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Old 12-04-2017, 07:43 PM   #1
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250W heater & Dual Batteries

Hi,

Is it possible to use a small heater 250W @2.1 amps with a 1000W inverter powered by two deep cycle batteries; is this possible?

I tried using one battery but it only ran for a short period of time.

Thanks Gem
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Old 12-04-2017, 08:31 PM   #2
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Well Gem, if you tried it with one battery, then you should expect to get double the time with two batteries of the same size and age. Why did the heater stop after a short while? Did the battery draw down to less than 50% (12.06 volts), if so then you are also destroying the battery (as in shorting the life of the battery)
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Old 12-04-2017, 08:41 PM   #3
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It is not impossible to run electric heaters and air conditioners with battery power. It just doesn't make any sense unless you spend about $10,000.00 on batteries. And I wonder if that kinda price makes any sense even if you can afford it.

Roadtrek and probably others offer this in their tiny motorhomes. Seems folks will spend this amount of cash to keep Fido cool while the owners are on walk-about.

BTW. 2.1 amps at 120 volts is much more at 12 volts. Your quiz for the day. How much more?

John

Pic at Mirror Lake in Yosemite Valley
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Old 12-04-2017, 08:59 PM   #4
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240 watts is roughly two hours on one 100 amp battery or about four hours on two 100 amp batteries (staying above 50 % charge to prevent damage from over-discharge).

But of course that assumes a fairly efficient inverter and nothing else using much using battery power.

That is why propane power heaters seem to be all the rage.
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Old 12-04-2017, 09:01 PM   #5
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250 watts delivers the heat of approximately four 60 watt light bulbs.
Too cold for me.
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Old 12-05-2017, 08:20 AM   #6
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The answer to today's quiz is a 250 watt heater on DC is 10 times greater (120 divided by 12=10) then the 2.1 amps on 120 volts AC.
So the 2.1 amps becomes 21 amps on 12 volts DC plus the loss in the converter.

Resistance heat is very inefficient both for your home and trailer compared to gas/propane.
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Old 12-05-2017, 08:55 AM   #7
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Originally Posted by Joe Romas View Post
The answer to today's quiz is a 250 watt heater on DC is 10 times greater (120 divided by 12=10) then the 2.1 amps on 120 volts AC.
So the 2.1 amps becomes 21 amps on 12 volts DC plus the loss in the converter.
Congrats Joe. You win the grand prize, which is the eternal esteem of your fellow FGRVers. That and $4 will buy you a cup of Starbucks coffee.

I am stretching here, but I believe most RV battery specs are calculated under much smaller loads. I suspect our batteries will perform less well under high loads. Do any of you folks understand battery chemistry and how capacity and life are affected by the size of loads? A 21 amp draw must require a serious chemical reaction rate.

John
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Old 12-05-2017, 09:20 AM   #8
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Lemmings flock together

Gemajams Hello!!! The consensus of observers is that this quest is folly at this point in our energy storage (battery) development.

However, there is a huge educational curve that can be crested by following the siren call to battery powered heat. Like Ahab strapped to the White Whale, my flapping arm beckons you forward.

If you are interested, I have a fairly developed thread you can check out on this subject:

http://www.fiberglassrv.com/forums/f...ter-82317.html

Lots of really smart people have been contributing with cat-calls and constructive criticism. Lots of formulas abound. Specs for heaters, coffee makers, etc. litter the discussion. See what you think.

My working hypothesis at this point in my exploration is that I may be able to take the edge off during limited bursts during the night in a quasi-survivalist experience. I'm running a 400 amp hour bank, a 2,000 watt sine inverter and, if I remember correctly, a 120v 750 watt 6 amp heater, which pulls 66 amps from the 12v side of the system. It feels like a luke warm hair dryer but it does raise the tempurature a bit in my very small enclosed egg.

It runs, but I'll have to ration the use during the night. I'm doing this for grins and giggles just to see what might be possible.
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Old 12-05-2017, 09:36 AM   #9
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battery=a/c

well if we need answers we can always go the Tesla route! But in order to do what you want your battery pack would have to be on a separate trailer!

bob
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Old 12-05-2017, 10:43 AM   #10
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Just looking at your photo of Mirror Lake. When I was there last fall the lake was completely dry so it’s fun to actually see both water and a mirror image in the lake!
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Old 12-05-2017, 11:12 AM   #11
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Just looking at your photo of Mirror Lake. When I was there last fall the lake was completely dry so it’s fun to actually see both water and a mirror image in the lake!
Yeah, the rangers turn off the water features after Spring to save water.

