Homegrown battery packs for a Resmed S9

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Oobie
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Homegrown battery packs for a Resmed S9

Post by Oobie » Thu May 28, 2015 8:19 pm

Hi,

I came across this today:

https://stacksocial.com/sales/intocircu ... a-0m8ddxmy

It is a 26 amp-hour 12-volt battery which appears to have the wattage necessary to support operation of at least the pump and perhaps an entire ClimateLine setup on an S9.

If I couple that with this: https://www.cpap.com/productpage/c-100- ... erter.html, it looks superficially like a chance to build an airline-compatible battery system for my S9 for $150, which has three times the wattage of the C-100 battery.

The question then becomes, what are the risks?

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Re: Homegrown battery packs for a Resmed S9

Post by wm_hess » Thu May 28, 2015 9:27 pm

No this will not power your device for any length of time. The battery you're showing is about. 31 kwh hours. This would relate to no more than 2 hours of power. Battery is 26 amp x 12 volt then divided by 1000. Gives you approx. 31 kwh. Your machine varies but I use. 08Kwh for my machine. Using 50% of. 31 gives. 15 Kwh of available power.

Please see here
viewtopic.php?f=1&t=98759&p=917353#p917353

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Re: Homegrown battery packs for a Resmed S9

Post by Oobie » Thu May 28, 2015 11:12 pm

wm_hess wrote:No this will not power your device for any length of time. The battery you're showing is about. 31 kwh hours. This would relate to no more than 2 hours of power. Battery is 26 amp x 12 volt then divided by 1000. Gives you approx. 31 kwh. Your machine varies but I use. 08Kwh for my machine. Using 50% of. 31 gives. 15 Kwh of available power.

Please see here
viewtopic.php?f=1&t=98759&p=917353#p917353
Oh, I don't agree. The 50% figure looks, by my review, like it's related to lead-acid batteries. Li-ion and Li-polymer batteries don't behave in the same way; you should be able to draw a median load all the way to around 2% of its full charge. People are reviewing the C-100 on CPAP.com as giving them four nights of use on one charge. That's a 97 watt-hour battery. The one I'm referring to is a 312 watt-hour battery.

My guess is that the S9 is probably drawing 60% of its rated power if it's pushing 12 cm of pressure. (I auto-titrate between 7 and 20, but the data shows 10 or 11 cm most of the night) 0.6 * 3.75 amps * 24 volts gives 54 watts. The battery should work for roughly six hours, worst case, probably nine without the humidifier or ClimateLine.

That's at half the price of a C-100 kit.

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Re: Homegrown battery packs for a Resmed S9

Post by wm_hess » Fri May 29, 2015 4:17 am

I would agree that you might be able to get 6 hours of power from a 26 amp battery with no humidification.

26 amp * 12 Volt = 312 Watts or .312 kilo watt hours (kwh).

I run an S9 Autoset as well with a pressure very similar to yours. I have measured my electrical usage with a Kill-a-Watt meter several times. I use .08 kwh for humidification and .05 kwh without.

.312(kwh)/.05 (kwh) = 6.24 hours of power. If you choose to drain the battery completely that is what you should get assuming a completely full battery.

As a note I did look at the reviews for the BPS battery and saw I believe 2 reviews that mentioned using them for four nights but they charged them daily. A couple of people mentioned getting no more than two days off of 1 charge.

-Bill

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Re: Homegrown battery packs for a Resmed S9

Post by CapnLoki » Fri May 29, 2015 5:00 am

wm_hess wrote:No this will not power your device for any length of time. The battery you're showing is about. 31 kwh hours. This would relate to no more than 2 hours of power. Battery is 26 amp x 12 volt then divided by 1000. Gives you approx. 31 kwh. Your machine varies but I use. 08Kwh for my machine. Using 50% of. 31 gives. 15 Kwh of available power.

Please see here
viewtopic.php?f=1&t=98759&p=917353#p917353
I think you're wrong on two counts - First of all, 31 kwh is 31 KiloWatt-Hours, which is a huge amount of power, more than most homes use in a day. Perhaps, you meant simply Watt-Hours, though I don't know where you got that number.

