richxd87
Observer
RELiON makes a "Low Temp" Battery with safe charging down to -4F. Is it worth the additional cost?
https://relionbattery.com/low-temperature-series-line
https://relionbattery.com/low-temperature-series-line
cold weather charge Lithium iron phosphate battery
- Thread starter Stan0
- Start date
I ran into this problem a couple nights over the winter with my battleborn battery. I had my diesel heater running all night which kept my interior pretty warm, but my battery, while being inside is in a spot next to my sliding door that still gets very cold. Some nights in the -20s, even though it was 50ish inside. The battery would have a good charge but I think the battery monitor that comes on the battery would shut it off.
Bought some hand warmers I could stuff next to the battery just Incase.
I looked at those heater pads. What I’d really like to do is figure out a temperature activated power switch, that would turn on a heat pad at 35 degrees or so and off at a slightly higher temp. I found some that looked like they could work but the temps for turning on/off weren’t what I wanted and the real deal breaker was that they were all 120v
Bought some hand warmers I could stuff next to the battery just Incase.
I looked at those heater pads. What I’d really like to do is figure out a temperature activated power switch, that would turn on a heat pad at 35 degrees or so and off at a slightly higher temp. I found some that looked like they could work but the temps for turning on/off weren’t what I wanted and the real deal breaker was that they were all 120v
Hillbilly Heaven
Explorer
Links are just a few post prior. I posted link to what I thought to be favorable to control the heating pad. Those thermostats I post should work fine with DC voltages.
If you want an economical heater try universal seat heaters. Use just the heating pad and the above tstat.
If you want an economical heater try universal seat heaters. Use just the heating pad and the above tstat.
dwh
Tail-End Charlie
There are a bazillion different snap-disk thermostats. Tons are used in HVAC and are usually 24v. The one I posted clearly states:
"Models with operating temperature ranges from -45C to +425C" (first bullet point)
This other page says:
"These robust thermostat switches can be used in high current applications; carrying up to 25 amps at 240VAC, for over 100,000 cycles (30 Amps at 12VDC for 30,000 cycles)."
http://senasys.com/automatic-reset-thermostat-options
Shouldn't be too tough to find one normally ooen that closes at 35F and opens at 45F.
"Models with operating temperature ranges from -45C to +425C" (first bullet point)
This other page says:
"These robust thermostat switches can be used in high current applications; carrying up to 25 amps at 240VAC, for over 100,000 cycles (30 Amps at 12VDC for 30,000 cycles)."
http://senasys.com/automatic-reset-thermostat-options
Shouldn't be too tough to find one normally ooen that closes at 35F and opens at 45F.
richxd87
Observer
@Alloy any idea what a safe contact temperature might be for LFP batteries if using something like the Kats 12v heater or Universal seat heaters?
Kat's Heaters Oil or Transmission Pan Heating Pad - 5" x 5" - 12V - 75 Watts Kats Heat
Place this heating pad under your oil or transmission pan to keep the fluid from thickening in the winter. Warm fluids lubricate better for a long-las
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Amazon.com: Dorman 628-040 Universal Seat Heater Kit: Automotive
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DC Battery Heater Kit FM316 by GTO ? NOT SOLAR COMPATIBLE
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DaveInDenver
Middle Income Semi-Redneck
You could probably just tell from the data sheet. For example a randomly selected 1868130 has a max charging temperature of +45°C and max discharging temp of +60°C.
So depends on how they are enclosed and the thermal resistance between the case and batteries. If your proposed heating pad never exceeded +45°C at the battery then seems like it should be safe. I'd personally be careful about keeping the battery temp under control, though. Boom!
One thing to consider is a pad like that is the least efficient way to heat batteries since it'll end up with a wide gradient from contact point to the opposite side. The thermal management systems take great care to equalize, so they enclose the air space around them and use fans to circulate warm air or have liquid jackets around the cells. I'd be thinking a heater on maybe an aluminum plate or old heat sink from an amplifier and circulate warm air inside a battery box.
So depends on how they are enclosed and the thermal resistance between the case and batteries. If your proposed heating pad never exceeded +45°C at the battery then seems like it should be safe. I'd personally be careful about keeping the battery temp under control, though. Boom!
