Understanding ResMed A10 24V Battery Power & Sense Circuitry

while I eagerly await the youtube video where you plug your abomination into your Air10, and promptly let the magic smoke out, it's only proper of me to say "DON'T DO IT!" (mainly to other people).

I do wonder what component will go bang first... please do post video.

For those technically competent few who can benefit from this information, here is the binary schematic for the 24VDC power & 3.3VDC/2.7K Ohm sense circuit listed in the OP.

We have added an optional 10Amp Schottky Diode Bridge so that the wires can be hooked up backward or forward, and the equipment will still work just fine.

The schematic was made using the freeware DipTrace schematic editor on Windows and Mac.

• Design with optional Schottky Diode (schematic1.dch)
• Design with optional Schottky Bridge (schematic2.dch)

verbatim wrote:Specifically, how do you test your own power supplies so that they won't electrocute your customers or burn their houses down?

Batteries don't have infinite power like your wall outlet.

Faulty grounds and bad isolation electrocutes people. Batteries are floating and aren't grounded, so neither of those is going to be an issue.

Perhaps a basic electronics course is in order, before you accuse the OP's circuit of being a fire hazard death trap.

verbatim wrote:

palerider wrote:while I eagerly await the youtube video where you plug your abomination into your Air10, and promptly let the magic smoke out, it's only proper of me to say "DON'T DO IT!" (mainly to other people).
I do wonder what component will go bang first... please do post video.

With Dunning/Kruger in mind, you seem to have not read (nor comprehended?) the last line of the original post, so I suggest a quick remedial reading of the first post in its entirety.

oh, it's easy to comprehend, it's a plea of "don't tell me I'm stupid, just play along"...

only, I'm not interested in playing along.

K8TEK wrote:

verbatim wrote:Specifically, how do you test your own power supplies so that they won't electrocute your customers or burn their houses down?

Batteries don't have infinite power like your wall outlet.

Faulty grounds and bad isolation electrocutes people. Batteries are floating and aren't grounded, so neither of those is going to be an issue.

Perhaps a basic electronics course is in order, before you accuse the OP's circuit of being a fire hazard death trap.

among verbatim's other excursions from reality, his latest fantasy seems to be that that I manufacture power supplies... *scratching head*

'''⌐(ಠ۾ಠ)¬'''
While the Schottky Diodes are only 75 cents (so the bridge isn't expensive), if someone doesn't want to use the diode bridge, here's a slightly simpler circuit for the benefit of the technorati:


Steve has tested these circuits to work on a variety of A10s.
The quotes below are for those technical enough to understand and assess the information provided.
If you've never designed your own power supply, this information is likely not for you.
It's for the 1 out of 1,000 people who understand such things (which is basically all engineers and most scientists).

sdb7802 wrote: To check the power capacity without a sense circuit, you would have to measure the output voltage under maximum load current. You could attempt to max out the current by maxing out the blower, heater plate, and tubing heater. For the blower to draw max current it would need some type of switchable flow limiter for the test. Or you could use a switchable dummy resistive load on the power input. Either way costs money and could possibly fail and inhibit normal operation.

So, ResMed apparently choose "the resistor to 3.3V" method to "check" for the 90W power rating. If the the voltage level or resistor value is not correct the machine will not work.

My tests on two units showed the voltage can range from 2.4 volts to 3.5 volts. The resistor can range between 2.3k to 3.55k ohms.

Some older Dell and Thinkpad laptops use a coded signal (a one-wire bus) to check the power supply. But they just issue a warning and don't shut down the machine.

I guess we should be grateful ResMed made it so easy to work around.

sdb7802 wrote:
1.) I ran input voltage tests on 3 different A10 AutoSet units. The maximum voltage I was willing to subject the machines to was 30 volts. With the blower running, all of the units function normally as the input voltage is varied between 20.5 and 30 volts. Below 20.5 volts, the machines shutdown completely and restart as the voltage is increased to 22.3 volts. The machines were tested while configured with a minumum load (4cm pressure, humidifier off, tubing heater off) to a maximum load (20 cm pressure, max humidification, max tubing temp). Fixed pressure and APAP modes were tested. Flow restriction was also varied.

From an unpowered state, the machines require at least 22.3 volts to power up to the standby (blower off) mode.

Input Voltage Range (to power up): 22.3V to 30V
Input Voltage Range (blower off/on): 20.5V to 30V

Machine variation: -3%

I'll look at the battery manual to see if the batteries can meet these specs.

2.) I think a 10A fast-blow fuse will work fine.

3.) I would change the 3.3 volt regulator to a LM2936Z-3.3/NOPB. This part has a 40V breakdown voltage which provides a greater safety margin than the 28V part. It is available in a TO-92 case which is easier to work with. Need to change the caps for this new part. I'll look into that.

4.) I like the idea about the schottky diode bridge for protection. I'll round up some part numbers.

palerider wrote:while I eagerly await the youtube video where you plug your abomination into your Air10, and promptly let the magic smoke out, it's only proper of me to say "DON'T DO IT!" (mainly to other people).

