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12-07-2017, 08:23 PM
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#1
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Senior Member
Join Date: Oct 2016
Location: San Diego
Posts: 912
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Using less battery overnight.
DW has a CPAP. I see that on its wall wart @ 120 volts it uses 2.1 AMP,
I read somewhere that would translate to 21 amps from the battery at 12 volt in round figures.
I notice its wall wart says the output is 12 volt @ 5 AMP.
8 hours x 21 Amps = 168 amps drawn from the battery via the inverter.
8 hours x 5 Amps = 40 amps drawn directly from the battery, no inverter needed.
Am I completely misunderstanding something?
__________________
2006 Allegro Bus 40 QDP IFS, 8.9L Vmspec, 1.5kw Solar + 400w Suitcase, 2@ 50amp & a 30amp Victron Smart MPPT's, 712BMV, SBS, CerboGX, 8.7kw LiFePo4, RR, MS2812, Max Transit, eero 6+ Mesh WiFi, Roof Mounted Starlink In-Motion dishy
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12-07-2017, 10:01 PM
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#2
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Senior Member
Join Date: Jul 2014
Posts: 35,317
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The numbers may be the max draw and max output.
It sure sound out of whack.
You would need to plug it into a Kill A Watt meter to see the actual amp draw.
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12-07-2017, 10:36 PM
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#3
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Senior Member
Join Date: Oct 2016
Location: San Diego
Posts: 912
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Quote:
Originally Posted by twinboat
The numbers may be the max draw and max output. It sure sound out of whack. You would need to plug it into a Kill A Watt meter to see the actual amp draw.
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I tried that a couple weeks ago and the dang thing won't run if its plugged into a killawatt. Never had anything else have that issue. I currently have that same killawatt feeding the coach 20amp cord.
I cannot explain why the resmed machine is a no go when plugged into a killawatt. The only thing i can see is the machine doesn't have a ground wire, not sure why a killawatt would need that.
__________________
2006 Allegro Bus 40 QDP IFS, 8.9L Vmspec, 1.5kw Solar + 400w Suitcase, 2@ 50amp & a 30amp Victron Smart MPPT's, 712BMV, SBS, CerboGX, 8.7kw LiFePo4, RR, MS2812, Max Transit, eero 6+ Mesh WiFi, Roof Mounted Starlink In-Motion dishy
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12-08-2017, 02:05 AM
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#4
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Senior Member
Join Date: Sep 2012
Location: Tasmania now, USA/Canada/Alaska in April
Posts: 2,473
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The problem arises in AC calculations because power is not Volts X Amps, it is Volts X Amps X Power factor and for many appliances with transformers that power factor can be a number considerably less than 1.
For your purposes, the current draw from 12V will be a maximum of 5 amps and probably somewhat less so the draw from your batteries overnight will be say 8 hours at 4 amps so 32Ah out of your battery. If you supply the unit from an inverter, the draw from the battery will be more than 5 amps, but nothing like 168Ah. Perhaps 60 Ah but would need measurements to confirm that.
If your machine had a humidifier mode then the draw would be much higher.
__________________
Tony Lee - International Grey Nomad. Picasa Album - Travel Map
RVs. USA - Airstream Cutter; in Australia - MC8 40' DIY Coach conversion & OKA 4x4 MH; in Germany - Hobby Class C; in S America - F350 with 2500 10.6 Bigfoot camper
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12-08-2017, 06:11 AM
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#5
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Registered User
Ford Super Duty Owner
Join Date: Nov 2014
Location: NW Ohio
Posts: 7,114
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If your wall-wart is putting out 12 volts, then you should be able to run the CPAP directly on 12 volts. The important thing will be determining correct polarity for the connector. See the link, its for a TV, but will be the same for the CPAP.
Will a 120 volt TV work on 12 volts DC – MAYBE – 2001 Coachmen Mirada 300QB
Conserve energy.
When boodocking, Your main consumers will be lights, the furnace and the CPAP. You can significantly reduce the lights consumption buy changing your lights out to LEDs.
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12-08-2017, 06:38 AM
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#6
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Senior Member
Ford Super Duty Owner
Join Date: Dec 2010
Posts: 1,799
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CPAPs are sometimes quite sensitive to voltage level. It all depends on the make and model. Remember we talk about 12 volts as the battery voltage, but it actually can vary from 11.5 to 14.5 depending on what is running (engine, converter, etc.) to many CPAP manufacturers THAT IS NOT 12 VOLTS! I agree that the consumption off an inverter will be much lower that the pate value that you wrote. Turn off the humidified and tube heater if it has one as these are major load sources. If you use an inverter, safest would be pure sine wave as some units do not like MSW waveforms.
