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[Equipment] How many DC Amps does my CPAP REALLY draw?
#1
Question 
I'm shopping for a deep-cycle 12V battery so I can take my REMstar Plus CPAP camping and I want to be able to approximate how many hours of use I'll get out of a certain amp-hour/size of battery before I buy it.

Now, I've done quite a bit of research and this should be fairly straight forward, however, in all of the scenarios I've read online, the 12C DC amp usage ratings for CPAP machines have all been 2.0 and lower (often in tenths below 1.0). The printed specs on my REMstar Plus, however indicate a DC power consumption of 5.0 amps.

Am I missing something here or does my particular machine really draw that much more power than the machines referenced on the web pages I've seen?

Any help or opinions on this would be most appreciated!

Thanks much,
Tim
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#2
Welcome to the forum ChoirPower!!! We are glad you joined us!!! Welcome

With respect to your question, there are two different types of current. There is "Peak inrush current" which is the current needed to start the device and "Running current" which is the current necessary to run the device after the machine is running.

This image shows pictorially what I describe above. Edited to Add: The image shows the typical power and current draw for an electrical motor.

[Image: drawingskey_2.jpg]

Normally, the "running current" is 5 - 10 times less than the peak inrush current.

I think the 5.0 Amps you found is the starting current.

You might want to check with your DME or with Philips Respironics to verify this information though.
INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#3
(07-22-2012, 07:49 AM)ChoirPower Wrote: I'm shopping for a deep-cycle 12V battery so I can take my REMstar Plus CPAP camping and I want to be able to approximate how many hours of use I'll get out of a certain amp-hour/size of battery before I buy it.

It depends on the pressure your machine is set at. The higher the pressure, the more current it draws. It depends even more so on the humidifier setting. The higher the setting, the more current you draw.

If weight is not an issue, then a good deep cycle lead-acid battery is the way to go. It would also help to have a solar charger. And don't use the humidifier.
Sleepster
Apnea Board Moderator
www.ApneaBoard.com


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#4
Hi ChoirPower, I don't know the answer to your question but I'd like to Welcome! you to the forum.! Just keep checkin' back into this board and there will be more answers to your question. Best of luck to you.
trish6hundred
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#5
It can vary a lot from machine to machine, and with pressure settings, leak rates, humidifier use, etc.

However, 3 amps or less average over the night is not a bad guess with humidifier. A heated hose might add to that.

You can often find a "Kill a Watt" power tester for a fairly cheap price. This tests the AC power. Use it to measure power into your power supply brick over an average night's usage and divide the accumulated kilowatts by the hours to get watts used by the power brick.

Assume the power supply is 100% efficient, and you have a maximum number for the 12V power coming out of the power supply. Divide your average watts by 12, and now you have an average amp reading.
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#6
(07-22-2012, 04:22 PM)archangle Wrote: It can vary a lot from machine to machine, and with pressure settings, leak rates, humidifier use, etc.

However, 3 amps or less average over the night is not a bad guess with humidifier. A heated hose might add to that.

You can often find a "Kill a Watt" power tester for a fairly cheap price. This tests the AC power. Use it to measure power into your power supply brick over an average night's usage and divide the accumulated kilowatts by the hours to get watts used by the power brick.

Assume the power supply is 100% efficient, and you have a maximum number for the 12V power coming out of the power supply. Divide your average watts by 12, and now you have an average amp reading.

have mine hooked to dc annd humidifier does not work on d/c so a draw of 1.5 is what i see
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#7
Hey ChoirPower...

I did that same research last year. I found a Phillips website that indicated that my unit would draw 1.8 amps during most of the night (without the humidifier), although I suppose that would depend upon the pressure.

I sometimes camp a quarter mile or so from the car, so weight is an issue for me. Also, I wanted the battery to be a backup for the car, since I sometimes am away from the car (and the grid) for several weeks. So I got a marine battery and a small solar panel.

I'd love to give you all the details, but I don't want to get tossed out on my very first post.

Anyway, it works great. Some long nights have resulted in the battery getting down to 12.4 volts, but the solar panel beings it back up in a couple hours. A normal night leaves the battery at about 12.65 volts. I've put in a total of about a month on the battery.
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#8
Thanks for the info, Wilder (and all)!

As it happens, I ended up purchasing a deep cycle marine battery that did not list it's rated AmpHrs, and took a shot in the dark on a camping trip from which I just returned. I didn't take scientific readings or do complicated math, but ended up getting about 4-5 good nights of sleep (no heat/no humidity) from my Responics Remstar before I needed to head back to civilization and find a plug - that is plenty enough for my outdoor needs.

Wilder, by any chance, do you remember the address of that Phillips website you found? I'm thinking that would be a valuable read for the future and haven't seen anything like so far. The Amp Hour draw rating listed in my user manual is a whopping 5.0/Hr., which is patently absurd.

Thanks,
Tim


(08-14-2012, 10:02 PM)wilder Wrote: Hey ChoirPower...

I did that same research last year. I found a Phillips website that indicated that my unit would draw 1.8 amps during most of the night (without the humidifier), although I suppose that would depend upon the pressure.

I sometimes camp a quarter mile or so from the car, so weight is an issue for me. Also, I wanted the battery to be a backup for the car, since I sometimes am away from the car (and the grid) for several weeks. So I got a marine battery and a small solar panel.

I'd love to give you all the details, but I don't want to get tossed out on my very first post.

Anyway, it works great. Some long nights have resulted in the battery getting down to 12.4 volts, but the solar panel beings it back up in a couple hours. A normal night leaves the battery at about 12.65 volts. I've put in a total of about a month on the battery.

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#9
I realize this thread is a few weeks old but I recorded some current draw info on a System One REMStar Plus w/ C-Flex this morning for interest sake and thought I would post it here. Measurement numbers are approximate.

Pressure setting: 10
C-Flex: 3
Altitude: 2

Brief test was without humidifier and then with humidifier on setting 5.

The graph (attached image, X-Axis: Time in seconds, Y-Axis: DC Current in Ampere) starts with power being plugged into the machine: ~0.2A current draw

At around 10seconds, mask on my face, I started "therapy." After a peak of just under 4.4A the current settles and fluctuates between almost 0A and ~1.7A. The higher number was when breathing in (blower motor has to work harder to keep the pressure up) and the lower when breathing out (blower motor just about stops).

At 50seconds I turned the humidifier on to the highest setting of 5. The current draw jumps significantly and fluctuates between roughly 3.3A and 5.1A.

I turned the humidifier off just before the 80 second mark and then stopped "therapy" shortly after that. The graph gives the total average current draw at 1.51A but that is not truly useful for anything as the test does not represent normal use of the machine.

The approximate the average current draw with no humidifier is roughly 0.7A and with humidifier 3.9A

Note that with the mask off and the machine running the current draw is higher (around 2A with no humidifier) since the motor is trying to reach the set pressure but not meeting any resistance so it just constantly blows as hard as it can for that particular pressure setting.

Hopefully this is useful to someone.

EDIT: If it would be helpful I can change the machine settings and run another test.


Attached Files Thumbnail(s)
   
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#10
This verifies that the amount of energy used depends on the pressure setting, and very heavily on the humidifier setting. I'd be intersted in knowing just how much of a difference the humidifier stting makes.

And it appears that the amount of energy used also depends on how you breathe!
Sleepster
Apnea Board Moderator
www.ApneaBoard.com


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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