Question for battery experts: proper inverter?

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Question for battery experts: proper inverter?

Post by Weacloa » Thu, 03 Jan 2019, 20:24

I've got a major 4x4 camping trip coming up in a couple of weeks. I have a deep cycle 50aH battery and one of those 18aH jump starters with ac outlet. I'd rather save the jump starter in case I need to do some actual jump starting, so I'm trying to make sure I have a suitable rig to run my cpap (without humidifier) off the deep cycle battery for maybe one, definitely not more than two, nights between charges.

I've already spent a ton on equipment and I'd rather not spend any more. Soooo ... what I have lying around the house is:

- the 50aH deep cycle battery
- a cable that has clips to attach to the battery on one end and a cigarette lighter-style outlet on the other
- a cigarette lighter inverter that claims to be rated 200w
- a trickle charger to charge the battery (and that I can plug into the ac outlets on my much larger inverter in my truck)
- AC adapter only for my APAP

I may try to mod a normal plastic battery box to make a pretty package, or I may just leave it as is.

My question is, can someone who understands batteries tell me if this set-up will work? I know I lose about 10% efficiency with the inverter as opposed to ordering a DC adapter, but will I still have enough juice to last a couple of nights? Finally, will a 200w inverter provide enough power to run the apap w/o humidifier?
Last edited by Weacloa on Tue, 08 Jan 2019, 19:01, edited 1 time in total.

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Re: Question for battery experts: proper inverter?

Post by antiscab » Thu, 03 Jan 2019, 21:08

What does the name plate on the AC adapter for your cpap say?

Volts and amps out?
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Re: Question for battery experts: proper inverter?

Post by coulomb » Thu, 03 Jan 2019, 21:50

I suspect that CPAP machines vary widely, but my wife's former machine took about an amp from 12 V when running (hard to measure as it fluctuates with breathing). So of the order of 10 Ah per night. Her latest machine seems more modern, smaller, and gives the impression of needing less power. Even with all the inefficiencies involved, I'd guess you will be ok.

Those jump starter things are more power than energy, but one does run my wife's machine for a night (I think that was the new one). So that could be your backup.
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Re: Question for battery experts: proper inverter?

Post by T1 Terry » Fri, 04 Jan 2019, 10:25

The battery you plan to use when new and fully charged can supply 25Ah before it starts to drop voltage below 12v and risk long term damage. The inverter will most likely use as much power just to run itself as the CPAP machine will use without the humidifier running.
You will get 1 night, but I doubt you will get 2 nights. Running from the 12v supply without the inverter you will get 2 nights as long as the battery is still in good condition and fully charged each time, not just till it reaches float stage but until it stops accepting current more than about 1 amp. This will take a long time, at least all day, if you have a solar controller and solar panel, set the charging voltage to 14.4v continuous so it can get the max recharge while the sun is out.

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Re: Question for battery experts: proper inverter?

Post by 4Springs » Sat, 05 Jan 2019, 17:50

Weacloa wrote:
Thu, 03 Jan 2019, 20:24
will a 200w inverter provide enough power to run the apap w/o humidifier?
It would help if you could find the power rating on the device. Or even better, measure how much current it draws when operational.
You can get 12V cpap machines, which would be more efficient and probably draw less power. Might be a good investment if you are going on many trips.

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