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My battery backup setup
The reason you use remote sensors vs just measuring voltage at unit is because voltage loss in the wires can give a false battery low result. By having the resistor as close to the supply as possible and a comparably higher resistance circuit the voltage drop from the wire is minimized and you get a truer result of what the battery condition really is.
I will give you an exaggerated example. You are trying to push 10 amps through 100 ft of wire. The resistance of the wire alone without looking at charts might be say 1 volt lower than at the source. so if sensing voltage at the unit, instead of 24 volts the unit now sees 23 volts, and it thinks the batteries are getting near depletion even though they are still in good shape. By using remote sensing, it still sees the true 24 volt condition of the source because it is not looking at the results of the voltage drop. It is using a sense line to get a truer result of the battery condition.
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But not needed.

It is there for padding the profit of the manufacturer. These systems don't need to be that complicated.

OMMOHY
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If you read their patent information you will find the reason for what they are doing and how simplistic it is. According to the patent, they have elected to include a fixed resistor inside the power supply brick that has different values for different power supply brick wattage ratings as follows:

1.0k ohms = 30 watt power supply
1.8k ohms = 60 watt " "
2.7k ohms = 90 watt " "
3.9k ohms = infinite watts available

Ergo, if no resistor is detected by the motherboard in the blower, it will not allow the unit to operate.

If a 1.0k ohm resistor is detected, the mobo will allow operation with components connected that will not exceed 30 watts.

If a 1.8k ohm resistor is detected, the mobo will allow operation with components connected that will not exceed 60 watts.

and so on...

That is the simplest and cheapest way they could incorporate some way for the power supply to tell the mobo how much wattage it was capable of delivering thereby making it possible for the processor on the mobo to determine and control how many accessories it would allow to be hooked up when the unit was being used. Simple and cheap, just the cost of a tiny resistor embedded in the power supply brick, a simple resistor bridge circuit on the mobo and a firmware change in the mobo processor.

It follows that the way to utilize these 3 conductor units with some 2 conductor power supply would require that that an outboard resistor of the proper value be connected between the center conductor and the outer braid of the 3 conductor cable. Obviously it should be the proper resistor to match the wattage of the power brick being used in order to maintain the safety feature provided by the new 3 conductor system.

All things considered, it seems like a good and reasonable feature since it prevents the user from overloading the power supply brick, which might result in not getting proper therapy. It also provides a degree of safety against overheating the power supply brick.

Dude
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That does not explain 47K ohm resistor value. I did not read anything like that on the s10. If what you say that line is for, why do you manually have to turn off humidifier and heated tubing when using there 12-24 volt converter. Instruction say you must turn them off yourself. If ir really did that function it would do it automatically. Also if it were looking for a resistor value, It would be just a resistor between center pin and outside. Not a voltage divider circuit.

Sense lines are not something new. Look at just about any Li-mh battery and and you will find 4 connections not just two. + and - like other batteries but also a ground and sense line. It brings both + and - sense lines separately. In 3 wire, the ground and - are combined.
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When you run the system from the 12-24 converter, you have lost the fixed resistor embedded in the power supply since it's no longer connected. That puts you on your own to take care not to connect excessive loads to the converter.

The voltage divider circuitry is inside the blower unit and on the mobo, not in the power supply. Consequently it can determine different values of the single resistor that is embedded in the power supply brick.

As for sense lines on batteries, they are generally connected to a temperature sensor inside the battery to prevent overcharging, which would produce dangerous heat levels.

Dude
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All passive components work with 5V dc and 3.3 Vdc, no sense feeding a PCB 24 Vdc to reduce both the voltage.

Someone to do this test in the S10 ?, I have a slight certainty that ResMed S10, 12 Vdc work without using the heated humidifier & hose.

I can not identify the PCB two pins Chip, can be a Zener diode.

If it Works with 24 V and 47 k, try 12 V and 20 K, it appears that your AS10 might work at 12 V if the Zener diode deceive.

Try if worked
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Well it gets more interesting, I have read that without any resistor the CPAP will not turn on-how does the DC-DC work without a resistor?
The resistor cannot be a sense resistor because there is little to no current in that lead, it cannot measure the voltage drop in the main power lead
They use 24VDC for the blow motor so they can drop the blow current in half and most likely for the heater also-again half the current. Perhaps this is to save money on MOSFETs or maybe they can get better control and response of the blower with the lower current.
There is obviously a resister in the unit to form a voltage divider because a large value resistor connected to the 24VDC line will work and you don't even need the 3 volt regulator, I am not at all sure that the CPAP could detect the difference between the different wattages when using a large resister because of the large steps between values at that range.
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(08-16-2016, 11:29 AM)Perchas Wrote: Someone to do this test in the S10 ?, I have a slight certainty that ResMed S10, 12 Vdc work without using the heated humidifier & hose.

If it Works with 24 V and 47 k, try 12 V and 20 K, it appears that your AS10 might work at 12 V if the Zener diode deceive.

My tests on three A10 units shows they require at least 22.3V to power up. Once you start the blower, it will run until you lower the voltage to 20.5V.

(08-16-2016, 11:29 AM)Perchas Wrote: I can not identify the PCB two pins Chip, can be a Zener diode.

Post a high res pic and I will try to identify the component. Which machine?

Just my personal opinion. My posts are not medical advice or a statement of fact. Please consult a qualified physician or other qualified medical personnel. Please comply with all applicable laws, codes, regulations, and protocols.
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I suspect there may be a resistor in the sense line circuit on the new version of the dc-dc converter since it is designed for the 3 wire system. I can't verify since I don't have one to measure. I also can't guarantee that the sense resistor values being used are the same as specified in their patent application. They may have elected to use different values and even use a different method of detecting those values but the process is basically the same. Let's face it, how else can a power supply brick communicate its wattage capability in such a simple manner and make for a simple detection method?

Dude
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Just an FYI: I've verified that the +3.3V regulator and 2.7k ohm series resistor circuit is actually present in the Resmed AC supply, the Resmed 12 to 24 volt converter, and the BPS 24 volt converter.
Just my personal opinion. My posts are not medical advice or a statement of fact. Please consult a qualified physician or other qualified medical personnel. Please comply with all applicable laws, codes, regulations, and protocols.
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