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LiFePO4 heating pad for cold temperatures

Two winters later . . .

Last year did not go so well. really low temps (-15 cel) and the watts the heating pad through out was not enough to keep up. Fortunately the BMS did and I switched to the lead carbon bank to maintain the heaters below zero. Seems to be the only way as the BMS shuts off the discharge power below zero, so no juice for the heating pad. I have played with a number of settings but he real kicker is to keep the snow off the panels or everything shuts down. Also I have about 50 watts of heat go into the aluminum on the bottom of the batteries but that draws constant when it is really cold. The best solution I can find here in Colorado is to keep the lead carbon bank on, LiFePO4 bank off and let the LC bank keep the Lithium bank from freezing. They are enclosed with some insulation but when the trailer is not heated and the wind blows outside, it is really hard to keep the Lithium warm enough to stay over zero. This year I check every week and the problem seems to have not gone away. At the end of the day it is about balance between your solar array and the power to keep the lithium bank warm enough.
 
Kristof said:
The best solution I can find here in Colorado is to keep the lead carbon bank on, LiFePO4 bank off and let the LC bank keep the Lithium bank from freezing.
Click to expand...
I plan to remain south of Colorado until things warm up a bit, but the idea of a second battery bank is interesting. Well, a second battery in my case. I replaced 3 gel batteries with one LifePo4, and although the gel batteries still have some life in them, I haven't been able to give them away. Maybe I'll put one back in my bus as a heater battery to keep the lithium comfy. Probably wouldn't work in the conditions you're dealing with, but maybe it'd be enough for nights that don't get too far below freezing.
 
so in the middle of the second winter for my setup, 16 25 watt pads wired in series parallel to get the output I want with no controler. the original setup had a controller but with all the controllers being 12, or 24 volts i was using a 48/12 relay to work between the controller and the heating pads and the relay kept burning its contacts, probably due to the fact that the pack is 54~55 volts and the relay is listed as 48 volt capacity this is the second one to burn out on me.

battery pack varies between 8°c and 15°c I had been datalogging it with a pair of 4 channel temp loggers but after 2 months I stopped logging and now only spot check in the early morning and at mid after noon to see how much swing I have from low to high. with 8 thermal probes spread out through the pack the data is pretty clear.

this is a 35kw bank with 5.6kw of panels due south at 45° angle and 1.6kw of panels vertical facing west to lengthen out the solar day.
 
Daddy Tanuki said:
so in the middle of the second winter for my setup, 16 25 watt pads wired in series parallel to get the output I want with no controler. the original setup had a controller but with all the controllers being 12, or 24 volts i was using a 48/12 relay to work between the controller and the heating pads and the relay kept burning its contacts, probably due to the fact that the pack is 54~55 volts and the relay is listed as 48 volt capacity this is the second one to burn out on me.

battery pack varies between 8°c and 15°c I had been datalogging it with a pair of 4 channel temp loggers but after 2 months I stopped logging and now only spot check in the early morning and at mid after noon to see how much swing I have from low to high. with 8 thermal probes spread out through the pack the data is pretty clear.

this is a 35kw bank with 5.6kw of panels due south at 45° angle and 1.6kw of panels vertical facing west to lengthen out the solar day.
Click to expand...
Racoon Dog,
Wow!! Very impressive.
I keep burning out controllers (2 of the cheapies) on a 12v heating pad. 300 watt panel on the roof of my Promaster, 4 cell battery.
Wonder how much damage I have done to the battery?
Old Toad
 
Oldtoad said:
Thank you very much.
Click to expand...
What about the FACON pads that are used underneath RV's to keep the tanks warm? They are set to above freezing, and work automatically when it gets cold. 12V, and I know Will covered these in an upload a while back.
 
Sanwizard said:
What about the FACON pads that are used underneath RV's to keep the tanks warm? They are set to above freezing, and work automatically when it gets cold. 12V, and I know Will covered these in an upload a while back.
Click to expand...
Got one but I heard there were problems with the thermostat.
Thought the controller would be better.
Ordered a Inkbird off the a'Zon, cheaper, better reviews than what I was considering.
 
Kristof said:
Two winters later . . .

