diy solar

diy solar

LiFePO4 heating pad for cold temperatures

Capt Bill said:
I would consider one or two of these for a freeze protect switch in a battery box, possibly connected to an older style light bulb:

Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com

Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com
www.amazon.com

and another interesting option I cam across was:


I was also thinking of an insulating layer of "Aircrete" (foam injected cement that has microscopic bubbles giving it insulation plus fireproof abilities) around battery bank / inside a battery box idea.

Food for Options ;+)
Click to expand...
Funny..... I ordered one of those just yesterday!
 
Capt Bill said:
I would consider one or two of these for a freeze protect switch in a battery box, possibly connected to an older style light bulb:

Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com

Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com
www.amazon.com

and another interesting option I cam across was:


I was also thinking of an insulating layer of "Aircrete" (foam injected cement that has microscopic bubbles giving it insulation plus fireproof abilities) around battery bank / inside a battery box idea.

Food for Options ;+)
Click to expand...

i ordered the motorcycle glove warmers - now looking for a simple thermostat control
the snap disk is the simplest, but it has a 5F variance, so 35F, could be as low as 30F, can't take that chance
need something with a little more accuracy
the inkbird has that, but is much LARGER and requires power
as i said, as simple as possible
haven't found any other solutions yet
 
Last edited:
Fred S said:
Could use these. Available in all temperatures, and as NO or NC.
https://www.amazon.com/gp/product/B07PFV4CFG/
I'd wire 2 or 3 NO in parallel, spacing them around, so the first one to close would engage a relay to call for heat. Like the snap disks, these draw no power.
Click to expand...

I have looked at those as well... but these only go down to 40C. That is over 100F. Way too warm.
 
Sorry, my bad. I mixed up one that I had purchased to turn on a cooling fan. Here is one rated for 5C:
https://www.aliexpress.com/item/32369432073.html?spm=a2g0o.detail.1000023.9.6c919495JOcblc

A few years ago I bought an automotive A/C sensor switch (gas charged mechanical with a bulb) that is designed to cycle an A/C compressor when the evaporator core gets close to freezing. This was used in the old days to keep evaporators from icing over. It was designed to switch DC 12v at 4-5a for many cycles, so I'm guessing it would work in this application. Anyway, it was very cheap and reliable. I can't recall where I got it, but if anyone is interested, I'll take the time to track it down. I doubt any are N.O. though, so a relay probably would be needed.
 
mkaye said:
after doing some more research, this would work, can't find any power consumption specs, but i would assume 50-100ma

MonkeyJack 12V Temperature Controller Thermostat Control Switch Probe 120W Digital : Amazon.ca: Industrial & Scientific

MonkeyJack 12V Temperature Controller Thermostat Control Switch Probe 120W Digital : Amazon.ca: Industrial & Scientific
www.amazon.ca

easy to mount and the output leads would be 12V, so easy to wire
Click to expand...
Not sure about that one; while sure there are losts of inexpensive options. Got light bulb flash when I saw something next to that one, to possibly consider for cooling an insulated battery box when outdoor temp rises high (my box will be inside). While wondering about how to keep my 1st DIY LiFePO4 battery build in optimal temp zone: This rang some bells as possible low energy use way (not necessarily the specific piece). for Cooling ;+)

 
Peltiers are relatively efficient heaters, but very inefficient coolers. Having said that, using them to cool a small insulated box may still be less energy than trying to do any kind of Air Conditioned room for the batteries. The idea was discussed in a thread a few months ago but I don't know if anyone did anything. If you decide to pursue this keep us posted.

