Resmed 10 on my camp 12V solar power

[LoBattery]

I spend five months of the year at my camp that is off grid. The setup is a
little unusual as it runs just on a 12V car battery from a vehicle we don't
bring with us. Everything runs only during the day when the sun shines. We get
refrigeration, lights, TV and hot water all from PV solar. It is not really
roughing it as my wife even has a dishwasher. Last year I went on CPAP and only
caught the very last six weeks of the season. I used a small 120V inverter
to run the CPAP. This year I designed a dedicated power source for it using a
$4 150W 24V boost converter that resides in the power shed.

There has been talk of how this could be done, but no one seems to have actually
done it with a Resmed Autosense 10. I started out with a HP laptop power plug which
is very similar. I believe that did not work because it has an insulated plastic
section on the end of the barrel and the real power pack is metal to the end. I've
noticed that the screen display will say plug not inserted fully if it is pulled
out even the smallest. If you ground down this plastic end with sandpaper, the HP
plug might work. Never had the time to do more before leaving.

The the inverter the first night at camp. Had a spare power pack so I just cut the
cable off of it, It could always be put back together. From the patent, the center
pin requires a 2.7K resistor from a 3.3V power source for the Resmed to determine
it is the correct power pack. To save parts it has been mentioned that a single
resistor to the +24V will work. I know some people just revel in doing things the
wrong way, nothing I say will ever change them. Adding one more resistor will make
it safe. The Thevenin equivalent is a voltage divider with a 20K resistor to the +24V
and a 3.3K resistor to common. These values are common and close enough that the
exact 1% resistor values are not needed. The outside of the barrel connector is
minus and the inside barrel is the +24V. Across this 24V I placed a 1,000uF capacitor
because it is 40 feet away from the boost converter. A diode for reverse voltage
protection is placed across the power leads. This will short out the voltage source
rather than burn up the Resmed should I get goofy and reverse the cables.

The 12V to 24V boost converter is actually in the power shed three feet from the
battery. It is a 150W module that can be found on ebay. As said before, this is 40
feet away. Sending 24V at lower current reduces the voltage drop of the wire. The
boost converter is turned on by a FET switch that goes to a wall switch in the bedroom.
I turn off that switch to save power each morning and turn it on before going to bed.
So it doesn't run all day should I forget to turn it off, an enable signal from my solar
panels disables it during the daylight hours. This is a lot like a very rude alarm
clock should I sleep late, waking up with no air pressure. I'm usually up way before
that as the bedroom window faces east and is 6 X 6 foot with no curtains.

This is an annoying feature of the Resmed machine. If it looses power while running,
it will restart once it is powered up again. I don't mind that, but it looks like it
will run forever without a person connected. It seems like it should time out if no
resistance or breathing is detected. I've come home from a concert at night to this
massive sound of rushing air. I'll probably fix that next year when I get time. After
all, the power cable components are just wrapped in a turn of black tape.

There is actually no need for you to go through this. The Resmed DC converter is a deal
at $90 just because it reduces power consumption by half from using a 120V inverter. I
just wasn't going to pay half of what a CPAP machine costs to get the factory unit.

[Goofproof]

That's why we buy brands that only use 12 volt neg ground power. Cheap cable, good to go. Hard way or Easy way, most of my toys are 12 v d/c neg ground, that's the first spec I check. Jim

[CapnLoki]

This year I designed a dedicated power source for it using a
$4 150W 24V boost converter that resides in the power shed.

There has been talk of how this could be done, but no one seems to have actually
done it with a Resmed Autosense 10...

There's a reason why no ones has done it
But its nice that someone tries

... As said before, this is 40
feet away. Sending 24V at lower current reduces the voltage drop of the wire.

Yes, in theory. But when you do the calculation, if you use 12 gauge wire the drop for 0.5 amps at 12V is only 0.5%, pretty small for this purpose. Even for 14 gauge its 0.8%, and I don't think I'd what to go thinner. If this were a bigger load, like 3 amps for a humidifier, then you can get to 5% with 14 gauge, while its only 1.25% for 1.5A at 24V. This is more significant. Bigger boats sometimes use 24v for high load applications, and it certainly makes a difference when you're sending 100 amps to an anchor windlass in the bow; but this seems a weak argument here.

