My battery backup setup

[sdb7802]

I think this will work. I would use a 5% resistor.

   

As shown, I would add a 0.1uF 50V ceramic monolithic capacitor between the regulator input terminal and its ground terminal. Repeat for the output terminal. This is necessary for proper regulator operation.

[verbatim1]

I think this will work. I would use a 5% resistor.

Thanks for updating the "schematic" for the ResMed home-grown 24VDC power supply with 90Watt sense circuitry.

So that everyone can leverage your efforts, here's my update to your update, for your review for accuracy.

As shown, I would add a 0.1uF 50V ceramic monolithic capacitor between the regulator input terminal and its ground terminal. Repeat for the output terminal. This is necessary for proper regulator operation.

Thanks Steve for explaining that, as the PDF for the MCP1804T showed only one circuit diagram, but that circuit diagram was for a 5-pin device, so I couldn't figure out how to translate the capacitors in that circuit schematic to the 3-pin device!



REFERENCES COLLECTED TOGETHER:

• ResMed Battery Manual (http://www.resmed.com/us/dam/documents/a...lo_eng.pdf)
  
• Microchip Voltage Regulator Datasheet (http://ww1.microchip.com/downloads/en/De...22200C.pdf)
  
• ResMed Patent Description (http://www.google.com/patents/US20140366876)
  

PS: Do you think this circuit is "cleaner" (with respect to EMI) than the ResMed up converter, which has to chop the 12VCD into square waves, and then transform those square waves to 24VAC and then to rectify them back to DC?

[justMongo]

Do I see an error in the resistor color coding?
2.7k, 5% should be Brown, Blue, Brown, Gold ?

Edit, yes, I am incorrect on the color code.

[sdb7802]

Thanks Mongo. I saw it as a generic resistor.

Verb, the color code is red violet red gold.

You can use this pic in your diagram if you wish.

   

[sdb7802]

PS: Do you think this circuit is "cleaner" (with respect to EMI) than the ResMed up converter, which has to chop the 12VCD into square waves, and then transform those square waves to 24VAC and then to rectify them back to DC?

Yes, it's cleaner than the converter but the A10 generates its own EMI with its internal switching power supply, motor driver, heater pwm, microcontroller, and logic circuits. That's part of the reason for the ferrite beads on the ac power supply and dc converter.

Personally, I wouldn't worry about it. Unless you notice UAVs circling your tent. They could be homing in on the EMI.

[verbatim1]

Thanks Mongo. I saw it as a generic resistor.

Verb, the color code is red violet red gold.

You can use this pic in your diagram if you wish.

Thanks for the correction.

We should make this as obvious to everyone as possible, so, it's GREAT that you found the resistor colors for others to match who haven't learned the decidedly politically incorrect resistor-color-code mnemonics we all learned ...

The way we've drawn this, it should provide a visual impetus for other people to try to build their own, given that we didn't draw it like a schematic but like the real thing would (sort of) look like.

As always, here's the corrected image, asking again for a review, so that we can leverage to everyone the combined knowledge here).

[sdb7802]

Looks good.

[verbatim1]

Looks good.

Thanks Steve for vetting that latest diagram.

Moving on to the analog sense circuitry, I noticed in the patent application that they extol the virtue of the fact that they use cheap analog sensing to figure out what the resistor value is.

It's actually not obvious to me HOW they sense the resistor value.
Do you think they might simply sense the RC time constant, as shown below?

If so, then the value of the capacitor could be critical.

[PoolQ]

jumping in here, this is interesting and sorry I did not read it sooner.
That diagram does not show an RC circuit, you will never pull down that 3.3V regulator through that 2.7K resistor.

Easy way to tell the resistance value is to have another resistor (to ground) inside the CPAP that makes it a resistor divider. the voltage at the center of the two resistors will tell you the value of the resistor with good accuracy.

[verbatim1]

jumping in here, this is interesting and sorry I did not read it sooner.

Thank you for caing about improviing our knowledge of how the non-standard power-supply-sensing circuitry works!

I asked the time-constant question because it "might" be that the capacitor value is important to the ResMed machine, "if" it affects the ResMed analog resistor-sensing circuitry.

That diagram does not show an RC circuit, you will never pull down that 3.3V regulator through that 2.7K resistor.

Thank you for pointing my error out as it explains something I was confused about.

1. When I first calculated the RC, I used this straight calculator, which only asked for a single voltage value (in addition to the R and C values):
[*] http://www.referencedesigner.com/rfcal/cal_05.php

2. However, when I displayed the graph, I used a different calculator which asked for TWO Voltages as shown below:
[*] http://ladyada.net/library/rccalc.html


This "assumes" that the center pin has 24VDC on it when the device is in use, which may or may not be the case (impossible to know without testing it using a "shunt" of some sort).

Easy way to tell the resistance value is to have another resistor (to ground) inside the CPAP that makes it a resistor divider. the voltage at the center of the two resistors will tell you the value of the resistor with good accuracy.

Thank you for the additional information. All I know (from the patent) is that they:
[*] Use cheap analog circuitry
[*] To sense the resistor value (2.7Kohm indicating a 90W power supply)

My question is whether the 0.1uF capacitor might "affect" that calculation.