(06-13-2016, 08:15 PM)sdb7802 Wrote: The S9 is different from the A10. It has a different input connector and requires a different dc converter.
You can find the A10 dc converter pdf here: google "directhomemedical airsense-cpap-dc-cord-instructions-for-use.pdf"
Thanks for that information that the S9 is different than the S10 even though they're both 24VDC.
I should have realized they'd make each power supply even more non standard, since the basic rule of Marketing is to turn a commodity into a monopoly.
Given there is no (good) reason in the first place for the power supply to be non standard, I should have guessed that would be the case.
(06-13-2016, 08:16 PM)OMyMyOHellYes Wrote: Is the discussion past the point, in terms of required effort, of making the expensive resmed power box look attractive?
1. There is never harm in UNDERSTANDING how things work.
2. There is USEFUL INFORMATION in Steve's tests of his equipment
3. When you design things, you learn even more stuff, so, designing both the simple and the idiot-proof system has merit.
However, I do agree that the simpler the system, the more it is likely to be built, so, we can only idiot-proof the system so far.
For example, the Schottky Diodes and 24VDC regulators are more for idiot proofing than they are required, based on Steve's input-voltage tests.
If we assume that the only ones who will actually build the circuit are "tinkerers", then the idiot proofing is more of an intellectual exercise than it is a requirement.
The main requirement is pretty simple:
1. The 2.7K Ohm pull-up resistor & the 3.3VDC "logic 1" sense circuit
2. The 24-volt (nominal) 3.75Amp power supply
Besides, if the simple circuit actually fails, then it makes the otherwise lousy decision of buying the expensive non-standard ResMed equipment easier to swallow.
(06-14-2016, 12:03 AM)PoolQ Wrote: The patent says they use the resistor to indicate the 90W power supply verses the smaller wattage one.
We don't know yet if ResMed even offers any other power supply other than the 90W power supply (i.e., 2.7K Ohm pull-up resistor), do we?
(06-14-2016, 12:03 AM)PoolQ Wrote: They simply have a resistor to ground inside the CPAP machine, say for example another 2.7K to ground. If the 90 Watt power supply is plugged in then a comparator will detect that 3.3VDC/2 is on the pin, if the lower wattage supply is powering the CPAP then the pin will have 3.3VDC and won't turn on the humidifier.
The patent did imply it was simple analog circuitry that detected the value of the pull-up resistor, and the patent did say that they prioritize power to the blower during the inspiration cycle based on the perceived power available.
(06-14-2016, 12:03 AM)PoolQ Wrote: They could also be trying to keep you from using anything but their power supply by using two different resistor values so "some" resistance must be there to work. They could have just used ground center for one wattage and 3.3VDC for the other wattage and not put any resistor in the circuit.
They will never say it, but they're happy to have a non-standard power supply because that means you have to purchase your 24 volts from them.
ResMed marketing managed to turn a 12volt commodity into a 24-volt monopoly.
Kudos to their marketing team; they did their job admirably well.
(06-14-2016, 12:03 AM)PoolQ Wrote: When customers mess with the power you really want to know if the machine burned up using the factory supply or some cobbled together home brew solution. Warranty impact you know.
First off, it's just a 24VDC power supply, for heaven's sake.
And it's just a simple 3.3Volt (2.7K Ohm) sense circuit, for heaven's sake.
As long as the voltage and current and resistance is within acceptable ranges, the equipment will not be harmed. (Of course, the acceptable range limits are what we strive to better understand!)
Resmed simply tried to put a patent on a basic power source, that's all.
Their marketing guys managed to turn a 12V commodity into a monopoly.
That's their job; and they did it well. I admire that they were smart enough to pull it off.
However, if anyone is really worried about using this circuit, then they should not use this circuit. It's a pretty simple decision.
If someone doesn't trust that 24 volts is 24 volts (or that the range is too great for the equipment to handle), then they shouldn't even THINK about using this circuit!
Remember, we're just talking about 24 volts, 3.75 amps, and 2.7K ohms, where ResMed doesn't own the rights to those values.
If someone is so worried about this circuit, then either they don't understand volts, amps, and ohms, or, they don't understand what the equipment does - or - they aren't the right person for this circuit.
Let's be clear. MOST PEOPLE ARE NOT the correct people for this circuit.
Maybe 1 in 1,000 are the correct people for this circuit.
a. Most people don't understand volts, ohms, and amps.
b. Most people don't build circuits
c. Most people would be AFRAID of this circuit
And, all of us are worried about the RANGE that the equipment can handle (since the input voltage from two batteries WILL vary).
So, this circuit was never intended for MOST PEOPLE.
It's for "tinkerers".
That's 1 out of 1,000, at best, don't you think?
(06-14-2016, 10:31 AM)OMyMyOHellYes Wrote: T'would all be so much more simpler if all manufacturers just used a 12 V system (or even 24 V) with standard plug configurations (with center the pwr side and outer barrel the gnd side) on everything. Their unnecessary complications lead my cynical side back to the follow-the-money theory.
But then they couldn't charge you about $100 ($85 + $15 for cables) for a simple power supply!
Simple MARKETING 101.
You need to turn a commodity into a monopoly.
They've essentially turned a 12Volt commodity into a 24-volt monopoly.
That's great marketing.
And, like with all manufactured monopolies, the people who lose are the consumers and the people who win are the manufacturers.