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LiFePO4 heating pad for cold temperatures

Simple and effective may not be the same thing in this situation. The Battle Born solution is very similar to what I came up with. It keeps the batteries warm enough that they can be charged at any time. If you go with the built-in warming solutions that warm the battery once a charge is detected then you're likely wasting as much as two hours of (daytime sun) charging time to the battery while the batteries come up to temperature.
 
I like simple and I like reliable. That's why I went with a solution that requires zero energy while monitoring and energizing the temperature control. I have found that the silicone heating pads kick out an amazing amount of heat, rather quickly.
I'm a little confused. The item you linked to is a refrigeration control unit, meaning it turns ON when the temperature gets above a certain set point, and turns off once it gets cooler than some amount below the set point. How are you using this to control your heating pads?
 
I like simple and I like reliable. That's why I went with a solution that requires zero energy while monitoring and energizing the temperature control. I have found that the silicone heating pads kick out an amazing amount of heat, rather quickly.
Yup. Those are similar to the ones I went with too. You can wire them in series to reduce the density. I am using 4 under 16 280ah cells. 2 in series for maintenance temp control and the other 2 for when I have had the vehicle in storage and let everything get cold and need to actually recover from -20C.
 
I'm a little confused. The item you linked to is a refrigeration control unit, meaning it turns ON when the temperature gets above a certain set point, and turns off once it gets cooler than some amount below the set point. How are you using this to control your heating pads?
It has a NO and NC set of contacts.
 
It has a NO and NC set of contacts.
Ok, that explains it. Thanks for that.

I think we've discussed this before: When you emphasize that this takes "zero energy" you obviously are not talking about the heating elements. Those can consume a fair amount (single digit to low teen) of amps. So I assume you are talking about the thermostat itself. Are you comparing it to the little digital thermostat that @HRTKD has used? His thermostat uses a few milliamps, which is very close to zero. Seems comparing zero to something really close to zero doesn't seem to mean much.
 
Ok, that explains it. Thanks for that.

I think we've discussed this before: When you emphasize that this takes "zero energy" you obviously are not talking about the heating elements. Those can consume a fair amount (single digit to low teen) of amps. So I assume you are talking about the thermostat itself. Are you comparing it to the little digital thermostat that @HRTKD has used? His thermostat uses a few milliamps, which is very close to zero. Seems comparing zero to something really close to zero doesn't seem to mean much.
There are lots of little Chinese components that can fail in that electronic device vs a thermo-mechanical device that has decades of dependability under its hood. I like, not depending on relays, 10k sensors and circuit boards put together by 10 year old children.

I know I can't avoid Chinese Electronics completely, but when given an equal or better choice, I will pursue the high road. In this case I feel it is a better choice.
 
I've read this entire thread with interest. It took a while to get through 23 pages of posts.

I am building a 24V 8S battery and am only stuck on the heating solution. I will be using it in an RV in the Rocky Mountains that will definitely see sub 0C freezing temperatures, but with plenty of solar power as long as the batteries are warm. I have not seen anyone mention using a simple 12V electric blanket which provides a low even heat, maybe 40W to 60W, seems perfect. I'll include a 24V to 12V converter right in the box to power the blanket and a simple 12V thermostat with remote probe.

I'm planning to tension 8 LiFePo4 280ah cells together with metal plates and threaded rods, wrap the sides and bottom of the cells with an electric blanket, and surround it all with rigid foam insulation inside a wooden box. Similar physical design to many others who posted here. But most of the other solutions I've read about put out way too much heat, require a heat sink or even 120V AC, seems dicey, I want slow steady heat starting at 5C (41F) and an electric blanket should work fine I'm hoping, with R10 to R20 around the cells to retain the heat. Thinking I should pack the blanket tight to the rigid foam so the cell bank doesn't move around too much.

My 280ah cells are way heavier than I expected but I don't worry about the electric blanket failing from the weight, people sit and lay on these blankets all the time.
 
I've read this entire thread with interest. It took a while to get through 23 pages of posts.

I am building a 24V 8S battery and am only stuck on the heating solution. I will be using it in an RV in the Rocky Mountains that will definitely see sub 0C freezing temperatures, but with plenty of solar power as long as the batteries are warm. I have not seen anyone mention using a simple 12V electric blanket which provides a low even heat, maybe 40W to 60W, seems perfect. I'll include a 24V to 12V converter right in the box to power the blanket and a simple 12V thermostat with remote probe.

