Has anyone added a 12v accessory plug (cigarette light plug) in the master bedroom? I want to add a plug to run a CPAP without running the inverter all night. What's the most convenient place to tie into existing 12v wiring? I am thinking I can tie into the bedroom stereo wiring and install the plug inside that cabinet. The CPAP draws about 1 amp so there should be enough power there. Any other suggestions?
Does the CPAP operate on 12 Volts? If so, then there should be no problem. If it operates on 120 Volts and you plan to use a small inverter, then remember that the 12 V current will be over 10 Amps, and you'll want to be sure the wiring is heavy enough to support that without excessive voltage drop.
Howdy bdale,
I haven't installed a 12vdc outlet, but, at least on our model, the 12vdc breaker box is at the foot of the bed, and would be easy to install an outlet.
Good Luck, Dave A
edit: 12vdc fuse panel
Yes, the CPAP is actually a 12v device. I was very close to buying and installing a small inverter when I discovered this. The 110v brick converts down to 12v DC. I have ordered the 12v cable which should completely cut the inverter and the power brick out of the picture, which will be a big help in saving my batteries. Good point on the extra load at 12v. The specs for the 12v plug, provided by the CPAP manufacturer, indicate that it ships with several fuse sizes between 3 and 7 amps, depending on CPAP model. Even at 7 amps I think the 12v breaker box under the bed, as Dave suggested, may be a safer option.
Verify with the CPAP manufacturer that it will be OK on 12.0-14.2 VDC. Many "12 volt" devices are just that-- they need 12.0 VDC. Others have a much wider tolerance range for voltage.
Then, yes, the 12 VDC panel at the foot of the bet would be a good place to tie in. Can't go wrong with larger than required wire.
This great advice saved me from destroying a TV. After Brett's caution, I contacted the manufacturer and was told NO GO on my plan to use a 12 volt outlet instead of the 110 to 12 wall wort. I hadn't really considered the voltage variation.
The attachment shows a simple regulator that can be used to set the voltage to exactly 12 volts no matter what the battery has. This should save your cpap machine.
Here's another, this one non-adjustable.
I have been looking into this and apparently I may have ordered the wrong 12v cord. They offer 2 different cords, one is $165 vs the one that I bought at $30. The only difference that I can tell is what must be a voltage regulator on the expensive one. I can't seem to find clear information about what my exact model requires. Therefore, the regulator that you suggested above may work but I think I need to do some more research. Better safe than sorry. Thanks for everyones warnings.
I would mount a dc-dc converter in the electrical space under the foot of the bed, wiring the input to a 12 volt bus and the output to a bulkhead mount cigar lighter receptacle. Then go ahead and use the unregulated cord.
Don't use one of those regulators unless you're sure the device really needs it. It's very inefficient, as evidenced by the big finned heat sink on it. This thing will run your battery down much faster than just running the device directly from the battery. It's also going to need airflow because it's obviously going to get hot from all the energy it's converting, possibly from DC to AC then back to DC again at a different voltage. It may not be much more efficient than running your inverter... So just make sure you really need this regulator, this is all I'm saying.
These are switching power supplies, inherently very efficient. Notice the one with fins takes 40 volts in. Neither will even get warm in this application.
The heat sink is probably for visual coolness. If this was a linear regulator dropping 40 volts down to 12 at 3 Amps, there would be over 80 Watts of heat to dissipate.
This is all very confusing, especially since electricity has a big voodoo element for me to begin with. Just when I think I'm understanding it something comes up that shakes my confidence. On the surface it seems so simple....supply a stable 5 amps at 12 volts DC, as listed on the back of the device, from a 12-14v DC source. That's really all that the $165 manufacturers 12v cord can be doing, right? See pic below for the cord. What are they doing in their magic black box and can I replicate that? The regulators seem like the answer but the machine is an expensive item to gamble with. As crazy as it sounds, would I be better off with a small inverter to go from 12v DC to 110v AC and then back to 12v DC with the original equipment brick cord? I would very much prefer to stay at 12v DC if practical.