The power rating for these battery pack is generally bogus and misleading, because they give "AmpHours" without saying what voltage is they are using. Typically they just use the sum of the individual Lithium cells, which makes a bit of sense if you're comparing to cell phone batteries which are one cell. But since the pack is used at a variety of higher voltages, it has little meaning. Watt-hours is better since it takes into account the voltage. This pack is probably 26 amp-hours X 3.6 volts (the cell voltage), or 94 Watt-hours. This is in line with the weight of the pack, and the 100 watt-hour limit for flying. Converting back to 12 Volts, we get around 8 Amp-hours. This will be enough to power a S9 at average pressure for about 10 hours, assuming no humidity and using the DC converter, not an inverter with the AC power brick. This might work is a one night airplane or camping use.

The risks are that the cpap current load is very variable, and the startup may trip the battery current limiter and shut it down. Or, the 12 volt output may be too low when the battery drains a bit, and the 16 volt output may be too high. And of course it may not have the power that I'm guessing. Make sure you buy from a source that will accept a return after its used. Amazon, BTW, has this battery pack. There are other battery packs with similar ratings that have had mixed success. The technology is the highest power for the weight, and the price has come down a lot, but unfortunately the available packs are configured for powering tablets which are a slightly larger market than cpaps. Personally, this is not usage that interests me, so I haven't tried any Lithium Polymer batteries, but there are other recent threads where you can find examples of battery packs that have worked.

for Resmed loads, refer to:
http://www.resmed.com/assets/documents/ ... lo_eng.pdf
If the load is 1 Amp, then 8 hours is 8 amp-hours, times 12 volts gives 96 watt-hours. Lithium packs don't really need the 50% safety margin if they are properly built with power management that will shutdown before undervoltage causes damage. For readers with Respironics, there is no company guide but my measurements show them to be a bit more effecient then Resmed.

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Re: Homegrown battery packs for a Resmed S9

Post by wm_hess » Fri May 29, 2015 8:36 am

Cap'n autocorrect strikes again! My response was from a telephone. If you look you'll see I'm saying point 31 kwh. I was saying if there is 26 amps times 12 volts then divided by 1000 to get to the point 312 kwh.

. 31/.05 kwh draw is about 6 hours of power at best, excluding the variables you mentioned.

-Bill

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Re: Homegrown battery packs for a Resmed S9

Post by CapnLoki » Fri May 29, 2015 1:11 pm

wm_hess wrote:Cap'n autocorrect strikes again! My response was from a telephone. If you look you'll see I'm saying point 31 kwh. I was saying if there is 26 amps times 12 volts then divided by 1000 to get to the point 312 kwh.

. 31/.05 kwh draw is about 6 hours of power at best, excluding the variables you mentioned.

-Bill
Yes, I kind of guessed it was autocorrect or finger memory. But also, I'm sure this pack is not 26 amp-hours at 12 V because it only weighs 1.5 pounds. If it were, it could power an S9 without humidity for several days since it would have as much useful power as the 24 pound AGM battery I've been recommending! It has to be around 8-9 Amp-hours at 12 volts.

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Re: Homegrown battery packs for a Resmed S9

Post by Oobie » Sat May 30, 2015 1:56 am

CapnLoki wrote:
This pack is probably 26 amp-hours X 3.6 volts (the cell voltage), or 94 Watt-hours. This is in line with the weight of the pack, and the 100 watt-hour limit for flying. Converting back to 12 Volts, we get around 8 Amp-hours. This will be enough to power a S9 at average pressure for about 10 hours, assuming no humidity and using the DC converter, not an inverter with the AC power brick. This might work is a one night airplane or camping use.
The pack rates 26 amp-hours. This battery has circuitry for a maximum 3.42 ampere power draw when set for 12 volts. 26 amp-hours / 3.42 amps = 7.6 hours at the *battery's* maximum current rating. This means that the battery will operate safely and correctly if the circuit connected to it is dissipating 41 watts. 41 watts * 7.6 hours gives 312 watt-hours. This confirms that the time to dissipate at maximum current matches the rating of the battery. The equations balance.

