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LiFePO4 Battery: New thoughts?
#1
Last year, we batted around the concept of the LiFePO4 (Lithium Iron Phosphate) batteries for CPAP use. Much much much much lighter than SLA or AGM batteries, but at the time, I called one of the bigger manufacturers (or marketers) of the batteries and asked about their use as storage/deep cycle batteries for use in a backup or portable fashion for CPAP applications.

I was told "no dice - they are starting batteries, not storage/deep cycle type batteries and that the AH ratings, while offered for comparability to SLA/AGM batteries, were not the same for this kind of use." They urged me in no uncertain terms to NOT use these for CPAP use.

However, I've googleated around some in the past few days and have started seeing LiFePO4 deep cycle/storage batteries. Still mucho expensive, about twice what a comparable SLA would be - but I am wondering if anyone in our little community has used or considered using this technology yet. I plan on calling around to a couple of manufactures or marketers and just seeing what they have to say.

The smallest I've been able to find is a 7/10 AH. The 10 AH SLA I have to power GPS and radio in non-electric 70 year old plane is about 7 or 8 years old - so replacement is likely to need to be done soon. If feedback is positive (no pun), I may go that route - they are only about two pounds - especially if I could be able to get a couple night's CPAP use out of one of those.

OMM
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#2
I applaud the manufacturer rep for his honesty. You can use these batteries BUT the amp-hour ratings are "lead equivalent" PB/EQ. The real available power is about 25% to 33% of the rated amp hours. So a 12 amp-hour battery is only going to give you 4 amp hours before it's gone. You will need a mucho expensive 36 a-hr battery to get you some capacity, and forget running the humidifier or heated hose.

A separate issue is that while Respironics machines will happily run on 12 volt battery power, the Resmed units want 24 volts. If you put an inverter into the loop the inefficiencies will kill your battery practically before you're asleep.

A number of people are running PR System One APAPs and BiPAPs on a Poweradd Pilot Pro 32000mAh Li-ion battery and getting two days of use on a charge. The battery puts out 12 volts as required by the Philips machines, and does not require any special connectors beyond what is provided with that battery. The batteries work great if you get a good one, but the quality has been such that there ia about a 50% chance you will have to return the first battery you get. Fortunately for those with Prime, returns are easy.
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#3
(02-08-2015, 11:13 PM)Sleeprider Wrote: A separate issue is that while Respironics machines will happily run on 12 volt battery power, the Resmed units want 24 volts. If you put an inverter into the loop the inefficiencies will kill your battery practically before you're asleep.

That is part of the reason that I am moving away from ResMed and trying different solutions. It seems to me that they do things intentionally to make life harder for their customers - tie them into their proprietary ecosphere. Even when their products ran on 12 v power, they came up with a non-standard wiring configuration that forced most people to once again go to their proprietary cord for a DC solution. Elegant looking product that works well, but from what I have gathered, is no better than competitive products. And these comptitive products, which by design or chance, are more user friendly for repair or flexibility of configuration. **end of rant**

I am eager to find if this new group of LiFePo4 batteries offered as "deep-cycle" units hold any promise as storage batts - as they appear to claim to be. They are prominently listed as "SLA Upgrade Replacements", cross referenced to SLA part numbers, and and show intended uses as such things as electric wheelchairs, UPS backup batteries, alarm system backup, etc. They are not labeled "Pb AH **equivalent**" as the starting batteries were when I looked at them a year or so back. These show straight Wh or AH just as the SLAs do. One of the main manufactures/marketers has both lines and clearly says the intended uses don't cross over.

For at home use, where I only have to move them from the closet to bedside, and maybe to the yard for solar charging, the heavy bulky SLAs are fine, but the portability of the lithium iron (Fe) would be really nice for travel or camping. And while more expensive than SLA batts, they still cost about a third of what dedicated "CPAP battery packs" cost. I will keep my fingers crossed and proceed with due diligence.

OMM
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#4
I have a Shorai 18 amp LiFePO4 battery. It cost about $184, and it lasted about a year on my motorcycle. Very lightweight and has a high discharge rate for cranking an engine. The battery chemistry does not do well with deep cycles and when discharged, may not recover. Hopefully your experience with a deep cycle version will do well.

AGM batteries are a little better than SLA, but still comparatively heavy. The Optima blue top batteries are best in class for AGM deep cycle.
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#5
From what I've read, the big advantage of LiFePO4 batteries vs. other lithium batteries is they're much less likely to catch fire.

When discussing AGM or Gel cell vs. wet lead acid battery, despite the hype, the difference is not being spillable and not needing to add water.
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#6
I spoke with a few companies that are offering these batteries.

They all say indeed that these are indeed deep cycle batteries and that the AH ratings should hold true. If you get a 7.2 AH battery, you should be able to run an appliance drawing 1.0 amps for seven hours and twelve minutes. So they say. They all said these are not the same batteries like the motobike starting batteries with "Pb equivalent AH" ratings.

I am intrigued. I will likely try one - maybe one encased to fill the same volume as an SLA battery - but that strikes me as volume inefficient, which is a consideration in packing. If I choose to go for overnight CPAP use, I may just go with cells bundled in shrink wrap battery packs to save size.

