Low Temp Heating Strategy in Remote Cold

[icyroads]

This is not a low temperature protection question.
I will have low temperature charging protection.

This is about getting batteries warmed back up off-grid after they’ve cold soaked to -10F and -20F, or keeping them warm enough while idle and unattended off-grid so that they can be used to start up a heating system to eventually get warm enough to charge.

I go ice fishing and snow camping where I park and could be away from my van for days, in temps down to -10F (intentionally) or even -20F (I try to avoid being out remote below -10F, but it happens).
What might be good strategies for keeping/getting the batteries warm in this scenario?

Assume a well insulated van and battery box.
Solar too, but cannot always count on that.

1) Let the van and batteries cold-soak, then heat them back up when I get back to the van, 1a) with a fuel heater or 1b) with electric pads or 1c) both?

2) Keep the van heated to 10F, 20F, 32F, or some other min? This is not about keeping them ready to charge, this is more about getting/keeping the batteries in a state so that they can get other systems going (eg heat), and then eventually warm enough to charge.

3) Use heating pads to keep the batteries warm all the time?

Even if I heat the van, I am concerned about the heat failing for some reason while I’m away and the van and batteries cold soak to -10F or -20F?
Could the batteries still deliver enough while that cold to eventually heat back up via manually switched electric pads, or is it better to keep the pads always connected to keep the batteries warm no matter what?

Thank you.

 

[Shimmy]

How big of a battery and what chemistry? I wonder if a chemical heat pad could a) activate, and b) provide sufficient heat for the initial warm-up.

An insulated box with 2" of foam, say 2' cube, and keeping the interior ~10F above ambient would need about 150Wh/day with an electric pad. I imagine you would need twice that to raise the temperature ~10F. At -20F you have less than half your nameplate capacity at a 0.05C discharge rate (lead acid).

I'm no cold weather survivalist, but I'd be worried about trying to keep the van warm while away. For the batteries, I would want them above 0F when I got back to the van, but that seems unrealistic (without a timer).

 

[icyroads]

Thank you Shimmy.
Interesting idea on using chemical pads.
Worst case I could get a wood fire going to heat up rocks, or to keep recharging the chem pads until the batteries are warm enough, but I imagine that’s a last resort before walking out.
A small gas generator as backup might also be an option.

Chemistry is LiFePO4, ~200Ah minimum as a 12v system, but I could go up to ~600Ah.

Starter batteries are dual 12v 60Ah AGM lead acid batteries wired up in parallel (120Ah total).

It’d be impractical for me to insulate the starter batteries beyond a simple battery blanket.
The house batteries will be well insulated, not just by the van but also in their own space/box.

 

[DThames]

I would consider a separate Lithium battery pack to power heaters like these. I fooled around making a body warmer by putting some of these type heaters between some of these jell packs so I wouldn't get hot spots. A battery would take the heat where my body wouldn't so no need for a gel pack. I ended up using a 5000mha 7.4v pack and a boost converter so I could adjust the voltage to somewhere that the heat output matched what I wanted. I think that I used a smaller 7 watt heater but it would run for 4 hours or so on 4 (2s2p) 18650 cells. 7.2v and 11.1v Li-ion drone type batteries would work, or some larger pack. These heaters get hot to the touch but not so hot to melt stuff. It might make some plastics soft if the heat was right against them. Some thermal mass can help spread the heat out, if needed. Stick one on the back of an 1/8" AL plate beside your battery and the heat should be spread out fairly well. As they are made from a plastic type stuff, I don't run them at full 12v as they smell a bit if they are enclosed/insulated enough that the heat can't get out.

 

[icyroads]

I would consider a separate Lithium battery pack to power heaters like these. I fooled around making a body warmer by putting some of these type heaters between some of these jell packs so I wouldn't get hot spots. A battery would take the heat where my body wouldn't so no need for a gel pack. I ended up using a 5000mha 7.4v pack and a boost converter so I could adjust the voltage to somewhere that the heat output matched what I wanted. I think that I used a smaller 7 watt heater but it would run for 4 hours or so on 4 (2s2p) 18650 cells. 7.2v and 11.1v Li-ion drone type batteries would work, or some larger pack. These heaters get hot to the touch but not so hot to melt stuff. It might make some plastics soft if the heat was right against them. Some thermal mass can help spread the heat out, if needed. Stick one on the back of an 1/8" AL plate beside your battery and the heat should be spread out fairly well. As they are made from a plastic type stuff, I don't run them at full 12v as they smell a bit if they are enclosed/insulated enough that the heat can't get out.

