My battery backup setup

[justMongo]

Two issues with using a computer UPS.
1) There battery is a SLA battery with much less A-Hr capacity than you can get for the same money.
-- The UPS just will not last the night.
2) Many UPS use a stepped Sine approximation when running on backup battery.
-- This does not work for some newer computer power supplies with active power factor correction.
-- For the same reason, it may not work with the power brick for a CPAP.

Then you have the double conversion mentioned by Sleepster. Wasted energy.

I would bet that the PR 12V cable also has a reverse polarity protection diode -- possibly a Schottky for low forward drop.

There are different solutions for different scenarios. For camping -- that's one scenario.
For home backup, the most elegant solution I have seen was proposed by, I think, OMMOHY.
A big 12 Volt SLA scooter battery, a switch mode power supply for charge and float charge; and a Super PWRgate PG40s Schottky diode bridge to autoswitch the load from Power supply to Battery; and permit recharge and float charge.

[OMyMyOHellYes]

+1
As usual what may seem like the "best" deal may not be. "12V Respironics DC battery adapter cable Respironics (Philips) $39.99' this is basically a USB cable with fewer wires and different connectors on the ends. Check the price of a USB cable and then figure the profit for that at $39.99

At least the Resmed cable actually boosts the voltage from 12V to 24V which is a switching regulator with magnetics in a box and not just some wire.

USB cable? Most certainly not. It is about an 18 or 16 ga wire w/ fused plug and two massive ferrite chokes to arrest RF interference (why? I don't know) and a very non-standard 7.4 mm coax barrel plug but it certainly NOT a USB cable. It should carry continuous 12 V at 15 amps. How would a USB cable do that?

And the purpose of the ResMed adapter? To me is seems to make more money for ResMed in that it is just as easy to come up with a 24 V battery as it is a 12 V battery. Well, at least as easy as it is to come up with two 12 V batteries. But teh benevolent jean-youses at ResMed make you still have to use their adapter even if you have a 24V battery. Because they made it that way. The real question is why did ResMed go non-standard. Why - I speculate it was solely to squeeze more money out of their customers, of course when they could do it themselves a WHOLE lot cheaper and more efficently.

Which is what I do with my Respironics and a 12 V 35 AH battery. And a charger. I do think that the Respironics assembly IS over priced (that's why I built my own) but it is nowhere as overpriced as the clusterfication that ResMed forces on people.

OMMOHY

[sdb7802]

FYI:

I've found that the A10 will run from a +24 volt power supply (non-ResMed) when the center pin is connected to +3.3 volts thru a 2.7k ohm resistor. I use a +3.3 volt three-terminal voltage regulator fed from the +24 volt power supply. The resistor functions as a pull-up resistor to +3.3 volts and tells the cpap the power rating of the supply. I've tested this on two units.

Steve

[player]

FYI:

I've found that the A10 will run from a +24 volt power supply (non-ResMed) when the center pin is connected to +3.3 volts thru a 2.7k ohm resistor. I use a +3.3 volt three-terminal voltage regulator fed from the +24 volt power supply. The resistor functions as a pull-up resistor to +3.3 volts and tells the cpap the power rating of the supply. I've tested this on two units.

Steve

Wow! You cracked it. Well done. How the heck did you figure that out?

[PoolQ]

+1
As usual what may seem like the "best" deal may not be. "12V Respironics DC battery adapter cable Respironics (Philips) $39.99' this is basically a USB cable with fewer wires and different connectors on the ends. Check the price of a USB cable and then figure the profit for that at $39.99

At least the Resmed cable actually boosts the voltage from 12V to 24V which is a switching regulator with magnetics in a box and not just some wire.

USB cable? Most certainly not. It is about an 18 or 16 ga wire w/ fused plug and two massive ferrite chokes to arrest RF interference (why? I don't know) and a very non-standard 7.4 mm coax barrel plug but it certainly NOT a USB cable. It should carry continuous 12 V at 15 amps. How would a USB cable do that?

