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Old 06-18-2021, 07:12 PM   #1
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12 v for CPAP

OK, I use a CPAP. need 110v. got a small inverter coming specifically for the CPAP, but will need a cigarette lighter (female) to use it. I'll be running it off my two 6v golf cart batteries, and charging them each day via solar or, if no sun, generator. so, my question is, can i wire the cigarette female plug to one of my lights? they seem to have very small wires, but I don't have access to to many handy dc circuits.
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Old 06-18-2021, 08:05 PM   #2
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The short answer is no, do not run from the light circuit.
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Old 06-20-2021, 09:01 PM   #3
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Best to look at back of cpap and see how many watts it uses.. then go ahead and run dedicated circuit that is fused as close to battery disconnect relay and Mark it with zip tie label.. so you can remember it.. that is what I did.. ofcouse use correct gauge of wire for load and length of run.. get back to us and let us know what you did.. I also added enough in for my oxygen concentrator.. I can run them both.. good luck...
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Old 06-20-2021, 09:07 PM   #4
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Sorry should have added.. most cigarette lighter type wiring is high load short time and normally not for long time.. you will burn out fuse or the lighter.. lighters are good for usb loads but i would not trust it all night... and maybe 1 night short time you could get away.. but not for long..
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Old 06-20-2021, 10:01 PM   #5
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And the reason for not connecting it to the light circuit; is that you could easily overload the circuit, as most of them are only 15 amp fused, so don't do it...unless you know exactly what is on the circuit, and you have the overhead available. But then again, I don't know how much load the 'accessory port' can handle.
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Old 06-20-2021, 11:42 PM   #6
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If your medical equipment is run of of a power supply that converts ac back dc. You can make your own 12v dc to dc power supply. My cpap is 24vdc and 90watts of power. So I bought this boost buck converter and made my own power supply I can plug into the charge port next to the bed.
I found a little plastic box to mount it in at Walmart

The Beadery Mini Utility Plastic Box

Now I can run off 12vdc or 110vac.

The out put voltage and amps is on the power supply. The end that plugs into you device will have to be the right size I measured mine with calipers and ordered off Amazon.
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Old 06-21-2021, 06:23 AM   #7
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I took a different approach.

I bought a used CPAP through my provider for $100 that runs on 12 volt DC. I just plug an inexpensive cord into the CPAP and the RV accessory outlet.

My expensive CPAP stays safe at home. My "RV" CPAP rides in the RV, gets taken on dirt camping trips, and I can shrug it off if it gets mangled.
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Old 06-21-2021, 06:46 AM   #8
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Cig lighter outlet was my choice. I used one that also has USB charge ports. I have had no problems running a CPAP for years.

Lighter outlets are usually rated for 10 amps DC.
10 a X 12 v = 120 watts
Use the wattage shown on the CPAP 12 volt adapter brick or cord to decide.

My Kodiak Cub 12 volt light circuits are wired with 14 gauge lamp cord. 14 gauge is rated for 15 amps, so 15 a X 12 v = 180 watts.

Lights on the 12 volt circuit are LED and so draw very little current. Cig lighter outlet is wired to light circuit. Fuse as delivered is 15 amps.
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Old 06-21-2021, 02:15 PM   #9
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Some cigarette lighter type 12 VDC power outlets are only rated for 100 Watts, maybe 200, so if your CPAP draw is less, then sure it could "work" HOWEVER I wouldn't advise splicing into a 12 VDC lighting circuit but prefer a more permanent hard wired circuit on its own with adequate sized wire and fuse protection suitable for your CPAP...Of course your connection method (power outlet or something more substantial) needs to be adequately rated. If you can power the CPAP direct using 12 VDC that saves the inefficiency and heat losses of a brick style converter. Some of the small 100 to 150 watt direct plug into power outlet Inverters are Modified Sine Wave MSW which sure can "work" but I prefer Pure Sine Wave PSW Inverters. While pressure, temp and humidity affects CPAP energy use, FWIW my Res Med Air Sense 10 only consumes around 25 Amp Hours of my 12 VDC house battery per night.

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Old 06-21-2021, 02:39 PM   #10
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You can also reduce your cpap electrical draw by turning off the humidifier
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Old 06-22-2021, 08:22 AM   #11
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Our Experience with CPAP machines

My wife uses a CPAP connected to a 12 volt cig lighter socket. The socket is connected to a lighting circuit with a 15 amp fuse. It works fine.

