Battery Power Rules!

mrhyak · Post by **mrhyak** » Wed Jul 13, 2005 2:30 pm

I enjoy camping and white-water rafting, so being able to operate my CPAP machine from battery power is important to me. I wondered why the manufacturers did not specify the power requirements of their machines in more exact terms. Of particular interest are the power requirements at 12 volts DC. Since I have some pretty nice electrical measuring equipment available to me, I decided to do some tests. My results:

Setup: I currently have a Respironics RemStar Pro, so this was used for measurements. I used a Fluke 123 scopemeter and built a 1 ohm shunt to allow me measure the current (amperage) of the unit under different conditions. A variable voltage power supply was used, set to 13.6 volts. The Fluke 123 has a “Trend Plot” function which will plot the measurement over time, and provide minimum, maximum, and average values. In each case, I allowed the machine to operate for 3 minutes before resetting the plot. Then I allowed the plot to run for 10 minutes and recorded the average value. I breathed normally (awake of course) at about 14 breaths/minute. The CPAP was set at 10cm H2O

Case 1: Swift nasal pillows, good seal and minimal if any leakage.
C-flex = Off Average current draw = 0.748 amps
C-flex = On Average current draw = 0.909 amps
Case 2: Ultra Mirage FF, some leakage.
C-flex = Off Average current draw = 0.972 amps
C-flex = On Average current draw = 1.025 amps
Case 3: Profile Lite, good seal
C-flex = Off Average current draw = 0.775 amps
C-flex = On Average current draw = 0.856 amps
Case 4: Free running (machine on, no mask attached)
First 2-4 minutes Average current draw = 1.305 amps
At either 2 or 4 minutes of free running, the current draw jumped to 2.609 amps, apparently a search mode of some sort.
Case 5: Machine powered but blower not running
Average current draw = 0.184 amps

Conclusions: As you can see from these measurements, the current draw of these machines varies directly with the circumstances, as could be expected (the more leakage, the harder the blower has to work, the more power consumed). I thought maybe that C-flex use would decrease the power requirements, but it had the opposite effect. This appears due to the increased current required to ramp-up the speed of the blower after each decrease consuming more power than is saved by the decrease in speed.

Since all of the current models of the RemStar appear to use the same blower, I would expect similar results with the other machines in the product line. The BiPap machine will likely be the biggest power consumer. I would expect the Auto to be in-between. When using my machine on batteries, I figure an amperage draw of 1 amp. In order to size a battery for 8 hours of use, use a battery of 16amp-hours (AH) minimum in size (when using a lead-acid battery), since the rule of thumb is to not draw the battery down by more than 50%. Also bear in mind the battery’s capacity will decrease with age.

Field Test: I recently completed an 8 day “field trial” of my battery system in the back country of Idaho, in the Frank Church River of No Return Wilderness. I used a 20 watt solar panel, and a 24 AH gel cell battery. I also had a spare battery of the same size (which was not required). Even with mostly cloudy weather and some rain during the first 4 days of the trip, the solar panel was able to fully recharge the battery each day. When the weather turned sunny, it took around 3-4 hours to recharge the battery. With the sound of the river in the background, I got some of the best sleep in recent memory, 6,7, even 8 hours one night! BTW, I forgot to mention my home brew humidifier. It uses ultrasonics instead of heat, works great, and uses only 3 watts! I’m considering publishing a DIY how-to for this, but I’m a bit concerned about the liability. Also, I’m working on a few changes to add a variable control. More soon. Sorry this is so wordy, I hope someone finds it useful.

Jim

chrisp · Post by **chrisp** » Wed Jul 13, 2005 3:15 pm

As I've said before. I run my 420E on battery every night. Never know when the power will fail. Its a bit bigger than your system I've tested it for 2 weeks between charges. It only needed 1 night of no power / no sleep to convince me. I also have a few jump starters as back ups.

Please post a list of materials with part numbers and cost so we can copy your setup.

Chris

johnnygoodman · Post by **johnnygoodman** » Wed Jul 13, 2005 3:46 pm

Howdy,

Here's another option for the less technical, hands on remote CPAP users out there:

https://www.cpap.com/productpage/AEIOme ... -Pack.html

In stock and shipping.

