CPAP machine w/ inverter. How much power?
Hi Folks, A little background. Not new to RVing, but starting to deal with battery issues more, now that I have a week long music festival coming up w/ no hookups. I decided that after last year, n...
Forum Discussion
Fully Regulated CPAP Power, using a Vicor Converter module
No- and I'm sure that you agree because of your next point: With such a cord, you are running "12V" directly at RV system voltage. Maybe as high as 14.6 volts during "bulk" charge; even 13.7V during "trickle" charge is a lot more than the output from the 120V power brick you use at home. As you say:
This is not merely when "the rig is started"; you will be exceeding that figure at any time a Power Converter decides to switch into "bulk" or "boost" mode. Example: Your RV, parked in a campground with full plugins.
So I agree with your post, warning people about this issue. But let me offer a completely different alternative: Vicor makes "power converter modules" which accept anything between 10-20 volts input from your RV "12V" power distribution, while creating out EXACTLY 12.0 volts on it's output terminals. They are even tunable! If you check the exact output ("12VDC") of your 120V "power brick" at home, you can match the voltage at plug-in end of your module and cord making up for the fact that your cord, downstream from the Vicor and into your CPAP, will have at least some power loss.)
My own 120VAC brick actually puts out 12.15 Volts at the CPAP connector, not 12.0. I added a resistor (4M) to the "tune for increased voltage", matching that figure. It will maintain that voltage under any possible state of 12V or discharging (except, of course, for totally dead batteries). 14.6V "Bulk" charging? the CPAP gets 12.15 Volts. 12.5V, or even 11.9V, discharging? the CPAP still gets 12.15 volts :B (Although it's a really bad idea to use it if your Trailer 12V system is rall the way down to 11.9 Volts.)
You can buy such a Converter (used) on EBay, for about $30. Just take care to be sure that the particular "converter" which you are getting is for 12V in AND 12V out - most of them are built for different voltage combinations. If you can find one with multiple outputs, you can "bridge" them together and achieve output wattage well in excess of the requirements for running with the humidifier. But that wiring is a bit more complicated, adding some "control bus" connectors between the multiple internal units. I bought a single-output 70 Watt module, and simply skip the humidifer when we're camping without 120VAC plugins.
The Vicor module, encolsoed in a plastic "project box", becomes a 12V alternative to your 120VAC power brick. Should I call mine "Brick, Jr."? ;)
MEXICOWANDERER wrote:
BEWARE! ! !
....(short snip).... My machine is TWELVE VOLTS D.C. (battery power). With a proper plug to fit the socket, a direct cigarette lighter socket/plug connection to the machine is appropriate. Most manufacturers in fact offer an ACCESSORY cigarette lighter cord to power machines. Operation is identical to that when using the brick and AC.
No- and I'm sure that you agree because of your next point: With such a cord, you are running "12V" directly at RV system voltage. Maybe as high as 14.6 volts during "bulk" charge; even 13.7V during "trickle" charge is a lot more than the output from the 120V power brick you use at home. As you say:
MEXICOWANDERER wrote:
,CPAP and BiPAP manufacturers warn against leaving the machines connected to 12 volts DC when a charging source higher than recommended is seen in the 12 volt power system. So converter power is OK, but manufacturers do not like to see machines connected when the rig's engine is started. I would say 14.0 volts is about the limit for comfort.
This is not merely when "the rig is started"; you will be exceeding that figure at any time a Power Converter decides to switch into "bulk" or "boost" mode. Example: Your RV, parked in a campground with full plugins.
So I agree with your post, warning people about this issue. But let me offer a completely different alternative: Vicor makes "power converter modules" which accept anything between 10-20 volts input from your RV "12V" power distribution, while creating out EXACTLY 12.0 volts on it's output terminals. They are even tunable! If you check the exact output ("12VDC") of your 120V "power brick" at home, you can match the voltage at plug-in end of your module and cord making up for the fact that your cord, downstream from the Vicor and into your CPAP, will have at least some power loss.)
My own 120VAC brick actually puts out 12.15 Volts at the CPAP connector, not 12.0. I added a resistor (4M) to the "tune for increased voltage", matching that figure. It will maintain that voltage under any possible state of 12V or discharging (except, of course, for totally dead batteries). 14.6V "Bulk" charging? the CPAP gets 12.15 Volts. 12.5V, or even 11.9V, discharging? the CPAP still gets 12.15 volts :B (Although it's a really bad idea to use it if your Trailer 12V system is rall the way down to 11.9 Volts.)
You can buy such a Converter (used) on EBay, for about $30. Just take care to be sure that the particular "converter" which you are getting is for 12V in AND 12V out - most of them are built for different voltage combinations. If you can find one with multiple outputs, you can "bridge" them together and achieve output wattage well in excess of the requirements for running with the humidifier. But that wiring is a bit more complicated, adding some "control bus" connectors between the multiple internal units. I bought a single-output 70 Watt module, and simply skip the humidifer when we're camping without 120VAC plugins.
The Vicor module, encolsoed in a plastic "project box", becomes a 12V alternative to your 120VAC power brick. Should I call mine "Brick, Jr."? ;)
