Deep cycle marine battery: Camping

Hi all,

I have searched forums, and not necessarily found my answer.

I have a camping trip set in late July, and am getting worried about 3 nights of sleep w/o my CPAP...

I am flying to my destination then my buddy will be driving me the rest of the way. I know he has deep cycle battery, so I am probably gonna ask him to bring it. Btw, I know not all deep cycle batteries are rated the same.

My question is, how many nights of use can I get out of my CPAP with an average Deep cycle battery? I know not using the humidifer will extend that use. I have the CPAP in my signiture line.

As a start, head to the following page at CPAP.com to calculate the battery life for your unit. This makes an effort to use your pressure in the calculation, so will tell you how long their batteries will last. With that information, you should be able to determine the number of amp hours you will need

https://www.cpap.com/productpage/3076?tab=power-options

Note: The calculator does not seem to work in Google Chrome .. You might want to try it in Firefox or IE.

You can also use a Respironics battery pack that is made for your machine. They list for about 300 but I got mine for 200 through my DME. I use a BiPap and was told my machine would run about 28 hours without the humidifier. Your machine should run longer so you should not have a problem getting three days out of it.
https://www.cpap.com/productpage/respir ... e-kit.html I have used mine for camping and used the humidifier but have not gone more than one night so far. I am also looking into using a solar charging set up to charge the battery pack.

Whatever set up you plan to use, try the set-up out at home for a few days to ensure that it will work in the wilds. My old CPAP (resironics brick) would not work on a gel marine battery. (Edit: It worked fine on a regular marine deep cycle battery with liquid acid cells.) That was a bummer and a lesson learned.

Is it a trolling motor battery or a boat battery? It will have far more capacity than any of the expensive solutions. Will there be a car and jumper cables? 20 minutes of a car idling should recharge a days use on a car battery sized deep cycle batter.

At work I use 8 truck sized deep cycle batteries that could run an electric oven at full heat for 8 hours and still be above 50% so it sort of depends on the size.

If you don't run the humidifier, you should be taking less than 10 watts unless your very high pressure but I don't know about your cpap device. If you figure a 12V battery, then 10 w is .83 amps (or .41 at 24 V) so you need an 8.3 amp-hours with a 12V battery to sleep for 10 hours -- assuming no other energy losses. The small car sized deep cycle batteries sold by west marine are 75 to 105 amp-hours when they are new (figure 1/2 of that when they are old). A car can recharge a deep cycle battery at about 600 watts an hour.

If you try the calculations, remember that an "amp-hour" is one amp times one hour not amp minus hours. I've seen engineering students make that mistake.

Ok my trip is tomorrow, luckily my buddy has a deep cycle maeine battery for me, I bought a power inverter. One last thing is passover mode. Is this simply turning off humidifier to zero?

Thanks looking forward to sleeping comfy while camping!

Dive Apnea wrote:Ok my trip is tomorrow, luckily my buddy has a deep cycle maeine battery for me, I bought a power inverter. One last thing is passover mode. Is this simply turning off humidifier to zero?

Thanks looking forward to sleeping comfy while camping!

Yup, you got it right...have a great trip.

nanwilson wrote:Yup, you got it right...have a great trip.

Thanks!

-tim wrote:Will there be a car and jumper cables? 20 minutes of a car idling should recharge a days use on a car battery sized deep cycle batter.

Unfortunately, that was not my experience last year. I had my deep cycle connected to my pickup with a switch so the pickup battery was not connected when I was charging the deep cycle. Even with 1 to 2 hours of charging with all the alternator output going to the deep cycle the battery did not recharge completely. After three nights use and 2 charging cycles it was down to about 1/3 to 1/2 charge remaining. I used the humidifier.

Apparently a car battery will accept a much higher charge current than will a deep cycle. 20 minutes will recharge a car battery.

idamtnboy wrote:

-tim wrote:Will there be a car and jumper cables? 20 minutes of a car idling should recharge a days use on a car battery sized deep cycle batter.

Unfortunately, that was not my experience last year. I had my deep cycle connected to my pickup with a switch so the pickup battery was not connected when I was charging the deep cycle. Even with 1 to 2 hours of charging with all the alternator output going to the deep cycle the battery did not recharge completely. After three nights use and 2 charging cycles it was down to about 1/3 to 1/2 charge remaining. I used the humidifier.

Apparently a car battery will accept a much higher charge current than will a deep cycle. 20 minutes will recharge a car battery.

Batteries tend to change in 8x their full discharge rate.
The alternator had a very good high current charge rate to your car's battery in excess of 70 amps. How much current was going into the deep cycle? You need jumper cable thick wires to deliver that kind of current and modern car's alternators are good for 150+ amps. An 80s car is good for 90 or so if it had A/C and power windows. A 60's MGB is good for 25 to 40 amps (unless it works like an Lucas MG electrical system which less). If you have a thin wire, the resistance will be so high that the external battery will be a volt or two higher and will get less than 1% of the change.

-tim wrote:The alternator had a very good high current charge rate to your car's battery in excess of 70 amps. How much current was going into the deep cycle? You need jumper cable thick wires to deliver that kind of current and modern car's alternators are good for 150+ amps.

The cable is a jumper cable modified with spade lugs replacing the clamps. Cable size and resistance is not a limitation. From what I find the recharge current should be about 5% to 10% of the 20 minute amp-hr rate, in my case about 6 to 12 amps for my 115 AH battery. If I used 30 to 40 AH for one night of CPAP use then that would be about 3 to 6 hours recharge time. What I suspect is the charging circuitry in the pickup, a 2005 Nissan Titan, is designed to tightly control the battery charging rate and that is what was limiting the recharge current.

When you connect two batteries in parallel, the one with the lower voltage will sometimes tend to hog all the charging current and the other battery may charge much more slowly.

archangle wrote:When you connect two batteries in parallel, the one with the lower voltage will sometimes tend to hog all the charging current and the other battery may charge much more slowly.

If you're referring to my setup with charging the deep cycle from the pickup, that wasn't the case. I have a switch in the pickup battery positive lead to cut it off the alternator after the deep cycle is connected. The alternator then was connected only to the deep cycle.

I noticed an interesting thing with two deep cycles in parallel and a float charger. Each battery, when connected by itself to the float charger, was at full charge according to the LED on the charger. But, if I connected them both in parallel to the float charger, the LED stayed lit indicating it was in steady charge mode. Don't know why that would be.