This is an annoying feature of the Resmed machine. If it looses power while running,
it will restart once it is powered up again. I don't mind that, but it looks like it
will run forever without a person connected. It seems like it should time out if no
resistance or breathing is detected.

I thought ResMed had this feature - Respironics has it, though it doesn't work well.

There is actually no need for you to go through this. The Resmed DC converter is a deal
at $90 just because it reduces power consumption by half from using a 120V inverter. I
just wasn't going to pay half of what a CPAP machine costs to get the factory unit.

You can get a new ResMed for $180??? Actually I've seen the Resmed DC/DC for $70, and the gear you've hacked must be at least $20-30, so maybe you're saving $50.

[yrnkrn]

Good work!

Observation regarding the voltage drop, using home-built 12v->24V converter for the A10 I had measured peak current consumption of about 2.5A on the 12V side when taking a very deep breath, which required quick speedup of the the motor. The current consumption was also high after taking off the mask until the machine turns off, don't recall how much.

[TheSnoringMan]

I designed a dedicated power source for it using a
$4 150W 24V boost converter that resides in the power shed. There has been talk of how this could be done,
but no one seems to have actually done it with a Resmed Autosense....

Nice work! I also built a converter box, and mine has also been working great. Instead of using two resistors, I used a $2 buck converter to create 3.3V from the 24V output, leading into the 2.7K resistor. Your way of obtaining 3.3V is more simple. Within my box, I used a slightly more expensive 12->24V *REGULATING* boost converter, because we use it in a Travel Trailer, where the "12V" load center might be as high as 14.4 (during "boost charging", from either the Solar System or the plug-in power converter.) Mine was also rated for 240W, and you can get by with cheaper/less powerful versions if you don't need the humidifier.

Subsequent to taking that picture, I switched the 'load stabilizing capacitor' from 2700uF (rated only 35V) to a 1000uF, rated at 50V -- so our systems are nearly identical. Even that might be unnecessary, because the boost converter definitely contains output capacitors on the inside. Just like you, I sacrificed a cheap "refurb" power supply to obtain the 3-wire cord and plug. We've used it for many nights, with great success.

Ignore the wire colors. Red wire nuts on the left connect +12V and Ground into the "silver" boost converter. The clamp-down wire nut at the top functions as a +24V "bus bar", providing 24V input to the Capacitor, the Resmed connector, and the Buck Converter "input". The clamp-down wire nut on the right functions as a "ground bus", connecting the Boost converter "Output Ground" to Ground terminals and wires from the Resmed cord, buck converter input, and stabilizing capacitor. The 2.7K resistor comes off the +3.3V buck converter output. I left the buck converter "output ground" unconnected, because it's wired to "input ground" within the converter module. The "Ground Bus" isn't a floating ground either - the boost converter also shares input and output ground within the module.

It took longer to write this than it took to build the thing. My "Build Thread" was viewtopic.php?f=1&t=156100

[LoBattery]

SnoringMan..... I hadn't been back here in six months so never saw your post. I see you got the same crap as I did when I said I was going to do this a year ago.

When I looked 12V machines were pretty old stuff. My source had Resmed tahat was reasonable. I run almost a half dozen voltages at the camp. Boost converters are a stock item there. All the electronics for the control system including inverters at the camp cost maybe $50. Electronics are dirt cheap.

I have two Autosense 10 machines One bought for $200 with about 200hrs and the second for $150 with 960 hours. Both came with new heated hoses. So, average is about $180.

The wire I actually used was four pair telco cable which is 22 or 24 gauge. One pair was used for control. This was buried underground with a number of other wires. Pulling a new wire was not an option. Line loss was a consideration.

What data I collected at 12V

12V BOOST INVTERTER

.55A STANDBY
.45A SLEEP
.05A BOOST CONVERTER ONLY

WH WP AH AP

6/13/17 63.8 17.7 5.14
6/14/17 62.0 22.7 5.02 1.7
6/15/17 71.5 25.5 5.79 2.08
6/16/17 60.4 19.6 5.08 1.57