And the purpose of the ResMed adapter? To me is seems to make more money for ResMed in that it is just as easy to come up with a 24 V battery as it is a 12 V battery. Well, at least as easy as it is to come up with two 12 V batteries. But teh benevolent jean-youses at ResMed make you still have to use their adapter even if you have a 24V battery. Because they made it that way. The real question is why did ResMed go non-standard. Why - I speculate it was solely to squeeze more money out of their customers, of course when they could do it themselves a WHOLE lot cheaper and more efficently.

Which is what I do with my Respironics and a 12 V 35 AH battery. And a charger. I do think that the Respironics assembly IS over priced (that's why I built my own) but it is nowhere as overpriced as the clusterfication that ResMed forces on people.

OMMOHY

I said it was "basically" a USB cable, as in meaning no electronics involved. As you described it fits my meaning exactly. The manufactured cost of that cable is close to a USB cable. To give them the benefit of the doubt lets say it costs $5 and they sell it for $40 provides them an 87.5% profit margin.

As for Resmed at least they have a boost converter in the cable.

Do they all want to make money on something that they sell very few of, of course.

Did they go custom connector and perhaps voltage to force the few that do this to spend more money, perhaps. My guess is that it is not really worth their time for the added revenue, even at that high profit margin. They do it to support their customer and to keep the unskilled customer from blowing up their CPAP and then claiming that it just caught fire in the middle of the night.

[surferdude2]

Computer motherboards running from ATX power supplies use a similar protection by feeding a common connection back to the PS to verify that all is well with the voltage prior to allowing it to be fully applied. It is common practice to use these power supplies in an outboard mode for other purposes, such as powering an external hard drive. When used in that mode, one ties down the signal line to the common line to fool the unit into fully powering up all output lines.

In the case of a Resmed unit, we may be left wondering if we are bypassing some important protective feature when we clamp the signal line with our own generation of the voltage signal. Could be, could not be, who's to say? Resmed tech opinion would be nice. Without a circuit schematic, we can't know for sure that we won't do some harm.

Dude

[justMongo]

Dude:
I guess we'll not be getting a SAM's Photofact manual on that!

[surferdude2]

It's likely ol' Howard would have had a problem there.

[sdb7802]

FYI:

I've found that the A10 will run from a +24 volt power supply (non-ResMed) when the center pin is connected to +3.3 volts thru a 2.7k ohm resistor. I use a +3.3 volt three-terminal voltage regulator fed from the +24 volt power supply. The resistor functions as a pull-up resistor to +3.3 volts and tells the cpap the power rating of the supply. I've tested this on two units.

Steve

Wow! You cracked it. Well done. How the heck did you figure that out?

1.) With the AC supply powered on and disconnected from the cpap; I measured +3.3 volts between center pin and common (outer shell) with a dc voltmeter.

2.) With the AC supply powered off and disconnected from the cpap; I measured 2.7k ohms between center pin and common (outer shell) with an ohmmeter.

3.) Using an oscilloscope, I verified that the signal on the center pin was the same whether being powered by the ResMed supply or my setup. No clipping or clamping was noted.

4.) I also varied the voltage and resistance until the error display came on. My tests on two units showed the voltage could range from 2.4 volts to 3.5 volts. The resistor could range between 2.3k to 3.55k ohms.

5.) I've tested both units (alternately) with my setup for 2 weeks.

I've worked in electronics for over 40 years and I know that just about anything can go wrong. Time will tell.

Steve

[surferdude2]

Good work Steve. Thanks for taking the time to do that and reporting the results. Now we may consider that the processor board of the flow generator has a simple logic chip that passes along a 3 volt D.C. potential to the signal wire unless the input voltage (24 volt) is higher or lower by roughly 20%. That's still a blind guess, since we still don't know what we don't know.

I doubt it would ever harm the equipment to provide a steady 3 volts to the signal wire and hook a 24 volt battery to the power wires (properly polarized). I wouldn't hesitate to do that to my own equipment but would caution others of the risk involved.

Dude