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Cpap use w/LiFePO4 for backup, actual power requirements

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Camp20144

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Nov 10, 2022
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Looking for comments regarding problems or issues and comments in general on my cpap backup.

I’m “building” a battery backup for my cpap. I have two purposes at this point. 1) to have it available and, 2) to get actual power requirements with just the cpap, cpap+heated humidifier and cpap+heated humidifier+heated hose. Right now it’s pretty basic. Battery, shunt and battery monitor.
My cpap is a Philips Respironics DreamStation. The 110V power adapter is rated at input 2.0-1.0 amp. Output 12V - 6.67 Amp. On the bottom of the cpap itself it says 12V - 6.67 Amps. I have the Shielded 12V DC power cord for the DreamStation.

A3E4D66D-8887-40BE-9B90-478E316A304E.jpeg

Also, the DC power cord has an 8 amp fuse. Do I need additional fuses/circuit breakers? One just before or after the shunt?
I queried cpap and didn’t run across my questions.
Thank you,
Mark
 
Camp20144 said:
The 110V power adapter is rated at input 2.0-1.0 amp. Output 12V - 6.67 Amp.
Click to expand...
If your battery is 12Vdc, why would you use an inverter to get 120Vac and then use a converter to produce 12Vdc from that?

Not sure a shunt and battery monitor will be useful since you will likely be asleep. I'd put a little volt meter on the battery to see how its doing at a glance. The BMS in the battery will protect low voltage. Put an 8-10A fuse on wire from CPAP to battery.

What could be simpler?

How do you intend to charge your battery?
 
@sunshine_eggo Thank you, I queried differently and received more listings. Looking through what came up, but would appreciate any thoughts and suggestions.
Thank you again,
Mark
 
@MisterSandals In my query on the cpap subject, I saw questions as to “what machine do you have?” I listed the info on my machine to provide that info.
My plan is to run my cpap with the 12V power cord.
I have to recheck, but I thought my battery monitor will save the battery use info for later review.
Thank you,
Mark
 
Put a Kill-a-Watt on your AC power supply, running from the house. Let it run through the night a time or three in any relevant configurations. Take off 10% for a likely power supply efficiency, or don't, and consider any additional runtime a safety margin.

Then get a 12V-12V regulated DC power supply that can handle at least 6.5A. Add in efficiency losses, and calculate against a safe battery capacity (say 60% DoD,) and you'll know how long it can run in a worst case with seriously degraded batteries.

ETA: if it's already got a cig lighter cord to run it, even easier. Don't need the DC regulator, as the cig lighter should expect up to 16.8V dirty, spiky voltage DC. If not, you might try to get input specs from the maker for your cord. If they'll tell you it'll take 14.6V or higher, you're fully safe with any 4S LFP battery.
 
@TorC I have the manufacturer’s 12V power supply cord. It has the “cigarette lighter” end on it. It also has two large barrel shaped “lumps”, one close to each end. The “cigarette” plug has an 8 amp fuse.

@MisterSandals Your suggestion for an 8-10 amp fuse prior to the cpap. This is in addition to the factory fuse in the power cord? This makes sense to me. Blow that aftermarket fuse before the factory fuse as it is likely easier to get replacement aftermarket fuses verses the Philips factory fuse.
 
Great, then either the machine can regulate the power internally, or that cig lighter has an internal regulator. If you care which, put a multimeter across it sometime and see whether you see 12V or battery voltage.

As for fuse, if you can open the cord and access the fuse, it's probably something reasonably standard. Maybe not what your local store carries, but should still be easy and inexpensive to find and keep a few. If that blows, however, you've probably got other problems on the machine side.
 
@TorC If I understand your comment regarding machine issues if the factory fuse blows. If I install a fuse holder (with 8amp fuse) before the power cord “cigarette” connection to the system and the factory fuse blows - that is a machine problem. If the fuse in the fuse holder, that I install, blows - that is problem from the battery side.

The two spare fuses supplied with the power cord.

7A291F51-BF6C-420E-871D-00589B8A16AC.jpeg

Thank you,
Mark
 
Those look like they're a standard form factor fuse, with near certainty. As for which 8A fuse blows, that's a question of two things, in order of import: 1. Fast or slow blow fuse. 2. Manufacturing tolerance, and which side of it each fuse happens to be on.
 
@MisterSandals I will be including a cig port in my wiring. A female cig port wasn’t included with the dc power cord so I will need to purchase one separately.
 
I have the same unit but mine is a bpap. I bought a 55ah Lifepo. A minnkota power box from amazon commonly used for trolling motors and has two cigarette plugs built in. Very simple 2 piece set up for Bpap or other uses.
Very lightweight.
I can run my Bpap for 4-5 days, 8 hours a night with humidifier set on 2 with power to spare.

As Sunshine_eggo said there are many posts concerning your inquiry.
 
@MrNatural22 Thank you for the info on your system. As I mentioned above, I didn’t come up with much when I queried prior to posting. After posting I queried again which resulted in more info.
I do appreciate folks willingness to provide information and details regarding their systems and ideas. Sometimes the smallest detail can be very helpful.
Thank you again,
Mark
 
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