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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,
 
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.
 
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?
 
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?
 
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.
 
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?
 
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.
 
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.
 
Last edited:
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,
Input:)
Use the inverter so a 120 volt stat and pads are good. The stats are about 25$. The pads I have used are either 16 watt snake tank heaters , 14$ each that only get to 106f in room temp. Also soil grow warmers 20watts work good. Same mild temps, 18$ each. I used the included tape to tape two about an inch away from batteries. Works great. Set at 41f is very good. If you need more heat just add a pad.
My other method uses direct battery hook ups but you would need 4-12 volt pad and a 48volt stat so this is harder to come by.
I would stay away from high temp pads. Too much concentrated heat on batteries.
 
Update:
No extra battery and panel and charger—-too much $ and less security.
Insulated box 1.5-2” Dow with 3/4” ply ext
Option one is as mentioned above—-120volt stat and pads
Option two is skip the inverter and get 4-12volt 12watt pads. Wire in series for 48volts. Use a DC remote bulb stat like American volt and power direct from batteries. Shut off inverter and use less power. Using 5ah a day would mean your batteries without any solar input would go at least 16 days per 100ah batteries without any solar charge added.
 
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,
Hi...I just thought I would tell you what I did with my off-grid system....I have a sim card router that is powered by my batteries (two 12v Chin 300 amp in series)...but when winter comes in upstate NY, the panels are covered for months...I also use five Wyze cameras to monitor the gauges and as security....all this is using DC voltage only, but will run down my 7000 watt stored power.....I installed a wifi switch to my generator in the shed...when my battery gets too low, I run the generator from home...I also installed two 100 watt panels directly to the outside south facing wall of my cabin....which brings us now to your (and my) problem....how do we keep our batteries warm? My choice was placing the batteries in an insulated plywood and styrofoam battery box....and then running a wire from the CC load out to a step down (24v to12v) converter in the battery box...I hooked up two 12V beehive heaters, connected to a 12v thermostat that has a temperature readout and I set it to come on at @35F--off @45F...this works great! In order to monitor what is happening, I also installed a wyze camera inside the box....the 2 100 watt panels help keep the system charged but eventually it does run down....I only ran my generator 4 hours this year and my batteries never went below 65%....So, wyze cameras, wifi travel router, a wifi switch, a couple more panels, a thermostat, insulated box, step-down converter, and you are all set! Hope this helps!
 
Hello, I too am facing the low temp charge care issue for winter here in upper Michigan.
After many hours of research into options (new high cost low temp batteries are not in the budget and have charge limits), I finally came up with my answer for 24volts and one that would work for 48 as well.
Simple, redundant, effective and low cost is my goal.
1. Well insulated battery box with a bit of stand off space for heating pads.
2. 4-12volt 12 watt pads wired in series for 48 volts. 2sets of these. $12 each pad from Amazon (bee hive heaters)
3. Mount each group on a thin metal heat transfer, these pads run about 140f also mount the snap stat just away from them.
4. Use one snap action 35 on 45f off thermostat for each 4 pad set at $13 each from Amazon.
5. Option of wiring an led indicator light showing outside box when one or other heat assembly is on. $4 each. Two 24 volt in series.
6. Get a remote bulb thermometer to Veiw inside box temp. Option of $12 Amazon.
Reasoning——-
A. Two heat assemblies are a redundant safety system.
B. One is enough and only one comes on at a time and only if that one fails does the second trigger.
C. The snap action stats have a function life of over 100,000 actions. They use zero watts from batteries and no extra electronics or panels to use up power. Very durable.
D. Option to shut off PV power if all this fails. Get a remote bulb thermostat rated at 22amps for $44 for each input string from Amazon and set each to shut off string leading into charge controller if box drops to 32f. This is extra security.
E. If extra panels are needed due to mount angles of existing ones then get just enough to add a punch into your main battery though small charge controller and mount the ?(maybe two). So snow will not shut them down.
Final thought is :::::: do the heated box part and shut system down when gone then use the heated box system for an hour if you go there in the freeze before turning full system on.

Low cost
High redundancy
Low energy drain

Just my two cents:)
Good luck!
 
Last edited:
Hello, I too am facing the low temp charge care issue for winter here in upper Michigan.
After many hours of research into options (new high cost low temp batteries are not in the budget and have charge limits), I finally came up with my answer for 24volts and one that would work for 48 as well.
Simple, redundant, effective and low cost is my goal.
1. Well insulated battery box with a bit of stand off space for heating pads.
2. 4-12volt 12 watt pads wired in series for 48 volts. 2sets of these. $12 each pad from Amazon (bee hive heaters)
3. Mount each group on a thin metal heat transfer, these pads run about 140f also mount the snap stat just away from them.
4. Use one snap action 35 on 45f off thermostat for each 4 pad set at $13 each from Amazon.
5. Option of wiring an led indicator light showing outside box when one or other heat assembly is on. $4 each. Two 24 volt in series.
6. Get a remote bulb thermometer to Veiw inside box temp. Option of $12 Amazon.
Reasoning——-
A. Two heat assemblies are a redundant safety system.
B. One is enough and only one comes on at a time and only if that one fails does the second trigger.
C. The snap action stats have a function life of over 100,000 actions. They use zero watts from batteries and no extra electronics or panels to use up power. Very durable.
D. Option to shut off PV power if all this fails. Get a remote bulb thermostat rated at 22amps for $44 for each input string from Amazon and set each to shut off string leading into charge controller if box drops to 32f. This is extra security.
E. If extra panels are needed due to mount angles of existing ones then get just enough to add a punch into your main battery though small charge controller and mount the ?(maybe two). So snow will not shut them down.
Final thought is :::::: do the heated box part and shut system down when gone then use the heated box system for an hour if you go there in the freeze before turning full system on.

Low cost
High redundancy
Low energy drain

Just my two cents:)
Good luck!
So visitors understand that I gave an earlier bit of input and this note is different its because the first method has been installed in a near exact system of a near by friends off grid camp/ home. It is running great but he lives there year round and can keep an eye on things. Running off the inverter for battery box heat allows him lots of options in pads and watts but does cost some extra running watts and if his inverter goes down for any reason it could lead to issues. He being there full time reduces this risk. The above system is the one I am installing in my camp about a half mile away from him. I may not be there for weeks on end so it has to be a bit more robust and redundant. Thus my second design.
I also my just turn all off and fire it us when I visit?
 
I was thinking as long as you batteries are low temp protected could you come up with a way to just run the heating pads off a 100 watt panel and a DC regulator? Once the batteries heatup they should start charging.
 
I was thinking as long as you batteries are low temp protected could you come up with a way to just run the heating pads off a 100 watt panel and a DC regulator? Once the batteries heatup they should start charging.
Yes. Although the main charging system should power the heaters even if the BMS blocks charging.
 
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