One thing to consider is a pad like that is the least efficient way to heat batteries since it'll end up with a wide gradient from contact point to the opposite side. The thermal management systems take great care to equalize, so they enclose the air space around them and use fans to circulate warm air or have liquid jackets around the cells. I'd be thinking a heater on maybe an aluminum plate or old heat sink from an amplifier and circulate warm air inside a battery box.
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Hillbilly Heaven
Explorer
That silicone pad mounted to copper plate will to do wonders for making a radiant heat source.
shade
Well-known member
Seems like cycling a load on a timer or thermostat (probe at battery) and insulating the battery would be the simplest & safest way to warm it up for charging. That would also allow the battery to somewhat manage the temperature with its on-board system, rather than relying on external heaters & timers that can't communicate with the battery.
I'm surprised battery manufacturers don't sell warming blankets that can be controlled by the battery's management system.
dreadlocks
Well-known member
ding ding ding, its completely safe to pull load out of a LFP below freezing.. and it dont have to be much of a load and it'll warm the battery up on its own.
for example, I set my BMV high temp alarm @ 120F.. if I run my Microwave for about 5mins it'll jump from ambient to 120F before the microwave is done.. thats like +40F warming in a few mins w/load.. if my LFP was sitting at 10F, it'd take me just a few mins to get it warm enough to take a charge.. and who cares if I burn a few AH out of it, its about to be hooked to a charge source.. unless I'm at like 5% SOC its not gonna be a problem..
If you dont have a big power draw you can use, like an inverter.. just get a dummy load and hook it up.. It'll take longer to dig out the load, open the battery box and hook it up than it'd take for it to warm you up to safe charge temps.
for example, I set my BMV high temp alarm @ 120F.. if I run my Microwave for about 5mins it'll jump from ambient to 120F before the microwave is done.. thats like +40F warming in a few mins w/load.. if my LFP was sitting at 10F, it'd take me just a few mins to get it warm enough to take a charge.. and who cares if I burn a few AH out of it, its about to be hooked to a charge source.. unless I'm at like 5% SOC its not gonna be a problem..
If you dont have a big power draw you can use, like an inverter.. just get a dummy load and hook it up.. It'll take longer to dig out the load, open the battery box and hook it up than it'd take for it to warm you up to safe charge temps.
DaveInDenver
Middle Income Semi-Redneck
What you're talking about is implicit in the battery thermal management algorithms for EVs and stand-by systems. The reason I suspect it's not a standard feature here is it does consume quite a bit of energy and it's not really critical if all you're doing is discharging. In an EV the batteries have to be prepared to accept a charge pretty quickly because of regeneration or that perhaps you might at any time plug in or drive straight to a charging station. If you are fully in control of the both charge and load then manually starting a battery warming or just relying on discharging before charging is fine and doesn't waste energy unnecessarily. Tesla or whomever had to assume you have parked your car outside all night and warming 7,000 cells from their design limit of -30°F to +32°F takes a lot of time, so they have to balance not letting the pack get too cold against how much range it consumes in a parked shut-down state. If you're using a lithium battery to run your RV house you might or might not need to burn whatever, say 20 watts, constantly overnight if you know first thing in the morning you're going to turn on lights and make coffee before the solar kicks in.
luthj
Engineer In Residence
You can treat the resistive heating pads as plain resistors. Putting them in series, reducing or increasing voltage to adjust output power. (consult ohms law). The thermostat should be placed in a location that will respond quickly to changes in case temperature. This will prevent spot overheating.
You should put an insulating box/blanket around the battery during the winter. This dramatically reduces the power needed to keep the pack warm.
There are numerous digital 12v temp controllers on the web/amazon. They have adjustable hysteresis, built-in relays, and a handy display. Some can also control and heating or cooling relay, so you could use such a controller to vent an enclosure in hot weather.
You should put an insulating box/blanket around the battery during the winter. This dramatically reduces the power needed to keep the pack warm.
There are numerous digital 12v temp controllers on the web/amazon. They have adjustable hysteresis, built-in relays, and a handy display. Some can also control and heating or cooling relay, so you could use such a controller to vent an enclosure in hot weather.
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