Originally Posted by carl762
My question: Any idea on what kind of mileage I'll get out of my 100 ah deep-cycle marine battery hooked up to a 5-watt solar panel?
I use a ResMed CPAP but never on the boat, yet. This isssue is also a concern of mine as I would like to liveaboard. My ResMed unit has both 110V/12V input. The 12V is listed at 2.5 amps. Interestingly, it also lists the 110V input as 2.5 amps.
If your CPAP is similar, we can calculate 2.5 amps x 8 hours = 20 amp hours. If this is the only thing that your battery is powering, you are in good shape.... but that is probably not the case.
Switching to 110V power. The documented 2.5 amps is very strange (in comparison to the 12V number) so I have connected the unit to a KiloWatt meter to record exactly what it is doing. The highest consumption number that I have seen is .5 amp. So, if we were to power this unit from an inverter, the consumption is something around 5 amps (12V) x 8 hours = 40 amp hours.
Depending on your location, hours of sun, etc... and assuming the CPAP is your only draw, your 80 watt panel is probably sufficient for the first scenario but not the second. I ran some numbers for my boat and 80 watt panel here: Electrical System | JdFinley.com
One question to be aware of; if you are going to run the CPAP from an inverter, is the CPAP happy with the output form? I've read generic statements that "medical devices" are particular and demand true sine wave power and so the more expensive inverter. I do not know if CPAP's fit into this category.