Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
thielj
Posts: 1
Joined: Sun Apr 28, 2019 5:46 pm

Re: Homebuilt '12V Converter' for Resmed Airsense 10

Post by thielj » Sun Apr 28, 2019 5:49 pm

A user on another board suggested that a 47k between +24v and center pin is sufficient.

TheSnoringMan
Posts: 21
Joined: Fri Jul 28, 2017 8:42 am

Re: Homebuilt '12V Converter' for Resmed Airsense 10

Post by TheSnoringMan » Tue Apr 30, 2019 8:29 am

thielj wrote:
Sun Apr 28, 2019 5:49 pm
A user on another board suggested that a 47k between +24v and center pin is sufficient.
Resmed made things 'complicated' in their own Power Supply Unit ("PSU"), with both a resistor AND a Voltage Converter. I think that implies the test (within the unit) measures current or voltage drop across the "sense" circuit at more than one level of "inline" internal resistance - verifying that both components are present in the PSU (The Voltage Converter AND it's own PSU resistor). I think that they made it a bit more complicated and expensive to build on purpose.

Did that "other board" User ever build his Resmed PSU (~12V --> 24V + 3.3V) and find it functional, or did he just quietly stop talking about it? This one continues to work great, with extremely low battery power wastage (in comparison to running the 120V PSU as the "output device" of a 12VDC --> 120VAC Inverter).

tinkerer1
Posts: 3
Joined: Sat Apr 28, 2018 6:48 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by tinkerer1 » Thu Jun 06, 2019 7:55 am

TheSnoringMan-
I should have written this reply a long time ago. Just wanted to say Thanks for all your information and replies about the converter. I have followed your plan and built it using a old laptop brick cable. It is working fine.
I did put a scope on the resistor and saw the 'sweep' you talked about. Odd looking thing....
And another reason for 'Why I built this..' was, I wanted a unit without a fan. Many converters saw online had fans that reports said were noisy, or went bad. Also, for camping I wanted a unit without the extra power loss of a fan.
Very happy.

eerray
Posts: 2
Joined: Wed Jun 19, 2019 1:46 pm

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by eerray » Wed Jun 19, 2019 2:20 pm

My English is not good. Can you show an electrical diagram of that camping converter? This makes it easier for me to make the right connections. Can anyone sign that for me?

kdauto
Posts: 5
Joined: Thu Jul 11, 2019 7:53 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by kdauto » Thu Jul 11, 2019 7:59 am

Question for TheSnoringMan; why is the resistor necessary at the output of the 3.3v buck converter? What is its function?

I think if the Resmed unit sees 3.3V on the center "sense" wire it should work,no? I am at the same stage you were a few years ago. I jjust bought a 12-24V DC converter for our 5th wheel along with managing to find 2 barrel connectors along with long pigtails for the Resmed inputs. We need to rewire for 2 of these CPAPs in the RV.

Our current setup is turning on a 2500/5000W pure sine inverter all night long. Sure makes for a drain on the battery bank.

Thanks so much for the detailed iinfo!

TheSnoringMan
Posts: 21
Joined: Fri Jul 28, 2017 8:42 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by TheSnoringMan » Thu Jul 11, 2019 9:00 am

Hi, kdauto !!
From 2 posts above:
Resmed made things 'complicated' in their own Power Supply Unit ("PSU"), with both a resistor AND a Voltage Converter. I think that implies the test (within the unit) measures current or voltage drop across the "sense" circuit at more than one level of "inline" internal resistance.
A "clone attempt" containing only a 3.3V voltage converter, or only a 47K resistor, doesn't match the Resmed design, and probably can't pass their verification testing (from the within the CPAP).

In order to run two CPAP machines from ONE 12-24V converter, you will need separate pairs of "downstream" 3.3V buck converters (each followed by it's own resistor). You do need a bigger 12-24 boost converter, and make sure that it's a REGULATED Converter (i.e., not a mere "voltage doubler"). But the +24V Bus output can be shared by all four consumers - 24V direct to each CPAP pigtail, and 24V into each buck converter. a 5-pin terminal like this one would be PERFECT for the 24V wires within your dual output system: https://www.amazon.com/Wago-222-415-LEV ... 07CN5974J/

User avatar
JayDee
Posts: 303
Joined: Fri Jul 13, 2018 5:13 am
Location: Atlanta, Georgia, USA

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by JayDee » Thu Jul 11, 2019 11:14 am

Though I'd still rather build one, if just for the fun of building it, there's one on ebay getting close to $40...

https://www.ebay.com/itm/254249744576

Thanks,
-JD
If you're not having a good time, *DO* something about it.

kdauto
Posts: 5
Joined: Thu Jul 11, 2019 7:53 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by kdauto » Thu Jul 11, 2019 11:17 am

I purchased a 10A, 240W dc-dc unit. From specs it should regulate to 24V even with varying input voltages from 11-14V. I am just about ready to click on a "buck converter" that'll give me 3.3 regulated (fixed) volts. I was going to mount all this on the roof of the underbelly near the battery area. I am planning to use ONE buck converter for the 2 CPAPs and I'm thinking one 2.7k resistor for each CPAP which I'd simply wire to the pigtails I bought.

