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WARNING to CPAP Users: PREPARE for the Unexpected - When the power goes out
(05-29-2015, 02:00 PM)GWild Wrote: My 18AH battery will power a third day

Then it cannot possibly be a lead-acid battery - are you sure it's not a lithium-ion or a AGM? You've actually hooked up your 12-volt 18 amp-hour lead acid battery to your CPAP machine and run it solely on that for 3 nights (8 hours x 3 nights) with no problem?? That's pretty much impossible with an 18AH lead-acid.

Why? Because when you get below 50% charge, the voltage drop on 12-volt lead acids is way too low to allow the CPAP machine to operate properly. If the voltage drops too low, modern CPAPs will simply give you an error message.

[Image: voltchart1.gif]

I suspect you have some other type of battery (not lead-acid) perhaps. Lithium-ions or AGMs will work for what you're suggesting you're able to do, but not lead-acids.



SuperSleeper
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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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Okay, Gwild just PM'd me to tell me his batteries are AGM batteries. I thought that he was telling me he was using the standard liquid-filled lead-acid batteries that have electrolites (acid) and lead fins (marine deep cycle types)-- where the liquid is sloshing around in the battery case. But his are AGM, which are a type of lead-acid (I didn't realize that), but do not have the liquid freely moving inside the battery.

So, AGMs do have better deep-discharge capabilities - unlike the standard liquid lead-acids of the type that are used in "marine" battery applications and many deep cycle batteries of that sort, which can be damaged if discharged too low.

Sorry for all the confusion!

SuperSleeper
Apnea Board Administrator
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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Technical speak follows. Disinterested parties should now place fingers firmly into their ears - or press <NEXT>.

Well - actually, depending on construction, deep cycle wet cells are just as good (and sometimes better) than the sealed lead AGM types. One manufacturer has a wet cell designed for 100% discharge and warranted for 10 years and thousands of full 100% charge/discharge cycles. Design matters (but a good design costs a lot more than the average design to build).

I just remeasured my machine in use - it consumes about 5 watts on exhalation and I managed to see 20 watts on an abrupt inhale. Suffice it to say I average about 8 to 10 watts during use, and that's on the brick power supply. NOTE: different people will consume different power due to how they breathe, how bad the apnea is, machine settings, etc. YMMV

But doing the math: 10 watts at 12.6 volts is about 0.79 amps. Over 8 hours, that is only 6 ampere hours.

My particular battery - an increased capacity version of the brands 18AH battery - 12V21AH [PSH-12180FR] - a sealed lead acid with an AGM design (AGM just means the acid is held in a sponge-like glass mat pressed against the lead-antimony plates).

I don't have the battery capacity spec for a 26 hour discharge rate of 0.79 amps, but it should be a bit more than the 20 hour rate of 1.05 amps or 21AH -- maybe 23 or 24AH?

So if I use 6AH a night, two nights adds up tp 12AH, and three nights 18AH. I charge at a two day interval because I'd rather help my battery last more than 200 cycles. At only 12AH consumed over two nights, I am closer to the 50% depth of discharge rating of about 500 charge/discharge cycles.

As for a UPS in this mode; a UPS is much less efficient than the switcher brick power supply and won't last as long given the same load as a direct battery to CPAP connection. But, a typical 1300VA or 1500VA (volt amp) UPS has two 12V 7AH or 9AH SLA-AGM batteries, and should easily last through one night of emergency use if the batteries are fully charged heading into the night. And a few 100% discharge cycles are the designed use of these things. They won't break or void the warranty if you do happen to discharge the battery (a good UPS turns off when the battery level drops below a preset level).

Anyone wanting more specific detail on what I put together can PM me ...
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I just got back from the Marine store. I bought a west-marine--15-amp-automatic-battery-charger-with-engine-start-timer--14982045
and a west-marine--gel-deep-cycle-marine-gel-battery, with 97 amp hours at 12v--P015020365

Archangle, did I get the right stuff? That is the charger the very experienced salesman told me I needed for my battery, and we even went on to a cpap site, and I showed him exactly what I was using it for.
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I don't know what your particular plan is (is this an emergency use backup or some sort of daily use/weekly recharge setup).