Johnny

mrhyak · Post by **mrhyak** » Wed Jul 13, 2005 4:23 pm

Good to hear that the Aura is shipping, but what about the humidifier? Although my friends may claim different, I usually only hack my stuff because I can't buy what I want in the first place. Did I miss the interview on this?

rested gal · Post by **rested gal** » Wed Jul 13, 2005 4:55 pm

The Aura rechargeable cpap would be fine for just a one night power outage or one night camping trip. But if no electricity is available to recharge it for the next night, people do still need to figure out another way to recharge it for the next night -- or buy extra battery packs for it.

mrhyak · Post by **mrhyak** » Wed Jul 13, 2005 5:08 pm

Good point, as usual RG -

My battery /solar panel will keep going for a long time off grid - probably until the dark days of winter here in Orygun. Although, even in winter another 20 watts of solar would likely do it. I wish a cpap mfg would come out with battery-powered ultrasonic humidifier - they are way more power efficient than using heat (3 watts versus 100 or more) and I found it works pretty well, especially with a heated hose (even though that's another 10 watts)

chrisp · Post by **chrisp** » Wed Jul 13, 2005 5:14 pm

Please list the parts and source.

:twis ted:

derek · Post by **derek** » Wed Jul 13, 2005 5:41 pm

mrhyak,
Your measurements match mine at about 0.8amps for the REMStar Plus. I was very (pleasantly) surprised because I had emailed Respironics and was told that the Plus drew 2 amps, and the Auto 3 amps. This didn't seem right because that is the ratings of the fuses.

I've been using the Auto on the boat every weekend for the past six weeks or so, and last weekend wired a dedicated +12v outlet by the bed for it.

I gotta say I sleep VERY peacefully on the boat, and last weekend scored a perfect zero (0 apnea, 0 hypopnea, 0 snore) with 9 hours of compliance

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): respironics, Hypopnea, auto

loonlvr · Post by **loonlvr** » Wed Jul 13, 2005 6:04 pm

Yes please publish the list of materials and part numbers. I too go camping here in the minnesota wilds and would love this set-up.I would take my Remstar Plus and leave my auto home. Was thinking of getting a dental mouthpiece but cost is about $1500, which I would pay about half.

Jeb · Post by **Jeb** » Wed Jul 13, 2005 6:48 pm

If I hooked up my cpap to my Chevy Tahoe's power outlet, would I run the battery down too far to start the truck in the morning?

chrisp · Post by **chrisp** » Wed Jul 13, 2005 6:59 pm

[quote="Jeb"]If I hooked up my cpap to my Chevy Tahoe's power outlet, would I run the battery down too far to start the truck in the morning?

john5757 · Post by **john5757** » Wed Jul 13, 2005 7:55 pm

Hi,

Do you thing that using a ultrasonics humidifier is going to humidify as clean as with a heated type?

derek · Post by **derek** » Wed Jul 13, 2005 8:29 pm

Just be careful of the type of battery you are using. Normal car "starter" batteries are not designed for deep-discharges, and to run them down will shorten their lives very significantly. You really should use a marine/rv "deep-cycle" battery that is designed for many, many charge/discharge cycles. Even so, for maximum life these batteries should not be discharged more than half their capacity.

Battery capacity is measured in amp-hours. Lead-acid batteries are specified by "Group" number; a common size is a Group 24, which has a capacity of about 70 amp-hours. Half of that is 35 amp-hours, and if the CPAP draws 0.75 amps, this gives a total of 35/0.75 = 47 hours, or about 6 nights between charges if we use the 50% discharge rule. (Note: a Group 24 will weigh about 40-50 lb, so it's not exactly portable )

For portable use a gel or AGM battery makes sense because they a spill-proof and can run in any position.

chrisp · Post by **chrisp** » Wed Jul 13, 2005 8:36 pm

1 nite. No problem. Remember. This is a Tahoe not a tercel. But yes, Derek is correct. Deep discharge is not good for auto batteries. For long term use get a Deep cycle battery. The bigger the better if mobility isn't a problem. You may need a special charger also.

Chris

johnnygoodman · Post by **johnnygoodman** » Wed Jul 13, 2005 10:23 pm

The humidifier for this unit is due out in late August. Right now the Aura CPAP, it's battery pack, and replacement batteries are offered.

Also, the battery is attached to the battery pack with only one screw so its pretty easy to pop one battery out and pop another one in.

Johnny

Machine	Mask

Battery Power Rules!

Battery Power Rules!

AEIOmed Aura with Rechargeable Battery Pack

ultrasonics humidifier