I'm planning to tension 8 LiFePo4 280ah cells together with metal plates and threaded rods, wrap the sides and bottom of the cells with an electric blanket, and surround it all with rigid foam insulation inside a wooden box. Similar physical design to many others who posted here. But most of the other solutions I've read about put out way too much heat, require a heat sink or even 120V AC, seems dicey, I want slow steady heat starting at 5C (41F) and an electric blanket should work fine I'm hoping, with R10 to R20 around the cells to retain the heat. Thinking I should pack the blanket tight to the rigid foam so the cell bank doesn't move around too much.

My 280ah cells are way heavier than I expected but I don't worry about the electric blanket failing from the weight, people sit and lay on these blankets all the time.
Although it may be more complicated than most people care to try, my solution (described here) uses two thermostats to prevent the possibility of the heating pad(s) getting too hot too fast. One thermostat turns on the heat when the temp gets low. This first thermostat is the normal thermostat on many implementations. The second thermostat has it's temperature probe also on the cells but closest to the heating pad(s), and has it's setting higher, like maybe 90°F-100°F. This thermostat turns off if the temp gets too high too fast. Both thermostats need to be ON for the heating pad(s) to get power. So if the temperature in the middle of the pack is below 40°F and the temperature on the pack near the heat is below 90°F, the heater is ON.

In practice I think this may turn the heater ON and OFF in some duty cycle that will allow the cells to warm, but warm slowly enough.

By the way, I'm also doing a 24V 8S pack, for a solar install at a cabin in the Rockies.
 
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This guy on youtube did a two part series on heating his batteries that i think would be useful here.

Part one

Part two
I suppose I should have mentioned that this guy shows what he uses and how he set it up to turn on a fan when it got too hot and a heater when it got too cold. The heaters also looked to be affordable and working very well also.
Hope this helps guys. :)
 
I've read this entire thread with interest. It took a while to get through 23 pages of posts.

I am building a 24V 8S battery and am only stuck on the heating solution. I will be using it in an RV in the Rocky Mountains that will definitely see sub 0C freezing temperatures, but with plenty of solar power as long as the batteries are warm. I have not seen anyone mention using a simple 12V electric blanket which provides a low even heat, maybe 40W to 60W, seems perfect. I'll include a 24V to 12V converter right in the box to power the blanket and a simple 12V thermostat with remote probe.

I'm planning to tension 8 LiFePo4 280ah cells together with metal plates and threaded rods, wrap the sides and bottom of the cells with an electric blanket, and surround it all with rigid foam insulation inside a wooden box. Similar physical design to many others who posted here. But most of the other solutions I've read about put out way too much heat, require a heat sink or even 120V AC, seems dicey, I want slow steady heat starting at 5C (41F) and an electric blanket should work fine I'm hoping, with R10 to R20 around the cells to retain the heat. Thinking I should pack the blanket tight to the rigid foam so the cell bank doesn't move around too much.

My 280ah cells are way heavier than I expected but I don't worry about the electric blanket failing from the weight, people sit and lay on these blankets all the time.
There are 100s of ways to accomplish this. Only down side of a 12v blanket I can think of is size. does it wrap nicely around the battery with no excess you have to fold up or need to manage in some way? If it does then it would probably be a great solution.

Personally I think silicone heating pads are the way to go. To much power? Stick 2 or 3 in series. Thats what Im doing. Two 120 watt pads in series and two in parallel. Reason for this is I am going to be letting mine get well below freezing when I am not using the truck. If I decide on short notice I need it, everything turns on and delivers full power to the aluminum plate that is air gapped under the cells. The parallel pads are connected to one thermostat that turns off at 20 deg C and the series turns off at 10. These both measure air temp between the aluminum plate and the battery. When the BMS allows the battery to begin charging (sensor is buried deep in between cells, not measuring air temp) , it also disables the high power pads and allows the 60 watt series pads to simply maintain the 10 deg C
 
I've read this entire thread with interest. It took a while to get through 23 pages of posts.

I am building a 24V 8S battery and am only stuck on the heating solution. I will be using it in an RV in the Rocky Mountains that will definitely see sub 0C freezing temperatures, but with plenty of solar power as long as the batteries are warm. I have not seen anyone mention using a simple 12V electric blanket which provides a low even heat, maybe 40W to 60W, seems perfect. I'll include a 24V to 12V converter right in the box to power the blanket and a simple 12V thermostat with remote probe.

