12 volt electric heat

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Ixneigh
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12 volt electric heat

Post by Ixneigh »

Abstract; by 2 in the afternoon on an average day my solar system is dumping power. If I got a 3rd battery specifically to operate a 12 volt 600 watt electric heater, it might warm up my bathroom a little if I ran it for 30 minutes. These heaters are pretty cheaply purchased online. I could top off the battery by plugging a jumper into a cigarette lighter socket.
My question is, is this a practical idea and, what is the smallest battery that would provide 30 minutes of service?

Ix
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Stickinthemud57
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Re: 12 volt electric heat

Post by Stickinthemud57 »

I am not knowledgeable enough in battery types and technology to answer your question, but I will offer the following thoughts;

-600 watts is a lot to ask of a battery, and one would need an inverter of fairly good size and cost to convert your DC to the AC that most electric space heaters use.
-Drawing 600 watts for 30 minutes will, I think, push the limits of most 12V lead-acid car/boat type batteries and doing this a lot would likely shorten the life of such a battery.
-There are several very affordable propane space heaters that use oxygen depletion sensors that purportedly make them safe for indoor use. You might want to look into these. Here is an example:

https://www.amazon.com/Mr-Heater-F21510 ... r=8-8&th=1
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Ixneigh
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Re: 12 volt electric heat

Post by Ixneigh »

Oh I should have specified these are heaters that operate on 12 volts, at 600 watts dc. I figured it’s much safer than 110 volts.
Apparently they are intended to defrost windows in the winter.
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Re: 12 volt electric heat

Post by Ixneigh »

Oh I should have specified these are heaters that operate on 12 volts, at 600 watts dc. I figured it’s much safer than 110 volts.
Apparently they are intended to defrost windows in the winter.
Re: purportedly safe, but I think
I’d need a real wood stove type Charlie noble to feel comfortable with heating with flame
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Re: 12 volt electric heat

Post by Russ »

Years ago I had a 12v hair dryer. It was a joke. Probably consumed 600w but sucked the battery down and didn't put out much heat.

Wait............you are in the Florida keys. Heat? I would think you'd be looking for cooling ideas.
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Ixneigh
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Re: 12 volt electric heat

Post by Ixneigh »

In The winter we have a few coolish days. Maybe twenty of them. That’s why I’m installing a wood stove or anything more complex than a portable unit.
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Be Free
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Re: 12 volt electric heat

Post by Be Free »

I'm going to assume that you want to run this heater in the morning or perhaps in the evening to take the chill off the head and that you are going to use the "excess" power in the afternoon to replace this power in the new battery.

600W / 12V (nominal) = 50 amps

50 amps for 0.5 hours = 25 Amp hours

Ignoring Peukert effect a 50 Ah deep discharge (not dual use) lead acid battery would work but I doubt that you can find one that small that can take a 50A discharge rate for 30 minutes. The limiting factor is likely going to be the 50A rate rather than the battery capacity. Any deep discharge lead acid battery that can be discharged at 50 amps continuously that is at least 50 Ah will work.

Regularly pulling a lead acid battery down to 50% state of charge will shorten it's life. Quickly bringing it back to full charge will help.

A 125 AH battery would only be pulled to 80% SOC and would be less stressed. It's also more likely to be able to take to 50A discharge rate.

A 50 Ah lithium battery would probably be able to handle the 50A discharge rate and would not be stressed at 50% SOC. If you are not already set up to charge lithium then this would be a very expensive heater.

Regardless of which chemistry is used, you will need to replace (a bit more than) 25 Amp hours in the battery with excess solar power each afternoon if you want to be ready for the next cycle.

Do you have enough excess solar capacity to do this?
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Ixneigh
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Re: 12 volt electric heat

Post by Ixneigh »

This is why I love this forum. There are some really smart people flogging about in these little boats.
I have not braved the lithium train yet on my boat. I’m currently experimenting with a simple system powering this little EV cart

Image

If it doesn’t catch fire or do anything else scary I might consider redoing my boats batteries with lithium when the Optima AGM batteries bite it (they are on their last legs now)
The 50 AH battery I have in the EV cost 109.00 dollars. I set up the EV with a charge regulator and a 100 watt solar panel
and it can go a few miles a day just on solar. The motor is a 350 watt 24 volt scooter motor which is connected to a step up 12 to 24 volt converter. So this is a similar draw.

Regarding charging capacity. In cooler weather I might be able to do this with a 225 watt solar array. In warm weather running the electric icebox, not so much. I don’t shower every day when I’m just laying about on the boat. I found certainly connect the heater battery to the system for a few hours during the afternoon.

Ix
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Re: 12 volt electric heat

Post by Be Free »

Ixneigh wrote: Fri Oct 25, 2024 3:21 pm This is why I love this forum. There are some really smart people flogging about in these little boats.
I have not braved the lithium train yet on my boat. I’m currently experimenting with a simple system powering this little EV cart

Image

If it doesn’t catch fire or do anything else scary I might consider redoing my boats batteries with lithium when the Optima AGM batteries bite it (they are on their last legs now)
The 50 AH battery I have in the EV cost 109.00 dollars. I set up the EV with a charge regulator and a 100 watt solar panel
and it can go a few miles a day just on solar. The motor is a 350 watt 24 volt scooter motor which is connected to a step up 12 to 24 volt converter. So this is a similar draw.

Regarding charging capacity. In cooler weather I might be able to do this with a 225 watt solar array. In warm weather running the electric icebox, not so much. I don’t shower every day when I’m just laying about on the boat. I found certainly connect the heater battery to the system for a few hours during the afternoon.

Ix
Are you trying to reinforce the upper Keys resident sterotype? :D

re: your scooter
350 W / 24 V = 14.6 A but since you are pulling this from a 12V battery then the battery has to supply a bit over 29.2 A (there is overhead for the step-up converter). If the scooter battery is lead then you should get around 45 minutes run time at full speed if the battery is fully charged and still delivering 50Ah. If it is lithium you should get about 2x the run time. Is that pretty close? A 100W panel should be just about perfect for keeping a 50AH battery charged as long as you are not pulling it down to 50% every day.

I'm at the same place you are with the switch to lithium. I have a large lead house bank that is past "last legs", probably closer to "one foot in the grave". I'm actually doing the cost/benefit analysis for a switch to LiFePO4 right now. Seven years ago lead was the clear winner; lithium is definitely in the running and may actually win out this time.

In the summer you won't need to run the heater will you? The icebox will be the major draw in the summer but it will not run nearly as much in the winter. You have the additional advantage that the solar panels will work better in the winter (when they will run cooler). A 225 W solar array should put out around 15A for battery charging. You should be averaging close to 6 hours of usable sunlight at your latitude so that is around 75Ah on a clear cool day with newish panels and a good charge controller.
Bill
2001 26X Simple Interest
Honda BF40D
"If I were in a hurry I would not have bought a sailboat." Me
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