What I'm thinking is that to measure a vooltage drop, the Resmed CPAP would need "access" to the voltage on both sides of the resistor. It only has physical connection to the downstream side of the 2.7 k-ohm resistor. I cannot see how they can measure voltage drop that way.

Maybe I missed this but have you tried using a fixed 3.3V input on the sense wire?

kdauto
Posts: 5
Joined: Thu Jul 11, 2019 7:53 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by kdauto » Thu Jul 11, 2019 11:19 am

Oh, I also missed this question, why do I need two 3.3V buck converters? I am trying to understand why one isn't plenty to supply 2 CPAPs.

TheSnoringMan
Posts: 21
Joined: Fri Jul 28, 2017 8:42 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by TheSnoringMan » Fri Jul 12, 2019 10:48 am

kdauto wrote:
Thu Jul 11, 2019 11:17 am
I purchased a 10A, 240W dc-dc unit. From specs it should regulate to 24V even with varying input voltages from 11-14V. I am just about ready to click on a "buck converter" that'll give me 3.3 regulated (fixed) volts. I was going to mount all this on the roof of the underbelly near the battery area. I am planning to use ONE buck converter for the 2 CPAPs and I'm thinking one 2.7k resistor for each CPAP which I'd simply wire to the pigtails I bought.

What I'm thinking is that to measure a vooltage drop, the Resmed CPAP would need "access" to the voltage on both sides of the resistor. It only has physical connection to the downstream side of the 2.7 k-ohm resistor. I cannot see how they can measure voltage drop that way.

Maybe I missed this but have you tried using a fixed 3.3V input on the sense wire?
Upon reconsideration -Your method sends perfect.

kdauto
Posts: 5
Joined: Thu Jul 11, 2019 7:53 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by kdauto » Fri Jul 12, 2019 12:55 pm

Have the buck converter arriving this weekend. If I get the chance to finish this installation within the next week I'll post results. My 1st attempt will be 1 buck converter set to 3.3 V and no resistor. We'll see how that pans out. Thanks.

TheSnoringMan
Posts: 21
Joined: Fri Jul 28, 2017 8:42 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by TheSnoringMan » Fri Jul 12, 2019 2:27 pm

kdauto wrote:
Fri Jul 12, 2019 12:55 pm
Have the buck converter arriving this weekend. If I get the chance to finish this installation within the next week I'll post results. My 1st attempt will be 1 buck converter set to 3.3 V and no resistor. We'll see how that pans out. Thanks.
THAT has zero chance or working correctly - wait for the resistors to arrive.

kdauto
Posts: 5
Joined: Thu Jul 11, 2019 7:53 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by kdauto » Fri Jul 12, 2019 6:01 pm

TheSnoringMan wrote:
Fri Jul 12, 2019 2:27 pm
kdauto wrote:
Fri Jul 12, 2019 12:55 pm
Have the buck converter arriving this weekend. If I get the chance to finish this installation within the next week I'll post results. My 1st attempt will be 1 buck converter set to 3.3 V and no resistor. We'll see how that pans out. Thanks.
THAT has zero chance or working correctly - wait for the resistors to arrive.
Which brings me back to my question, what does the resistance do? AFAIK the sense wire should have no load on it? I cannot see how they are measuring voltage drop when the Resmed unit has no "access" to the upstream side of the resistor. I was thinking you wre using the resistor to drop the voltage down some although I have not done the math on it.

2 tiny resistors aren't gonna break my bank at this point. 1/4 watt 5% tolerance should be fine I imagine? The 2.7k is just a bit hard to source locally. I will check the very few remaining electrnic parts stores left. Thanks for hanging in with me.

KCrane
Posts: 1
Joined: Sat Nov 23, 2019 10:44 am

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by KCrane » Sat Nov 23, 2019 11:18 am

Thank you for posting your plan. I have purchased the parts and am in the process of assembling the converter. When I fully cut my sacrifice converter wire, while I was expecting 3 wires, I found only 2 wires inside the jacket, red and black. I twisted the red and black wires back to the converter and checked the barrel plug for voltage. I have 24 volts on the inner cylinder and 3.3 volts on the center pin. Not sure how the center pin is being charged with 3.3 volts. My sacrifice converter is aftermarket. The dc cord has an inline cylinder (looks like a choke) molded onto the cord about six inches from the barrel plug, same as my stock Resmed cord. I tested the patched aftermarket cord and converter with my Resmed and found that it started and ran the same as the stock cord.

It appears that I cannot use the buck converter or the resistor since I don't have a third wire. I am puzzled to how the center pin is getting voltage.

eerray
Posts: 2
Joined: Wed Jun 19, 2019 1:46 pm

Re: Homebuilt '12V Camping Converter PSU' for Resmed Airsense 10

Post by eerray » Sun Nov 24, 2019 5:56 pm

I have successfully completely recreated the 12v campimg converter from TheSnoringMan.
A 1000uF Electrostatic Capacitor, rated at 50V I have not built in.
Everything worked perfectly on vacation. Thanks!