Philips Respironics power supply questions

[Guest]

That adapter cable is way expensive

You think $30 is expensive check out the one for Resmed.

[linuxman]

That adapter cable is way expensive

You think $30 is expensive check out the one for Resmed.

Yeah, but that's a DC to DC to converter (12V -> 24V). That requires a somewhat specialized part (still..agreed not $84 worth). The Philips cable should be 5 bucks though..sans any required special signal, it would only need to be a passive adapter.

[Guest]

The Philips cable should be 5 bucks though..sans any required special signal, it would only need to be a passive adapter.

I made one for an older model for $10.

Yeah, but that's a DC to DC to converter (12V -> 24V). That requires a somewhat specialized part (still..agreed not $84 worth).

All other mfgs run on 12V - me thinks Resmed could too (IF they wanted to).

[jtravel]

So this is interesting. I don't doubt that it's the case - this kind of thing is done in many other types of products as well. What causes me pause though is that the 12v adapter cord (for car/battery) for the Dreamstation (https://www.cpap.com/productpage/pr-dre ... -cord.html ) doesn't really look like it would be likely to have active circuitry in it that could generate such a signal. The two round things in the cable are very likely just noise reduction coils. I guess they could put the special circuitry in the cigarette lighter adapter plug..it just seems not terribly likely. Whatever the signal is, it has to be something that's not DC..and thus able to be filtered out for detection. When I get a chance I'll take my Dreamstation power supply and hook it up to my oscilloscope to see if I can tell what the special signal is (assuming it's not something that's transient). This is all sort of academic of course, but I am curious. That adapter cable is way expensive and that certainly makes it more likely to have some funky signal generator in it :/.

I wonder if it's just a matter of the Dreamstation power supply doing a better job of filtering Noise and AC Ripple out of the DC power.
The Dreamstation could detect the ac ripple or noise and refuse to power if it was above spec.
Might be as simple as adding a passive noise reduction coil to the older power supply cable.

[linuxman]

So this is interesting. I don't doubt that it's the case - this kind of thing is done in many other types of products as well. What causes me pause though is that the 12v adapter cord (for car/battery) for the Dreamstation (https://www.cpap.com/productpage/pr-dre ... -cord.html ) doesn't really look like it would be likely to have active circuitry in it that could generate such a signal. The two round things in the cable are very likely just noise reduction coils. I guess they could put the special circuitry in the cigarette lighter adapter plug..it just seems not terribly likely. Whatever the signal is, it has to be something that's not DC..and thus able to be filtered out for detection. When I get a chance I'll take my Dreamstation power supply and hook it up to my oscilloscope to see if I can tell what the special signal is (assuming it's not something that's transient). This is all sort of academic of course, but I am curious. That adapter cable is way expensive and that certainly makes it more likely to have some funky signal generator in it :/.

I wonder if it's just a matter of the Dreamstation power supply doing a better job of filtering Noise and AC Ripple out of the DC power.
The Dreamstation could detect the ac ripple or noise and refuse to power if it was above spec.
Might be as simple as adding a passive noise reduction coil to the older power supply cable.

Yep, that's possible too. I'll try to get the power supply on my scope this weekend to see what there is to see. I actually have a Series One Remstar as well that I bought as a backup, so I can compare.

[Guest]

Yep, that's possible too. I'll try to get the power supply on my scope this weekend to see what there is to see.

Since I don't have a DS, I'm gonna guess that if there are no components the 3rd pin is tied either to ground or +.

All other mfgs run on 12V - me thinks Resmed could too (IF they wanted to).

iirc the S8 was 12V so it was an intentional change to 24V.

[linuxman]

Since I don't have a DS, I'm gonna guess that if there are no components the 3rd pin is tied either to ground or +.

Oh, I didn't even notice that it had a third pin. Indeed, that's probably what it is.

[LoBattery]

The third pin is likely similar to to the Resmed, a pull up resistor connected to a 3.3V supply. Resmed has various resistance values to identify the power level of the supply. In the main unit it pulls this voltage down with another resistor and they read the voltage to identify. In addition in later units it can use this for onewire communications to identify over temp and other problems.

[jtravel]

From another board:

I should probably point out that Philips Respironics has already joined the ResMed proprietary club with the introduction of the DreamStation line.

They use they same type of plug (same dimensions, but right angled) as the A10 but they use a simple 20k ohm resistor to +12V on the center pin.
some testing with a power supply and a decade box shows the DS needs to see between 18.9K to 26.2K to power up and run without an error screen. The blower will not start with the wrong resistance.
Outside barrel of plug is Ground
Inside Barrel of plug is Positive
Center pin is positive.

[Rob K]

Good find. Looked at my 80 watt supply for my Remstar S1 auto 560p and it does indeed have 3 conductors at the plug. So no "propriety signal", just a third pin with a different voltage to distinguish one power supply from the other. Far less expensive than having more costly circuitry to produce a signal. Makes sense that they would do it this way.

The outside of the barrel is ground. The inside barrel measures +12.45vdc to ground. The center pin measures +12.38vdc to ground. These were measured with power supply disconnected from the machine, no load. I'm not going to open my only machine and check the voltages when loaded. I'll leave that to someone else. I'm trying to decide which is the model number on my power supply. It's not very clear. There's a reorder#70801477.

[palerider]

The original poster has to buy another power supply. The old ones are the same spec to work with the new machine, but they don't have the proprietary signal. The manufacturer will sell more product in this case. I don't imagine it happening too often though. I believe it's mostly to keep people from using the wrong power supply.

So this is interesting. I don't doubt that it's the case - this kind of thing is done in many other types of products as well. What causes me pause though is that the 12v adapter cord (for car/battery) for the Dreamstation (https://www.cpap.com/productpage/pr-dre ... -cord.html ) doesn't really look like it would be likely to have active circuitry in it that could generate such a signal. The two round things in the cable are very likely just noise reduction coils. I guess they could put the special circuitry in the cigarette lighter adapter plug..it just seems not terribly likely.

in this day and age of miniature electronics, they could have the active circuitry in the plug that goes into the machine.

I've got a cable for a cms50d+ oximeter that *looks* for all the world like a plain ordinary USB cable, but it's not. it's got a serial to usb converter in the USB A plug end, a regular USB cord won't work with that oximeter.

[Rob K]

I agree it would be no problem to have some very small active circuitry built into the cable. The size of electronics these days is pretty amazing. In the early days a computer took up a whole room. Now you can carry them around in your pocket(smartphone).

As far as the power supplies we have been talking about it seems they took the easiest and cheapest route based on the information that was posted. Makes sense financially for the manufacturer also. A three pin plug with a ground, +12vdc, and a resister to drop the voltage on the third pin. The third pin has to be a certain voltage in order for the machine to accept/recognize the power supply. Any of the power cables whether they plug into the wall, cigarette lighter or have connections for a battery post will likely be made the same way. If you have the means it would be very simple to make an adapter to get the old power supply cables to work with the new machine. Though, for most people, this is not going to be an option.