I do wonder what component will go bang first... please do post video.

The forum bully has arrived.

verbatim wrote:

palerider wrote:oh, it's easy to comprehend, it's a plea of "don't tell me I'm stupid, just play along"...
only, I'm not interested in playing along.

If only it were true that you would just go away, this web site would be immensely grateful to you for leaving.

The problem with Palerider is that (it) hasn't grown up yet, mentally.
(I don't know if Palerider is male or female so I'll just call it an it because it adds no value anyway.)
Basically, Palerider is a troll who is stunted at about the elementary school level in mental development.

The problem with dealing with such trolls is that they will destroy a thread no matter WHAT you do - because that's what trolls like it absolutely love to to.
They THRIVE on destroying the content of a thread.
It makes them feel ALIVE to destroy a thread.

It is no different than any other troll.
The only difference is that it is here.

• Never adding any value (just look and see what lack of value it adds in multiple posts to this thread)
• It ruins everything it touches
• It can only naysay; it can never add any technical value whatsoever to this thread.
• It can't even describe where the EMI is coming from that it decries, nor how you're going to get "electrocuted" from a 24VDC battery (given megaohm resistance across your SA node via the skin), etc.

Fundamentally, it adds no value because it can't add value.
It is a troll.

There are basically three ways to deal with the troll:

• Don't feed the troll (in which case, it will eventually go away - but it will destroy the thread before doing so - because THAT is what energizes it)
• Mock the troll's very words (this is so easy to do that you'd think the troll would get it - but remember - the troll is stunted in development - so the mockery is only seen by others - not by the troll itself)
• Get into heated pitched battles with the troll (which is EXACTLY what the troll wants - since the troll feeds off of the attention paid to it).

However, due to the nature of trolls, the troll will ruin the thread in any case.
That's because it takes no intelligence to ruin a thread - which is all the troll can do.
And because the troll THRIVES on ruining any thread it touches.

One other thing, common to such trolls, is that they must have the last word - and - again - like a crying child in an library where others are trying to get something done - you have to let the troll have the last word.
Which it will.

Agree 100%, should be a block feature on this forum.

lordvader wrote:Agree 100%, should be a block feature on this forum.

well, your prayers have been answered... click on my smiling pic, and then "add foe". just don't farce choke me, m'lord

verbatim wrote:

palerider wrote:oh, it's easy to comprehend, it's a plea of "don't tell me I'm stupid, just play along"...
only, I'm not interested in playing along.

Verbatim wrote: "If only it were true that the troll would just go away, this web site would be immensely grateful to the troll for leaving."

Verbatim,
I'm not part of this debate, just curious why you are speaking for this website having just joined the forum or do you have another stage name?

▄︻̷̿┻̿═━一 ¦̵̱ ̵̱ ̵̱ ̵̱ ̵̱(̢ ̡͇̅└͇̅┘͇̅ (▤8כ−◦

K8TEK wrote: Batteries don't have infinite power like your wall outlet.

I realize you were responding to someone else, who clearly doesn't understand even the simplest of basic electrical circuits.
However, I will take this opportunity to mention that the word "mains" was used in the diagram in the manner that ResMed used the word in its patent application.

• Power management in respiratory treatment apparatus US 20140366876 A1

In the patent description, ResMed explains that they "plan" on prioritizing power in the future for the inspiration cycle over the less immediate needs of the heater and humidifier, but it's shockingly clear that this goal has absolutely nothing inherently to do with the non-standard 24volt supply, nor the 3.3-volt "logic 1" signal.

It doesn't even have anything CURRENTLY to do with the 2.7 Ohm sense resistor, which is patently obvious to everyone once they read the patent description and then compare that over arching description with the very limited set of power supplies that hat ResMed actually currently builds.

In summary, there are various claims made in the patent, with respect to:

• logic 1
• sense resistor
• inspiration priority

Some of which are NOT implemented in the current ResMed equipment!

The 3.3 volts DC merely acts as a "logic 1" to the device (where 0 volts would be a logic zero). That is, if the device is attached to a perfectly good power supply that does not have the 3.3 volt "logic 1" signal, the ResMed device will refuse to work, even though the power could be better and certainly far cleaner than that which they supply in their own power supplies.

In addition to the 3.3VDC "logic 1", there is also a wattage-indicating "sense resistor" in the center communications line.

The patent calls the pull-up resistor optional, when it says "optionally, a pull up resistor may be implemented to code information about a component coupled with the bus such that different resistors may indicate different components or different component functionality".

In my 90Watt ResMed power supply is a 2.7K Ohm pull-up resistor embedded in the central communications line of the power supply whose value is sensed by the "analog sensing elements of the transceiver" master controller.

Basically the patent explains, in words, the circuit used, as it says "if the pull-up resistor represents the type of power supply, a detection of 3.9 K ohms may be interpreted by a master controller that the power supply is an infinite supply (mains).".

