Originally Posted by dig4gold
and I have to run a generator every night because I use a CPAP. So . . . do you think I need to get $100 + batteries or will the "Walmart brand" do the trick?
Generator just to run the CPAC machine???? Lets do the math....
If you get two DEDICATED standard RV/Marine Interstate 85Ah batteries (170Ah's of which 85Ah is useable - 50% rule), to run your CPAC machine.
So with 2 of the above batteries you have 1020 Wh (watt hours) that you can use for your CPAC machine [85Amp hours*12 volts=1020Watt hours]
I believe your CPAC machine's power source (transformer) is the same or close to mine. The transformer is a 12VDC transformer, check yours. Mine is rated at 5 amps at 12VDC, of which I have yet to hit 4 amps, with the CPAC humidifier on. If yours is not 12VDC, check with the mfr about a 12VDC CPAC adapter.
So, I will use 5 amps as the CPAC load, just in case yours may use 5 amps.
5 Amps * 12VDC = 60 watts.. 60 Watts *8 hours of sleep = 480Wh (Watt hours)..... not a bad number for a GOOD nights sleep.
If you look above, we calculated (2) 85Ah batteries will supply 1020Wh. So in theory, you could make it on one 85Ah battery (510Wh), but I think that would be cutting it a little close with no reserve.
A 100Ah battery would supply around 600 Watt hours, a little better.
I have no clue as to what you spend in a season on generator gas, but I believe going this route, will let you keep a few buck in your wallet.
You could wire in another small charge controller just for the CPAC battery(s) that will charge them when you run the generator during the day.
Or, install 250Watts of roof SOLAR wired directly to the CPAC batteries and forget about them (just regular maintenance, battery water). The batteries will be charged by noon or 2 the latest (clouds)
Oh yes, there is another benefit... no night time generator noise....
Just my thoughts,
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