Understanding ResMed A10 24V Battery Power & Sense Circuitry

I just don't have the social skills to deal with stupid people.
If all engineers and scientists were as stupid as the people here appear to be, we'd all still be sailng naos and caravels.

Cop out as usual.
You don't need anything special in the way of social skills not to make death threats and to be polite.

I have worked with scientists and engineers most of my working life as a software developer. A lot of them had social skills issues BUT you my friend are faking it.

I see that verbatim has tremendously improved his contribution to this thread... except that stupid drawing is still at the front. isn't even CLOSE to the diagram in the patent.

As a service to those who are highly competent (such as all engineers and most scientists should be), the latest schematic binaries are provided below.

• 30KB DipTrace schematic with Schottky Diode (schematic1.dch)
• 30KB DipTrace schematic with Schottky Bridge (schematic2.dch)

These schematics were created using the DipTrace schematic editor (which is freely available on both Mac and Windows).

I'm not the smartest guy with Electrical things, and I don't understand a couple of .1 uF capacitors in the diagram. Please offer a bit of "coaching":

The capacitor along +24V (placed near the 3.3V converter device). Q1, Doesn't the battery itself provide adequate 'filtering'?
And WRT both Capacitors, Q2: why can't they be placed 'inline' (along the +24V and 3.3V wires respectively) rather than "leaking" some power out to Ground?

Thanks in advance, for teaching me about this.

awaitingUserActivation wrote:I'm not the smartest guy with Electrical things, and I don't understand a couple of .1 uF capacitors in the diagram. Please offer a bit of "coaching":

The capacitor along +24V (placed near the 3.3V converter device). Q1, Doesn't the battery itself provide adequate 'filtering'?
And WRT both Capacitors, Q2: why can't they be placed 'inline' (along the +24V and 3.3V wires respectively) rather than "leaking" some power out to Ground?

Thanks in advance, for teaching me about this.

https://en.wikipedia.org/wiki/Decoupling_capacitor

that said, 'verbatim' knew less than you, and came up with a hugely overengineered solution, where a resistor would work.

awaitingUserActivation wrote:I'm not the smartest guy with Electrical things...

Then you really shouldn't be messing with this. He was trying to decipher an undocumented interface because he felt ripped off by the need for an $85 24v dc adapter. While it is a bit overpriced, the ResMed converter is high quality, seemingly very efficient, provides a clean power source and for most people is absolutely the way to go. Why you would want to build this device and risk your cpap, especially if you're not an electrical hacker, is beyond me.

BTW, "verbatim" went to another forum where he enlisted others to help with the design. It was built, tested briefly, but verbatim was never heard from again!

If you want help running a cpap from a battery, start a new thread for that. You can check out the link in my signature.

I recently put together a Converter Unit for "11-15VDC to Resmed 24V + 3.3V", and it works great. It is massively overbuilt, including a 24V regulated output "Boost Converter"; a mini-board "Buck Converter" (for conversion back to 3.3V), a big electrolytic "Filter Capacitor" (similar to the one included in Resmed AC-DC Power Supplies); the notorious 2.7k-Ohm resistor; and a pilfered Resmed 24V CPAP Supply cord (tri-axial connector on one end, big chokes on both ends).

It was not cheap to assemble. I created a new Thread, which I hope to be reserved only for discussion of my PSU, here: viewtopic.php?f=1&t=156100&p=1187797#p1187797

Thats exactly the thought I was having. The issue with using the battery directly is that its a little to high when fully charged and a little to low when partially discharged. I ended up buying a laptop adapter that can run from 12v DC or 120v ac. It is capable of being set to 24v output at 120W. I ended up coming up with the same information that people figured out here by simply opening up the power adapter (its screwed together with four small screws hidden under the rubber feet rather than glued or sonic welded like most are) Mine is an S9 (the power supply works the same) so I had to get the correct plug. Its actually quite common and used on various things like flat panel displays and camera equipment.) Its often called a "power DIN" but its not really a DIN at all. Its called a "Snap and Lock" connector. by a company called Kycon. The three pin variant that the S9 uses is part number KPPX-3P . CUI makes a clone of it with the part number PDP-30. I ended up getting a no name Chinese clone of it from Ebay for 2 bucks. (Mouser and DigiKey would have had them to me in a few days ,but I had to wait a month to get the one from Ebay, but it was dirt cheap and I was in no hurry)

The S9 power supply is nothing special. Its made from parts from NXP and ST and and is very similar to the NXP reference design.(Presumably the A10 is similar, but I haven't opened one of those) The third pin is also nothing special. Laptops supplies are similar. Usually its a resistor between the third pin and ground to indicate the power rating of the supply. In the case of the Resmed supply, there is a 3.3V linear regulator connected to the third, smaller pin through a 2.7K resistor. (the value of the resistor indicates the rating of the supply). I just used a little 3 terminal regulator in a SOT23 package (Diodes incorporated ZXTR2012FF, soldered directly to the pins inside the connector,along with little surface mount capacitors and a little 2.7k resistor. IT works perfectly.

thanks, mrussell, for your input.

could you, please, send some pictures of your setup?

thanks

Hi,

An excellent article (despite the external noise). I am wishing to re-plug a 12V Resmed original DC-DC supply for the Resmed 8 to use on a Resmed 10. Can you tell me the name / type of the cylindrical plug that I need for this 'conversion'?

Regards
BernieG

zombie thread alert.