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

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
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DepartmentOfMeteors
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Re: Using D cells for that once-in-10-year emergency event

Post by DepartmentOfMeteors » Wed Jan 12, 2022 3:21 pm

randye80 wrote:
Wed Jan 12, 2022 2:47 pm
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.
That's... strangely disappointing. If a CPAP draws 53W then a 24V supply will average 2.2A. Over an 8 hour period, that means almost 18AH. So each of those 16 batteries will need to deliver 1.1AH. A lot of LR20s are rated at more than 10AH, but I heard that even pessimistically, you can expect 2AH out of an alkaline D-cell. What did I miss? Does the last of that charge come dribbling in at 0.2V?
AirSense 10 w/humidifier and heated hose. Eson2 small nose piece.

randye80
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Re: Using D cells for that once-in-10-year emergency event

Post by randye80 » Wed Jan 12, 2022 4:16 pm

One thing that you may be missing is that battery performance is not linear, and such a small battery can only deliver high current for a short time (with rapid voltage drop).

I would expect a 10AH battery to be able to supply 0.1A for 100 hours, but not 1A for 10 hours, nor 10A for 1 hour. A D-cell just isn't designed for that much continuous current.

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

Post by DepartmentOfMeteors » Wed Jan 12, 2022 4:55 pm

I see. So to get the charge you want, you have to adjust the current appropriately. How about a switching supply, that allows for 10s at 5A then then nothing for 23s? It'd be a honking big capacitor bank though, even if they are electrolytic.
Oh well, I guess I know now why no one came up w/that idea before.
AirSense 10 w/humidifier and heated hose. Eson2 small nose piece.

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

Post by Goofproof » Wed Jan 12, 2022 5:09 pm

Dog Slobber wrote:
Wed Jan 12, 2022 12:50 pm
zonker wrote:
Wed Jan 12, 2022 12:35 pm
Dog Slobber wrote:
Wed Jan 12, 2022 12:20 pm


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!!!
:lol: :lol: :lol:
Aren't we all. :)
Some of us have the knowledge, and the ability to do this, and more, but life has taught us when our ideas are worth the effort, when others have already built a round wheel that works, and probable never put a square wheel on their wagon.

To make a power supply that would last as long as a golf cart battery (35 amp) would take over 1,000
D cells., but at least it would run a CPAP over 30 minutes. Jim
Last edited by Goofproof on Wed Jan 12, 2022 10:17 pm, edited 1 time in total.
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palerider
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Re: Using D cells for that once-in-10-year emergency event

Post by palerider » Wed Jan 12, 2022 5:53 pm

Dog Slobber wrote:
Wed Jan 12, 2022 9:54 am
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.
The Resmed converter will work from 12 to 24 volts.
Get OSCAR and come chat on IRC: #cpaptalk on irc.libera.chat

Accounts to put on the foe list: dataq1, mper!?, DreamDiver, Geer1, almostadoctor, sleepgeek, ajack, stom, mogy, D.H., They're often post misleading, timewasting stuff.

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

Post by palerider » Wed Jan 12, 2022 6:04 pm

DepartmentOfMeteors wrote:
Wed Jan 12, 2022 4:55 pm
I see. So to get the charge you want, you have to adjust the current appropriately. How about a switching supply, that allows for 10s at 5A then then nothing for 23s? It'd be a honking big capacitor bank though, even if they are electrolytic.
Oh well, I guess I know now why no one came up w/that idea before.
Because nothing is 100% efficient.
Get OSCAR and come chat on IRC: #cpaptalk on irc.libera.chat

Accounts to put on the foe list: dataq1, mper!?, DreamDiver, Geer1, almostadoctor, sleepgeek, ajack, stom, mogy, D.H., They're often post misleading, timewasting stuff.

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

Post by DepartmentOfMeteors » Wed Jan 12, 2022 6:33 pm

25% would have been plenty
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zonker
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Re: Using D cells for that once-in-10-year emergency event

Post by zonker » Wed Jan 12, 2022 7:12 pm

Dog Slobber wrote:
Wed Jan 12, 2022 12:50 pm
zonker wrote:
Wed Jan 12, 2022 12:35 pm
Dog Slobber wrote:
Wed Jan 12, 2022 12:20 pm


Nope, not suggesting that at all.
thanks for the explanation.


i'm doooomed!!!
:lol: :lol: :lol:
Aren't we all. :)
not me. i plan to live forever or die trying.
resmed airsense 10 autosense for her
p10
"nothing in the world is more dangerous than sincere ignorance and conscientious stupidity.” -mlk jr

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

Post by Goofproof » Wed Jan 12, 2022 10:25 pm

palerider wrote:
Wed Jan 12, 2022 6:04 pm
DepartmentOfMeteors wrote:
Wed Jan 12, 2022 4:55 pm
I see. So to get the charge you want, you have to adjust the current appropriately. How about a switching supply, that allows for 10s at 5A then then nothing for 23s? It'd be a honking big capacitor bank though, even if they are electrolytic.
Oh well, I guess I know now why no one came up w/that idea before.
Because nothing is 100% efficient.
The reason Nothing is 100% efficient, is because he doesn't finish doing it... :lol: Jim
Use data to optimize your xPAP treatment!