BTW: Back in my over-clocking days I played with peltiers on a liquid cooled system but had a devil of a time dealing with condensation. If you set something up, think through where the condensation would drip
 
I can say a word about some experiments I did with Peltier modules some time ago. I wanted to do more quantitative measurements before reporting but didn't find the time yet so here's already some qualitative feedback:

I used 4 Peletier modules (TEC1-12706) wired in series and hooked to 12V power supply. I intended to have the Peltier function at low intensity, this is where they are the most efficient, but it also means they don't transfer as much heat compared to having them run at nominal voltage. I had them sandwiched between two aluminum radiators, with some insulating polystyrene around to try to only have thermal transfer through the Peltiers. I added fans to the setup to maximize the heat exchange of the radiators. They were 24V fans hooked in parallel to the 12V supply so they didn't draw much and still were rotating fine.

IMG_2459.JPG

I tried to cool down a polystyrene box in which I cut a rectangle in the cover to put the whole "fans-radiator-Peltiers" sandwich in. Overall the insulation of the box must have been quite significantly lowered by doing this, but I went on. I tried a few scenarios, including cooling down the box air (without anything in) 10°C lower than ambient temp. It could not reach such a lower temp with the setup running at 12V, but more like -7°C compared to ambient temp. The whole setup with the fans was pulling around 1.2A, meaning you're burning 15W to keep the enclosure 7°C cooler (with my 16s battery in, that should not change the insulation of the box, just take longer to get to this temperature).

Warming up the enclosure 10°C above room temp was easier to achieve (by reversing the polarity of the power supply on the Peltiers), which is expected since they themselves produce a bit of heat while transferring some more through them. So I tried to put a thermostat that would maintain the enclosure between +5 and +10°C above room temperature. On one cycle, the setup took 7 minutes to bring the enclosure temp from +5°C to +10°C (with the Peltiers and fans ON), and then it took 20 minutes for the temp to go back down to +5°C (with Peltiers and fans OFF) before starting a new warming cycle. That means a duty cycle around 25%, so you burn on average a bit less than 5W to keep your enclosure between +5 and +10°C compared to room temp.

A good thing to do would have been to compare that with the consumption of simple resistive warming in the insulated box before I cut a large whole in the cover, but I didn't ?‍♂️. Still I think 5W is too much consumption for this contraption, and that the box cools much faster than it should if it were well insulated. One thing that I think we didn't take into account for this setup idea, is that during the time the Peltiers are not running, they behave like a big thermal bridge between the interior and exterior of the box (all the more with the radiators!), and largely weaken the insulation properties of the box. So thermal energy flows through very easily. When you put a resistor in the box without cutting it and putting heat transfer radiators on each side of the hole, the heat should be kept much more easily in the box. And I don't think that the slightly increased yield of Peltier modules compared to resistors is nearly enough to compensate the huge thermal leak.

So from all this I would keep two things: heating the battery in winter with a Peltier setup doesn't seem to be a good idea, resistive heating in a well insulated box should be better (although I didn't test it...). And for cooling, yes it can work, but it will suck quite some power if you want the temperature difference to be significant (here I got 7°C delta for 15W). Then again if it's summer and you have too much solar energy it can be fine.
 
astronom said:
I can say a word about some experiments I did with Peltier modules some time ago. I wanted to do more quantitative measurements before reporting but didn't find the time yet so here's already some qualitative feedback:

I used 4 Peletier modules (TEC1-12706) wired in series and hooked to 12V power supply. I intended to have the Peltier function at low intensity, this is where they are the most efficient, but it also means they don't transfer as much heat compared to having them run at nominal voltage. I had them sandwiched between two aluminum radiators, with some insulating polystyrene around to try to only have thermal transfer through the Peltiers. I added fans to the setup to maximize the heat exchange of the radiators. They were 24V fans hooked in parallel to the 12V supply so they didn't draw much and still were rotating fine.

View attachment 14027

I tried to cool down a polystyrene box in which I cut a rectangle in the cover to put the whole "fans-radiator-Peltiers" sandwich in. Overall the insulation of the box must have been quite significantly lowered by doing this, but I went on. I tried a few scenarios, including cooling down the box air (without anything in) 10°C lower than ambient temp. It could not reach such a lower temp with the setup running at 12V, but more like -7°C compared to ambient temp. The whole setup with the fans was pulling around 1.2A, meaning you're burning 15W to keep the enclosure 7°C cooler (with my 16s battery in, that should not change the insulation of the box, just take longer to get to this temperature).