The patent goes on further to say "A detection of 2.7K ohms may be interpreted as a 90 Watt power supply.", which, incidentally, is the wattage of "my" 24-volt power supply (and, apparently, the ONLY power supply that ResMed builds, as far as anyone has stated in this thread).

Additionally, they outline that "a detection of 1.8K ohms may be interpreted as a 60 Watt power supply" and that "a detection of 1.0K ohms may be interpreted as a 30 Watt power supply" (which is approximately a linear progression of about 1K ohms per 30 indicated Watts).

Presumably the ResMed devices doesn't need to prioritize power to the inspiration cycle when the full-wattage power supply is used, and presumably a varying amount of inspiration prioritization of power needs to be applied for the progressively lower power supplies (none of which actually exist, as far as anyone has indicated in this thread).

So, ResMed apparently implemented "just enough" of this patent description to make their power supplies non standard, but not enough of this patent description to actually implement all the "good things" that the patent describes are possible.

There are other oddities about this patent description. For example, I find it odd that these actual numbers are listed in a patent, simply because there is nothing whatsoever inherent in the resistor values that decrees the indicated wattage, especially considering patents are generally rather purposefully vague on such essentially-meaningless intrinsic values.

In keeping with patent generalities, the patent does state the all-inclusive obvious, which is that "other voltage levels and coding schemes may also be utilized to code information about the power supply unit in this analog manner. ", so, that bolsters my surprise that they bothered to list the actual resistor values.

As would be expected, in addition to the analog resistor sensing, the patent does vaguely mention that "optionally, digital messaging may also be utilized to detect information about the power supply unit or other components of the bus. ", which simply means that the patent is trying to garner rights over putting "anything" in the power supply line to provide once-removed information about said power supply.

Of course, a digital signal presupposes a "smart" power supply, which is exactly what they hint at when they mention in closing that "a data message with information from circuits or memory of the power supply unit or based on signals from the detectors or sensors of the power supply unit may be sent from a processor of the power supply unit to a system level controller or processor.".

It should be noted that I don't see anything in this patent application which is novel. Even my old Thinkpad laptop had a sensing line, as do Dells and other laptops. The only thing novel is their specific choice of sensing resistors (which is meaningless in the larger scheme of things).

/X\('-')/X\

K8TEK wrote: Faulty grounds and bad isolation electrocutes people. Batteries are floating and aren't grounded, so neither of those is going to be an issue.

Anyone who has taken physiology knows that the sinoatrial node (aka, the SA node) is the "pacemaker" of the heart and, as such, it is what is most sensitive to the 50Hz or 60Hz frequency of the mains voltage of 120VAC or 230VAC (depending on where in the world you live).

Given the resistance of your skin, when you touch the mains, there is plenty of voltage to "overpower" your SA node, such that your heart is depolarized and polarized at a rate equal to the frequency of the mains, which is unsustainable in a human heart. What happens when the voltage is removed is that your heart, if it's not badly burned by the heat of the current flow, will almost invariably go into ventricular fibrillation (aka vfib). Without a defibrillator or other (physical) shock to "restart" your heart, your chances of surviving vfib are slim.

However, again given the resistance of your skin, when you touch a 24 volt battery source, there is generally NOT anywhere near enough voltage across your SA node to depolarize your heart. If, of course, you were to vastly reduce the resistance by puncturing the thumbs of each hand such that they each bled, and then you were to hold your thumbs across a typical AA-cell battery, there would be PLENTY of volts across your SA node to overpower your heart. Your heart would beat at exactly zero volts, which would render you unconscious in short order.

If the heat of the current flow didn't badly burn your heart in the process, when you fell down unconscious, you would likely drop the battery, and there is a good chance your heart would spontaneously start up again, because you would likely not have gone into vfib.

While these aren't experiments you should try, the point is that, in general, 24 volts DC is not enough voltage to "electrocute" someone, unless they tried real hard to be electrocuted.

On the other hand, the amperage available by either the mains or a typical 12VDC battery certainly is sufficient to cause enough heat to start a fire, but anyone who knows anything whatsoever about electricity knows enough to properly fuse and insulate a 24VDC circuit such that the risk of fire is less than the risk of being killed in a shopping cart accident at the local supermarket.

In fact, anyone who is THAT worried about the risk of fire has absolutely no business even READING this thread, let alone making dire statements about the risks involved in building a simple power supply (which is something millions of people do all the time, including most engineers and many scientists).

verbatim wrote: Most people here (and everywhere) do NOT wish to wade through your off-topic banter and that of the troll above, just to try to learn more about how the power supply sense circuitry works.

So let's delete these two highly off topic posts, shall we?

Please do not assume that you speak for most of us. I see 3 different threads for basically the same topic. Very few people actually participating. And I can't figure out what the actual goal is.

Are you trying to make something cheaper than what is available? How will it be better than what is available? What is the purpose of reinventing something that is already available and seems to do the job properly? Why would somebody want to risk destroying their cpap machine?

How is any of this discussion useful to the people on this list? Are you making something we can buy? How many people here are going to actually make one of these?

♞▀▄▀▄♝▀▄