I'm planning to tension 8 LiFePo4 280ah cells together with metal plates and threaded rods, wrap the sides and bottom of the cells with an electric blanket, and surround it all with rigid foam insulation inside a wooden box. Similar physical design to many others who posted here. But most of the other solutions I've read about put out way too much heat, require a heat sink or even 120V AC, seems dicey, I want slow steady heat starting at 5C (41F) and an electric blanket should work fine I'm hoping, with R10 to R20 around the cells to retain the heat. Thinking I should pack the blanket tight to the rigid foam so the cell bank doesn't move around too much.

My 280ah cells are way heavier than I expected but I don't worry about the electric blanket failing from the weight, people sit and lay on these blankets all the time.
I like the way you think. KISS.
Simple is good. Let us know how it works for you!
 
I too spent the night looking through all 23 pages, and I hope this idea doesn't result in any forehead-slapping.

If the goal is to get the insides of the battery up above 0ºC before charging, what about heating the electrodes directly through conduction into the terminals? These chassis-mount 8-ohm resistors could be mounted with some heat sink grease directly to the series (or parallel) links between cells. The leads of the resistor are electrically isolated from its body by a layer of ceramic, so they could be run off any voltage available in the pack.

In the case of a 4S LFP pack using three resistors, (one on each inter-cell coupling link,) 12.8 volts would dump 57 watts total heat if the resistors were fed in parallel, with the bulk of that heat dissipated directly into the battery terminals. Some heat would escape from the bodies of the resistors themselves and from the links, but in an insulated enclosure that might still be useful. The resistors are $2.65 each plus shipping.

Affixing a temp probe to the pack's + or - output terminal would detect warming through the battery, so it would give a conservative indication when the internal components warmed above freezing.

Maximizing the effectiveness of this approach might require minimizing heat loss through the wires connected to the positive and negative busses, but if the pack's main fuse was located close to a terminal, that would be suitably inefficient at letting heat pass. In any case, it still might be more efficient than heating the outside of the cell case's insulation.

Another thought: How much internal cell heat is generated by charging/discharging itself? Is is possible some posters who've noted their "batteries hold heat pretty well" have actually been seeing the temp maintained by charge/discharge losses?

I'm contemplating building a four-cell, 12.8-volt 280AH prismatic pack for use in a remote, outdoor location, so I've appreciated reading everyone else's ideas!
 
Or use the heater I suggested on the aluminum plate that spreads out the heat as well?
There is a link to the video showing it working like I said as well. :)

Anyone else have a proof of use ?
 
So, what do you all recommend for passive insulation to keep a battery warm in the winter? I have a self-heating battery, works quite well in warming things up, but I still want to add some insulation around the battery so that it keeps warmer than ambient. I find that that my battery is only 5oC warmer than ambient (in my shed), so when it goes does down to -30oC outside at night, I don't want my battery to be at -25oC despite the self-heating function which will only work when the sun comes up in the morning.

would something like this work? thanks

 
So, what do you all recommend for passive insulation to keep a battery warm in the winter? I have a self-heating battery, works quite well in warming things up, but I still want to add some insulation around the battery so that it keeps warmer than ambient. I find that that my battery is only 5oC warmer than ambient (in my shed), so when it goes does down to -30oC outside at night, I don't want my battery to be at -25oC despite the self-heating function which will only work when the sun comes up in the morning.

would something like this work? thanks

I think that item will do next to zero to insulate the battery. What I did and several others have done is using 2" XPS rigid foam. In my case I lined the inside of a box with it. It has an R-value (US units) of 10, so it does provide fairly good insulation. If you read through the rest of this thread you'll see several approaches, but I don't think any of them take advantage of a self-heating battery.

I started a thread with some of the math about keeping an LFP battery warm: https://diysolarforum.com/threads/on-keeping-lfp-warm.17629/

I also have a show & tell thread on the box with warming system that I built: https://diysolarforum.com/threads/horseflys-cabin-solar-lifepo4-upgrade.27472/
 
So, what do you all recommend for passive insulation to keep a battery warm in the winter? I have a self-heating battery, works quite well in warming things up, but I still want to add some insulation around the battery so that it keeps warmer than ambient. I find that that my battery is only 5oC warmer than ambient (in my shed), so when it goes does down to -30oC outside at night, I don't want my battery to be at -25oC despite the self-heating function which will only work when the sun comes up in the morning.

would something like this work? thanks

If you haven't seen this thread it will give a good idea of a possible in closure. Maybe @HRTKD will chime in.
https://diysolarforum.com/threads/lifepo4-battery-warmer-install.14485/
 
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