The capacity of a 12v batt is in the area between 13 and 14 volts. A batt at 12.4 volts is only 50% charged. So if you have a 100 AH batt you are already 50% discharged with 50 AH remaining, that is roughly 2 hours of use before you batt is at 0%. This is why your inverter is telling you that there is no DC power, your inverter thinks/knows your battery is dead. BTW a batt at 11v is considered completely dead. You need to charge it to about 13 plus volts to get a 100% charge.
My CPAP requires 2.1 amps AC to operate, that directly translates to 21 amps DC not including the power it takes to run an inverter. This will deplete a 100% charged RV/Marine BATT in about 5 hours. BUT on DC it only takes 5 amps DC. Using a normal 100% RV/Marine deep cycle batt, you can run about 10 hours without depleting your batt beyond 50%. On my solar system, I can run the CPAP 30 hours and still not use half of my capacity. A battery that has been abused is not likely capable of being charged to 100% again.
Many people try to use the generator to charge their battery. But all they achieve is a bullk charge not the finishing charge the finishing charge is where all the AH are. They think that the batt is 100% but in actuality its maybe 65 to 70%. The generator would have to run all day long to bring the battery to 100%. This is why solar is so important. Look into a solar panel that will charge a 12v 100 AH batt from 50% charge to 100% charged in 8 hours. dedicate that system to your CPAP and your problem is solved.
Also, never miss a chance to charge the batt, If you're on pedestal power make sure you charge the batt to 100%. Worst case scenario you can add a second batt, But then my suggestion is to install an industrial RE (renewable energy) deep cycle battery which will last for days instead of hours. If you system is augmented with solar even the single 100 AH batt can last a couple of days even with an inadequate solar panel.
IF you rig a good 12v DC line into your bedroom with a DC socket, buy the right DC line for your machine you can go through the night easily with a RV battery, you can charge that battery with a small solar panel and never start your generator for your CPAP ever again.QUOTE=klindgren;326544]This past week we dry camped for the first time in this new rig. Nights one and four I was able to run the genny all night (sure burns up the propane doing that) but nights two and three I had to just run off of 12 volt power due to tent campers near by. Everything worked as it should except my CPAP machine. The 12 volt inverter I had would turn the machine on and start the CPAP but when the air blower would kick in, the inverter would kick out and give me a low battery error message. I have a 410 watt inverter which, according to my CPAP manual should be more than enough to run the unit. I also tried a 500 watt and 800 watt inverter with the same results. I'm wondering if I need to have a second battery installed???? Everything else 12 volt worked as it should, only the CPAP would not. Any thoughts???[/QUOTE]
