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Minimum DC Voltage to Operate CPAP?
#31
RE: Minimum DC Voltage to Operate CPAP?
@khw210 Re Charging the Lithium battery
I don't recommend you under charge the lithium battery, rather keep it charged up to 100%, with it's proper charger as this will prolong it's life time.
That being said I can see in your request for help you are having trouble about the excess higher DC voltage that would be presented to the CPAP machine.

OK, you havent supplied the following information needed to see how people here can help you, we need to know the "output" from the brick or wall power supply, what it actually is.
In watts or amps, this helps people to work out what opshions avaliable.

You need to lower the OUTPUT voltage of the Lithium battery to a safe 12V DC so that the CPAP machine will work OK as though it was working with the Wall Pack Brick, to do this you will need to get yourself a DC to DC Converter.

ITEM 1
The DC to DC converter you are looking for is something that is in this following ball park, Input up to 18volt or 19 volt DC with an Output of 13v DC.
You can find these on EBay. I will see about emailing you later (got some chores to do ASAP) 

ITEM 2
You will need to get the DC to DC Lead made by Philips Part No1097568 this is the Cigarete plug (with the 76 inch lead) to the matching 12v Plug to plug into the back of your CPAP machine.

ITEM 3
You will need the Cigarete Lighter SOCKET which has the wires already attatched that can be secured onto the Battery Terminals.

All this information is assuming yours is a Respironics System One Series 60 CPAP Machine made by Philips.



OK once you get the parts, you set it up like this.
1 Connect the EBAY 19volt input DC to the DC Converter to the Battery

2 The "output" wires from the DC to DC Converter are connected  the Cigarete Lighter SOCKET wires with the round eyelets.

3 Plug the Supplied DC Cigarete 12v plug into the Cigarete Lighter socket.

4 Plug the small plug from the end of the long lead into the back of the CPAP machine.

    
Jim
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#32
RE: Minimum DC Voltage to Operate CPAP?
    That's exactly what I do but I didn't mention it in my post because I thought it would over complicate my point. Those DC-DC Step Down Transformer Modules (aka Buck Converters) are nifty little devices. I also use one with my Ham Radios which require 13.8 volts. I've attached a photo of my CPAP setup. It's difficult to see in the photo but the voltage output from the Buck Converter is 13.81v. The battery voltage is at 16.25v.
I do take issue with charging and storing a Lithium battery at 100% SOC. I've done my research. One of the best sources is BatteryUniversity.com. Take a look at this article:  

https://batteryuniversity.com/learn/arti..._batteries

When it comes to storing Lithium based batteries, the recommendation is to store them at about 50% SOC. That would be 3.82 volts per cell. Therefore my 4S Lithium batteries are happiest when stored at 15.28 volts. Take a look at this article on BatteryUniversity.com:

https://batteryuniversity.com/learn/arti..._batteries

Lithium batteries aren't cheap, so I strive to do what's best for them. Along with my CPAP, I use them to power my Ham Radios, and Drones. If you can document a differing point of view, please post your reference on this string. I'd be very interested.
Thanks for your thoughts. You seem to have looked into this stuff as well.
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#33
RE: Minimum DC Voltage to Operate CPAP?
I have a completely different battery question to figure out.

I have recently purchased a 'gently used' S9 VPAP Auto without humidifier, which is set to 15-25cm, and averages about 17cm over the course of a night. I also have a lot of 40V tools, including several batteries, of which three are 6.0 AH and two are 6.6AH. I am betting that I can get more than a full night out of any of these batteries, but I don't know what I might need to convert the power to what the S9 needs. For the record, I can't find any adapters from the manufacturer (Ryobi) to connect one of the batteries to plain wires, but I can probably find a broken 40V tool somewhere and cannibalize it for the connector.

Any suggestions?

Edit:
Omigod! I have the solution! I went to Home Depot's US website and found that Ryobi sells inverters for their 40 volt batteries and also for their 18 volt batteries (which I have even more of). On the page for their 18 volt inverter, when I looked at the questions people had asked, of the 93 questions, the very second one was if it could be used to power a CPAP machine! One of the answers was "Check the specs on your CPAP, I used my Resmed 9 (w/o humidifier) And got about 6.5 hours of run time from a 4AHM battery. I have not tested any other batteries. Considering that CPAP batteries cost upwards of $300, this is a reasonable solution."

I should add that they are selling the 18 volt inverter for $60 and the 40 volt inverter for $80. But I should caution that I was on their US site, and, although I know Ryobi battery operated tools are sold in the UK and down under, the power output of the inverters for the North Amerian market put out 120V 60Hz AC. Still, I have an easy solution, and if others already have Ryobi battery operated tools, you may have a solution too!

