Heating with 12v DC

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I plan on going off grid using solar/wind and i'm just wondering if its practical to heat plants off 12v DC with a 120mah battery.

My lights are all LEDs and run off 12v DC so they are fine and dont really consume much.

In the winter months however it can drop to 35-40F here and i can see that being a major power issue.

Currently on the mains i use a fish tank heater submerged in a couple inches of water and that does a fairly good job of maintaining temps at 75F.

I could use an inverter to power it off 12V DC but i'm guessing this would drain the battery in a matter of hours not to mention inverters arent very efficient.

One option i'm considering is heating wire/matts with foam insulation around the sides of the tank but i think i might be expecting too much to raise the temps from 35F to 75F.

Has anyone managed to heat a tank using only 12v DC?

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30 minutes ago, manders said:

120mah = 120/1000*12 watts for 1 hour ~ 1.5watts for 1 hour before your battery is knackered?  If i got that right then its not even going to power an LED light?  Did i miss something?

Sorry my bad its a 120ah battery not mah that would be silly :laugh:

I already have the LEDs running off it on a 14 hour cycle and they have been perfectly fine.

I just need to figure out how to sort the heating without going crazy on cost.

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Heating anything with electric takes a lot of power. I live off grid using a 500W micro hydro-electric generator and 300 Watts of solar panels.

A lot depends on how much power you are generating. If you have a good windmill it wont be a problem on a windy day but on a still dark day in the winter...

I've used those heat mats for seedlings and they're generally 50W at 12v (they have a 240v to 12v transformer block plug usually which you could just bypass).  50W for 24 hours is 1.2KW/hrs


A battery rated for 100 amp hours will provide 5 amps for 20 hours. If we have a 12 volt battery, we multiply 100 by 12 and determine that the battery will provide 1200 watt hours. To apply the metric 'kilo' prefix, we divide the result by 1000 and determine that the battery can supply the 1.2 KW hours.

Every off grid system has a 'dump load', it's a resistive load of some kind, usually a water heating element or air resistive load (looks like an old electric fire element) that is used to dump the power when the battery is fully charged. Maybe you could find a way to use a heat mat as your dump load, that way you wont run your batter flat and you wont waste any power when the battery is charged.




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Thanks Trev. Sounds like a fantastic setup you have there.

I only have 100 watts of solar panels currently which i'm experimenting with. Off the top of my head they give around 8 amps when the sun comes around so i could possibly offload that into a heater of some sort...

The mats i'm not sure will be up to the task as the plants will be in an unheated greenhouse so to expect them to raise the temp from freezing is probably expecting too much.

The immersion type of heaters you can get seem more upto the task but at 300 watts they are going to be power monsters and certaintly wouldnt be feasable on my current setup.

I do plan to add hydro and a wind generator to my setup but its just getting around to it all... I actually have a stream that turns to a river in winter so there could be some serious power to be harnessed there and i'm sure that would run a heater and more.

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I'm indeed following this post. I run most of my GH with a 260w solar system with 3 185ah batteries, a mppt controller for efficency and a 1kw inverter. After testing different loadouts I decided to run everything (lamps, ventilation, hydrofogger) but the heating with solar 'cos it is the most taxing of all the appliances. 

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I'm going to look at setting up one of these micro hydro-electric generators so i can increase my power output as it doesnt seem like i can do much at all with 100W. I've heard good things about these pelton style wheels so probably going to go down that route. Need to research it all first and source parts so for me atleast the heating is going to be postponed for a while

I did come across this earlier http://www.ebay.co.uk/itm/12V-300W-Portable-Car-Tungsten-Heater-Thermostat-Fan-Defroster-Demister-/371937147277?epid=883964974&hash=item56992e798d:g:g5QAAOSw~y9ZCFkN

Not sure how efficient it would be at heating a large area like a greenhouse but it might be worth a try.

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I have a 40w tubular heater in my small grow tent, it has a thermostat which I monitor the heat and is slightly dry heat but is no issue if you either have a humidifier or high humidity anyway, didnt cost a bomb but does require good air circulation to get rid of hotspots or missed areas I have it sitting slightly off centre. With the thermostat on low it shouldnt drink too much juice?

Also , like a gremlin, don't get it wet when watering,  it will require removal of the unit temporarily while you water the plants as the safest option.

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  • 3 years later...

Make sure that this electrical installation it's going to function. If you want to make sure that everything is working, I would call an engineer to fix the problem. Recently, our AC from the house has broken down and we had to call someone to fix the issue. It was during a hot day and we were literally feeling like we were in an oven. He did an aircon chemical cleaning and everything was ok after that. I simply don't get why do these things are breaking so often. I don't know if we have bought a faulty one and everybody has the same issues haha

Edited by PippaScott
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