CPAP on a battery

What is Stupid is, not buying a XPAP that runs on 12 volt d/c, 2 wire power, if you don't have A/C or plan not to. Jim

Um, GP, that would be too easy.

palerider wrote:

TheSnoringMan wrote:and the DC motor (brutually reactive, asymmetrical square wave)

Only, it's not, not even close... which does tend to call your other "SWAG"s into question.

Yeah, I was waving my hands pretty wildly... and couldn't even spell 'brutally', I was getting so over-excited. In any case, I've now finished building my version - AND using it. I built using two highly integrated products, and I added just two components. #1, the infamous 2.7k Resistor; and #2, a "Filter Capacitor". (The capacitor is one I had on hand, with specifications I don't like). The big aluminum box is a DC-to-DC "Boost" Converter, 10V-18V to 24V regulated out. The small board with the LED is an integrated "Buck Converter", with an LED Voltage Display built-in: I tuned this one to convert regulated 24.0V down to 3.3V, for the Resistor and the Center pin.

The picture is ugly, and the wire colors I used don't make any sense. But the implementation is really simple:

• Red Wire nuts connect +12VDC and "Ground" into the 24V regulated Converter inputs.
• +24 VDC Converter Output (Yellow) goes into a push-down wire connector, operating as the "+24V Bus".
• Regulator "Output Ground" (Black) goes to another push-down wire connector, the "Ground Bus".

The "Filter Capacitor" has one connection to each bus (properly polarized, of course). The input side of "Buck Converter" board also has one connector to each bus. The Buck Converter +3.3V output goes into the Resistor (2.7k Ohms), and that goes into the "middle Pin" wire of the Resmed cord. (That's a genuine Resmed cord, with a pair of big inductors built-in). The "Ground Bus" connects a wire to the "outer cylinder" wire of the Resmed cord (yellow wire nut), and the "24V Bus" connects a wire to the "inner cylinder" wire of the Resmed cord (another yellow wire nut).
Shared Image: https://drive.google.com/open?id=0Bw_TW ... kNDV2ZMdTg

I am unhappy with the current "Filter Capacitor" for two reasons. First, it is rated for only 35V, which (IMO) isn't enough "headroom" for a 24V circuit. It is also 5x larger than the corresponding capacitor in the now-destroyed Resmed AC-DC unit, from which I stole the output cord. I will be replacing that with a 50V, 1000uF capacitor when today's shopping package arrives in the mail. Earlier today, I connected the homebuilt "White Box" to the 12V Battery on one of the SUVs. (Hood open, SUV not running). After several turns on the "Buck Converter" adjustment screw to bring the output Voltage down to 3.3V for the center pin), I re-verified the three output voltage measurements against the "genuine" Resmed AC-DC power adapter in the house, and brought the Resmed CPAP out to the SUV.

Plugging it in, I got the usual "Warning, SD Card Activity" message, Logo, and menu options. I pressed the 'Power On' button, and it started running - just like inside. It soon adjusted for the fact that I wasn't wearing the mask and breathing properly (increasing flow and pressure); and it shifted back to lower pressure after I put the mask on. I let it run a couple minutes, and then went back in the house, plugged in the genuine AC-DC Power Supply - and got the usual startup sequence again, exactly as I had received with the homebuilt "White Box" at the SUV.

Next step: After the replacement filter capacitor is installed, I'll use a 12V connection into an idling PC, and run it for a couple of full nights.

TheSnoringMan wrote:

palerider wrote:

TheSnoringMan wrote:and the DC motor (brutually reactive, asymmetrical square wave)

Only, it's not, not even close... which does tend to call your other "SWAG"s into question.

Yeah, I was waving my hands pretty wildly... and couldn't even spell 'brutally', I was getting so over-excited.

I believe you missed my point, which is that there is no DC motor in the Resmed S9/AC10 machines.

The Buck Converter Board "- Output" doesn't need a connector, it's common with the "- Input" connection. And actually, the 24V Converter "Ground Wires" are also common with each other. (I might have preferred a "floating Ground" output implementation, but that's not what they did). The 24V Converter almost certainly contains a substantial electrolytic "Filter" capacitor inside - so my big one, outside, might be completely unnecessary.... but I'm chicken, and they only cost 50 cents.

Speaking of cost: This was obviously not a money-saving alternative. I spent $27 on the regulating Booster Module, although it can now be bought for about $17. (This one: http://www.ebay.com/itm/AweKing-Waterpr ... 2401317134). The sacrificial Resmed AC-DC PSU cost me $18, and the 'Project Box' cost about $6 more. The Buck Converter mini-board was cheap ($2.25), and there's about $4 of miscellaneous bits (wire connectors, strain relief, filter capacitor, etc.). So my total was $57, before adding on about $20 for my fancy twist-lock connectors. My experiment was fun, but it did not save money.

In a rebuild, perhaps the sacrificial Resmed PSU could be avoided, buying just the plug (and sliding a couple of tape-on inductors for a cheap 3-wire cord). And of course, my exact Booster Module can be had from China for less than $15, and a much cheaper unit might be able to do the job as well. (If you slap on some "helping" EMI filtration components, you probably have a lot of options) . And per advice above: "cigarette lighter" sockets and plugs probably are sufficient. Using the same Booster as I did, I can see this costing about $25... and a "cheaper" budget Booster Module could maybe knock off another seven bucks.

YMMV, etc.

palerider wrote:I believe you missed my point, which is that there is no DC motor in the Resmed S9/AC10 machines.

I did completely miss this, and I haven't a clue: If not a brushless DC motor, what generates the air pressure?

TheSnoringMan wrote:

palerider wrote:I believe you missed my point, which is that there is no DC motor in the Resmed S9/AC10 machines.

I did completely miss this, and I haven't a clue: If not a brushless DC motor, what generates the air pressure?

Perhaps a Fan, or maybe the Cicadas's I hear in my head 24/7 rubbing their wings together. Jim

TheSnoringMan wrote:

palerider wrote:I believe you missed my point, which is that there is no DC motor in the Resmed S9/AC10 machines.

I did completely miss this, and I haven't a clue: If not a brushless DC motor, what generates the air pressure?

You started out with "DC motor (brutually reactive, asymmetrical square wave)" and now you're waffling, tsk.

Resmeds have a 3phase motor with variable frequency drive. that's how they can accomplish the 4hz FOT pressure fluctuation.

palerider wrote:Resmeds have a 3phase motor with variable frequency drive. That's how they can accomplish the 4hz FOT pressure fluctuation.

(As I slap my forehead) of course, it has to be VFD. Good thing I used their connector cable, and added that beefy Filter Cap. Thanks again!

BTW, I slightly hijacked the Thread by describing my "solution", which is uniquely for Resmed A10 from a 12VDC power source. I've just created a new Thread specific to that topic. Should I delete posts from here, or leave them in place for historical reasons?