ResMed S9 with 4S LiPo Battery and DC/DC Converter??

[GTSSportCoupe]

Hi All. I am new here. I'm an electronics designer trying to help my cousin build a portable battery setup for his ResMed S9 CPAP machine. He needs a very light weight and efficient setup that will last for five days. He will be hiking part of a very long scenic trail and has been hired to do landscape painting along the way.

I had planned on simply using a generic DC/DC converter with some 4S 16Ah (12V-16.8V) LiPo Battery packs. As I've discovered reading here, the ResMed S9 units have an intelligent data bus in their power plugs, and thus only work with ResMed power supplies.

So, back to the drawing board as they say!

Easiest option would be to buy the ResMed DC/DC Converter (intended for 12V or 24V DC lead acid batteries). However, I'm unsure if these adapters will accept the voltage range of the LiPo Battery packs we bought (LiPo 4S 12V-16.8V range). I'm hoping someone with the adapter would be able to tell me if this is possible?

Second option would be for me to find an efficient inverter (that can accept the LiPo battery voltage input) and simply plug-in the ResMed AC Adapter. This is undesirable as it is less efficient. My understanding is the 90W adapter wastes a lot of power.

Third option is I could buy a used ResMed AC Adapter, rip it apart and use only the 'smart' component to trick the ResMed S9 into thinking I'm using an AC Adapter, but really I will piggy back my generic DC/DC converter on it to supply power.

Fourth option is to reverse engineer the ResMed power converter data bus and design my own circuit to talk to the ResMed. But I really don't have the time to do this right now, as I need to complete this in the next week or so.

Looking for any ideas. Most specifically if the ResMed DC/DC converter will work with the LiPo 4S (12V-16.8V) input. I'm concerned it will get confused as it is looking for specific lead acid battery voltage ranges. However, if it does accept this input, I'll buy the DC/DC converter immediately and use it.

I saw a few technical threads on here, hopefully some of those guys can chip in with some info. I will share what ever I discover with this.

I bought five of these batteries:
http://www.hobbyking.com/hobbyking/stor ... ouse_.html
This DC/DC converter:
http://www.digikey.ca/product-detail/en ... ND/5931170
This charger:
http://www.hobbyking.com/hobbyking/stor ... arger.html

[GTSSportCoupe]

Thinking out loud here.

Perhaps what I'll do is purchase the ResMed DC/DC converter. I'll use my 24V DC/DC converter to provide 24V input to the ResMed converter. Two DC/DC converters in a row is not as efficient, but probably not that bad at the end of the day. The one I bought is 92% efficient. This way the ResMed unit will get the 24V it wants.

I may try the ResMed DC/DC converter with the LiPo 4S voltage range though (with a current limiting power supply to prevent potential damage of course), who knows; maybe it will work.

For those who may be concerned about LiPo battery safety, the LiPos will be stored in a hardshell case to prevent any sort of puncture etc. Every thing is fused. We have a suitable smart charger. There is a low voltage alarm slash voltage monitor for the LiPos to make sure we don't under charger them.

I'll provide some details on the setup when it's finished.

I'd still love to hear some thoughts and input though! Any techies out there with these things?

[CapnLoki]

Lots of stuff here - First, I've never heard that the 12/24 converter is inefficient, I've always guessed 90%. I've assumed it handles any voltage between 12 and 24 but could be wrong.
Instead of LiPo why not LiFePO4? You can get a 4S pack with BMS that has a good 12v output.
Or, get Philips 560 apap that runs on 12v and use that as a travel/backup machine?
More thoughts later...

Sent from my SM-G900T using Tapatalk

[Perchas]

Research the charging system Iphone and Ipad, use the same technique, the solution is very easy
I also found that Respitonicis fed 12 VDC. if the humidifier heater or the hose is not used CPAP consumes only 500 mA (0.5 Amp (5W), if heated you need 55 W or 5 Amp.

The solution, find it by Apple chargers. feeding a third wire with 2 V and it can be fed with any charger other than Apple

http://www.extremetech.com/computing/11 ... smartphone

Basically, it looks like wall chargers communicate to the device that they ARE a wall charger by shorting the data lines (D- and D+). When the device sees shorted data lines, it knows that it can draw up to 1.5A -- that's what the Battery Charging Spec dictates.

If the Touchpad doesn't do that, then my guess is that HP isn't implementing the spec exactly. Apple used to negotiate amperage by communicating using the power supply (2V = up to 1A, 2.5V = 1.5A, or whatever). Maybe HP is trying something like that.

Would guess that the older smartphones don't implement the Battery Charging Spec.

The spec says they only *have* to source 0.5 A, and then they can drop the voltage to 2 V, and then shut off.

[yaconsult]

Why not pick up a respironics machine as a travel machine/backup? Unfortunately, you missed a recent sale by our sponsor that was selling them brand new for $310. They are also available on amazon.com. And some members here probably have suitable machines for sale. Respironics run on 12 volts and only Resmed uses 24 volts.

There was a recent thread here that included a schematic to build an adapter that supplies the signal that the resmed unit requires to run off batteries - use the search function.

[GTSSportCoupe]

Lots of stuff here - First, I've never heard that the 12/24 converter is inefficient, I've always guessed 90%. I've assumed it handles any voltage between 12 and 24 but could be wrong.
Instead of LiPo why not LiFePO4? You can get a 4S pack with BMS that has a good 12v output.
Or, get Philips 560 apap that runs on 12v and use that as a travel/backup machine?
More thoughts later...

Sent from my SM-G900T using Tapatalk

Thanks for the reply! Good to know the ResMed DC/DC Converter is likely decently efficient!

