Another battery heating project

[glamsland]

Hi.

I have a cabin with a 24v 12kw li-ion battery setup. 230v/3000w inverter.

Its installed a heating cable in the insulated batterybox that is controlled by a 230v temp thermostat. In wintertime, when i arrive at the cabin , i turn on the inverter, the heating cables heats the batteries to +10°c.

After a day or so I charge with the generator if needed. Then i dont charge freezing cold batteries..
Works fine.

But here's my idea;

What if .. i set up a single solarpanel connected to a some sort of 12v(?) heating element in the batterybox. Need a thermostat set to +10 or 15°c. Then all year round this panel will feed the heating element to set the battery to 15°c, when the fall comes with colder weather its still sun to heat the battery, and in december and january it might not be much sun but the whoke battery mass is warm so it will keep itself warm for a long time. Maybe, then when i arrive in december in like -15°c , it will need less heating from my 230v heater before i run the generator.

What do you think? Will it work? Worth the effort?

Can a heating element work without a charge controller? Like a 250w panel running a 100w heating element? With weak sun, just a litle heat, good sun warm heat..
The thermostat can be powered from the main battery, just the relay connected to the heating.

 

[Texas-Mark]

Can a heating element work without a charge controller?

Sure. A solar panel can be used 'stand alone' with any resistive load (i.e. heater element). However the output of course will depend on the amount of sun

Like a 250w panel running a 100w heating element?

Now this would not be a good idea because at full sun, that 250w panel would probably burn up a 100w element.

The thermostat can be powered from the main battery, just the relay connected to the heating.

Why use a thermostat at all for the setup you propose? I doubt you would overheat anything is it ran all day. If you did use a thermostat, it would be best to be set at a higher temp to turn on, so you can actually build up some heat for the night.

 

[LakeHouse]

Now this would not be a good idea because at full sun, that 250w panel would probably burn up a 100w element.

Not if you select the right heating element. Panels are Current limited, and resistive heaters are just resistors, which means that they have a fixed resistance. With a current-limited source and a fixed resistor, the maximum power possible (at the heater) would be I*I*R, current square times resistance. If Isc of your panel is 5A and the resistance of the heater is 4 Ohms, you couldn’t possibly make more than 100W of heat at the heater.

I doubt you would overheat anything is it ran all day. If you did use a thermostat, it would be best to be set at a higher temp to turn on, so you can actually build up some heat for the night.

For this to be effective, you probably want to provide at least some insulation, in which case you really want to have some temperature control to avoid overheating.
But I wouldn’t use a powered thermostat. Go low-tech and use snap-disk thermostat switches, they draw no power at all.

There’s a great resource here. Simple, low-tech, reliable.

 

[Texas-Mark]

Not if you select the right heating element. Panels are Current limited, and resistive heaters are just resistors,

Yes, panels limited to whatever they are rated for. Ohms law will give you the resistance needed to sink 100w. But you can’t just grab any 100w element without knowing what voltage it was rated for that 100w. In other words that element needs to be the correct resistance.

 

[LakeHouse]

Yes, panels limited to whatever they are rated for. Ohms law will give you the resistance needed to sink 100w. But you can’t just grab any 100w element without knowing what voltage it was rated for that 100w. In other words that element needs to be the correct resistance.

I agree.
But usually you do know the power and voltage rating for a heating element, and from that you can calculate the resistance as power divided by voltage squared.
Then you could calculate the power you’d get from any specific solar panel/heater arrangement. If you’re going to use the method at the resource linked above, it’s good to know how much heating power you’ll get from a panel/heater arrangement.
And to the point of my original post; the heating element will only draw so much power, regardless of the size of the pane it’s connected to.

 

[time2roll]

Why not run the heater direct from the battery? Yes get some solar to keep the battery topped off.
My small battery is set up like this.

 

[Texas-Mark]

But usually you do know the power and voltage rating for a heating element, and from that you can calculate the resistance as power divided by voltage squared.

Perhaps I should have stated things differently. Many of the off the shelf small element heaters are designed for lets say a 12v battery. Using one directly on a 250w panel would most likely exceed the element's rating and could possible overheat it. Using a 100w element that is designed for the max current the panel can deliver would work fine.

 

[Texas-Mark]

Why not run the heater direct from the battery? Yes get some solar to keep the battery topped off.

I think the OPer may be concerned that a small heater may not keep it under freezing when it gets really cold since it sounds like the cabin is unattended a lot. Plus if snow covered the panels and the batteries died, now he has cold dead batteries that he has a harder time warming up to be able to charge with the generator.

 

[glamsland]

I think the OPer may be concerned that a small heater may not keep it under freezing when it gets really cold since it sounds like the cabin is unattended a lot. Plus if snow covered the panels and the batteries died, now he has cold dead batteries that he has a harder time warming up to be able to charge with the generator.

Yes, the best would be to have a standalone panel just for the heater. Then it wont mess with the batteries.. maybe the panel will be covered in snow, maybe not. With luck, the temperature in the battery is on the +side when i get there in the winter.

Is'nt it like using a 100w heater on a 250w panel the same as connecting a 100w heater to a battery (12v 100a - 1200w) , the heater will not overheat.
100w is 100w regardless of voltage.(?)
Just a example..?

