toprudder wrote:
professor95 wrote:
The RV furnace is the biggest user of 12 VDC power in your RV. It takes a lot of battery to keep the furnace blower spinning fast enough for the sail switch to keep the furnace running.
Not always the case. In my old camper (28' class C, no slides) on a night that dipped down to 35 degrees or so, I paid close attention to the furnace. It would come on twice an hour, and run for 6 minutes. It pulled 10 amps while running. That equates to 2 AH per hour of operation, or 16 AH over an 8 hour period. If you turn on just a few incandescent lights, that will pull more out of the battery. I suspect, though, that a pulsed high-current load will bring down a battery quicker than a smaller continuous load, given the same apparent AH discharge.
I have not paid much attention to the heater in my new camper (20' toyhauler), but I have boondocked on a night that dipped down to freezing and still had more than half the charge left on my single G24 battery. No lights, no TV, only the fridge on propane (about 1A load when running).
Bob R.
Well Bob, I must say that you have an extremely well insulated camper! For every "rule" or situation there is always an exception. I would be elated if our 38' Cedar Creek triple slide fiver could keep us warm (68 to 71 degrees F) in 35 degree weather by only running 12 minutes out of an hour. BTW - the CC is cold room tested to zero and is extremely well insulated with tight fitting gaskets on the slides.
My load measurements were similar to yours at 12 amps with the fan running. Yes, incandescent and halogen bulbs can quickly suck a battery down which is why I have replaced 90% of my lamps with LED units. But, even with the old array of halogen it worked like this: 6-20W lamps in the LR/K ceiling, 4 more 20W lamps in the hall and bathroom. The remaining halogen were 10W units that also totaled 10.
Add it all up and we have 300 watts, or if you prefer 300/12.6 = 23.81 amps, which is a lot of load. But, we do not light the camper up like a Christmas tree. So, if we
only use four of the 20 lamps at any given time we drop to a little less than six amps. Overall their duty cycle comes out less for us that the furnace fan on a cold night. Of course, switching to LED's has saved us even more in wasted power as our previous 300 potential watt load is now about 40 watts if
all of the lights are on (a few incandescent and hallogen bulbs remain).
I know, this is picky and trivial, but the furnace is one heck of a battery and propane burner - which is why we also use indoor safe LPG catalytic heaters when boondocking in the colder temps rather than the furnace.
Whatever the loads are on a battery we will eventually need to recharge with some form of auxiliary power. When our solar panels don't, the gas generator comes into play - as does the converter/charger. This brings us back to the beginning - either juggling the manner in which we charge batteries or sizing a generator to handle the converter/charger load.
One approach that has not been mentioned is if you are using paralleled 12 volt battery banks you can install a marine type battery selector switch to isolate batteries. I have such a switch that has 3 positions - battery bank A, bank B or both. I keep one bank in reserve and draw power from the other. If the charge load is too great for both, drop back to a single bank, let it charge and then go to the next bank. This allows a smaller inverter genny to operate an otherwise power grabbing charger and should negate hauling around a smaller portable automotive battery charger.
Professor Randy T. Agee & Nancy Agee. Also Oscar, the totally ruined Dachshund.
2009 Cedar Creek 5th Wheel - 2004 Volvo VNL670 class 8 MotorHome conversion as toter.
Turbocharged, 12L, 465 HP and 1,800 ft. Lbs. of torque.