John

Here is another view of Mirror Lake, in March 2015 if memory serves, a increasingly rare phenomenon. It seems nicely named.
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Old 12-05-2017, 11:38 AM   #12
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Yes you can but it won't last very long. Resistance heaters and anything with an electric motor will be a real power hog. Even resistance (filament) bulbs suck up a lot of power. The energy efficiency just isn't there.
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Old 12-05-2017, 12:26 PM   #13
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.... Even resistance (filament) bulbs suck up a lot of power. The energy efficiency just isn't there.
But thats a good thing in this case. It all gets turned into heat - and that is what he is trying to achieve.
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Old 12-05-2017, 12:59 PM   #14
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time

maybe 30minutes use 12v to 110 wont work

bob
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Old 12-05-2017, 01:22 PM   #15
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But thats a good thing in this case. It all gets turned into heat - and that is what he is trying to achieve.
Yes, it is worth pointing out that electric heat is actually very close to 100% efficient, in that all the energy going into the device is turned to heat (although if it has a fan, there can be some loss there).

The problem is the methods of making & storing the electricity are not efficient, which is why a propane furnace makes more sense.

To compare the two systems, a 20 lb propane tank holds 430,270 BTUs. If you have a 12,000 input BTU furnace, the output will be in the neighborhood of 10,000 BTUs and you can expect it to run a bit over 35 hours on a tank.

A 1500 watt electric heater produces 5100 BTUs (or around 1/2 the heat) and will completely deplete a 150 amp hour battery in less than an hour.
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Old 12-05-2017, 01:55 PM   #16
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Originally Posted by Jon Vermilye View Post
Yes, it is worth pointing out that electric heat is actually very close to 100% efficient, in that all the energy going into the device is turned to heat (although if it has a fan, there can be some loss there).

The problem is the methods of making & storing the electricity are not efficient, which is why a propane furnace makes more sense.

To compare the two systems, a 20 lb propane tank holds 430,270 BTUs. If you have a 12,000 input BTU furnace, the output will be in the neighborhood of 10,000 BTUs and you can expect it to run a bit over 35 hours on a tank.

A 1500 watt electric heater produces 5100 BTUs (or around 1/2 the heat) and will completely deplete a 150 amp hour battery in less than an hour.
This is the simple and accurate way of describing the situation. Instead of a yes or no answer, it begins to explain why it is extremely impractical to use a battery to run an electric heater.

Expansion on that idea would include the losses when charging and the lower overall energy available from a battery when it is supporting a high load.

Bottom line: Of course you can run an electric heater from a battery and inverter. Question is, will it work in a practical and useful way? Certainly not in any way that makes sense to me and my use pattern.

I guess I could fill one glass with water and attempt to hydrate an army with just that one glass. Then, when needed I could re-fill the glass with an eye-dropper and continue satisfying the thirst of the group. Next, I'll start my diesel with some AAA flashlight batteries. Or even better, I'll drive it around town, or tow my trailer, by just turning the key and running the starter motor. This will save having to buy some expensive fuel and filling the tank.

Sometimes the basic physics of things, required to get the wanted outcome, just don't prove to be practical. And if they did, it would be an industry accepted way of doing it.

We, as campers, all have to learn the limitations of batteries. I'm always managing that deficiency and have learned to be careful with the loads and time between charging them. Some experience will quickly reveal the limits and requirements.
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Old 12-05-2017, 02:32 PM   #17
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Operating electrical heaters and AC using solar and batteries isn’t really feasible. Unless you want to spend a ton of money for lithium batteries. Not worth the money for the return on investment IMO. I connect my solar battery bank to my house batteries on cold nights and that allows me to run the onboard propane furnace without depleting the house batteries. I also have a 60 watt bed warmer that keeps me nice and toasty on cold nights that I can run off my battery bank. I have a small 700 watt coffe maker that I run for a few minutes in the morning so I don’t have to boil water. The coffee maker is a big drain on the batteries but its only for a few minutes and the batteries bounce right back . Solar isn’t the silver bullet that most people think it is but it doesnt allow you to run small electronics.
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Old 12-06-2017, 06:49 AM   #18
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Lol
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Old 11-15-2018, 11:33 PM   #19
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Quote:
Originally Posted by Jon Vermilye View Post
a 20 lb propane tank holds 430,270 BTUs. If you have a 12,000 input BTU furnace, the output will be in the neighborhood of 10,000 BTUs and you can expect it to run a bit over 35 hours on a tank.

A 1500 watt electric heater produces 5100 BTUs (or around 1/2 the heat) and will completely deplete a 150 amp hour battery in less than an hour.
We get so many threads where folks are asking about the practicality of solar and batteries that I have been trying to compare the respective amounts of energy contained in a tank of propane versus that contained in a fully-charged 12VDC battery.

So, in this corner we have 20 pounds of propane weighing in at some 430,000 Btu.

In this corner, the contender, a 100 amp-hour 12 VDC battery. My math says:
  • 100AH/2 = 50 amp-hours nominal usable capacity without damaging the battery.
From there I see
  • 50A x 12V = 600 watts.
  • 600 W x 3,600 seconds (one hour) = 2,160,000 joules.
  • 2,160,000 J / 1,055 J/Btu = 2,047 Btu.
From the above, it looks like the winner and continued champeen would be a one-pound cylinder of propane weighing in with some 21,500 Btu versus the humble automotive battery at about 10% of that value.

So, is my math correct, or did I manage to foul this up?
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Old 11-15-2018, 11:45 PM   #20
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I'm not sure watt you're saying.
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