Using D cells for that once-in-10-year emergency event

[DepartmentOfMeteors]

I've seen a lot of talk about batteries for different needs (camping, traveling, etc.) but I'm more concerned w/the situation where I have to spend the entire night w/out power. I've been researching various threads and there are some pretty good solutions, but it seems to me a couple of dozen LR20s (that's dry D cells) would be even more economical.
I've had my Darth Vader machine for the better part of 10 years now. There's only been one time when I didn't have power and I wanted to sleep, but even that was only for a good chunk of the night--not the entire night. But that entire night will come and the way I think climate change will go, this will become an increasingly serious problem! Since you can get a decent D cell that has 5 and 10 year shelf lives, it seems to me that having those somewhere in the utility room would get me through at least one night, maybe even w/the humidifier. I see this thread: https://www.cpaptalk.com/viewtopic/t401 ... -idea.html has already come up w/the idea, which was address somewhat pessimistically, but that was more than 10 years ago.
My CPAP takes 24Vdc. It has a humidifier and a heated hose, but I guess those are optional.

[billbolton]

I'm not sure that is a good idea, but if you want to pursue it, you might want to look at multiple 6V Lantern Batteries as an alternative to multiple 1.5V D cells.

[chunkyfrog]

I suspect that the OP is hoping for a solution that can be thrown together
on short notice from supplies commonly kept on hand.
Trying to do it for a 24 volt machine with crazy proprietary connections--
---good luck with that. You will need it.

[SleepGeek]

I suspect that the OP is hoping for a solution that can be thrown together
on short notice from supplies commonly kept on hand.
Trying to do it for a 24 volt machine with crazy proprietary connections--
---good luck with that. You will need it.

Thing is he doesn't need 24V but does the special magical Rezmeds cable. Then he can use any 12V battery he has on hand. Or use another cpap that works on 12V.

DepartmentOfMeteors if you put something together out of D cells please do post your results in this thread.

[DepartmentOfMeteors]

It's not something that I can throw together on short notice, but something that will cost as little as possible, since whatever I get will probably expire before I can use it. If I have to spend 30$ every 5 years for something I never use, that's a bargain.
Ok, judging from SleepGeek's comment, it looks like I'm blazing this trail. Which I don't mind doing, but I'd appreciate any help I could get finding components off the shelf, such as battery holders and compatible connectors. I have my own soldering gun.
A quick Google reveals https://www.digikey.ca/en/products/deta ... 6DL/814091 to be the biggest one I can find. At 6 cell bays, I'd have to have 2 of them plus a single 4 pack to make 24V. So I'd definitely want to mount them to something, and fortunately, these holders seem to come w/eyelets for mounting. But what I would mount them to, would be another question. I'd have to find some kind of project box.
Any other ideas? I'm drawing a blank on the connector so far.

[Dog Slobber]

You don't *want* to go 24 volts. As SleepGeek pointed out, you shuld go 12v and use the ResMed DC-DC converter.

ResMed Air 9/10/11 devices don't accept straight 24 volts. They require a cable providing 24v (power), 3.3v(control) and ground. The connector is different, depending on whether you have the 9, 10, or 11.

Your options are:

• Create a battery, providing 12V and then use the ResMed DC-DC converted (expensive) or a cheaper off brand alternative.
• Create a battery, providing 24V and then create the proprietary cable and circuitry to provide 24V and 3.3.

[DepartmentOfMeteors]

In that case, a few other issues get brought up:

1. I don't think the 8 LR20s that would get my 12V would have the required charge. I can still use the same number of batteries in parallel, but I also don't have much experience designing for dry cells that are in parallel, so I don't know how uneven voltages could cause problems.
2. How much is this DC-DC converter?
3. How does the proprietary cable make 3.3V out of 24V? A regulator? What can anyone tell me about the load the 3.3V pin takes?

[loggerhead12]

[*]How much is this DC-DC converter?

About $85.

https://www.cpap.com/productpage/resmed ... iAQAvD_BwE

[Goofproof]

Using (D) cells to power a XPAP makes no sense whatever, the power required is too high to run A XPAP for any worth while time. There are many worthwhile solutions to your XPAP power back-up needs listed on this forum, the difference is they do the job. Jim

When designing a wheel, start with a Circle, not a Square.

[Dog Slobber]

In that case, a few other issues get brought up:

1. I don't think the 8 LR20s that would get my 12V would have the required charge. I can still use the same number of batteries in parallel, but I also don't have much experience designing for dry cells that are in parallel, so I don't know how uneven voltages could cause problems.
2. How much is this DC-DC converter?
3. How does the proprietary cable make 3.3V out of 24V? A regulator? What can anyone tell me about the load the 3.3V pin takes?

This is really starting to fall into the category of, if you need to ask how to do something, you probably should not be doing it.

https://www.youtube.com/watch?v=IzWJ1ZNSU80

[zonker]

This is really starting to fall into the category of, if you need to ask how to do something, you probably should not be doing it.

https://www.youtube.com/watch?v=IzWJ1ZNSU80

so, unless someone is born with knowledge, they can't learn anything?

i'm doooomed!!!

[Dog Slobber]

This is really starting to fall into the category of, if you need to ask how to do something, you probably should not be doing it.

https://www.youtube.com/watch?v=IzWJ1ZNSU80

so, unless someone is born with knowledge, they can't learn anything?

Nope, not suggesting that at all.

One has to be realistic about asking how to do some tasks. Some tasks require an existing basic knowledge level. The question he asked, as well as other comments and questions he's made about his project, suggest pretty strongly his electrical/electronics knowledge is novice/basic.

My skill level for car repair and maintenance is pretty basic.

If I were to go car mechanics web forum and ask, "My transmission is blown, can you guys tell me how to fix it?", everyone would accept that simply asking such a question, demonstrates I'm not *yet* ready for such a task.

The transmission analogy is a little more extreme, but still re-enforces the point.

i'm doooomed!!!

Aren't we all.

[DepartmentOfMeteors]

In that case, once I find out what to do, I'll keep the how questions to a minimum. And I have a pretty good idea of how to do it, but that presumes the what. Beyond what I've already discussed, I'd think I'd be building a precision regulator powered by a couple of AAs. But to know if that's even feasible, I'd have to know the required precision of the 3.3V pin as well as the load. None of the documentation I have tells me that.
I had the idea that when I entered my equipment data in the control panel, it would be shared w/my posts, but it looks like the board is respecting my privacy. I have an AirSense 10 w/a humidifier. What the documentation does tell me about the electricals is that the peak power is 104W but the typical wattage is 53W. The 24V pin needs to deliver as much 3.75A but it doesn't even acknowledge the 3.3V pin.

[Pugsy]

I had the idea that when I entered my equipment data in the control panel, it would be shared w/my posts, but it looks like the board is respecting my privacy.

Normally the equipment profile is shared with each post but you probably missed this sticky.
https://www.cpaptalk.com/viewtopic/t181 ... ryone.html

Sticky: Equipment profile is missing for everyone

[randye80]

I just looked up the datasheet for a Duracell Coppertop D-cell battery.

The largest current application they give in the curves is 2 amps. At this draw, the single cell voltage drops to 1.1V in 30 minutes, and to 0.8V after two hours.

IMO, this type of battery lacks the power density required for this type of use.