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Dealing with -30° F Winters.

A

Adarondax

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Joined
Oct 9, 2022
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I have an off-grid, water access camp in northern NYS's Adirondack Mountains. I've been using 12V solar panels, deep cycle group-29 lead acid marine batteries, sine wave inverter and a PWM charge controller for years. It works OK. I use it to power LED strip lights, ham radio equipment, small water pump, vacuum cleaner, laptop computer, and webcam.


When the sun is low and batteries are cold in the winter, system voltage can drop below 12V. The camp, built on posts, is unheated when it's unoccupied. Night time winter temperatures can get down to -30° F or even -40°. The batteries are located on the floor behind the wood stove. I'd like to use LiFePo batteries but from what I'm reading, this would only be possible for three seasons Spring-Summer-Fall. Is there a Li battery that can be used and charged in my situation? Is there a Li battery that can even be stored safely at -30° F or would I need to take them home for the winter? This story describes just how cold it gets there.

www.northcountrypublicradio.org

Why Lake Clear is so very cold

The village of Saranac Lake has a reputation for cold. During the winter, it's frequently the coldest spot on the North Country weather map, sometimes the coldest in the lower 48 states. Overnight or early morning temperatures in January can hit 20 and...
www.northcountrypublicradio.org www.northcountrypublicradio.org
 
Here is the section of an EVE LiFePO4 spec sheet dealing with temperature.

1665338183995.png

So, you can discharge the battery cells as low as -35°C (-31°F), but they don't want them stored long term below -20°C (-4°F). An of course they are not supposed to be charged below freezing.

It really becomes a question of how you can mitigate the cold temperatures. If you store them in an insulated box, the cells will experience the average daily temperature as their thermal mass will even out the lows and highs. You could add a heating pad powered from solar to bring the temperature up some. (There are BMS models with the heating pad control built in).

If you need to charge and use them during the winter, I assume you heat the cabin anyway. However, you would have the delay of bringing them up to temperature.

Winston made the Thundersky line of cells that had added yttrium to the chemistry. From their web page here, they claim very low temperature operation capabilities. I have no idea about availability or cost.
1665339008130.png
 
Most “marine deep cycle” batteries aren’t true deep cycle batteries. They’rea combo starter battery and have a bit extra Ah than a regular engine starter battery.

I’d say you’re better off sticking with lead acid, but get some real deep cycle batteries. Make sure they’re sealed, like AGM or GEL, not FLA (flooded lead acid). The latter can release explosive hydrogen gas and should not be used near an ignition source like your wood stove.

Like hankcurt said, there are LiFePO4 batteries that have a self heating function. I don’t know how cold they’re rated to work, but I would think -40F would be pushing it if not too much, unless you build a heckuva insulating box, maybe that would work? And the self heating function would suck up a ton of juice at -40F, I would expect. Sounds like more risk and hassle than it’s worth, but I’m sure there’s more experienced people doing what you’re doing in similar conditions.

Edit to say that this self heating LiFePO4 isn’t rated to be used or stored in your conditions. It simply extends the usable temp range a bit. There are 12v water tank heating pads that Will recommends that could work, but they use about 70w of power. MAYBE an insulated box with a self heating LiFePO4 with an additional water tank heat pad or two would make your situation doable, but then your battery bank is going to be using a lot of it’s stored energy simply to keep the batteries warm when the wood stove isn’t doing the job. My vote is for AGM.
 
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Thanks guys. The place is so hard to get to in the winter (snow shoes), no thief would risk it.
I've thought about an insulated box and heater. Problems there are roof top solar panels can be buried in snow for a month or more. I have a couple more vertical panels hanging off the front porch but with the sun low in the southern sky, I don't know how much heat that would generate. Same thing for self-heating batteries. How long will they stay warm before power is depleted?
I was hoping there would be some kind of "Aha!" solution but I guess not. I just replaced my four 12-year-old Walmart Maxx marine batteries with new ones. While I got 12 years out of them, the last two years were on fumes. I'm generally not a big power user though the K-cup machine gets used once a day. I just replaced the plug-in Hoover vacuum with a rechargeable Dyson clone. The webcams, router & laptop don't use much power. I'll look into those other types of lead-acid batteries. If I were to get a set of four 100AH Weize LiFePo batteries, what would be the best way to switch them in and out of the system with the lead-acid batteries? Need to switch solar panels and load.

Thanks again for the advice.
 
Adarondax said:
I use it to power LED strip lights, ham radio equipment, small water pump, vacuum cleaner, laptop computer, and webcam.
Click to expand...

