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LiFePO4 Battery: New thoughts?
(02-11-2015, 07:25 AM)OMyMyOHellYes Wrote: 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.

It is certainly true that the mere capacity of the power supply does not tell you everything and doesn't tell you the actual power that will be drawn in use. It does, however, give you an idea of the maximum power the unit can draw.

I wouldn't say it is "nonsense" to determine the current draw - at the very least you can determine the maximum current draw if you know the power rating of the power supply and the voltage it supplies.

Batteries do not supply constant voltages of course, and they will never let you draw all of their theoretical capacity out of them.

But knowing the power rating and the voltage will at least let you calculate a reasonable "ballpark" figure. If I needed a battery to last ten hours at 5 amps I wouldn't get a 50 amp hour battery though, I would add in a fudge factor of about 100% to that just to be safe.

Ed Seedhouse

Part cow since February 2018.

Trust your mind less and your brain more.

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15 times the actual current draw is not a "reasonable ballpark figure". To me it does sound kind of like "nonsense" [not my word]. (at least for the Respironics 560 - I picked that because its 60 w power supply works out to 5 amps offered in that scenario and because I have measured its consumption at around .35 amps for 8-9 cm setting).

But what current CPAP blower out there will draw 5 amps? None. They do not exist in the real world. If you hang a bunch of power hungry stuff off of it you might get there. Something like an S-9 AutoSet/Elite with the H5i humidifier and the Climate control tube and temperature set to 30 deg centigrade/86 deg F running at 9 cm (per Resmed's published Battery guide ver. Oct 2011 - which, BTW, recommends about a 75 AH battery for 10 hrs w/ that setup- Resmed's reference used here since Respironics doesn't publish).

That kind of load is what the power bricks are sized for.

But don't do all that on battery power. If you think you need all of that stuff, then give up on ever finding a convenient portable solution. It won't happen until we get cheap micro cold fusion generator cells to market.

Running the S-9 blower alone uses about half an amp at 9 cm (again per Resmed's published Battery guide ver. Oct 2011 - which would recommend about a 7.5 AH battery). So a 5 amp estimate would be an overkill factor of 10 for that unit.

So hey, if it sounds prudent to schlep a 65 lb/30 kg, 100 AH SLA battery around to just be sure it will run a CPAP blower for 10 hours, if a 6.6 AH battery at 2 pounds/880 g will do the same thing, then by all means, feel free.

On a side note, a 100 AH LiFePO4 deep cycle battery weighs 28 lb/12 kg as opposed to the 65/30 for the SLA - which the analysis of if the LiFePO4 capacity is comparable to SLA capaity is actually what we were hoping to find out in this discussion.
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(02-11-2015, 03:41 PM)Fat Rat Wrote: My set works four nights at eight hours each with humidifier ... another night could be possible, but ist not tested.

Fat Rat

I have not tested the Respironics with the heated humidifier on and they refuse to provide current draw information so I am a little bit in the dark here. However, running the 24 AH battery you are using I would not be surprised at getting multiple nights. Without the humidifier, I would expect to get at least 6 (and in a perfect world, almost a theoretical 9) nights at 8-9 cm H2O.

And you are using the LiFePO4 battery for this application which begins to answer the question "are the LiFePO4 deep cycle batteries' AH ratings comparable to lead chemistry deep cycle AH ratings?" From what I have been reading, the LiFePO4s may actually be more conservatively rated and yield more power over time than equivalently rated Pb batteries. I am finding more and more references to using them in things like electric cars which are definitely deep cycle applications.

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That is the starting phase of my 562.
Settings: 8 mb - no auto, flex 2, humidifier 2, w/o heated hose

You can see peaks up to 6 A. Maximal measured peaks were 6.54 A. The power supply is electronicly controlled and must deliver power peaks even of settings at 20mb and humidifier at 5! That is the reason the power supply is as big as it is.

Cheap accus for charging iPhones et altera mostly have an electronical short cut fuse that will not accept even short peak currents of this level. Most of them will not work. If you consider to use such a device have a look at the maximal current the device could deliver!

The current averaged over several hours I determined my settings a current of .83 A. Without humidifier it should be lower that .5 A. I have lost that data. Huh

I have currently enormous difficulties even to read English ... sorry!Dont-know

Fat Rat
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I would like to note a little bit off topic ...

Much of our discussion seems to me quite a bit academic - even my posts. We all always want the very best ... Cool

Backup for blackouts due to snow storms, earthquakes ... Even starter batteries will work, unless they are constantly emptied completely. Belonging to a frequently used vehicle they are so cheap that they could be exchanged after 2-3 years.

Portable outdoor, is very expensive because LiPo (small, light), problem is rather the CPAP-device that despite minimum comfort has to be small and light.

Air travel: Have a look for accurate information by the airline, which batteries they will accept. From airline to airline, there seem to be large differences. I've read that one ranks equal batteries of every chemistry (<100Wh). Another prohibits LiFpo4 complete (- why?). Visit respective websites!


Very important seems to me that only people assemble batteries themselves and tinker connections with knowledge about. Shorts are not funny - whether in the home, in your backpack or on a plane! Even the unlikely possibility of an accident must be excluded, even if a cable breaks off!

Fat Rat
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Fat Rat, your amperage readings are based on 12 Volt DC? So we can expect a range from 10 Watts without humidifier after startup, to peak power of as much as 72 watts at startup with humidifier, dropping to 48 watts with humidifier on DC power. Does that also include a heated hose?
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No heated hose. 12VDC

.83 x 12 = 9.6W (with humidifier at the settings above, average over some hours.
Peaks to 6.54 A max. (maybe seen more with an oscilloscope!)

about .5 A w/o humidifier (I don't remember exactly .45 .. .48?) average ...
.5 x 12 = 6 W

The original fuse in the cable is an 8A fine ...

I don't know the exact capacity of the battery, it is specified as 22 AH. It seem to exceed specifications at that low consumption? It is a golf cart battery.

Fat Rat
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Thanks for making the measurements. It's good reference information.
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It is definitely not a monster power consumption as is often claimed - not even with the humidifier.

But beware, the consumption depends on the individual breathing habits and the settings. Every breath a power peak; less breaths - less peaks. X-Flex setting 0 = higher mean pressure = higher consumption; setting 3 = lower consumption ...

Provide always plenty of reserve in the battery! Otherwise, you might ought to count: 2345 breaths left, 2344, 2343, ... to the stop of the machine!Oops

Fat Rat
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I sure wish I had found this thread before I created my own thread, asking about Amp draw on my REMstar Auto A-Flex 60 Series.

If my machine truly is only pulling .35A (average), it's going to make me VERY happy!
Mounting my system in my van, I'm not as worried about size/weight as someone planning air travel, so I'll be going with a full-size 12V 80 Ah AGM battery and a 160W solar panel.
That set-up will give me a 2:1 Watts:Ah ratio and more than enough total Ah in the battery to run other stuff (lights, computer, fan, etc).

This is a major load off (pun intended) my mind. Dancing

"To me it does sound kind of like "nonsense" [not my word]. (at least for the Respironics 560 - I picked that because its 60 w power supply works out to 5 amps offered in that scenario and because I have measured its consumption at around .35 amps for 8-9 cm setting)."

"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."
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