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Discussion Starter · #1 ·
We are in the second day of a major blizzard. I use a cpap that will run off 12volts at 1.5 amps. I have a couple lead acid 12 volt batteries out of computer ups that I was wondering about making a portable battery backup to the cpap machine. How do I calculate how long a battery will last me?

Commercially available battery backups for cpap sell from $300-500. I would like to build something that is much more economical and reliable and rechargeable.

Last night I disconnected my computer ups and slept without worrying if the power was going to stay on all night.

thanks
joeinnm
 

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Just hope it don't go off for a week.....

Joe....I use a deep cycle marine battery...and keep it charged up in the bedroom closet. I tested it when I first got it. Used it for 4 nights and was still working. Now, I just use it when juice goes off and then recharge when juice is back. When going camping (hunting) with the grandsons, I just haul it along too. Worked for 4 nights in NM last year elk hunting. It's nice that I don't have to haul a generator anymore.
 

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Joe, I haven't a clue what a cpap is, but I know something of batteries.
I will assume, since we are 'po boying' this, that they are automotive, flooded lead acid, batteries. (FLA)
Somewhere on the label there should be a mention of "AH", or 'Ampere Hour' rating. This is a number arrived at by discharging the battery, at a steady rate, from 12,8 volts, to 10.25 volts, over a 20 hour period ("20 hr rate"), and is an accepted industry standard, for capacity.
A 100 AH battery, then, could be used at a 5 amps draw, continuously, for 20 hours, or, extrapolating, a bit over 4 amps, for 24 hrs, with the voltage staying above 10.25 volts.
If it is an option, but a better type of battery; Google 'Hawker Energy', and look at their 'Odyssey' battery line, paying close attention to the shelf life, retained charge in extended storage, and tolerance for deep discharge, cycling!
They are the wave of the future; I use them in all my (7) motorcycles, and any of them would start my truck, or serve as back-up power, at the house, if needed; just my .02. Terry
 

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Discussion Starter · #4 ·
cpap is an assisisted breathing machine

for sleep apnea, it draws 1.5 amps. The batteries I was looking at are a sealed lead acid battery that is out of a computer ups. It is rated at 6.4 amp hours. I would assume that would be good for around 3 hours right?

I am looking to match what is commercially available at less then their cost and still be highly portable. A full size car battery is not portable or safe in home use. Gel battery would be next choice or Lithium ion, the sealed lead acid are safe for long term storage without having to maintain a charge to them.
 

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Hi joe, typical UPS battery is about 12-20 Amp hours. 12/1.5= 8 hours, 20/1.5=13 hours. A car battery is about 75-100 amp-hours or two days worth, Redgards, Ed.
 

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Is your cpap a continous draw or only cycle with your breathing. The actual time for the draw can be calculated with the time of the cycle. It is different that if you use a light bulb, that is a continous draw.
 
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