Warming up the enclosure 10°C above room temp was easier to achieve (by reversing the polarity of the power supply on the Peltiers), which is expected since they themselves produce a bit of heat while transferring some more through them. So I tried to put a thermostat that would maintain the enclosure between +5 and +10°C above room temperature. On one cycle, the setup took 7 minutes to bring the enclosure temp from +5°C to +10°C (with the Peltiers and fans ON), and then it took 20 minutes for the temp to go back down to +5°C (with Peltiers and fans OFF) before starting a new warming cycle. That means a duty cycle around 25%, so you burn on average a bit less than 5W to keep your enclosure between +5 and +10°C compared to room temp.

A good thing to do would have been to compare that with the consumption of simple resistive warming in the insulated box before I cut a large whole in the cover, but I didn't ?‍♂️. Still I think 5W is too much consumption for this contraption, and that the box cools much faster than it should if it were well insulated. One thing that I think we didn't take into account for this setup idea, is that during the time the Peltiers are not running, they behave like a big thermal bridge between the interior and exterior of the box (all the more with the radiators!), and largely weaken the insulation properties of the box. So thermal energy flows through very easily. When you put a resistor in the box without cutting it and putting heat transfer radiators on each side of the hole, the heat should be kept much more easily in the box. And I don't think that the slightly increased yield of Peltier modules compared to resistors is nearly enough to compensate the huge thermal leak.

So from all this I would keep two things: heating the battery in winter with a Peltier setup doesn't seem to be a good idea, resistive heating in a well insulated box should be better (although I didn't test it...). And for cooling, yes it can work, but it will suck quite some power if you want the temperature difference to be significant (here I got 7°C delta for 15W). Then again if it's summer and you have too much solar energy it can be fine.
Click to expand...
Your results don't surprise me. I knew the peletiers were not very efficient coolers and had wondered about the 'heat bridge' effect you mentioned.
What might solve the heat bridge problem with a liquid cooling system. (the peltier remains outside the box). However that is going to be a lot more complicated and probably less efficient.
 
Bulwinkle said:
This is good info... there is a whole community of us who are Overland Camping folks. Overland Bound and Expedition Portal are 2 great sites... The issue of battery freezing vs efficiency is on my mind. I live in Maine and will only use the Overland Trailer once and awhile, but it also could get cold while using... What do you recommend for something that can get cold and not used full time??.
Click to expand...
I've insulated the battery bank in my OLT pretty well. I'm using (16) 50Ah LifePo4s with a 15W heating pad and mini fan (I think from a 3d printer). I've set them to turn on@ 40F and off@ 55F. I didn't see if there were panels on your tent cover but I would recommend at least 1 50W connected to mitigate any load draw (if 12V). In that setup, I'm using two battery temp sensors for cutoff and heater/fan management.
 
offgriddle said:
Presently, lithium batteries, which out perform flooded lead acid and AGM lead acid in so many ways, cannot be charged below 32 degrees and apparently should not even be stored below zero degrees. I guess if you need low temp tolerant batteries, go with AGM. Ayuh.
Click to expand...
This is looking like the best advise for me.
Bought some venting AGM's but it looks like the sealed AGM is the way to go in the Promaster camper.
Anyone have a better idea(s)?
 
For me it's better to just keep the batteries above 0c. Even though my cells say I can charge as low as -10C.

I think it's a good idea to warm your batteries even if you have AGM. They will perform better and take a charge better. It really depends on how you use them. I use mine in a truck camper and need to keep the plumbing above freezing anyway so it's a no brainer to go with lifepo4.
 
Freep said:
For me it's better to just keep the batteries above 0c. Even though my cells say I can charge as low as -10C.

