Best way to run cpap while camping?

[superj]

I was going to test out the set up next time i go to leakey to see my parents. I could flip out the platform, set up the tent and mat, hook up the solar panel system to the battery pack (i decided more than one is better by what yall have said) and plug the cpap in that night to try out in their driveway so i feel like i am really camping.

I will also test it out at my house prior to going to their house for the initital shake down. Their house will be the second run to see what else shakes out

 

[RobbieD]

Another possible option, which would need looking into, would be to put an auxiliary battery in the host vehicle, using a battery isolator. Power the CPAP with a 12V-to-24V converter (they do make these, for medical devices).

The auxiliary, typically a 12V marine deep-charge battery, could be recharged as needed by running the host vehicle (the isolator prevents running down the vehicle primary battery), a shore-power battery charger, or a 12V solar charger.

I think that the key to how well this would work, would be doing the math on what a 12-to-24 converter would pull, amp wise, versus the capacity of the aux battery. If the math works, then you can compare the component costs to your other options.

 

[pentode]

I was going to test out the set up next time i go to leakey to see my parents. I could flip out the platform, set up the tent and mat, hook up the solar panel system to the battery pack (i decided more than one is better by what yall have said) and plug the cpap in that night to try out in their driveway so i feel like i am really camping.

I will also test it out at my house prior to going to their house for the initital shake down. Their house will be the second run to see what else shakes out

That's a good approach, especially if you have a way to monitor voltages/battery capacity etc of whatever setup you decide to go with. You'll start to see right away if you have any weak spots in your setup.

Oh, here's a thought: one component you might want to consider is an alarm that warns you when your battery voltage drops too low. Shouldn't be an expensive piece if you're not in a hurry to get it.

 

[pentode]

Another possible option, which would need looking into, would be to put an auxiliary battery in the host vehicle, using a battery isolator. Power the CPAP with a 12V-to-24V converter (they do make these, for medical devices).

The auxiliary, typically a 12V marine deep-charge battery, could be recharged as needed by running the host vehicle (the isolator prevents running down the vehicle primary battery), a shore-power battery charger, or a 12V solar charger.

I think that the key to how well this would work, would be doing the math on what a 12-to-24 converter would pull, amp wise, versus the capacity of the aux battery. If the math works, then you can compare the component costs to your other options.

Yes, this is a really nice way to solve the problem, and you could use the solar to top off everything with the right solar controller. And it's true that DC-DC converters can be very efficient, way up into the 90s of percent.

 

[pentode]

I'll state the obvious, but given that batteries aren't cheap, one thing I like about using 2 smaller 12V batteries for projects like this is that you can run them in parallel if you end up running with 12V but if you ever decide to do a 24V project, you can just run them in series, get your 24V and not need to buy more batteries.

Anyone that wants to double check or correct my math on this, please do, I'm getting old and senile. But you need (absolute bare minimum, in a perfect world) 100 watts x 8 hours, so 800 watt hours, or roughly 67 amp hours @ 12V. With inefficiencies, a safety margin, and all the other variables, I would be aiming for at least 1600 watt hours or 135 amp hours at 12V. If I had a way to lay my hands on some inexpensive deep cycle batteries, I might even aim for 2000+ watt hours or 175+ amp hours. That might be overkill for one night, but it might very well get you through 2 nights in the event you didn't have good sun for charging.

Testing really is the way to go with this stuff, everything is a variable and the real world always tends to make the math look optimistic.

 

[alwaysFlOoReD]

I'm not knowledgeable about most of what you guys are talking about. That said, I bought a battery on sale for half price, and kicked myself for not buying two. A month later it went on sale again so I bought another. They were bought on spec but I think they will work great for my computer UPS, which needs batteries. The Amazon clanker said 9.5 amp/hours, 114 watt/hours. So maybe a dozen would work for CPAP? I paid C$25 each on sale for half price. They are lead calcium.

 

[pentode]

That looks a lot like a typical 7ah SLA battery - it may well be 9.5ah or it may be Chinese marketing optimism, but either way, at $25 that's a really good deal. Actually if that's USD it's a good deal, if that's CAD it's a borderline steal. I haven't seen much outright counterfeiting in lead acid batteries... Not enough hype around it anymore to bother probably.