Thank you DThames.

Why a separate battery?

Seems like these applied directly under the batteries, and run from the same batteries (LiFePO4) would heat up both from the pad and the internal resistance of the battery, helping the battery to heat up more evenly.

Even so, I still have the question of whether to always keep the batteries warmish (eg >=0F), or to let them get cold and heat them back up when I get back. I’m thinking now that it’s more a question of capacity vs how cold it gets vs how long I’m away. Short enough and “warm” enough where the battery capacity would not become too diminished it’d be easier, even safer to keep the batteries warm. But if battery capacity is at risk of running out before I get back, probably better to heat the batteries back up when I get back.

 

[DThames]

Thank you DThames.

Why a separate battery?

Seems like these applied directly under the batteries, and run from the same batteries (LiFePO4) would heat up both from the pad and the internal resistance of the battery, helping the battery to heat up more evenly.

Even so, I still have the question of whether to always keep the batteries warmish (eg >=0F), or to let them get cold and heat them back up when I get back. I’m thinking now that it’s more a question of capacity vs how cold it gets vs how long I’m away. Short enough and “warm” enough where the battery capacity would not become too diminished it’d be easier, even safer to keep the batteries warm. But if battery capacity is at risk of running out before I get back, probably better to heat the batteries back up when I get back.

Separate battery....I was not sure of your situation. If the battery was critical, you wouldn't want to deplete it trying to keep it warm so it would later work.

Not an expert on heat loss and where/when it would make sense to maintain a certain temp level, but a little heat added off and on will hold a system if there is not a huge heat loss. I would think it ideal that the heat go to directly (as much as possible) into the battery itself and then let the battery loose the heat to the enclosure, rather than trying to heat the enclosure and let the heat sort of soak into the battery.

 

[schmism]

I thought the goto for this application was the silicone heating mats. You sit the pack ontop of it or weave it around between cells. PID controller using temp probes you monitor cell temp.

 

[icyroads]

I thought the goto for this application was the silicone heating mats. You sit the pack ontop of it or weave it around between cells. PID controller using temp probes you monitor cell temp.

Yep, but my question is more about whether/when to keep them warm vs letting them get cold and heating them back up.
And, if I do opt to keep them warm, what’s a bare minimum to keep them usable enough to quickly get things going again, eg a heating system, warming up and starting the van, but not charging.

 

[notarichman]

This is not a low temperature protection question.
I will have low temperature charging protection.

This is about getting batteries warmed back up off-grid after they’ve cold soaked to -10F and -20F, or keeping them warm enough while idle and unattended off-grid so that they can be used to start up a heating system to eventually get warm enough to charge.

I go ice fishing and snow camping where I park and could be away from my van for days, in temps down to -10F (intentionally) or even -20F (I try to avoid being out remote below -10F, but it happens).
What might be good strategies for keeping/getting the batteries warm in this scenario?

Assume a well insulated van and battery box.
Solar too, but cannot always count on that.

1) Let the van and batteries cold-soak, then heat them back up when I get back to the van, 1a) with a fuel heater or 1b) with electric pads or 1c) both?

2) Keep the van heated to 10F, 20F, 32F, or some other min? This is not about keeping them ready to charge, this is more about getting/keeping the batteries in a state so that they can get other systems going (eg heat), and then eventually warm enough to charge.

3) Use heating pads to keep the batteries warm all the time?

Even if I heat the van, I am concerned about the heat failing for some reason while I’m away and the van and batteries cold soak to -10F or -20F?
Could the batteries still deliver enough while that cold to eventually heat back up via manually switched electric pads, or is it better to keep the pads always connected to keep the batteries warm no matter what?

Thank you.

maybe you could use an extension cord to keep your engine warm overnight and tie in warming packs for a battery inside the car. then when you go fishing, pull the battery out of the car to use in the fishing hut. the battery shouldn't cool off too fast...especially if insulated in a cooler.
i have one of those heater/coolers that run off 12v in my truck. i can keep food/coffee warm in it and could keep a battery warm at the same time.
they take a lot of power, but the battery could be stored in your house until you are ready to go fishing.

 

[HRTKD]

I use warming pads to keep my two LiFePO4 batteries above 32°F at all times. The batteries and pads are fairly well insulated inside an RV trailer that sits at the storage lot (no shore power) in the winter. I do have 640 watts of PV on the roof and that's more than enough to offset what the warming pads consume. It can go for a few days without getting a full charge from the PV (due to snow).

