First time actually boon docking - power question

[KanzKran]

I don't know what common specs are for a CPAP unit, but the one I saw online says 2.0A at 120V, so that's around 20A (plus inverter losses) at 12V. 8 hours of use would take at least 160 Ah from the batteries.

Perhaps a 12VDC unit will draw less, if anyone makes such a thing. But again, that's just the first one I found on-line. Your particular unit may use less energy. Or more.

And you can always add another battery or two, if that's what it takes.

[CWP3]

Originally Posted by KanzKran

I don't know what common specs are for a CPAP unit, but the one I saw online says 2.0A at 120V, so that's around 20A (plus inverter losses) at 12V. 8 hours of use would take at least 160 Ah from the batteries.

Perhaps a 12VDC unit will draw less, if anyone makes such a thing. But again, that's just the first one I found on-line. Your particular unit may use less energy. Or more.

And you can always add another battery or two, if that's what it takes.

I know a bunch more now than when I decided to install 2 12v 125ah... I’d have gone with 4 6v with twice the ah. Oh well, live and learn. I’m considering biting the bullet and buying another one.

I’m also thinking about trying to jury rig the cpap to run on dc only. But only after some more research.

[CWP3]

Originally Posted by Mark_K5LXP

Shutting off the inverter is worth turning off if what it powers can go through the night unpowered, but there's no reason to deny yourself something like a CPAP for the sake of battery preservation. You know your capacity, so figure out your loads and come up with a routine of device use and generator run time to work for you. A battery monitor will go a long way to give you confidence in the system as you go.

Mark B,
Albuquerque, NM

Yep - I’ve got a monitor on my “to do” list. When I get back to wv this weekend I’ve got to winterize, then put together a prioritized list for spring.

[Ray,IN]

Originally Posted by CWP3

We will run the gen for the next air conditioner requirement. Then after it cools off we’ll shut them off. And just before bed we’ll turn in the inverter (1800w) for a while. Then before bed, probably just turn it off and try to sleep without the cpap.

There are several CPAP users here who dry-camp/boondock using the inverter without and issues. The coffee maker will also run off the inverter, just don't leave the hot-plate function running. DW has an insulated carafe to keep her coffee hot, plus she can have a cup while we are driving.

Unless you have a residential refrigerator, set the refrigerator to run on propane when dry camping.

[AnotherMike]

Originally Posted by CWP3

The only 120 will be the fridge (and opened sparingly), water pump, and my cpap.

Do you have a older ammonia fridge (electric or propane) or a residential compressor type (120vAC only)?

My propane fridge is spec'd at 120vac at 2.7 amps in AC mode. The DC mode uses 12vDC at about 1 to 1.5 amps idle, about 18 amps when actually cooling.

A compressor type fridge draws 1 to 2 amps at 120vAC. A good rule of thumb is than an inverter uses 10-11 amps at 12v to make 1 amp at 120vAC.

As to the CPAP... My CPAP is a 24vDC unit (Airsense 10). It makes no sense to take 12v and invert it to 120vAC and then to convert it to 24vDC.

There is always a loss when converting one voltage to another...

So going from 12vDC to 120vAC and back to any lower DC voltage has double losses.

This is why I tell everybody to use a 12v source for as many low voltage things as possible. My cellphone charger, razor charger, tablet charger, laptop charger, and home-made CPAP converter all run off of the house battery. The cellphone and tablet are 5v, the razor is 3.5v and I use common commercially available chargers. The laptop charger is a 12vDC to 18vDC one made by Lind corporation intended for police cars and ambulances. I built up a 12vDC-to-24vDC converter (under $35 for the parts) for my CPAP... yes there is a conversion loss, but only one level of loss.

If your CPAP is 214v and want to duplicate my custom 12vDC to 24vDC CPAP converter just let me know.

Mike

[CWP3]

Originally Posted by AnotherMike

Do you have a older ammonia fridge (electric or propane) or a residential compressor type (120vAC only)?

Electric residential...

[AnotherMike]

Originally Posted by CWP3

Electric residential...

I'm still using a propane fridge so I have no personal experience with that... I'm sure that others have and will chime in with true-to-live experiences.

Mike