I assume your power needs are significantly smaller when you aren't there. Do you still run the webcam?

If not, then is your real goal to make a heated storage chamber for your batteries so that the cold storage doesn't damage them?
 
It is workable with an insulated box and pad heater, but you will need to make sure you can inhibit charging at low temperature. You might also want to power the charging pad directly from solar, or blocking diodes to pick the higher voltage between the battery bank and solar (downstream of an under-voltage relay). It is possible you could use BMS functionality to achieve this, but not sure what product would be best.
 
Shimmy said:
It is workable with an insulated box and pad heater, but you will need to make sure you can inhibit charging at low temperature. You might also want to power the charging pad directly from solar, or blocking diodes to pick the higher voltage between the battery bank and solar (downstream of an under-voltage relay). It is possible you could use BMS functionality to achieve this, but not sure what product would be best.
Click to expand...
No, I'm not talking about keeping the solar connected to the charge controller, I'm suggesting the batteries just "sit" all winter in a box that's heated with a solar panel driving a heater through a thermostat
 
Leeds said:
No, I'm not talking about keeping the solar connected to the charge controller, I'm suggesting the batteries just "sit" all winter in a box that's heated with a solar panel driving a heater through a thermostat
Click to expand...
You don't even need a thermostat for that. You aren't going to heat the batteries to a dangerous level if that is your approach.
 
Leeds said:
No, I'm not talking about keeping the solar connected to the charge controller, I'm suggesting the batteries just "sit" all winter in a box that's heated with a solar panel driving a heater through a thermostat
Click to expand...
Or even better, charge lead acid batteries to run a heater pad and the lithium can sit disconnected for the winter, reconnect during winter when you snowshoe in and have heated up the wood stove.
 
Leeds said:
I assume your power needs are significantly smaller when you aren't there. Do you still run the webcam?

If not, then is your real goal to make a heated storage chamber for your batteries so that the cold storage doesn't damage them?
Click to expand...
Yes. The webcam, which includes 3 cameras, a router, a 600W sine wave inverter, and a 12v timer runs 365 days a year.
 
Leeds said:
No, I'm not talking about keeping the solar connected to the charge controller, I'm suggesting the batteries just "sit" all winter in a box that's heated with a solar panel driving a heater through a thermostat
Click to expand...
Problem is solar power is seriously reduced by snow cover, short days, and trees during the coldest months. I doubt solar would produce enough heat.
 
Tomthumb62 said:
Or even better, charge lead acid batteries to run a heater pad and the lithium can sit disconnected for the winter, reconnect during winter when you snowshoe in and have heated up the wood stove.
Click to expand...
Unknowns for me would be how long will the lead acid batteries produce heat and how would this kind of discharge affect their life.
 
Adarondax said:
Problem is solar power is seriously reduced by snow cover, short days, and trees during the coldest months. I doubt solar would produce enough heat.
Click to expand...
Perhaps go old school? Any chance you can dig a hole below the frost line? ?
 
Tomthumb62 said:
Or even better, charge lead acid batteries to run a heater pad and the lithium can sit disconnected for the winter, reconnect during winter when you snowshoe in and have heated up the wood stove.
Click to expand...
Unknowns for me would be how long will the lead acid batteries produce heat and how would this kind of discharge affect their life.
Adarondax said:
I have an off-grid, water access camp in northern NYS's Adirondack Mountains. I've been using 12V solar panels, deep cycle group-29 lead acid marine batteries, sine wave inverter and a PWM charge controller for years. It works OK. I use it to power LED strip lights, ham radio equipment, small water pump, vacuum cleaner, laptop computer, and webcam.


When the sun is low and batteries are cold in the winter, system voltage can drop below 12V. The camp, built on posts, is unheated when it's unoccupied. Night time winter temperatures can get down to -30° F or even -40°. The batteries are located on the floor behind the wood stove. I'd like to use LiFePo batteries but from what I'm reading, this would only be possible for three seasons Spring-Summer-Fall. Is there a Li battery that can be used and charged in my situation? Is there a Li battery that can even be stored safely at -30° F or would I need to take them home for the winter? This story describes just how cold it gets there.

www.northcountrypublicradio.org

Why Lake Clear is so very cold

The village of Saranac Lake has a reputation for cold. During the winter, it's frequently the coldest spot on the North Country weather map, sometimes the coldest in the lower 48 states. Overnight or early morning temperatures in January can hit 20 and...
www.northcountrypublicradio.org www.northcountrypublicradio.org
Click to expand...
OK. I guess the thing to do is build an insulated box, put a heating pad in the bottom, set an old lead acid battery on top for thermal mass, and use a recording thermometer to track box and ambient temperature over the winter. Then I'd have some data on how much heat solar makes during the day, and how much it'll cool off overnight.
 
