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Old 09-29-2020, 12:34 PM   #1
jeremyseattle
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Default How to keep above freezing while parked this winter (not winterizing)

Hey all, looking for some advice. Here's my situation: I'm planning on using my motor home during the weekends this winter, and parking it mid-week. I have a place up in Glacier, WA, about a half-hour from Mt. Baker Ski area. I plan to drive up to the mountain and camp Friday and Saturday (sometimes Sunday) nights. During that time, I'll be able to keep the furnace and/or 110V space heater on, so no concern there.

The issue here is the rest of the week - the remaining 4-5 days that I'm not camping, I'll have the MH parked in Glacier. It doesn't get super-cold there, but freezing is a risk - it gets down in the 20s (sometimes teens) overnight. I'll be covering the RV while it is parked mid-week, so running the furnace is a no-go - even if that was a good idea to leave it on unattended. The fan would probably kill the battery anyway.

So what I'm considering is a small space-heater with a thermostat set to ~35. Leave the bathroom door and kitchen cabinets open so warm air can reach the water pipes.

Power is the main concern here - no shore power available, so coach batteries would have to carry the load. My coach batteries are pretty old, so I'm planning to get new ones - looking at either 2 100ah or one 200ah Renogy AGM or something similar.

Anybody have experience with anything like this? It seems a 12v heater would be more efficient than a 110v running on an inverter. I have a really small ceramic space heater that's surprisingly effective, but I'd have to figure out a thermostat solution. Ideally, I'd like a 12v heater with a built-in thermostat, but haven't been able to find one that you can actually dial-in a specific temperature.

Any ideas?
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Old 09-30-2020, 09:55 AM   #2
Chuck v
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Jeremy,


Heating with electricity using batteries is very inefficient and will draw much more power than just the fan on your furnace. If you have 200 AH of 12 volts that can be utilized not much more than 80% discharge without harm to the expensive batteries -- this works out to about 2000 watts between charges. A very small 500 watt heater would not make a real dent in heating your rig, but would only run 4 hours on this battery. I am sure you can see the limits here...


When I had my coach active year round but was away for extended periods during cold weather, I was connected to shore power so small electric oil filled heaters worked well and did not need internal fans since the 'radiator-like' heater housing uses air convection to circulate the heat. I usually set the thermostat to around 50 degrees since there are lots of thermal losses from the source to the RV walls where some of the plumbing is run. I turned off and drained the ice maker for this reason -- its plumbing was located where coach heat did not reach very well, and the access door on the exterior to allow servicing the refrigerator does not offer any real insulation.


I am not familiar with the layout of your rig nor if its basement is heated...but the usual case is the tanks and some of the plumbing counts on this heated space to keep things from freezing when not winterized. For my live aboard coach, I had small ceramic heaters running at low settings on shore power to heat this space a bit such that it stayed well above freezing (the normal basement heat is from the gas furnaces and furnace fans which were not active when I was away for a week or more...)


One more thing -- the water manifold on my coach was accessed from the same basement door that allowed the water pump and filter to be serviced, and this too is an area of freeze concern. I used the small stick heater called a 'goldenrod' running from shore power in this panel...just the right amount of heat for this application.


You really need to find a place to have your rig on shore power to be sure you can keep everything functional without winterizing -- you likely will not need a full RV connection, just a 20 amp 110 volt power source to allow your heaters to cycle on and off.


Chuck
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Old 09-30-2020, 11:07 AM   #3
jeremyseattle
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Thanks Chuck. Having access to some residential power would definitely help - I'll have to ask my community maintenance guy about plugging in somewhere, but it's not likely to be available where I'll be parking.

Like yours, my manifold is in the same basement comparment as the pump, so that's a concern. The Goldenrod is a great idea! Also thinking about some extra foam insulation inside the hatch.

I've currently got a line on a bank of six 12V 100AH AGM batteries for $300. They're a couple years old, but were just under test conditions on an experimental solar setup and on a good charger, so I think they've got good life left in them. I know how you feel about those and would recommend 6V golf cart batteries, which is what I have now - just two of them and they're 8 years old. I would get new ones, but for the price, these AGMs are hard to pass up. I like the low maintenance aspect too... I would also upgrade my converter's charger because I have the notorious Magnetek 6345. A new charger would make those batteries last a lot longer, I think...

I probably wouldn't even put in all six batteries - I'm not even sure that many would fit, and the weight would be too much. But four of those might be enough to keep a little heater going on/off for a few days. I think I'm just going to have to do some testing this fall and see how much the heater(s) drain the batteries...
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Old 09-30-2020, 11:42 AM   #4
Chuck v
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Jeremy,


Four times 100 amp hours of 12 volt battery capacity is 4800 total watts AT MOST! That 100 amp hour rating is for a 20 hour rate -- meaning that the constant draw should be 100 divided by 20 or 5 amps drain. Note that 5 amps at 12 volts is just 60 watts of continuous drain per battery, or at most 240 watts total (and of course 20 hours is not even one full day...) If you draw higher currents the capacity of the battery goes down -- for a 6 hour rate the 100 amp hour rated battery will only supply 63 amp hours as you can see here in this industry discussion:
http://gbindustrialbattery.com/Batte...H_Ratings.html


Having once worked as an engineer for a solar power company, and having had an off grid home for years myself, I am keenly aware of the uses of battery power and its limitations when stand alone and absent continuous recharging.


You are welcome to do your own experimental testing...please post results here for the community to benefit from.


Chuck
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Old 09-30-2020, 12:12 PM   #5
jeremyseattle
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Thanks again Chuck - your expertise is unquestionable. I know it's really pushing the limitations of the system. Like I said, it doesn't usually get super-cold up there - it's only about 1000 ft. elevation. So I would only plan on the heater(s) running an hour or two per day, with 3-4 days between charges. Might add one or two 100W solar panels to provide a little more, although the days are very short. I'll try to find an alternative parking spot with power - or drive the 2 hours back to my house - for the coldest weeks.

I will definitely share results of whatever I do.
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