 

[Texas-Mark]

100w is 100w regardless of voltage.(?)

Not really. A wattage rating is based on voltage applied and the resistance of the element.

For example. 100W @ 12v = 8.3 amps and 1.44 ohms Now double the voltage through the same 1.44 ohm element and you have 16 amps and 400 watts. A 240w panel can source about 17 amps (dead short). So that 100w (12v) element might possible burn up.

Point being, if driven directly from a panel, you have to calculate the highest voltage it can produce and pick your element accordingly. The drawback is it may not get very warm except at peak sun (when you likely need it the least). So while feasible to directly drive a resistive element, using a battery to regulate the voltage is best.

 

[Daddy Tanuki]

get the small 25 watt silicone pads and wire them in series until they hold the temp you are looking for. no controls necessary. I have 16 of them in series and it keeps my 3p16s pack hovering between 15°c and 20°c with no controllers to mess with or relays to burn up this is at -10°c temp. i just turn them on in the fall and turn them off in the spring.

below is a photo when i was consolidating my pack to remove a few underperforming cells and had it torn apart. you can see 4 pads on the side, there are 4 on the other side and 8 on the bottom. all are wired in series. final power consumption is about 26 watts @52 volts.

just the heating elements run at a lower temp and its more spread-out across the aluminum heat sink , nice slow gentle heat with no hot spots the entire pack is then enclosed in the blue 2" xps foam.

you could do the same with a single solar panel. just put multiple pads on and then wire them one at a time in series until you hit the sweet spot for the panel. i would start out with either four or six on the bottom do a little testing over a day or two to get a baseline and then wire in additional units on the sides till you hit the temp you want to hold vs the panels out put.

 

[SolarInMaine]

get the small 25 watt silicone pads and wire them in series until they hold the temp you are looking for. no controls necessary. I have 16 of them in series and it keeps my 3p16s pack hovering between 15°c and 20°c with no controllers to mess with or relays to burn up this is at -10°c temp. i just turn them on in the fall and turn them off in the spring.

below is a photo when i was consolidating my pack to remove a few underperforming cells and had it torn apart. you can see 4 pads on the side, there are 4 on the other side and 8 on the bottom. all are wired in series. final power consumption is about 26 watts @52 volts.

just the heating elements run at a lower temp and its more spread-out across the aluminum heat sink , nice slow gentle heat with no hot spots the entire pack is then enclosed in the blue 2" xps foam.

you could do the same with a single solar panel. just put multiple pads on and then wire them one at a time in series until you hit the sweet spot for the panel. i would start out with either four or six on the bottom do a little testing over a day or two to get a baseline and then wire in additional units on the sides till you hit the temp you want to hold vs the panels out put.


View attachment 190460

Love the suggestion. Been thinking about doing pretty much exactly the same to help melt snow from my panels in the winter. Basically, Id connect heating pads in some yet to be determined arrangement of series and parallel until I had enough pads for my needs, putting out a temperature appropriate for the job. Then Id secure the pads to the backside of my solar panels and dedicate a couple of "easily reached to be brushed off" panels to power them. Im not talking about covering the entire rear side of my panels with heating pads. I figure just one located near the top or perhaps in the center might suffice. Itll definitely be worth experimenting with.

 

[Daddy Tanuki]

Love the suggestion. Been thinking about doing pretty much exactly the same to help melt snow from my panels in the winter. Basically, Id connect heating pads in some yet to be determined arrangement of series and parallel until I had enough pads for my needs, putting out a temperature appropriate for the job. Then Id secure the pads to the backside of my solar panels and dedicate a couple of "easily reached to be brushed off" panels to power them. Im not talking about covering the entire rear side of my panels with heating pads. I figure just one located near the top or perhaps in the center might suffice. Itll definitely be worth experimenting with.

consider put them upon the aluminum frame at the top, a few per panel would be enough to get the snow to melt at the top which would be enough to start the snow to slide.

 

[v_green57]

You can run heat tape directly off the battery. Just scale the output - if you have 120V / 5W per foot HT, you will get 1W / foot at 24VDC.

If things are well insulated, the amt. of heat you actually need is very small. I keep all my exposed piping from freezing using only 25W as I have installed pipe insulation over the heat tape / pipe bundle.

You can use one of the 12V thermostats from Amazon to manage things.

This would require some experimentation in your case to see if you can get by with your existing heat tape.

 

[Daddy Tanuki]

You can run heat tape directly off the battery. Just scale the output - if you have 120V / 5W per foot HT, you will get 1W / foot at 24VDC.

If things are well insulated, the amt. of heat you actually need is very small. I keep all my exposed piping from freezing using only 25W as I have installed pipe insulation over the heat tape / pipe bundle.

You can use one of the 12V thermostats from Amazon to manage things.

This would require some experimentation in your case to see if you can get by with your existing heat tape.

this is also not a bad idea, you could place it on the aluminum frames and "pinch" it between the panel frames. a little foam strip on either side would keep wind from entering making it more effective not sure which is the better bang for buck though as I have no clue what the heat tape costs per foot.