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Old 05-08-2013, 09:19 PM   #1
Join Date: Jul 2011
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Running heater fan on battery

How long should I expect to be able to run the heater fan in my 2010 model 1007 on battery (fully charged, of course) alone ? I'm guessing not long. But I don't know how to calculate draw vs. battery power etc. Could I get a total of a couple of hours maybe? Even an educated guess would help.

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Old 05-09-2013, 04:57 AM   #2
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You might want to check a local tool rental shop to see if you can rent a meter....make sure it has DC AMP measuring, not a common feature...


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Old 05-09-2013, 09:51 AM   #3
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Depends on how cold it is, how often the heater cycles, and how long it stays on for each cycle...difficult to answer this one.
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Old 05-12-2013, 06:22 PM   #4
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At most I would guess 2 days, but there are a lot of variables.
No I am NOT retired. I work full time.:D

Tracy from Central PA

2010 Jayco 17Z Ex-Port
2004 Ford Explorer V8 with the tow package
2010 Camping Stats
Nights Camping 132 - Nights Camping in My Z 102
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Nights camping 133 - Nights camping in my Z 128
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Nights Camping 66 Nights
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Old 05-13-2013, 09:52 PM   #5
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Look at your battery(s) and see how many amp hours they contain - listed in Amp Hours. Then remember that if you draw your battery down below 50% you are doing damage to the battery. Then look at how much power you furnace draws in amps.

Taking all of that, you start with a full battery that contains 85AH, and your heater pulls 4 Amps - in theory you could run the heater for 10 hours (85 / 2 / 4). Now, that is assuming you run NOTHING else and that your system has no loss due to other factors.

Personally, we are conservative on power use, and with a typical 85AH battery that is good shape and well charged, I'd be comfortable with one night of fairly cold weather (40 degree's).

Other factors are the amount of space being heated (affects the run time) and how cold it is as well as how well insulated your trailer is. Its an unanswerable question with the info provided, but hope this helps on how to figure it out

- 2005 Dodge 2500 CTD 6spd manual
- 2010 Starcraft Autumn Ridge 246RKS
- 2003 Casita Spirit Deluxe (sold)

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Old 05-14-2013, 09:47 PM   #6
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It does help, thanks!
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Old 05-15-2013, 06:26 PM   #7
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CHAKARA - I was just using your simple calc on my usual camping experience off the power grid here using a 255AH battery bank.

I use a 600WATT PSW Inverter for two multi-drop 120VAC circuits coming from the Inverter - One located at the Home Entertainment Center location and the other drop near the Bedroom location. Of course I have several 12VDC items directly connected to the battery bank including LED lights etc...

What usually happens each day is that I will draw around 2AMPs from most of my keep alive drains and from 8PM to 11PM will draw around 20AMPS of current running all the items we want to have on during the evening before lights out like the HDTV, etc...

With my 255AH battery bank starting out fully charged charged I will reduce this down to about 12.0VDC by 8AM the next morning. This is when I will connect my trailer shore power directly to my 2KW generator and am able to re-charge the battery bank back up to its 90% charge state in as little as three hours... Then I do this all over again for the next day/night battery run off the batteries.

Using your simple formula 255/2 for dropping to 50% charge state and /20 for the home entertainment and other loads drop I get just over 6 hours of use. This fits right in with my 3 hours use which this much drain. The 20 or more amps being drawn by three hours early evening battery drain is measured around 300WATTS being consumed from my batteries.

Then using 255/2/2 for the all day battery drain for the keep alive items I get some 60 hours of time to reduce the 255AH battery bank to 50% charge state.

What I actually see at 8AM the next morning is my 255AH battery bank is reading around 12.0VDC which is a quick way to represent the batteries may be down to their 50% charge state. I am using a home made Battery Meter Panel that is monitoring the 12VDC level of the two battery banks and a separate DC current meter that is monitoring the total battery drain by the trailer.

This is quick schematic of my three 85AH 12VDC battery banks (total 255AHs)

I have been camping off the power grids for the past five years doing this with my off-road POPUP camper as described above and very successful about making it through each day/night battery run. I will do these 50% to 90% discharge cycles for about 10 days before having to recharge my 255AH battery bank to 100% charge state so that I won't do any harm to them.

Just curious how one would calculate all of this on paper...

Any of this close to your calculations? or is there a better way to calculate this...

Roy Ken
Roy and Carolyn
I claim Horse Creek Country in Southern Ill - Momabear is from North Texas
We live in King George VA

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Old 05-17-2013, 09:09 PM   #8
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Your rig impresses me every time you post about it I can't imagine using that much power - but we honestly don't spend much time in the camper typically - either out and about or at the campfire. Weather forces us in (like it did last weekend) and we use a bit more, but even then just lights/water and the phantom loads. If it's the wife and I we read and talk and if friends are taking shelter with us we play games typically. Also charging and playing with gadgets - but nothing like your entertainment system. When we get to the point where we spend more time on the road, this will change....

But, yes, your numbers add up.

Total AH 255A
Daily -48A 2 amps @ 24 hrs
Night -60A 20 amps @ 3 hrs

Remaining 147A

If anything, you are a bit above 50% used (255A/2 means 127.5 is the half way point).

The voltmeter test for capacity is marginal at best (but is what I use). The amount of load on the system at the time of measurement and "rest" time seem to have a pretty big impact on the battery DC voltage reading as well. They say, for the voltage test to be accurate you have to disconnect all loads for a few hours, and then take the reading. Clearly not practical while camping!

I've been considering a Trimetric RV meter. This system uses a "tap" to accurately measure current in and out of the battery bank and thus let you know where you stand. The solar guys love them, but from reading they perform well for us generator guys too. Although your "dual bank" system would complicate that as it wouldn't' know which bank you are on. I'd think you'd have to have 2 of the damn things which probably isn't realistic.


At the same time, I mostly weekend so with the current system I can get through a long weekend without the need to haul the generator or have concerns about staying warm at night. (Memorial Day week, 4 of our nights will be sequential without power and while I'm not convinced I'll need it, we will be taking the Honda 2k)

Obviously you've built a great system for high power demand off-grid camping. I am curious why you use GP24's as opposed to golf cart batteries? I'm a believer in getting the most amp hour in the least space/weight for the least cost. Costco GC batteries fit that bill for me, I think I have around 225AH with the two of them. They are a bit bigger/heavier so that is a consideration, but hey, 4 of them would nearly double your capacity!

Anyway, thanks for reaching out.....


- 2005 Dodge 2500 CTD 6spd manual
- 2010 Starcraft Autumn Ridge 246RKS
- 2003 Casita Spirit Deluxe (sold)

My Write-up on managing 12V and batteries
LED Bulbs and what I did
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