CPAP DC Input Voltage - How Much Can it Vary?

[Brian McMahon]

My remstar pro has a dc input plug and notes operating voltage nominally at 12v.  I have a lithium battery from another CPAP that lists its maximum voltage at 16.8 v.  Is this close enough to the CPAP nominal voltage to use without stepping down the voltage?

I can put a step-down (buck) converter into the system but would like to avoid additional components if the the remstar will tolerate the slightly higher voltage.

[Raymond Hallett]

I would tend to think this is too much input voltage. 12 to 16 doesn’t sound like much but you have to consider it in terms of percentage. That’s a 33% increase. The manufacturer of your machine should be able to supply you with a number to work with. For instance they should give you a spec on input voltage like this:  input 12vdc +-3v or 12 Vdc +- 5% Normally input should be held to 5%; 10%, or 15% at the very max. Let me know what you find out.   Ray

[Raymond Hallett]

I looked up your machine and couldn’t find a percentage input rating on it. I’m quite sure piping over 33% increase input voltage into your machine would have adverse effect on your machine. In other words I would not do it!   Ray

[Brian McMahon]

Thank you very much Ray.  I'll go ahead and add the step-down dc-dc converter to be sure it will get right at 12v.

[OMyMyOHellYes]

12V is usually really 11.something volts (depleted battery) up to 13-14.something volts (fully charged) in most applications. 12 V appliances usually run fine in those ranges. An example would be hamateur radios which are normally referred to as 12V. They will run in the "12V" range but pretty much universally run at around 13.8 V. And for the most part, the electronics in those are a bit more sophisticated and sensitive than anything in a CPAP (though for the most part, we're talking an electrical motor, not electronics when we talk CPAP). Your car has a "12V" electrical system. It doesn't run at 12 V. The voltmeter on the dashboard routinely shows 14.something which is what the alternator is putting out into the car's system.

It is not steady, constant in most applications when using batteries. The power supply I run my primary CPAP off of is putting out just over 14V in order to supply enough voltage to keep the backup battery charged (float charged through a regulated smart charger). The CPAP does fine with that.

I don't think I would run it at almost 18v though. The converter is pretty simple and install/testing/adjustment usually pretty straight forward.

OMMOHY

[trish6hundred]

Hi Brian McMahon,
WELCOME! to the forum.!
Good luck with CPAP therapy.