She had a previous CPAP machine that ran directly on 12 volts. The 12 volt cord supplied by the CPAP manufacture had a straight connection except for a fuse.

Her current CPAP is a 24 volt model. The 12 volt adapter for this CPAP is a 12 volt to 24 volt converter specifically designed for this CPAP. You can't get more efficient than that.

Before we got the 12 to 24 volt converter cord, we used a 1000 watt inverter and the 110 volt brick to run the CPAP. With the inverter, the set up used almost twice as much battery power. It was still not very much, but every little bit counts when dry camping.

Try it. Connect it all up temporarily to a near by lighting circuit. Turn on the CPAP. Turn on the lights. If the fuse does not blow, you are good to go.

If a fuse blows, fish a 14 gauge wire through to the battery. Add a 15 amp fuse holder. Replace the blown fuse. Now you are good to go.

I wish you good luck and happy trails ahead!
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Old 06-23-2021, 06:35 AM   #12
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Good point, if you operate a CPAP at twice the Voltage (24) it only draws half the current. ANY conversion (DC to DC or DC to AC or AC to DC) is less then 100% efficient due to heat losses, so if they can be avoided and the CPAP ran direct THATS MY PREFERENCE !!!!!!!!!!!

While convenience (IE power OTHER then lighting) outlets, be they 12 VDC such as Cigarette lighter type power outlets, sure can "work" fine powered by tapping into a lighting branch circuit, when I practiced power distribution however, we were taught NEVER to power convenience loads or outlets using lighting branch circuits BECAUSE IF IT BLEW A FUSE WE WERE LEFT IN THE DARK as if it wasn't already hazardous enough !!!! We were taught and the practice in the trade was to use any Lighting branch circuit ONLY for lights...not other power or convenience or devices or appliances ...NOT to mix n match lighting and other loads lol

ALSO when designing a branch circuit a primary design criteria was to size the conductors to have a minimum ampacity of 125% of the Maximum Continuous Current meaning the conductors never had to pass long term over 80% of their rating. IE if a lighting branch circuit uses 15 Amp rated wire, my design as I was taught and used in the trade limited the designed for current to be no more than 80% of the MCC or 12 Amps.

NOTE 1 This may or may NOT have anything to do with RV 12 VDC circuits !!! Im NOT saying it does!!!! but the theory regarding ampacity and heat dissipation and insulation integrity due to long term heat remains true REGARDLESS, so its remains my "advice" to take or leave as you like.....

NOTE 2 What I was taught and when and where I practiced may or may not have anything whatsoever to do with RV circuits and may or may not be applicable DONT TAKE MY WORD FOR IT consult current trained professionals, electricians, engineers and qualified RV Techs.......

NOTE 3 I'm a supporter of anyone to do as he or she pleases in THEIR RV, its THEIR choice, NOT anyone else, NOT mine..

NOTE 4 My Res Med Air Sense 10 CPAP draws very little current and sure could likely be powered by tapping into an existing lighting branch circuit and especially since its used at NIGHT ONLY with NO problem.........

HOWEVER it must remain my professional "advice" (but I want people to do as they like) NOT to power NON LIGHTING RV devices or appliances by tapping into LIGHTING branch circuits, BUT INSTEAD use separate and independent power DIRECT from the house battery using the appropriate size of wire and Overcurrent Protection......

NOTICE: Im NOT saying it cant work to power a CPAP by tapping into a Lighting branch circuit IT OBVIOUSLY CAN.........I AM SAYING my "advice" (based on a lifetime of training and experience in electrical power distribution) is to power a CPAP direct from the battery versus tapping into a lighting circuit

Sooooooooooo do as yall please, its YOUR RV, YOUR money, YOUR choice don't take my word for it.........

Best wishes yall, have fun, be happy, be safe.

John T BSEE,JD Electrical Engineer and 50 year RV owner
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Old 06-23-2021, 06:50 AM   #13
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I sure am glad my travel trailer came setup with a 120 volt circuit and an outlet specifically located on each side for CPAP machines. I guess if someone actually carried an alarm clock on a camping trip, it could also be used for that.

I have to agree with OldJohnT, I would not want to be tapping off a light circuit. I am always a bit nervous anytime I have to tap power and can't go all the way back to the source power to get it.
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