Quote:
Originally Posted by whoward
Hi all,
<<SNIP>>
I'm looking at a 2017 Salem Cruise Lite by FR model 261BHXL. So here's what I'm wondering... During the nights at deer camp it gets pretty chilly in November (usually down to the mid 20's).
If I have to run on battery power to use the furnace (assume I use nothing but the furnance) how long will I be able to make it last? I'll only use the furnace with propane during the nights, during the day we sit around the campfire when we aren't hunting. So only when trying to stay warm enough to sleep. A nice hot shower every day would be nice too.
<<SNIP>>
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One 12-volt group 24 (standard sized) battery won't do the job. As others have said, more battery capacity combined with solar (and/or generator) charging will be needed.
Several things to consider:
1) Power demands of your particular furnace. You may find this on a "data plate" somewhere on the body of the furnace...perhaps behind the decorative cover.
If I recall, the furnace in my PUP uses 5 amps. The one in your rig may be more like 10 amps when the blower is running...especially if it ducts the heated air throughout the camper. While I don't know your furnace's power requirements, I'll assume 10 amps to make things easy.
2) The power consumption info may be in your furnace owner's manual. If you don't have your original owner's manual, you
might find it here.
3) You get to use about 1/2 of the battery's total capacity before requiring a recharge. In the case of the standard group 24, the battery has a capacity of about 75 amp hours. You get to use about 37.5. Any more and you begin to damage the battery. Fully draining (and not immediately recharging) a battery ruins it.
4) So let's assume your furnace uses 10 amps. Run it for an hour straight and it consumes 10 amp hours. 10 amps for one hour = 10 amp hours.
Now let's assume it's cold and the furnace must run 50% of the time to maintain the desired temp...and you sleep for 8 hours. So that's a 50% duty cycle at 10 amps for 8 hours = 40 amp hours. If your battery is fully charged and healthy, it could survive that for ONE night assuming you can fully charge it the next day...and have no other draws.
5) You do have other draws: the CO/Propane detector is always on and always sucking a trickle out of the battery...24/7 so it adds up. Other draws would be the fridge ignition (why not use the fridge?), water pump (you probably won't use that, but you might), occasional lights, and so on. You've already used slightly more than half, and now you're adding more loads. That's a recipe to kill the battery.
6) 2 x 6 volt golf cart batteries in series will increase your available (usable) amp hours considerably.
A "typical" 6 volt golf cart battery has a total capacity of about 225 amp hours. 2 in series do NOT double the amp hours, but they do double the voltage to 12 volts. So, with that arrangement, you can safely use about 110 amp hours before charging....a vast improvement over a single 12 volt. The dream setup (aside from Lithium and other exotic batteries) is 4 x 6-volt golf cart batteries in series/parallel delivering 225 USABLE amp hours. But you probably have no room for such a massive battery bank without significant modifications to the rig. But you CAN fit two batteries on the A-frame of most rigs.
7) Solar can recharge your batteries daily.
This is a good solar package that's inexpensive and would maintain a 2 x 6 volt golf cart battery bank. Renology is another good brand. All you need to do is: mount the panels on the roof; run the wire thru a
gland high on a side-wall into an inside cabinet; mount the charge controller on the cabinet wall; run the wires to the battery; attach the output of the charge controller straight to your battery bank....no muss no fuss. There are no special connections to enable this to work in parallel with the onboard converter/charger in the rig. I can provide more details if you wish....I have solar on my PUP.
8) The 400 watt system with two batteries allows for short fall/early winter days and grey skies. Depending on the weather, you may not get a full charge each day, but you will restore a lot of the battery bank's capacity even in bad weather. Keep the snow off the panels if that happens.
9) A 2 kilowatt
Predator brand generator from Harbor Freight (<$500) will back you up and make you 100% energy independent for indefinite boondocking. Generator snobs may denigrate this machine, but Consumer Reports recommends it, and a friend has one and loves it.
10) This
calculator is very handy for assessing your loads...especially if you decide to get an inverter to make 120 volts along the way. Always plug 12 volts into the calculator, because your ultimate power source is the battery bank. But if you have an appliance that runs on 12 volts and is rated in watts instead of amps, this calculator will help you determine the number of amp-hours used for every device.
Once you get more battery capacity and go solar, you'll want to be able to estimate your power consumption so you can enjoy the amenities built into your rig...like lights. And you may just decide to take your kids camping in the boondocks, because you'll be able to.
11) Since you plan short trips, you could leave the rig on site between visits and let the solar do its job to top off the idle batteries. Better is bringing it home and hooking up to shore power for about 24 hours or so to let the converter/charger bring the batteries up to full charge. Extended trips on solar run the risk of never fully charging the batteries, and this causes
sulfation. If you're out for a week, run the generator for about 8 hours to help top off the batteries. The generator will work in parallel with the solar to fully charge your batteries.
12) All this exercise on the batteries gives them a real workout. Stash a gallon of distilled water in your rig...near the furnace...and check your electrolyte often...at least monthly...to keep them topped off.
Your "mileage" will vary, of course. Your furnace's actual amps draw is not likely to be exactly 10. Depending on the weather and how warm you keep your rig, your furnace may run more or less than half the time on a cold night. And battery use is FAR more complex than just using 50% of the rated amp-hours - especially if you start drawing big loads through an inverter and so on. But you get the idea. And these are all good rules of thumb to start with. They work well enough for typical RV uses...such as the furnace.
Unlike a good tent (thoroughly ventilated), don't let it get too cold in the camper, because condensation from human breath is a real problem in a cold camper. You'll regret that. Ventilating helps, but on a still (no breeze), cold night, there will be little air exchange, so the camper will literally be dripping (or frosting up) inside without adequate heat. Cracking a window defeats the purpose of running the furnace, and there is a LOT of space for warm, moist air to collect above the windows in an RV. And it's no fun to be sleeping in a camper that's below freezing inside anyway.
P.S. The links are more like illustrations than specifications. E.g. the gland may need to be bigger to accommodate larger (say #6 AWG) wire from the panels. Assembling all the right components is dependent on the capacity of the solar array.
Battery University is a great resource for all things battery...revisit the link attached to the word sulfation and explore.
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