As an emergency backup - for when you expect several days off grid - in my opinion, the battery is probably fine. For that emergency situation, you probably only need a float charger to maintain the battery between panics. The full fledged 15A charger you bought, again IMHO, isn't a good choice for a simple maintenance charge situation. A small 1A changer with a GEL float setting would be better.

With what you have purchased, you can do this: charge the battery today until it reaches float, then unplug everything (battery fully disconnected), then three to six months from now repeat the charge to float. That will keep the battery topped off (also keep the battery clean). Not optimal, but workable.

Assuming the battery is rated for 20 hours, and you don't draw down at a 20 hour rate, you can expect the battery to last a bit longer than it's 20 hour capacity. As much as 20% more - here is data from a 12V102AH gel spec:

5-Hr Rate == 85AH
10-Hr Rate == 94AH
20-Hr Rate == 102AH
100-Hr Rate == 108AH

Also - the temperature you store the battery has a huge impact. Cooler is usually better:



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(05-29-2015, 05:00 PM)GWild Wrote: I don't know what your particular plan is (is this an emergency use backup or some sort of daily use/weekly recharge setup).

As an emergency backup - for when you expect several days off grid - in my opinion, the battery is probably fine. For that emergency situation, you probably only need a float charger to maintain the battery between panics. The full fledged 15A charger you bought, again IMHO, isn't a good choice for a simple maintenance charge situation. A small 1A changer with a GEL float setting would be better.

With what you have purchased, you can do this: charge the battery today until it reaches float, then unplug everything (battery fully disconnected), then three to six months from now repeat the charge to float. That will keep the battery topped off (also keep the battery clean). Not optimal, but workable.

Assuming the battery is rated for 20 hours, and you don't draw down at a 20 hour rate, you can expect the battery to last a bit longer than it's 20 hour capacity. As much as 20% more - here is data from a 12V102AH gel spec:

5-Hr Rate == 85AH
10-Hr Rate == 94AH
20-Hr Rate == 102AH
100-Hr Rate == 108AH

Also - the temperature you store the battery has a huge impact. Cooler is usually better:

It is for emergency backup in case of a power outage. I am storing the battery in a room upstairs that has air con. I don't yet know how much power my Aircurve 10 would draw, without humidifier or heated hose on, because ResMed does not yet provide stats on my machine. Archangle, please chime in on this for me, too.

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I just called the marine store back, and they told me that the charger I bought has a float setting, and it doesn't always charge at 15 amps.
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Yes - the larger charger does have a float setting, but it kinda-sorta-seems like a lot of charger for when all you need is a few milliamps 99.999% of the time.

A possible downside of a large charger is that when power does fail, and why I personally think it isn't ideal, is that some of the larger chargers don't do a great job limiting how much load they place on the battery when the grid is down. Meaning, they can actually discharge the battery quite a lot between when the grid drops and when you need the battery. Smaller maintenance mode chargers - sometimes - do a better job of holding the charge when the grid drops.

Most chargers don't spec this level of detail; and the West Marine guy probably doesn't know the answer, either. If he does, and comes back with something like "The sense load of the charger is only 100uA.", then you're okay. However, if the manual says something like "Disconnect the battery when line power isn't available." its essentially telling you it'll drain the battery while you're not looking.

Again - lots of variables - and you're probably okay. Just be aware of possible unexpected consequences.

ps: you can always insert an ammeter between the charger and the battery, pull the power plug and see just how much the charger pulls from the battery. If a a milliamp or less, probably good to go. If tens of milliamps, or more, then probably best to do the charge then disconnect method.

(05-29-2015, 05:55 PM)JVinNE Wrote: I just called the marine store back, and they told me that the charger I bought has a float setting, and it doesn't always charge at 15 amps.

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Oh Boy!
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ps: I am done on the subject... lol.
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