Last year did not go so well. really low temps (-15 cel) and the watts the heating pad through out was not enough to keep up. Fortunately the BMS did and I switched to the lead carbon bank to maintain the heaters below zero. Seems to be the only way as the BMS shuts off the discharge power below zero, so no juice for the heating pad. I have played with a number of settings but he real kicker is to keep the snow off the panels or everything shuts down. Also I have about 50 watts of heat go into the aluminum on the bottom of the batteries but that draws constant when it is really cold. The best solution I can find here in Colorado is to keep the lead carbon bank on, LiFePO4 bank off and let the LC bank keep the Lithium bank from freezing. They are enclosed with some insulation but when the trailer is not heated and the wind blows outside, it is really hard to keep the Lithium warm enough to stay over zero. This year I check every week and the problem seems to have not gone away. At the end of the day it is about balance between your solar array and the power to keep the lithium bank warm enough.
Click to expand...
It appears as though you were targeting 38-42° as your minimum battery temp.

In retrospect would targeting 34-36° have allowed you to ride through long enough? Or was snow load a multiple day event that would have failed either way?
 
Sanwizard said:
What about the FACON pads that are used underneath RV's to keep the tanks warm? They are set to above freezing, and work automatically when it gets cold. 12V, and I know Will covered these in an upload a while back.
Click to expand...

I talked with one of the companies that makes the RV pads, but not the one in your link. They warned me to not use those on a battery. They're configured to be installed against a plastic tank with water in it, not against a metal or plastic battery with dense material inside it. The thermostats in them may not cover the temperature range you're looking for (45°F to 68°F)

That same warming pad company that I talked to made a set of pads for me with no thermostat inside the pad and sold an external thermostat to go with it. I found that those thermostats were unreliable and of course, not programmable. I let them know about the problem and provided my data. I did get a response a while afterwards that I wasn't the only one that encountered that problem and they were working on it. I went with a programmable thermostat with a temperature probe that connects to the thermostat. After two years, it's working very well.

Yes, I paid a lot for my pads and their flawed thermostat. But I sleep real good at night when the temperature is below 0°F.
 
got mine going today:
these heating pads get pretty hot ~150F. I have them in the airspace between my SOK batteries and the metal wall of the battery compartment of our Minnie Winnie. I also added insulation around the outside of the battery box. I'll run it for a few days (although we may have missed the coldest temps in OR for he year.

we'll see...
https://www.icloud.com/sharedalbum/#B0cG9Gd2NGiCR4p
 
I did not find proper information regarding what energy is needed to heat up a battery in order to get it to a working temperature. So I did some experiments with my 48V 280Ah battery. With 1kWh I was able to heat it up from 2C to 22C. This is with proper heat insulation (6cm EPS) and in a 24-hour time window.

Let's consider the insulation perfect. The total cell weight is ~90kg. This means that you need ~1W of energy per kilogram of LiFePo4 cells to heat them by 1 degree Celsius.

Now let's consider the information on the internet about the LiFePo4 cells' specific heat energy. The numbers are at ~1000J/kg. Or roughly 0.3W per kilogram of cells to heat them up by 1 degree Celsius. Looks likely the insulation I have is far away from perfect.

This should give a rough estimate of the required heating time with a specific heating pad. I guess this would be useful when somebody is trying to decide what heating element is needed for his case.
 
brum said:
I did not find proper information regarding what energy is needed to heat up a battery in order to get it to a working temperature. So I did some experiments with my 48V 280Ah battery. With 1kWh I was able to heat it up from 2C to 22C. This is with proper heat insulation (6cm EPS) and in a 24-hour time window.

Let's consider the insulation perfect. The total cell weight is ~90kg. This means that you need ~1W of energy per kilogram of LiFePo4 cells to heat them by 1 degree Celsius.

Now let's consider the information on the internet about the LiFePo4 cells' specific heat energy. The numbers are at ~1000J/kg. Or roughly 0.3W per kilogram of cells to heat them up by 1 degree Celsius. Looks likely the insulation I have is far away from perfect.

This should give a rough estimate of the required heating time with a specific heating pad. I guess this would be useful when somebody is trying to decide what heating element is needed for his case.
Click to expand...
I tried to address this mathematically in a thread a couple of years ago: https://diysolarforum.com/threads/on-keeping-lfp-warm.17629/
 
Markboettcher said:
Hi, my apologies if this has been suggested already. After going through about 18 of the 36 pages of replies here, I decided to just go ahead and describe the dead-simple, cheap and effective battery warming system that I used last winter.

I have an off-grid cabin here in Bethel, Vermont. The cabin temperature frequently reaches subfreezing temperatures for several days/weeks in a row.

Electrical system consists of four 360W solar panels, two Growatt SPF 3000TL LVM-ES inverter/charger/MPPT controllers in parallel (120v). Batteries are one Jakiper 48v 100ah lifepo4 running in parallel with four series-connected 12v 200ah AGM batteries.

I built an easily removable enclosure, similar to the engine covers used with inboard speed boats - 2x4 frame, 1/2" OSB and interior lined with 1 1/2" rigid foam.