Second edit:
Looking at the page for the 40V inverter there were lots of questions about CPAP, and here's one of the answers: "With the hose heater and humidifier off, my 4ah ran my Dreamstation cpap 8.8 hours." And now I'm off to buy one!
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#34
RE: Minimum DC Voltage to Operate CPAP?
Bingo! You think like I do. The cost of CPAP manufacturers' battery setups is ridiculous. That's why I looked for other options. Takes a little research,  some common sense, and a willingness to think outside the box. 
The new LifePO4 (Lithium Iron Phosphate) batteries are also a great option. Light weight, the right voltage, high capacity, deep discharge, and thousands of recharge cycles. Cost more than other rechargeable batteries but still way more affordable than the what the manufacturers offer. A 12v 6Ah or 8Ah LifePO4 would be a great choice.
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#35
RE: Minimum DC Voltage to Operate CPAP?
Inverters are extremely inefficient in converting to the required voltage for CPAP. In the case of Resmed, you want 24 V DC voltage supplied on the center pin, and most people just buy the proprietary DC -connector. There are Li-ion batteries sold that do the job well without the inverter. By converting the battery power from DC 40 V to AC, then using your AC adapter to convert back to the 24 V DC power you will lose about 60% of the battery capacity to the conversions.
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#36
RE: Minimum DC Voltage to Operate CPAP?
I was aware that converters/inverters are inefficient but didn't know it was to that extent. Buck Converts on the other hand, are very efficient. You can expect 90%+ efficiency. My Buck Converter is somewhere in the neighborhood of 96% efficient.
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#37
RE: Minimum DC Voltage to Operate CPAP?
(08-13-2020, 05:58 PM)Sleeprider Wrote: Inverters are extremely inefficient in converting to the required voltage for CPAP.  In the case of Resmed, you want 24 V DC voltage supplied on the center pin, and most people just buy the proprietary DC -connector.  There are Li-ion batteries sold that do the job well without the inverter.  By converting the battery power from DC 40 V to AC, then using your AC adapter to convert back to the 24 V DC power you will lose about 60% of the battery capacity to the conversions.

You are absolutely correct, although I think the percentage of loss varies a lot depending on the exact equipment used!

But I have four 40V Ryobi batteries and each will get me over 10 hours of sleep with my S9 VPAP. From the line outlets in my house they take over two hours to charge fully, but who cares? The power from the street can be out for four days before I need to sweat it. And even then, I have a small 12V inverter that plugs into a cigarette lighter in my car, and I've used it to power the 40V Ryobi charger. But hey! After four days of living in this house without electricity I'll be ready to travel - anywhere, as long as it's got power!

I should have added that my inverter (pure sine wave, by the way) was $80, and if you need a 4AH Ryobi battery, add another $90, and a charger for $20, so the total comes to $190 for someone who doesn't already have the pieces that I have. That's still not bad, compared to what some systems dedicated for CPAP use cost, but I mention it just to be clear that what worked for me might not be as good a deal for someone else.

And I should also repeat that Sleeprider makes a good point - my system is inefficient. So if you are dedicated to saving the planet, there are much more efficient and earth-friendly ways to get a backup power source. Plus, I'm not sure what would happen if I pack a Ryobi Li-Ion battery and try to schlepp it with me on an airplane. They're also kind of heavy - it makes my back ache just thinking about backpacking and hauling a few of them up the side of a mountain.
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#38
RE: Minimum DC Voltage to Operate CPAP?
Hi khw210, thanks for the email,
Yes I agree with you, seems you and I are operating the CPAPS very similarly, LOL, I bet there are lots of others doing the same.
Been to the https address, good articles there about batteries, thanks. Thanks

I want to add my observations, I have noticed a fluxation of current drain from my battery, when using the heated hose because as the night progresers, the room temperature drops so the CPAP compensates by increasing the current drawn to keep the humidified hose at the set temperature.
This fluxes up and down all night long, but it works out OK for me.

Last night when I went to bed I did not turn on the charger, I wanted to see what was left in the batt after a really long sleep, I drew down the battery to 30% but it is back on charge.
Another experement I want to do is connect 2 wall charges in parallel and see if I can half the charging time, this will have to wait a while.... 
I see one chap has done this on YT using 4 in parallel, he uses GZ like I have here .

Another thing I have never seen anyone do is to charge their CPAP batteries using Hydro, now that would be interresting......

I slept 8 hours, from midnight till 10AM this morning, not bad at all.

Jim
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#39
RE: Minimum DC Voltage to Operate CPAP?
Hi Sleep rider,
That's excelent advice, I totally agree with you about not using the inverter.
They hog current like it's going out of fashion, will flatten the battery in no time at all, very wasteful use of energy.

That's why I use the 12v DC output power from the GZ yeti lithium battery and pass it to a 12v to 24v DC to DC converter made by Resmid.

@JJJ
Best bet is to buy a fully built battery that is suitabable to run your CPAP machine. 


Jim
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#40
RE: Minimum DC Voltage to Operate CPAP?
(08-13-2020, 11:43 PM)daddyoh Wrote: @JJJ
Best bet is to buy a fully built battery that is suitabable to run your CPAP machine. 

Jim, I would definitely do as you suggested, but I already have four batteries, each with enough power to provide 10+ hours on my S9 VPAP, and that's after the loss due to the inverter. To get four nights worth of battery backup cost me just $80 for the inverter, far less than buying a 'fully built battery' for my machine.

I picked up the inverter this morning, and tonight we'll see what happens.
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