We usually have electricity at our sites whenever we camp, but we've always wondered how long we could run the propane furnace in our 21BHS on battery power (along with the fridge, interior lights, water pump, etc). For battery power, we have two deep cycle 6-volt golf cart batteries tied together in series. In August we dry camped for 4 days and only used up 35-40% of our battery capacity (down to 12.2 volts), but it wasn't cold outside and we didn't need to run the furnace. We would like to have an idea of how long we would be able to be in our camper in cold weather in an emergency situation (if something ever happened and we were stuck there, probably a bad storm). Our batteries, when fully charged and adequately rested, register around 12.9 or 13.0 on the volt meter. So if we camped for 4 days (without using the furnace) and the batteries only went down to 12.2, that gives us an idea of what our average daily power usage is without the furnace. Is there any way to factor in usage of the furnace and then estimate how many days we'd be able to get? We realize that it's not going to be 4, but would like to know how long we might be able to camp with the furnace running regularly. Any help or thoughts will be greatly appreciated! Thanks!
OK, let's do the math. Your two GC batteries (hurray, great choice) have a capacity of 220 Ahs. If after 4 days of normal, ie no furnace, usage you have used 40% then your daily usage is (220*.4)/4= 22 Ahs each day. This is close to my experience.
As a guess, the furnace fan draws 6 amps. It takes a little each firing cycle to ignite the furnace, but that is minimal. But a lot depends on how cold it is outside and what temperature you set your thermostat. I remember a night at Lake Tahoe where it got down to the low 20s. We set the thermostat low, about 50. It cycled about 1/3 of the time on. So during the 8 hour overnight period we used 8*6/3= 16 Ahs. If you kept the furnace set to 65 during the day and it averaged 45 degrees then it would probably cycle the same and use another 16*6/3= 32 Ahs or a total of 48 in a 24 hour day just for the furnace. Add your non furnace loads and it will be 70 Ahs.
So, I would say that furnace use is sort of an emergency situation. It will work, but it will use a lot of Ahs. If you start with fully charged batteries then you could run for about 38 hours and not discharge your batteries below the recommended 50%. But, FWIW it won't do that much harm if once in a while you discharge down to 25% remaining. In that case you can go ((220*.75)/70)*24= 56 hours. Just be sure to recharge your batteries fully when you get back home.
David
Thanks David. That's about what I was guessing. Yes, continual usage of the furnace would likely be an emergency situation (and no shore power). And we realize that it's going to vary depending on the temperature outside and what temp we have the thermostat set at. Appreciate your quick help. I haven't yet gotten used to figuring out these kinds of things (electrical or power related)!
[font size="3"]David, et al,
Per the manual the Atwood furnace draws 3.4A from the 12V source. That's the good news.
[/font]
Planning a longer report soon, but we've boondocked, with some furnace use, for up to five days.
We have just under 200amp/hours, with two 12v "Deep Cycle" batteries in parallel.
Saving grace seems to be the solar panel we bought. We've drawn the battery down to near 12.2 volts overnight, but about 3 or 4 hours of direct sunlight brings it back up to full.
You can see the panel here, which can hook up to either the front or the rear battery, which are hooked together regardless:
[img style="max-width:100%;" src="https://c8.staticflickr.com/9/8874/28305658343_599fa9d833_z.jpg"]
Like I said, longer post on boondocking in the works.
[quote timestamp="1477183699" author="@charliem" source="/post/25488/thread"][font size="3"]David, et al,
Per the manual the Atwood furnace draws 3.4A from the 12V source. That's the good news.
[/font][/quote]That is a bit surprising, but if so you can add about 50% to my hour estimates in the calcs above.
David
Not series, parallel.
Two 12 vdc in series will give you 24 vdc.
Your 12's must be wired parallel.
Quote from: @diversteve" timestamp="1477222023" source="/post/25501/threadNot series, parallel.
Two 12 vdc in series will give you 24 vdc.
Your 12's must be wired parallel.
I knew that, of course, and just corrected it in my post. In fact, a single wire attaches them via a selector switch, normally left on "BOTH", and the frame is used for the ground connection for the rear battery*.
But thanks for pointing that out.
Yet ANOTHER senior moment!
*My installation is described in a thread I started on "Boondocking Options", starting here: [a href="http://livinlite-owners.com/post/20796/thread"]http://livinlite-owners.com/post/20796/thread[/a]
[quote timestamp="1477184016" author="@fasteddieb" source="/post/25490/thread"]Planning a longer report soon, but we've boondocked, with some furnace use, for up to five days.
We have just under 200amp/hours, with two 12v "Deep Cycle" batteries in parallel.
Saving grace seems to be the solar panel we bought. We've drawn the battery down to near 12.2 volts overnight, but about 3 or 4 hours of direct sunlight brings it back up to full.
You can see the panel here, which can hook up to either the front or the rear battery, which are hooked together regardless:
(https://c8.staticflickr.com/9/8874/28305658343_599fa9d833_z.jpg)Todd
Todd,
That's the one: https://www.amazon.com/dp/B00HR8YNK6/ref=cm_sw_r_cp_tai_.Grdyb36S1B72
Very happy with it so far.