CPAP update

[aedgington]

So I started a thread a while back on this topic, but it just said "supplying power all night", so I thought I'd start a new one w/ a more relevant topic.

After installing an inverter & doing research on a dual battery setup (LX), two things happened:

1) I realized my CPAP has a 12v DC power adapter available.
2) I found a group 24M marine battery in a truck I bought.

So, I bought the adapter ($25) and charged the battery. It lasted 7 1/2 hours. So I think either a slightly larger (27?) battery or a 2nd battery would do the trick.

My CPAP is a Remstar Plus, and I don't know the setting other than it says "2837" when it powers on, and "13cm" when it's running.

Hope this helps anyone else.

 

[rgsiii]

The setting would be 13 cm of water. That is the constant pressure that the CPAP unit would deliver. 2837 would likely be the number of hours that you have used the machine.

 

[NorCalDoug]

Just get one of these and be done with it. It's what I suggested before.

 

[i4c4lo]

I have a large battery in the truck and I use the CPAP machine and the ARB fridge and I can sleep for 8 hours or so and the truck still starts. I have done this 3 days in a row (camping) and it still goes. I also have the 12v adapter. I don't have the truck hardwired so I actually have to have the key in the ACC position.


I4C 4LO

 

[aedgington]

Just for reference, my 24M marine battery lasted 10 hours @ 13cm of pressure. Just used it one night, so I don't know what it's capacity is, but it easily did the night.

 

[MrMoMo]

The key number that you are looking for in sizing a battery is the Ah rating (Amp hours) This tells you how much time you have at a specific amp load. (Reserve capacity)

An average group 24 Marine deep cycle battery will have about 75Ah.
An average group 27 Marine deep cycle battery will have about 100Ah.
An average group 31 Marine deep cycle battery will have about 130Ah.

To put this into #'s that mean something to you...

A battery with a reserve capacity of 75Ah will power a 50W load for aproximately 7.5 hrs - leaving your battery at a state of 1/2 charged. (safe discharge limit for a deep cycle battery)

So from that I will assume that your CPAP uses aproximately 50W of power. (aprox 4A at 12V)

Take that 50W and go to a group 27 battery and you will get aproximately 10 hours, and with a group 31 you will get aproximately 13 hours. (this is all asuming that your CPAP uses around 50W)

Now, your other option was to make a battery bank. Two 24's will have more than a single 27 or 31. Two 24's should get you 15 hours, two 27's should get you 20 hours, and two 31's should get you 26 hours.

This is also assuming that your group 24 is a deep cycle, not a cranking battery.

Hope that helps. - If you read the back of your adaptor it should give you a power rating in amps or watts. If my number is out by a lot let me know and I can re-calculate for you.

Bruce

**EDIT - should also not that if your grp 24 battery is old, it may not charge to full capacity - so my assumption of it drawing 50W could be out as your reserve capacity could be depleted **

 

[cruiseman]

If you have the room, go with two 6volt deep cycle batteries like the 145's used in john deere E-gators. You will get more time between charges. Any golf cart supply or even a napa can get these. You should not spend more than $55 each.
Good luck,
SC