom slide, 1 in the front compartment of the 5th wheel where the the batteries/ inverter/ scc are mounted and then the individual cell temps on all 20 cells themselves.
8/17 16:00 96f ambient, 93f compartment 78-80f cells
18:00 93f ambient, 93f compartment, 80f cells
19:45 90f ambient, 93f compartment, 82f cells
8/18 06:00 72f ambient, 82f compartment, 80f cells
20:15 85f ambient, 92f compartment, 82f cells
8/19 05:45 68f ambient, 82f compartment, 78f cells
This morning 07:00 68f ambient, 78f compartment, 73f cells

For your build I would make a box with the foam (rubber on the bottom, foam sides) try it out. Seeing your CO and using it for hunting in the late season as a hunting camp.

After 4.5 years of using these in all temps the cells are normally always cooler than the ambient temp outside during the summer and cells temps are 40-45f even on the coldest nights into the teens. There are always loads on the pack from 2-8ah during the night, 175-200a during the day at various SOC.

Cell temperatures while the trailer is being occupied are much less of a concern than when the trailer is sitting at the storage lot. I'm certainly not a full timer like you are. :) Yes, I could pull the batteries during the winter. But I don't do that now with my Trojan batteries. I "visit" (my wife's word, not mine) the trailer at least once a month to do routine maintenance (run the generator, etc). Removing/installing the batteries that frequently would be a pain. Hence, the investigation into the heat wraps.

I have a set of wraps being custom made for me now. I'll update the thread with pictures and results.
 
I would imagine that CO can get pretty cold in the dead of winter.
It will be interesting to see what the battery cell temps are after sitting for a month in that weather. I would guess that everthing will be turned off (parasitic loads) along with your bms so there will be no vampire load.

I wonder if the bms would have an issue with condensation? Start warming the batteries any heat transfer to bms and thawing ice crystals that possible formed on the electronics, just a thought. :eek:
 
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.
 
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?

Alternatively if you do have your reasons for wanting to keep the electrical system in operation, and you have a high quality charge controller like a Victron, you could limit the charge current to a few amps. This would (1) when its cold: allow safe charging at lower temperatures (2) when its hot: generate less heat internally.
 
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?

Alternatively if you do have your reasons for wanting to keep the electrical system in operation, and you have a high quality charge controller like a Victron, you could limit the charge current to a few amps. This would (1) when its cold: allow safe charging at lower temperatures (2) when its hot: generate less heat internally.

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.
 
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 take your time with the initial top balancing you might be surprised how little balancing the cell actually need. Have you decided what your charging voltages will be?
 
If you take your time with the initial top balancing you might be surprised how little balancing the cell actually need. Have you decided what your charging voltages will be?

No decision. I have a big issue I need to deal with before any solar stuff gets installed. A corner of the roof on my trailer is rotten.
 
I saw that post on the other forum. Sorry to see that. You did well with your other repairs.
Idle hands are the devil's playground, you'll be safe for a short while. :devilish:
 
Yeah, I'm positively angelic since I have no time to go camping.
angel.gif
 
If you are trying to use a lifepo4 battery in freezing cold temperatures, battle born just released a 12v heat pad for keeping the batteries warm without melting the case. This pad should work for any standard lifepo4 battery. Just slap it under your batteries and connect it to 12v and you are done.

I think it is over priced though. It can be found here: Click Here for battle born heater pad


If you cannot afford the battle born pad, you can use a septic tank heater pad. It works in the same way but may possibly melt your battery case if you are not careful. You can avoid this by adding some protection or a way to distribute the heat across your entire battery bank. I would personally put the batteries in a insulated container, then add a thin sheet of conductive material like sheet aluminum over the pad so that the heat it produces can warm up your entire battery bank.

Cheaper heater pad source: Click here for heater pad
I'll probably wind purchasing the Battle Born heating pad, but I would like to be able to tighten up the heating range can you give us any ideas Will.
 
Feels like I'm in over my head on this.
Assume it is COLD, the 280AH Lifeo4 batteries are in an insulated box. There is a 3D printer heating pad in the box with a thermostat.
Powering the heater using the solar panels is the goal, can it be done before the MPPT, is that a smart idea?
 
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