We got the LiPo's for a good price ($50USD each) - the primary reason we bought them.

Yes, a different machine might be a good option, but I'm out of time for that now. Certainly something we'll look at for the future.

I just read part of a thread on another forum where they were discussing the power adapter interface for the ResMed A10. I don't know if it is the same for the S9 or not. The guys there reverse engineered the interface. It is a simple analog voltage read by the CPAP machine to identify the power capability of the power adapter. From what I've read, I get the feeling the S9 uses an intelligent digital interface though. Correct me if I'm wrong, as I'd love to simply use the analog voltage method.

Here is the thread where I was reading about the analog interface in the A10: http://www.apneaboard.com/forums/Thread ... tup?page=7 (read the pages after this one too....)

[GTSSportCoupe]

Why not pick up a respironics machine as a travel machine/backup? Unfortunately, you missed a recent sale by our sponsor that was selling them brand new for $310. They are also available on amazon.com. And some members here probably have suitable machines for sale. Respironics run on 12 volts and only Resmed uses 24 volts.

There was a recent thread here that included a schematic to build an adapter that supplies the signal that the resmed unit requires to run off batteries - use the search function.

No time to buy another unit now unfortunately.

I will search for that schematic, thanks a lot! I did find something similar for the A10 unit, but was unsure if the S9 unit was different.

[Guest]

setup for his ResMed S9 CPAP machine

Resmed makes several models. Be certainly to use exactly the model as written on the machine to get more accurate info or a comparable Respironics replacement which makes more sense.

Or, get Philips 560 apap that runs on 12v and use that as a travel/backup machine?

Why not pick up a respironics machine as a travel machine/backup?

Both excellent ideas... .check your local craigslist under health & beauty for a comparable respironics model.
Or search this forum for people selling cpaps.

[palerider]

Easiest option would be to buy the ResMed DC/DC Converter (intended for 12V or 24V DC lead acid batteries). However, I'm unsure if these adapters will accept the voltage range of the LiPo Battery packs we bought (LiPo 4S 12V-16.8V range). I'm hoping someone with the adapter would be able to tell me if this is possible?

the resmed convert is a boost converter, it's spec'd for 12-24v input.

Third option is I could buy a used ResMed AC Adapter, rip it apart and use only the 'smart' component to trick the ResMed S9 into thinking I'm using an AC Adapter, but really I will piggy back my generic DC/DC converter on it to supply power.

Fourth option is to reverse engineer the ResMed power converter data bus and design my own circuit to talk to the ResMed. But I really don't have the time to do this right now, as I need to complete this in the next week or so.

according to a resmed patent application, the cpap senses the type of power supply based on a pullup resistor between the third pin and vcc.
https://www.google.com/patents/US20110162647 section 54 and 55.

[palerider]

Why not pick up a respironics machine as a travel machine/backup? Unfortunately, you missed a recent sale by our sponsor that was selling them brand new for $310. They are also available on amazon.com. And some members here probably have suitable machines for sale. Respironics run on 12 volts and only Resmed uses 24 volts.

There was a recent thread here that included a schematic to build an adapter that supplies the signal that the resmed unit requires to run off batteries - use the search function.

No time to buy another unit now unfortunately.

I will search for that schematic, thanks a lot! I did find something similar for the A10 unit, but was unsure if the S9 unit was different.

that 'schematic' was, I think you'll find, drawn by an idiot.... the same one that was being egged on in the thread you posted above.

[palerider]

Research the charging system Iphone and Ipad,

[CapnLoki]

Why not pick up a respironics machine as a travel machine/backup? Unfortunately, you missed a recent sale by our sponsor that was selling them brand new for $310. They are also available on amazon.com. And some members here probably have suitable machines for sale. Respironics run on 12 volts and only Resmed uses 24 volts.

There was a recent thread here that included a schematic to build an adapter that supplies the signal that the resmed unit requires to run off batteries - use the search function.

No time to buy another unit now unfortunately.

I will search for that schematic, thanks a lot! I did find something similar for the A10 unit, but was unsure if the S9 unit was different.

that 'schematic' was, I think you'll find, drawn by an idiot.... the same one that was being egged on in the thread you posted above.

I never saw the point of reinventing the converter whose only problem was a slightly high price tag.

Sent from my SM-G900T using Tapatalk

[palerider]

I never saw the point of reinventing the converter whose only problem was a slightly high price tag.

the advantage (possibly) in this case could be a better form factor, and lighter weight, the resmed converter is fairly heavy.

[GTSSportCoupe]

I never saw the point of reinventing the converter whose only problem was a slightly high price tag.

the advantage (possibly) in this case could be a better form factor, and lighter weight, the resmed converter is fairly heavy.

In my case I was hoping to know if it would work with the slightly higher voltage LiPo batteries I have before I go and buy it. I suppose I could also add a three or four diode drop between the battery and Resmed DC/DC converter if it doesn't like the higher voltage. Probably the route I'm going to go....

Thanks for your help everyone. And if anyone has any more info on the S9 power adapter interface, please let me know. Or experience with 4S LiPo batteries for that matter.....

[palerider]

I never saw the point of reinventing the converter whose only problem was a slightly high price tag.

the advantage (possibly) in this case could be a better form factor, and lighter weight, the resmed converter is fairly heavy.

In my case I was hoping to know if it would work with the slightly higher voltage LiPo batteries I have before I go and buy it. I suppose I could also add a three or four diode drop between the battery and Resmed DC/DC converter if it doesn't like the higher voltage. Probably the route I'm going to go....

well, like I said, the converter says it's good for 12 to 24 volts dc input. like most boost converters, it's not that picky about what it eats