Separate system for Battery Heating pad

wtrey613

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Jan 15, 2021
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So i wanted to get some opinion on setting up a separate system, 100W panel with a small battery that would run a heating pad for our Bigger 5KW LiFePO4 battery.
Our specs (48V 5.12KW LIFePO4 battery from signature solar, 48V growatt 5000es, and 4S2P, 2,280 Watt solar array)

We currently have an off grid cabin that we visit on the weekends during the winter months (November - January). So while we are gone during the week days, we want our batteries to be above 32 Degree Fahrenheit and charging.

Our first idea is to connect heating pad directly to our battery, but our battery is a 48V system and the heating pads are 12V. we could buy a step down converter but when the batteries die, and there are snow on the panels, the temperature will drop and everything would shut off until the sun clears the panels and the temp is above 32F to charge the batteries.

We thought it might be best to create a separate system, which runs off a 12V AGM battery, 100watt panel (Mounted at a steep angle). Is this over Kill to have a separate panel and battery for the battery heater? ive seen systems where they have separate system for a well pump.

Would love to hear some thoughts and what other people do during the winter months when they are not around.
Thanks,
 

wtrey613

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Jan 15, 2021
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Again, to clarify, we are trying to design a solution for our worst case scenario: Snow on our Main Panels, Our main 5kw Battery shuts off due to < 20% discharge, and we are not there to clean off panels.
In that case, we would want a separate 100W panel at a steep angle to act as a back up and run a battery charger.
 

Sillyputty

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mopat

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how would this help?
A pit/shaft/box below ground would be for your batteries; it would keep them from freezing.

I lined the bottom of my battery pit with 2-3" of gravel and 2" of polystyrene (lime green 2"x4'x8' sheets at big box). Did the four sides and tripled the top/cover. Polystyrene is suitable for ground/soil contact.

A cozy battery coffin.

What is consuming power "when we are gone during the week days"?
So your idea is to run battery charger and battery heater off a steeply mounted 100 watt panel?
 

time2roll

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Mar 20, 2021
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Our first idea is to connect heating pad directly to our battery, but our battery is a 48V system and the heating pads are 12V. we could buy a step down converter but when the batteries die, and there are snow on the panels, the temperature will drop and everything would shut off until the sun clears the panels and the temp is above 32F to charge the batteries.

We thought it might be best to create a separate system, which runs off a 12V AGM battery, 100watt panel (Mounted at a steep angle). Is this over Kill to have a separate panel and battery for the battery heater? ive seen systems where they have separate system for a well pump.

Would love to hear some thoughts and what other people do during the winter months when they are not around.
Thanks,
Separate system is still subject to low voltage sun down cascading to the main battery. Especially with a smallish solar panel.

Consider putting the heat pads in series to match the main battery voltage. Insulation should be used to minimize heat loss. Add more battery and/or solar to the existing system to provide for the additional power requirements.

Otherwise does something need to run? Can all be disconnected and just let it chill for the winter?
 

wiseacre

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Aug 8, 2021
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North of the Adirondacks
A pit/shaft/box below ground would be for your batteries; it would keep them from freezing.

I lined the bottom of my battery pit with 2-3" of gravel and 2" of polystyrene (lime green 2"x4'x8' sheets at big box). Did the four sides and tripled the top/cover. Polystyrene is suitable for ground/soil contact.

A cozy battery coffin.

What is consuming power "when we are gone during the week days"?
So your idea is to run battery charger and battery heater off a steeply mounted 100 watt panel?
This is a good idea but one must remember that during spring thaw there's the potential for a hole in the ground to fill with water. I have a water pressure tank installed much like you describe next to my well pump. In spring there can be a few inches of water in the pit. A lot depends on the drainage of where you dig.
 

wtrey613

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Jan 15, 2021
Messages
41
Separate system is still subject to low voltage sun down cascading to the main battery. Especially with a smallish solar panel.

Consider putting the heat pads in series to match the main battery voltage. Insulation should be used to minimize heat loss. Add more battery and/or solar to the existing system to provide for the additional power requirements.

Otherwise does something need to run? Can all be disconnected and just let it chill for the winter?
thats a great idea to put the heating pads in Series. I did not think about that.

And at the end of the hunting season, Yes, we would unplug everything. But there are two-week gaps where we leave things plugged in and we are not there to wipe the snow off the panels. One issue though with our growatt, we don't want to expose that to below 32F temps because if moisture builds up inside the internals, we don't want the ice freeze to destroy/ruin components.

do you happen to have heating pads? and how often to they run?
 

wtrey613

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Joined
Jan 15, 2021
Messages
41
A pit/shaft/box below ground would be for your batteries; it would keep them from freezing.

I lined the bottom of my battery pit with 2-3" of gravel and 2" of polystyrene (lime green 2"x4'x8' sheets at big box). Did the four sides and tripled the top/cover. Polystyrene is suitable for ground/soil contact.

A cozy battery coffin.

What is consuming power "when we are gone during the week days"?
So your idea is to run battery charger and battery heater off a steeply mounted 100 watt panel?
we can't do that because it's in a cabin/outhouse structure 5 feet above the ground. also ground temps in NY are freezing in the winter.
 

Rednecktek

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Just to throw in my $0.02 here, I think it's a good idea. Being able to disconnect the load off the batteries will help, but they'll still discharge a bit in the cold. Having a second little 12v system will help them stay warm and will actually be easier to build than trying to rectify and such, or at least more fun. I'd go with 2 of the 100w panels and a simple PWM controller just to make sure they get fully topped up.

If you haven't thought about it already, and the physics say you can do it, you can put your batteries in a cooler to keep insulated and warm easier for pretty cheap. No need to spring for the Name Brand tax on that one, just find the cheapest one that will fit your batteries, drill a hole for the wires with some grow foam, and any extra space around the sides can be filled with sheet foam. Since you're running Lifepo4's you don't have to worry about ventilation and having it all enclosed will also help keep the bugs and rats out.

Just a thought.
 
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