I prefer a solution that warms the batteries directly (direct contact) instead of something that warms the box that the batteries sit in. I have a temperature sensor on the top of the battery to monitor the temperature of the battery. The sensor is insulated from the ambient air so I'm reading the battery temp, not the air temp. It's not perfect, but it's working well.

 

[icyroads]

To wrap this thread up, thank you everyone for your suggestions.

I did find some mechanical freezer switches that I might be able to modify to close at 0F instead of open at 0F. However, that’s a hassle and not a sure thing.

Instead, I’m just going to experiment this winter to see whether I might really need something like this.
Yes, the batteries will have charge protection for below 32F and low voltage discharge protection.
Worst case I can heat up the batteries when I get back to them. It may take a bit longer but that may be worth it for the very few times that the batteries will actually get that cold.

Thanks again!

 

[HRTKD]

It can take hours to bring the batteries up to above 32°F. They're pretty dense.

 

[Supervstech]

A battery cold soaked to -10F or colder will take DAYS to sufficiently warm up above 32F to be safe for charging…
If it is going to be needed, I would have a heavily insulated box, with heaters on the exposed sides, with airspace around the batteries, and a thermostat in the box keeping the heaters going when the airspace gets to 34F and maintain the air temp in the box.

 

[icyroads]

A battery cold soaked to -10F or colder will take DAYS to sufficiently warm up above 32F to be safe for charging…
If it is going to be needed, I would have a heavily insulated box, with heaters on the exposed sides, with airspace around the batteries, and a thermostat in the box keeping the heaters going when the airspace gets to 34F and maintain the air temp in the box.

Thanks, that’s one of the things I’ll be looking into from the safety of my driveway.

My main concern is that the batteries are/get just warm enough to produce enough so that I can get things started back up, and then eventually heated back up even if it takes days. I’m not that concerned about waiting to recharge, at least not yet.

 

[icyroads]

It can take hours to bring the batteries up to above 32°F. They're pretty dense.

That’s kinda what I’m counting on. If it takes hours/days to heat up, then it’ll take hours/days to cool down. If I’m not away for too long then it might not be an issue.

 

[tonyg]

This may come in handy for someone in an off-grid installation:

Lerway Seedling Heat Mat With Temperature Controller Thermostat Seed Sprout 30W | eBay

Find many great new & used options and get the best deals for Lerway Seedling Heat Mat With Temperature Controller Thermostat Seed Sprout 30W at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

There are other models as well, but thought to share.

Still looking for some heat pads myself .

 

[icyroads]

This may come in handy for someone in an off-grid installation:

Lerway Seedling Heat Mat With Temperature Controller Thermostat Seed Sprout 30W | eBay

Find many great new & used options and get the best deals for Lerway Seedling Heat Mat With Temperature Controller Thermostat Seed Sprout 30W at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

There are other models as well, but thought to share.

Still looking for some heat pads myself .

I have one of those for a small greenhouse.
I would not use it for keeping a vehicle or batteries warm —it requires 120v AC, and so would require an inverter to be running.
Much better to use DC powered thermostats, switches and heaters — keep the energy usage and the heat right where you need it, not lost to an inverter that’s sucking power even when it’s not needed.

 

[robstrom]

Sask prairie winter last year. LifePo4 CHARGING above 0 issues, not using it. Mine fired up my diesel heater (12 amps)fine after a week of true -30 +windchill. I tried the heat pad, and got a dead battery. Not advice, just my experience

 

[Kapow_Network]

I use warming pads to keep my two LiFePO4 batteries above 32°F at all times. The batteries and pads are fairly well insulated inside an RV trailer that sits at the storage lot (no shore power) in the winter. I do have 640 watts of PV on the roof and that's more than enough to offset what the warming pads consume. It can go for a few days without getting a full charge from the PV (due to snow).

I prefer a solution that warms the batteries directly (direct contact) instead of something that warms the box that the batteries sit in. I have a temperature sensor on the top of the battery to monitor the temperature of the battery. The sensor is insulated from the ambient air so I'm reading the battery temp, not the air temp. It's not perfect, but it's working well.

Can you tell us which brand / model warming pads you use for this?

 

[HRTKD]

Can you tell us which brand / model warming pads you use for this?

Here's my write-up:

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...

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