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Scott Brownstein
Palm Island, Florida
2015 Georgetown 335DS
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12-08-2017, 07:44 AM
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#7
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Senior Member
Join Date: Jul 2014
Posts: 35,317
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Did you use the Kill A Watt on shore power or MSW inverter power ?
MSW messes with meters.
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12-08-2017, 07:55 AM
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#8
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Senior Member
Join Date: Jun 2017
Posts: 2,807
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Quote:
Originally Posted by BigBillSD
DW has a CPAP. I see that on its wall wart @ 120 volts it uses 2.1 AMP,
I read somewhere that would translate to 21 amps from the battery at 12 volt in round figures.
I notice its wall wart says the output is 12 volt @ 5 AMP.
8 hours x 21 Amps = 168 amp-hours drawn from the battery via the inverter.
8 hours x 5 Amps = 40 amp-hours drawn directly from the battery, no inverter needed.
Am I completely misunderstanding something?
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FTFY
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12-08-2017, 09:51 AM
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#9
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Senior Member
Join Date: Oct 2016
Location: San Diego
Posts: 912
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Quote:
Originally Posted by twinboat
Did you use the Kill A Watt on shore power or MSW inverter power ? MSW messes with meters.
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I was using shore power at the sticks & bricks. Also, I replaced our MSW with a higher wattage PSW shortly after we purchased the coach.
__________________
2006 Allegro Bus 40 QDP IFS, 8.9L Vmspec, 1.5kw Solar + 400w Suitcase, 2@ 50amp & a 30amp Victron Smart MPPT's, 712BMV, SBS, CerboGX, 8.7kw LiFePo4, RR, MS2812, Max Transit, eero 6+ Mesh WiFi, Roof Mounted Starlink In-Motion dishy
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12-08-2017, 10:20 AM
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#10
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Senior Member
Join Date: Aug 2017
Posts: 2,091
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Is the output from the wall wart AC or DC ? If it's DC the machine should be able to run directly off the battery. If it's AC , it still might run off the battery , but possibly not. You should be able to get some info from the manufacturer about it's power requirements or maybe even an adapter to go from a 12v battery source to the CPAP.
On most equipment , when the input is 12 volt , it will operate from 10.5 to 16 volts .
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1993 Tiffin Allegro Bay 32'
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12-08-2017, 10:26 AM
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#11
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Senior Member
Ford Super Duty Owner
Join Date: Dec 2010
Posts: 1,799
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I wouldn't risk it. CPAPs are extremely sensitive, complex...and expensive. There are DC to DC converters available for them (some run on 24 volts.) PSW inverter to power supply is the safe way and I doubt that it is much less efficient than the DC route since the DC converters are active as well.
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Scott Brownstein
Palm Island, Florida
2015 Georgetown 335DS
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12-08-2017, 01:40 PM
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#12
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Senior Member
Outdoors RV Owners Club
Join Date: Dec 2014
Location: Nowhere, now here. Freedom!
Posts: 4,602
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If the manufacturer of the CPAP offers a 12VDC plug set, you can use it plugged into batteries. When I had a CPAP, I had a separate AGM battery in a box that I ran the machine off of so that my house batteries were saved mostly for the furnace at night. I turned the humidity level to zero and then recharged the battery off a solar panel during the day. It worked really well.
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ORV 19B Full Timer from '15 to '20, '14 Ram 2500 Diesel and a GSD. Vancouver, WA
de K7NOL 146.52Mhz Safety? (CLICK ME!)
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12-08-2017, 01:58 PM
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#13
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Senior Member
Join Date: Apr 2014
Location: On the Road
Posts: 1,608
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Double check your machine or the brick. My wife's ResMed machine converts it to 24 volt-not 12. I bought a converter from them ($$) and spiced into the closet 12v for hers. I think you can get a 12-24 converter cheaper than what I did. She doesn't use the heater and hers draws very little amp hours overnight.
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2012 Nu Wa 363RSBDA
2016 Ford F-350 Dually 6.7
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12-08-2017, 04:50 PM
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#14
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Senior Member
Join Date: Oct 2016
Location: San Diego
Posts: 912
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I called the manufacturer, they gave me the part number for the car adapter, $35 on amazon.
__________________
2006 Allegro Bus 40 QDP IFS, 8.9L Vmspec, 1.5kw Solar + 400w Suitcase, 2@ 50amp & a 30amp Victron Smart MPPT's, 712BMV, SBS, CerboGX, 8.7kw LiFePo4, RR, MS2812, Max Transit, eero 6+ Mesh WiFi, Roof Mounted Starlink In-Motion dishy
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