Battery care in winter

[whistler]

I have an off grid cabin in northern Minnesota. I would like to move towards a battery-powered system (probably solar/wind/generator backup) but am not sure how the batteries would fare and would like some feedback from the experts.

• I generally get to the cabin at least once a month in the winter
• The cabin is fully heated (wood) while I am there, but not at all when I am not
• It will hit -40 farenheit each winter and -55 farenheit in the occaisional winter
• I would like to be able to use the batteries while I am at the cabin in the winter

Any thoughts or advice?


Whistler

[WisJim]

If your batteries were charged by a PV system with a good charge controller, they would be kept fully charged when you were not around, unless the PV panels were totally, completely, and thickly covered with snow all the time. (Unlikely unless they PVs were installed so snow could not slide off). A fully charged battery shouldn't freeze until it is colder than 40 below, and the charging process produces some heat, so it the batteries are in an insulated battery box that helps retain what heat is available, and they are kept charged, you would have functioning batteries and power whenever you visited the cabin. The batteries would be less efficient (less power available) at very low temps, but they would still work, and using them would also heat them a bit.
My batteries are enclosed in an unisulated box in an insulated unheated (so far) garage, and the garage space might get down to 20 above when it is 30 below outside. Lately, though 20 below has been about as cold as it gets in the winter for more than a few days. Haven't had much of that minus 40 for a week in years.

[whistler]

Originally Posted by WisJim

If your batteries were charged by a PV system with a good charge controller, they would be kept fully charged when you were not around, unless the PV panels were totally, completely, and thickly covered with snow all the time. (Unlikely unless they PVs were installed so snow could not slide off). A fully charged battery shouldn't freeze until it is colder than 40 below, and the charging process produces some heat, so it the batteries are in an insulated battery box that helps retain what heat is available, and they are kept charged, you would have functioning batteries and power whenever you visited the cabin. The batteries would be less efficient (less power available) at very low temps, but they would still work, and using them would also heat them a bit.
My batteries are enclosed in an unisulated box in an insulated unheated (so far) garage, and the garage space might get down to 20 above when it is 30 below outside. Lately, though 20 below has been about as cold as it gets in the winter for more than a few days. Haven't had much of that minus 40 for a week in years.

Thanks much WisJim. This is what I was thinking but wanted someone with some real world experience to share their insight.

The battery array will be sized to fit my summer usage which is higher (I'm there more often) than winter usage. Thus, I think the system will generate an excess of electricity in the winter (although the efficiency of everything will drop with the cold temps). Is it possible to use this excess electricity to put some kind of heat tape or other resistor inside the insulated battery compartment so as to keep the batteries warmer than ambient temperature?

Whistler

Edited to add: You are right, the winters have been pretty meek lately. I, for one, am dissappointed. The decided lack of mind-numbing cold has let the population of non-native invasive species explode. I am primarily thinking about persons from the East or West Coasts.

[Jim-mi]

Yes you could add a circuit board in there that would energize a relay turning on and off a 'load'. This would happen only when the bats are topped off. I do that here for when the wind or sun is generating far more power than what the house load is-----and the bats are topped off. ( I run a 900 watt heater in the house).
But -----I'm here all the time and can be selective in using that thing.
For you (not being there) its more items in the system that *could--can* go wrong.
Might better just let the charge controler keep the bats fully topped off.
A fully charged bat will not freeze to way below zerro..........
But of course at 30 below you wont get much energy out of them either.
Make darn shure that when you leave *on sunday afternoon* that your bats are not depleted to much or they may freeze before the PV can get them back up (generator time).

[Rick]

Originally Posted by Jim-mi

Yes you could add a circuit board in there that would energize a relay turning on and off a 'load'. This would happen only when the bats are topped off. I do that here for when the wind or sun is generating far more power than what the house load is-----and the bats are topped off. ( I run a 900 watt heater in the house).
But -----I'm here all the time and can be selective in using that thing.
For you (not being there) its more items in the system that *could--can* go wrong.
Might better just let the charge controler keep the bats fully topped off.
A fully charged bat will not freeze to way below zerro..........
But of course at 30 below you wont get much energy out of them either.
Make darn shure that when you leave *on sunday afternoon* that your bats are not depleted to much or they may freeze before the PV can get them back up (generator time).

Jim-mi

Is that a 12 volt heater (do they even exist??)

Rick

[Cabin Fever]

I’m just kind of wondering what you think you need batteries for in a weekend cabin during the winter? We have a one-room cabin that we used all the time during the winter in the middle of Minnesota’s northwoods. This cabin is now our guest cabin. We did have batteries in a flashlight, a radio and a cell phone. That’s the only need for electricity that we had. For lights we used Aladdin lamps and a PetroMax lantern. No need for a refrigerator in the winter in Minnesota. It would be silly to heat or cook food using batteries. Again, I ask, what do you need electricity for? If you what power for TV and electric lights, just wirre the place with a few 12 volt lights and get a 12 volt TV. A deep cycle battery should last you all weekend for these purposes.

[whistler]

Originally Posted by Cabin Fever

I’m just kind of wondering what you think you need batteries for in a weekend cabin during the winter? We have a one-room cabin that we used all the time during the winter in the middle of Minnesota’s northwoods. This cabin is now our guest cabin. We did have batteries in a flashlight, a radio and a cell phone. That’s the only need for electricity that we had. For lights we used Aladdin lamps and a PetroMax lantern. No need for a refrigerator in the winter in Minnesota. It would be silly to heat or cook food using batteries. Again, I ask, what do you need electricity for? If you what power for TV and electric lights, just wirre the place with a few 12 volt lights and get a 12 volt TV. A deep cycle battery should last you all weekend for these purposes.

Good question.

The biggest use for electricity in the winter would be for fans to circulate the warm air throughout the cabin. It is about 1000 sq. feet including a room-in-attic. The stove heats the whole place fine, but the fans help speed the process up. I do have a non-electric fan that we use at night but it just doesn't have the oomph to cover the whole cabin. I recently got a petromax lantern (whoa, those babies are bright) and have a couple of smaller propane lights. So lights are not really an issue. Neither is a TV -- I have better things to do at the cabin.

So besides the fans in the winter, my system really will be designed for heavy summer use. Chest fridge, lights, fans, and radio being the primary electrical appliances. I haven't sized it all out but I guesstimating 8-10 trojan deep cycle batteries. Those are more than unwieldy and I don't want to be hauling them home and back in the spring and fall. To get to the cabin is a four hour drive, a three mile boat ride, up a 40 foot bluff and 300 feet back into the woods over rocky uneven terrain.

In summary, the 12V system isn't being put into place for winter use but summer use. I don't want to dissassemble/reassemble it every spring and fall so I bring the batteries home. I want to leave them there, use the system lightly in the winter, and make sure I don't ruin $800+ of batteries.

Whistler

[Jim-mi]

Rick......Not a 12v heater but a very conventional oil filled, looks like a radiator. Two elements--600 & 900 watts AC.

whistler from you last post 'not wanting to disasemble'---thats all the more reason to keep the bats really topped off.
Then again there are some controllers that will go into a diversion mode that could 'warm' the bats.

[wy0mn]

Yes they make 12v heaters.
I don't particularly care for them. Energy sucking monsters, like the ex-wife.
I have a "BackSeat Heat Plus" that will drain two auto batteries with the engine running.Lex

[whistler]

Thanks for the help everyone.

whistler