"The art of medicine consists in amusing the patient while nature cures the disease." Voltaire

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

Post by chunkyfrog » Wed Jan 12, 2022 10:46 pm

Not quite--one of the primary laws of physics is that there will always be wasted energy.
The trick is to keep it low enough so the project is worth doing.
Maybe this plan IS doable.
Over-engineering is a common waste of resources.
Disposable components are possibly a good plan if durability is not required,
or is simply not practical.
Resmed Airsense 10 Autoset FOR HER, p10 mask

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loggerhead12
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Re: Using D cells for that once-in-10-year emergency event

Post by loggerhead12 » Thu Jan 13, 2022 10:55 am

DepartmentOfMeteors wrote:
Wed Jan 12, 2022 3:21 pm
That's... strangely disappointing. If a CPAP draws 53W then a 24V supply will average 2.2A. Over an 8 hour period, that means almost 18AH. So each of those 16 batteries will need to deliver 1.1AH. A lot of LR20s are rated at more than 10AH, but I heard that even pessimistically, you can expect 2AH out of an alkaline D-cell. What did I miss? Does the last of that charge come dribbling in at 0.2V?
But those numbers don't prove out. Mine draws about .8 amps at 12 volts, and I average less than 7 amp hours in a night.

Don't give up on it, I was kind of fascinated where it was going. You could test the theory for very little money.

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

Post by stevenal » Thu Jan 13, 2022 2:05 pm

DepartmentOfMeteors wrote:
Wed Jan 12, 2022 3:21 pm

That's... strangely disappointing. If a CPAP draws 53W then a 24V supply will average 2.2A. Over an 8 hour period, that means almost 18AH. So each of those 16 batteries will need to deliver 1.1AH. A lot of LR20s are rated at more than 10AH, but I heard that even pessimistically, you can expect 2AH out of an alkaline D-cell. What did I miss? Does the last of that charge come dribbling in at 0.2V?
So you took 18Ah/16 cells =1.1Ah per cell. Trouble is, we have the same number of hours (8) and the same number of amperes (2.2) in each cell. Cells in series increase voltage, not amps. If your starting numbers are correct, each D cell will need to supply the full 18 Ah. If you want 1.1 Ah per cell, you will need 16 parallel strings of 16 cells in series, or 16^2 cells total.

The math is much easier if you use Wh. Series or parallel, the Wh simply adds. Run it through the Resmed DC to DC convertor and you just need figure in the convertor losses.
AirSence 10 Autoset, System One awaiting recall, Swift FX, Freedom V2 battery, Z1 for travel.

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

Post by DepartmentOfMeteors » Thu Jan 13, 2022 2:44 pm

loggerhead12 wrote:
Thu Jan 13, 2022 10:55 am
DepartmentOfMeteors wrote:
Wed Jan 12, 2022 3:21 pm
That's... strangely disappointing. If a CPAP draws 53W then a 24V supply will average 2.2A. Over an 8 hour period, that means almost 18AH. So each of those 16 batteries will need to deliver 1.1AH. A lot of LR20s are rated at more than 10AH, but I heard that even pessimistically, you can expect 2AH out of an alkaline D-cell. What did I miss? Does the last of that charge come dribbling in at 0.2V?
But those numbers don't prove out. Mine draws about .8 amps at 12 volts, and I average less than 7 amp hours in a night.

Don't give up on it, I was kind of fascinated where it was going. You could test the theory for very little money.
Your CPAP draws 800mA and 12Vdc? That's not even 10W. I don't know what model it is, but mine averages 53W. I think the only thing worth doing right now is put my CPAP's adapter on a smart plug and see the power consumption. After that, I'd have to see what the efficiency would be if the output of that adapter is only 10W.
AirSense 10 w/humidifier and heated hose. Eson2 small nose piece.

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

Post by stevenal » Thu Jan 13, 2022 2:48 pm

loggerhead12 wrote:
Thu Jan 13, 2022 10:55 am

But those numbers don't prove out. Mine draws about .8 amps at 12 volts, and I average less than 7 amp hours in a night.

Don't give up on it, I was kind of fascinated where it was going. You could test the theory for very little money.
Let's try this example: Assuming both Logger and Meteor are using the same efficiency DC to DC convertors, that part goes away. Stepping up to Meteor's 8 h: .8 A * 12 V * 8 h = 76.8 Wh.
If the 2 Ah per cell figure is correct, that would be 2 Ah*1.5 V= 3 Wh per cell. 76.8 Wh/3 Wh/cell = 25.6 cells. Better round that up a bit. Also need at least eight in a string to get 12 V. 4 strings of 8 cells perhaps? I would worry the voltage might go too low when the batteries start to discharge. 3 strings of 9 is closer to the target. 2 strings of 13 is right there. One string of 26 will put the voltage too high.
AirSence 10 Autoset, System One awaiting recall, Swift FX, Freedom V2 battery, Z1 for travel.

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

Post by Goofproof » Thu Jan 13, 2022 4:04 pm

I'm for the U.S.A. Plan when I watch others that do electric projects without the understanding of how things work.

It comes down to, The Red, White, & Blue Results! Red, is for the flames when you plug it in, if you are lucky, you see the White the color of the smoke coming from inside the case, even more exciting is, The Blue, the Arc when plugging the power in, (may also hear a POP or Bang)!

If you get all three results, you get to study the project plans again! :lol: Jim
Use data to optimize your xPAP treatment!

"The art of medicine consists in amusing the patient while nature cures the disease." Voltaire