CPAP machine w/ inverter. How much power?
Hi Folks,
A little background. Not new to RVing, but starting to deal with battery issues more, now that I have a week long music festival coming up w/ no hookups. I decided that after last year, not knowing what I should about battery use, maintenance, etc, I figured I would learn EVERYTHING I could this year, by reading this forum. After about, oh maybe 1000 or so posts, I feel I have a really good knowledge basis, but a question looms.
My brother is visiting next week, and he wants to use his CPAP machine. He linked to good article, explaining the different models, and giving their current draw. His machine on 120AC, draws approx 2 amps. Thereis no DC mode, and it needs to be powered by a small inverter. My first question relates to the efficiency of various inverters on the market. I have read some posts giving detailed info on some of the better quality units, obtained from actual testing by the posters. I, however am stuck with one of 2 units. The first is a 300 W Radio Shack brand that I have had for many years. I use to use it for running a small TV and DVD player (in my cruiser when I was a police officer!!, before smartphones.)
The other is a 1000 watt off brand I bought from BJ's about 10 years ago to run a few lights when the power went off.
I just purchased 2 brand new Exide Group 27 Marine batteries to use( in parallel) exclusively for the unit. I know, Exides probably suck, just like every other Marine dual-purpose, but for 85 bucks a piece, I figured what the heck. I couldn't justify the more than double that for a true Deep Cycle like a Trojan, especially only using them maybe two or three times a year for boondock camping.
For this festival, I am also borrowing a nice little Honda 1000w generator from a friend, to top off these, as well as my house battery on the fifth wheel. I would like to use my Schumacher 3 stage charger ( 2-20-75 watt) on the 20 watt setting, to do this.
So, just how much battery do you think I will go through with just the CPAP running, IOW, how much more current are these inverters gonna eat up on me? I would do a test, but I am afraid to run the batteries down below 50 or 40 percent or more in the process, shortening their already crappy lifespan. I will be getting a new digital multimeter ( Radio Shack again?,other suggestions welcomed) to monitor the voltage of the bats, but I don't think its practical to try to wire it up to measure current draw in line with the inverters right now.
As the weather appears to be continuing a hot humid pattern the next week, I would love to run an AC window fan at night ( low setting of 3 speeds) also, but I know I am asking for trouble with that. I don't have the time right now to purchase a DC one, that would be more efficient.
So a few questions.
1. Do you think I am good with the 2 Group 27s for a good 7 hours straight, with one or the other inverter, w/ the CPAP?
2. Should I even think about the window fan?
3. Bonus question. If I run the bats down to 50 percent every night, ( I assume that would be about 100AH, one battery's worth) how long will I have to run my Honda 1000W gen w/ charger on 20 AMP setting to get back to 90%.
Thanks to all on this forum, I have gained a tremendous amount of knowledge this past year from all of you
edit: reading some other posts, looks like I'm gonna need a bigger charger, 20 amps aint enough. I don't wanna hear the gen for more than 3 hours
A little background. Not new to RVing, but starting to deal with battery issues more, now that I have a week long music festival coming up w/ no hookups. I decided that after last year, not knowing what I should about battery use, maintenance, etc, I figured I would learn EVERYTHING I could this year, by reading this forum. After about, oh maybe 1000 or so posts, I feel I have a really good knowledge basis, but a question looms.
My brother is visiting next week, and he wants to use his CPAP machine. He linked to good article, explaining the different models, and giving their current draw. His machine on 120AC, draws approx 2 amps. Thereis no DC mode, and it needs to be powered by a small inverter. My first question relates to the efficiency of various inverters on the market. I have read some posts giving detailed info on some of the better quality units, obtained from actual testing by the posters. I, however am stuck with one of 2 units. The first is a 300 W Radio Shack brand that I have had for many years. I use to use it for running a small TV and DVD player (in my cruiser when I was a police officer!!, before smartphones.)
The other is a 1000 watt off brand I bought from BJ's about 10 years ago to run a few lights when the power went off.
I just purchased 2 brand new Exide Group 27 Marine batteries to use( in parallel) exclusively for the unit. I know, Exides probably suck, just like every other Marine dual-purpose, but for 85 bucks a piece, I figured what the heck. I couldn't justify the more than double that for a true Deep Cycle like a Trojan, especially only using them maybe two or three times a year for boondock camping.
For this festival, I am also borrowing a nice little Honda 1000w generator from a friend, to top off these, as well as my house battery on the fifth wheel. I would like to use my Schumacher 3 stage charger ( 2-20-75 watt) on the 20 watt setting, to do this.
So, just how much battery do you think I will go through with just the CPAP running, IOW, how much more current are these inverters gonna eat up on me? I would do a test, but I am afraid to run the batteries down below 50 or 40 percent or more in the process, shortening their already crappy lifespan. I will be getting a new digital multimeter ( Radio Shack again?,other suggestions welcomed) to monitor the voltage of the bats, but I don't think its practical to try to wire it up to measure current draw in line with the inverters right now.
As the weather appears to be continuing a hot humid pattern the next week, I would love to run an AC window fan at night ( low setting of 3 speeds) also, but I know I am asking for trouble with that. I don't have the time right now to purchase a DC one, that would be more efficient.
So a few questions.
1. Do you think I am good with the 2 Group 27s for a good 7 hours straight, with one or the other inverter, w/ the CPAP?
2. Should I even think about the window fan?
3. Bonus question. If I run the bats down to 50 percent every night, ( I assume that would be about 100AH, one battery's worth) how long will I have to run my Honda 1000W gen w/ charger on 20 AMP setting to get back to 90%.
Thanks to all on this forum, I have gained a tremendous amount of knowledge this past year from all of you
edit: reading some other posts, looks like I'm gonna need a bigger charger, 20 amps aint enough. I don't wanna hear the gen for more than 3 hours