Here's a BMS question. We know LiFePo batteries should not be discharged below -4°F. Does the battery's BMS count as discharge?
 
Adarondax said:
Here's a BMS question. We know LiFePo batteries should not be discharged below -4°F. Does the battery's BMS count as discharge?
Click to expand...
It's not a cliff as I understand. It's more like 10a load = destruction of internal chemistry pretty fast but a small trickle discharge is not so bad on the chemistry kind of thing. And the colder the worse the destruction curve gets. So yes, the BMS counts as a discharge but it's not at the same level as running a load. But even so, seems like a good BMS should cut-off itself :)

I don't have this issue as my worst possible case is only 20F (our home left empty/powerless at the one or 2 weeks of winter when this occurs) and my BMS shuts everything (including itself) off before 40F - so I'm following to see the ideas and perhaps what you decide to do.
 
Last edited:
Adarondax said:
OK. I guess the thing to do is build an insulated box, put a heating pad in the bottom, set an old lead acid battery on top for thermal mass, and use a recording thermometer to track box and ambient temperature over the winter. Then I'd have some data on how much heat solar makes during the day, and how much it'll cool off overnight.
Click to expand...
There are insulated boxes, and then there are INSULATED boxes. The answer to your question is calculable if you know the combined square footage of surface area of all sides of your box, the temperature difference you want to maintain, and the R-value of your insulation. This assumes you have no thermal bridges in the insulation and no air leaks.

For instance, if you build a box that is 2 ft wide, 2ft high and 3 ft long (which would be enough space for a 15kwh LiFePO4 battery), it would have a total surface area of 32 sq. ft. If you want it to be 60°F inside when it is -30°F outside, and the box has R-15 walls, the loss of heat would be 192 BTU per hour. There are 3.41 BTU/hr per watt, so the power required to keep it warm would be 56 watts. To maintain that over a day would require about 1.3 kwh of energy. Better insulation, a smaller box, or a reduced temperature difference all will reduce the power required.

The heat loss calculator is available on this web page.
 
Adarondax said:
Yes. The webcam, which includes 3 cameras, a router, a 600W sine wave inverter, and a 12v timer runs 365 days a year.
Click to expand...
When unattended in winter, how much power is needed to run these items? Even with a good pure sine wave inverter, there is a loss of efficiency in conversion, and in idle consumption. I am guessing it doesn't consume anything near 600 watts when unattended. Would there be a way to eliminate the inverter and go with only 12v DC? Or maybe use a smaller pure sine wave inverter for unattended use (300w?)---something that uses less power, and gives you a little better overall yield and duration from the solar you can collect.
 
Adarondax said:
Thanks guys. The place is so hard to get to in the winter (snow shoes), no thief would risk it.
I've thought about an insulated box and heater. Problems there are roof top solar panels can be buried in snow for a month or more. I have a couple more vertical panels hanging off the front porch but with the sun low in the southern sky, I don't know how much heat that would generate. Same thing for self-heating batteries. How long will they stay warm before power is depleted?
I was hoping there would be some kind of "Aha!" solution but I guess not. I just replaced my four 12-year-old Walmart Maxx marine batteries with new ones. While I got 12 years out of them, the last two years were on fumes. I'm generally not a big power user though the K-cup machine gets used once a day. I just replaced the plug-in Hoover vacuum with a rechargeable Dyson clone. The webcams, router & laptop don't use much power. I'll look into those other types of lead-acid batteries. If I were to get a set of four 100AH Weize LiFePo batteries, what would be the best way to switch them in and out of the system with the lead-acid batteries? Need to switch solar panels and load.

Thanks again for the advice.
Click to expand...
if you got 12 years out of a SLA battery then thats what I would go with. most folks don't get that much from unsealed lead acid and while DIY LiFePo4 packs are the rage at the moment none of us have a real clue as to how long they will hold up in such cold conditions. I built a heater pad and insulated box for mine but the coldest it gets where i am at is maybe 0°f...not -40 :) and i am basically at my cabin every weekend through the winter so I can at least regularly check them.

I would stick with the batteries you used before, maybe up the bank size a bit for those long times with no or low sun and go with what you know! Good luck.
 
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