In the box I have a $20 120v electric baseboard heater thermostat like this one connected to the inverter that controls a 120v socket. Heating pad plugged into that and lying on top of the lithium battery. Alternatively, one or two (for redundancy) low wattage (~15w) light bulbs. Not too close to the thermostat. Have thermostat set to turn on when temperature in box drops below 40°-50°F.

An afternoon's work, $100 or so in parts and materials, simple, reliable. Little technical expertise needed. In the spring, take the box off and stick it in a corner.
Click to expand...
I have a converted bus with 2-200 ah lifepo4 batteries stowed in the unheated underbed storage. Last year we lived in the RV for most of the winter while staying at several ski areas with many sub-zero days. It required we run our diesel heater more than necessary to try to get enough heat to keep the batteries above freezing. This year I am going to move the batteries closer to the living section wall, insulate with additional 2" foam insulation, add small fan to pull air from the heated space. I am going to use your idea of the baseboard heater thermostat. I am going to try using a 19.7x19.7, 12v, 35w pet heating pad with a possible programmable timer.
 
Bus Driver said:
I have a converted bus with 2-200 ah lifepo4 batteries stowed in the unheated underbed storage. Last year we lived in the RV for most of the winter while staying at several ski areas with many sub-zero days. It required we run our diesel heater more than necessary to try to get enough heat to keep the batteries above freezing. This year I am going to move the batteries closer to the living section wall, insulate with additional 2" foam insulation, add small fan to pull air from the heated space. I am going to use your idea of the baseboard heater thermostat. I am going to try using a 19.7x19.7, 12v, 35w pet heating pad with a possible programmable timer.
Click to expand...
The 12V self regulating mobile tank heaters work fairly well. I used them in my unheated garage in NY during winter, and they kept the battery box above freezing the whole time.
I moved south, so I have two if you want them. They are 8x25 inches. I covered them in high heat tape to prevent any electrical shorting to my LiFePo4 cells. (I never trust the blue plastic).
 

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Sanwizard said:
The 12V self regulating mobile tank heaters work fairly well. I used them in my unheated garage in NY during winter, and they kept the battery box above freezing the whole time.
I moved south, so I have two if you want them. They are 8x25 inches. I covered them in high heat tape to prevent any electrical shorting to my LiFePo4 cells. (I never trust the blue plastic).
Click to expand...
How did you insulate your battery box? I'm about to put together a system for my father & stepmother that'll run the garage door openers, but have been trying to figure out what type and how much insulation to use building the box.
 
hightecrebel said:
How did you insulate your battery box? I'm about to put together a system for my father & stepmother that'll run the garage door openers, but have been trying to figure out what type and how much insulation to use building the box.
Click to expand...
I made the battery box out of a truck toolbox. It fit 32 x 280ah cells perfectly. I glued fairly thin foam padding inside on the sides and bottom before putting the cells in.

I then added half inch cutting board material over the terminals to hold the BMS's, and make sure the box cover chains never hit a terminal. I added rubber padding between each cell to avoid shorts (dont trust the blue cell covering!) Lastly, I laid Rock wool insulation, which is non-conductive, fire proof and water proof. I put the two heating pads along the front and back of the box along the cells.
 

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Sanwizard said:
The 12V self regulating mobile tank heaters work fairly well. I used them in my unheated garage in NY during winter, and they kept the battery box above freezing the whole time.
I moved south, so I have two if you want them. They are 8x25 inches. I covered them in high heat tape to prevent any electrical shorting to my LiFePo4 cells. (I never trust the blue plastic).
Click to expand...
Bro how did those run you? i would not mind playing with a set of those for shits and giggles. let me know how much and a palpal addy and if we can agree on costs, i will take them off your hands to play with.
 
Daddy Tanuki said:
Bro how did those run you? i would not mind playing with a set of those for shits and giggles. let me know how much and a palpal addy and if we can agree on costs, i will take them off your hands to play with.
Click to expand...
What is your zip code? I will check on shipping costs.
 
Sanwizard said:
What is your zip code? I will check on shipping costs.
Click to expand...
96349-0113 for the military mailing address, 238-0026 for the local Japanese address whichever is easier for you, if same then give me price for both so I can compare with and without import taxes. (no import taxes for base, but limited on size etc.
 
Daddy Tanuki said:
96349-0113 for the military mailing address, 238-0026 for the local Japanese address whichever is easier for you, if same then give me price for both so I can compare with and without import taxes. (no import taxes for base, but limited on size etc.
Click to expand...
No cost for the heating pads. Just shipping. I will package them up in a box. PM me with your full address. What service? Air Force?
 
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