There's your key: If it says that it will accept a large voltage range..."from a 12-14v DC source", then you "may" be good to go. That is still narrower than what happens inside your coach, as you should be keeping your battery at least at the 12.2 volt level...but depending on your alternator/battery charger setup, you might get up to 15 volts on the high end. If I were you, I would contact them and ask, like Brett suggests.
My TV wants 12 volts...period. Your machine SEEMS to be more tolerant. They just need to verify for you that 15 volts won't kill it...or never have a charge going to your battery (alternator or charger) with the CPAP plugged in. THAT would keep it at the 12-14 range they specify.
The one with the clips just delivers battery voltage to the machine, fine if no charging is taking place.
The one with the cigar lighter plug has a regulator in the box, probably similar to the ones I showed you.
If the cpap machine can handle 12-14 volts, you should be fine with the clip on adapter as long as the engine is not running. Add a regulator and you should be safe no matter what.
I see now that my wording was a little misleading. The only information on the back of the device is "12v - 5A". I added the 12v-14v range as being my understanding of the normal range of the battery, since they provide the plug with battery clips....clearly intended to be connected to a battery. Either way, I have now found reliable information that suggests the $165 plug is in fact for a much older machine and not required for mine. I'm pretty comfortable that I have the right plug. I will contact the manufacturer to find out if they recommend a power stabilizer or if it can survive voltages over 15. I did see somewhere that it was not recommended to be used while the engine is running, which pretty much answers that question. So, I think that a stabilizer is a smart option combined with unplugging the unit when charging is active. I have to remember, "No CPAP while I drive." But, I'll be very happy to get it off of the main inverter.
Well then. My advice (worth 2 cents) agrees with Tom to use a little regulator. I might even try one of those for my TV after I check its amperage needs. When Brett stopped me before, my plan had been to avoid using the inverter to watch TV on a sleep timer at night.
Tom's find looks like the ticket, if one can find one with the proper amperage at 12 volts. I had never heard the term "Buck-Boost" before.
Pretty cheap! 5 30V to 0 8 28V DC Boost Buck Converter 5A Constant Current Volt Regulator | (http://www.ebay.com/itm/5-30V-to-0-8-28V-DC-Boost-Buck-Converter-5A-Constant-Current-Volt-Regulator-/301057850532?pt=LH_DefaultDomain_0&hash=item4618723ca4)
On edit: This one will not do the trick. It says maximum wattage is 30 watts. Ohm's Law says 12 volts times 5 amps = 60 watts. Ergo, it is good for about 2.5 amps only (30=12*2.5).
Although I am more of a digital than analog or power engineer, I have done some designs in that area. A boost converter is a switching power supply that boosts a lower voltage and a buck is one that reduces a higher voltage. By nature a boost-buck supply must be a switcher, making it modern and efficient. Also, likely to put switching noise on the power line, not good for audio unless well designed and filtered.
I had FOT install a 12V plug next to the bed in my first coach ( it was a 1996). It was flush with the base of the the small cabinet at the head of the bed and completely invisible. I'm not exactly sure where they accessed the power from, but it was a great having a plug there that was completely out of the way and out of sight. My 2002 has a radio in that cabinet so 12V power is readily available. I ran my CPAP off a marine deep cycle battery for five days on an Elk hunt in Colorado; which leads me to believe that they are not to finicky about the power source as long as you have the proper cord.
There is a 12v outlet in the drivers side upper bedside cabinet in my coach. Looks like an add-on. There is 12V wiring in the over bed cabinets that you can tap into. It's under the carpet at the back in my coach. Just watch the amps draw.
Keith
I tied it into the 12v fuse block at the end of the bed. There was a circuit labeled "optional 12v accessory" that powers a plug in one of the front bays and I think that's all it does. We have never used that plug so it will pretty much be a dedicated circuit for the CPAP. I also confirmed with the manufacturer that I do have the right plug and that it can take a normal range of automotive voltages. They couldn't give me an exact range but they say it is designed to be used in cars and that it should be fine. I plan to unplug it anytime the engine, generator or shoreline are charging. I may still add the voltage regulator later. For now, I'm calling this one done and moving on down my list.