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Comparative Current Draw - Battery Use Estimate
#1
Comparative Current Draw - Battery Use Estimate
Well, I have come to the end of my current experiment (no pun intended) to see what kind of current (amps) that various CPAPs drew and calculation of how long my standby batteries should last.

Parameters of the test included:
  • No heated humidification
  • Average measurement over multiple nights - test period 8 nights each (PR 560 only the 4 nights without heated humidification included for this comparison)
  • Average amps measured with Agilent U1233A multimeter
  • Power supply - Astron SS12, 12A power supply, nominally ~14V (to provide for battery charging) through West Mountain Super PWRgate 40 backed by 12V 35 Ah AGM battery
  • ResMed S9 Autoset was powered off of the same power supply, through the ResMed 12V-24V DC converter
  • For battery life estimates, I used a safety factor of 50% over the average observed current draw
The summary results surprised me a little bit.  The units were surprisingly close in their current draw across the board.  The DeVilbiss Intellipap Auto, the Respironics System One 560, and the Resmed S9 Autoset all averaged between approximately .41 and .42 amps at my pressures and breathing patterns.  The Resmed S8 Autoset II pulled slightly more current, averaging approximately .46 amps.  

The current numbers for the Resmed units were lower than those listed in the Resmed Battery Guide, but I guess they have to take a conservative approach and give the worst case scenario for any given machine and at a given average pressure just to be "safe".  Everyone's breathing patterns are different and so I am guessing this number would be different for everyone.  Also, keep in mind, that my "sample" was limited to ONE machine of each model so not representative of the entire line.  (My exercise was not to determine current draw for others; it was to determine how long I could expect to use my backup batteries.)

Based on the observed results for my experiment, I think I should be able to conservatively pull 8 nights out of my 35 AH batteries and 9 nights out of my 39 Ah batteries, at least for the Intellipap Auto, PR System One 560 Auto and S9 Autoset units.  With the S8 Autoset II, I think I should be able to get 7 nights out of the 35 Ah batteries and 8 nights out of the 39 Ah batteries.

I thought this might be of general interest to some on the forum (I had at least one ask that I share the results).  Please keep in mind the limited scope of my test - it is for me and me alone to see how my machines respond to my usage.  Individual results with your machines as you use them may be considerably different so please don't rely on my presentation for your use.  Note that my configuration was put together for the most power efficient usage I could get; higher pressures, and especially heated humidification, would result in higher - sometimes drastically higher - power consumption and much shorter battery life.

OMMOHY

   
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