If the Z-1 comes in at around .35 amps draw, I think a 6AH battery should be sufficient for two nights w/ 50% reserve and should maybe all bundle up nicely in a small shaving kit I found at the big store that specializes in selling containers. Note that I average around 6 hours of sleep a night.

OMM

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#7
(02-09-2015, 09:35 PM)OMyMyOHellYes Wrote: I spoke with a few companies that are offering these batteries.

They all say indeed that these are indeed deep cycle batteries and that the AH ratings should hold true. If you get a 7.2 AH battery, you should be able to run an appliance drawing 1.0 amps for seven hours and twelve minutes. So they say. They all said these are not the same batteries like the motobike starting batteries with "Pb equivalent AH" ratings.

I am intrigued. I will likely try one - maybe one encased to fill the same volume as an SLA battery - but that strikes me as volume inefficient, which is a consideration in packing. If I choose to go for overnight CPAP use, I may just go with cells bundled in shrink wrap battery packs to save size.

If the Z-1 comes in at around .35 amps draw, I think a 6AH battery should be sufficient for two nights w/ 50% reserve and should maybe all bundle up nicely in a small shaving kit I found at the big store that specializes in selling containers. Note that I average around 6 hours of sleep a night.
OMM
What you are saying in effect is that a 7.2 Ah Battery can produce a current flow of 1 Ampere for 7.2 hrs. Of course it cannot do that. The first reason is because a battery cannot fully discharge itself (if it did it would not recover) & second is the available voltage will drop as the battery discharges. A storage battery cannot hold its terminal voltage from fully charged to fully discharged. At full charge a 12V battery would be around 14.2V this voltage would slowly decrease as the battery runs down. To prevent low voltage damage to your machine a much larger capacity battery would be needed. An S9 consumes around 70 Watts of power which gives a current draw at 12V of about 6 Amperes. For this machine a 7.2 Ah battery would run the S9 for a bit more than an hour depending on your pressure settings. The Z1 has an AC power consumption or 35Watts max. which causes a current draw of 2 Amperes. Therefore a 7.2 Ah battery would at max. pressure, last 2 hrs. I don't know how they get it to run for 1-2 nights on a single charge. It defies Ohm's law.
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#8
(02-10-2015, 09:43 PM)woozie38 Wrote: An S9 consumes around 70 Watts of power which gives a current draw at 12V of about 6 Amperes. For this machine a 7.2 Ah battery would run the S9 for a bit more than an hour depending on your pressure settings. The Z1 has an AC power consumption or 35Watts max. which causes a current draw of 2 Amperes. Therefore a 7.2 Ah battery would at max. pressure, last 2 hrs. I don't know how they get it to run for 1-2 nights on a single charge. It defies Ohm's law.

Using the wattage of the power supply to try to determine current draw of an appliance is an illogical exercise. Futile. Technically, you could run any of these units with a 1200 watt power supply. By that theory, the machines would be drawing draw 100 amps. The blower units are only going to draw what they need to run, not the full current capacity of the supply. And of course, the supplies are over-spec for what the blowers use: trying to determine current draw as a function of the furnished power supply is about like trying to determine a car's gas mileage by the size of its fuel tank.

Using that misguided approach, if Respironics powers its System One (12V) with a 60 W power supply, it would pull 5 amps. In reality, it pulls about .35 amps (measured) at my average pressure. So, for an eight hour night, I would plan on pulling 2.8 amp. A 4 AH battery would get me through just fine, with about a 50% built in margin for other factors such as charge state at the start, inefficiencies due to age of battery, etc. For an overnight flight from say Dallas to Hong Kong, with no aircraft power supply, a 9 AH battery would get me all the way there and back, assuming an overnight flight in each direction. With no recharge in Hong Kong.

In their published literature, Resmed says that the S9 pulls between .46 and .55 amp at my average pressure and I suspect they overstate that from a conservatism/safety standpoint ... And BTW, the S-9 is perfectly happy using the Resmed 30 w power supply.

Once, for kicks and giggles, I ran an Intellipap Auto (12V) for 6 nights, 6-7 hours a night, off of a 35 AH battery with no problem. It could probably have run another night or two if I had pushed it (note that DeVillbiss says the unit draws .744 amps at my average pressure.) With a safety margin, I would estimate reliable power for about 4 days on that battery with the Intellipap. 8 nights for the Respironics System One referenced above (theoretically up to 12 nights if you remove the safety fudge factor and run it down to 11.something V).

Note that the current draws are for no heated humidifier. Can't imagine anyone trying to run one of those off of a battery anyway.

Oh, and BTW, the rated AH on a battery is the useable charge (what it is likely to put out between 14.something and 11.something V), not the capacity to total discharge.

OMM
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#9
ok,ok don't say I didn't warn you.
[Image: signature.png]Keep on breathin'
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#10
(02-11-2015, 07:25 AM)OMyMyOHellYes Wrote: ...
Note that the current draws are for no heated humidifier. Can't imagine anyone trying to run one of those off of a battery anyway.
...
OMM

Battery-Powered

My set works four nights at eight hours each with humidifier ... another night could be possible, but ist not tested.

Greetings
Fat Rat
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