I think it's a good idea to warm your batteries even if you have AGM. They will perform better and take a charge better. It really depends on how you use them. I use mine in a truck camper and need to keep the plumbing above freezing anyway so it's a no brainer to go with lifepo4.
Click to expand...
No pluming in my rig, just maybe a composing terlet.
The van can get very hot in the summer, is your LiPo4 good when it gets really hot?
 
Oldtoad said:
This is looking like the best advise for me.
Bought some venting AGM's but it looks like the sealed AGM is the way to go in the Promaster camper.
Anyone have a better idea(s)?
Click to expand...

I was going to suggest flooded batteries but I guess you probably don't want those in a vehicle. AGMs are really expensive and at that point you are almost better off with paying a little more for lithium. But I think AGMs are considered one of the better lead acid technologies, so probably the best bet if cold temperatures are a concern. Just make sure you don't charge them too hard when they get hot. You don't want them to vent. When they vent, it means they are basically losing life. Not like flooded where you can just add water.
 
You can buy 12v temperature controllers for less than ten bucks on Amazon. Just put that in series with any heat/cool source. I use a Honeywell temperature controller to make a single cavity freezer into a 50 F beer cooler/fermenting box. You don't need anything that fancy to control a heat pad.

You can also use a Kool-bot to control a small air conditioner the same way. If you get a compressor unit that reverse cycles you can keep a room chill or warm at very low power consumption. Thousands of farmers use Kool-bots to turn an insulated box in old barns into a walk-in fridge so you can go really small if you just need something to manage your power system. The difference between my controller/Kool-bot is they have circuits that protect the compressor from sudden power outages and coming back online too quickly. If you don't have a compressor, you just need a simple one that turns off/on. I also use Redi-Heat heat pad controllers and Hydrofarm heat pads to keep seedlings warm in early spring. The heat pads are constantly wet so you can even put them outside on your solar panels as long as the plugs are in a dry box. You might find what you are looking for in greenhouse supply stores.

Integrating a controller into your system takes some thought. You need to have adequate power in order for the circuit to work and make sure the system isn't on when it isn't supposed to be.
 
For you guys that are using a heating pad and insulation on your LiFePO4 batteries to keep them warm in the winter, what are you doing in the summer? Are you removing the pad and insulation? My batteries are going to be in a tight location. The last thing I'm going to want to do is remove a pad and insulation. Removing the insulation (rigid foam panels) might not be too bad, but the pad will wrap around three sides of the battery, making it likely that extracting the battery to remove the pad is the best way to go.
 
HRTKD said:
For you guys that are using a heating pad and insulation on your LiFePO4 batteries to keep them warm in the winter, what are you doing in the summer? Are you removing the pad and insulation? My batteries are going to be in a tight location. The last thing I'm going to want to do is remove a pad and insulation. Removing the insulation (rigid foam panels) might not be too bad, but the pad will wrap around three sides of the battery, making it likely that extracting the battery to remove the pad is the best way to go.
Click to expand...
There shouldnt be a need should there, any temperature sensor should be just keeping any heater off
 
HRTKD said:
For you guys that are using a heating pad and insulation on your LiFePO4 batteries to keep them warm in the winter, what are you doing in the summer? Are you removing the pad and insulation? My batteries are going to be in a tight location. The last thing I'm going to want to do is remove a pad and insulation. Removing the insulation (rigid foam panels) might not be too bad, but the pad will wrap around three sides of the battery, making it likely that extracting the battery to remove the pad is the best way to go.
Click to expand...


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.
 
You must log in or register to reply here.

Similar threads

R
12V LiFePo4 for shed
Replies
4
Views
437
chrisski
chrisski
S
Lifepo4 heater solution
Replies
6
Views
251
chrisski
chrisski
Solarcabin Channel
Reptile Heating Pad To Keep LFP Batteries Warm?
Replies
2
Views
583
gotbeans
gotbeans
V
Heat pad wattage for winter charging
Replies
8
Views
419
S Davis
S Davis
J
BATTERY HEAT
Replies
5
Views
675
OM617YOTA
O
Back
Top