I am thus looking for some predictions about how the S9 will work with a 12-volt, 3.42 amp sustained output battery. A converter connected to the battery will convert from 12 to 24 volts, and must be rated to draw 3.42 amps and supply the S9 with the current it needs at 24 volts of EMF. The S9, when not used with its h5i humidifier, can connect to a 30 watt output power supply. 30 watts is the same as 30 amp-volts. The maximum designed current draw for the S9 is, therefore, 30 watts / 24 volts = 1.25 amps.

The battery, rated for 26 amp-hours, will drive an s9 drawing 1.25 amps for 20 hours. 26 amp-hours / 2* 1.25 amps = 10.4. Around 9 hours for a 90% discharge. 8 hours to allow for inefficiencies because there would have to be a converter also in the circuit dissipating some heat. Presumably that would be 8 hours at 30 watts, or, 240 watt-hours, which is below the rating for the battery. Working only from the data sheets, the battery should last for most of a transatlantic flight.

Now, if we assume that 1.25 amps is the power draw for 20 cm of pressure, then it seems reasonable that 70% of that is a good fudge-factor for 10 cm, allowing for the dynamic features of the S9. That would mean the battery would last for 11 hours at least. Probably more.

Li-polymer batteries, I'm told, are very lightweight. 1.5 pounds is not impossible.

Whether they'll let it on a plane is another question. The official guidance is actually a little bemusing; Delta seems mostly concerned with the mass of lithium found in the battery and whether it's packaged safely. I can't see any information about that, but there are reviewers on Amazon discussing its use on a plane.

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Re: Homegrown battery packs for a Resmed S9

Post by sleepyb » Sat May 30, 2015 3:51 am

Well, I wish battery companies would tell the truth, but a 12V 26Ah battery would be about the size of a large motorcycle battery, so we can rule out honesty with this battery company. Yes, all lithium battery companies post mAh, but the more honest companies also post Watt hours. As CapnLoki wrote, it is most likely a 94 Wh battery which is just under 8Ah and would weigh about 1 1/2 lbs. That, without the humidifier would get you a full nights sleep, but do you really want to do business with a company that isn't honest?
Also, there is a huge difference in quality with lithium batteries. Some good, some not so good. This is one product where you get what you pay for.
There is a reason why some of these supplies cost over $200 and others are much less.

As for the converter, you are on the right track. When going from battery to your S9, that is a much better way to go than an inverter. Much less power loss.

The airlines will allow up to 100Wh lithium batteries without a note, but the 101-160Wh batteries can be iffy and when I asked I was told I would need a note from the airlines for a 153Wh battery. I suspect you could get away with it without a note from the airlines, but I would hate to have to leave it behind. If I was just using it for camping I would probably go with the 153Wh battery pack from Amazon that uses quality Panasonic cells. ($209.00) I do have a couple 34Ah AGM batteries for home backup but they are too heavy to travel with.

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Re: Homegrown battery packs for a Resmed S9

Post by CapnLoki » Sat May 30, 2015 7:08 am

Oobie wrote:
CapnLoki wrote:
This pack is probably 26 amp-hours X 3.6 volts (the cell voltage), or 94 Watt-hours. This is in line with the weight of the pack, and the 100 watt-hour limit for flying. Converting back to 12 Volts, we get around 8 Amp-hours. This will be enough to power a S9 at average pressure for about 10 hours, assuming no humidity and using the DC converter, not an inverter with the AC power brick. This might work is a one night airplane or camping use.
The pack rates 26 amp-hours. This battery has circuitry for a maximum 3.42 ampere power draw when set for 12 volts. 26 amp-hours / 3.42 amps = 7.6 hours at the *battery's* maximum current rating. This means that the battery will operate safely and correctly if the circuit connected to it is dissipating 41 watts. 41 watts * 7.6 hours gives 312 watt-hours. This confirms that the time to dissipate at maximum current matches the rating of the battery. The equations balance.
WRONG!!! There is no such thing as "rating 26 amp-hours" unless you specify a voltage! In this case the voltage is not 12V, its 3.6 or 3.7, which is the voltage for Lithium Polymer cells. This is common for battery packs. The reason the "equations balance" is that they are circular, based on the same faulty assumption.
Oobie wrote:I am thus looking for some predictions about how the S9 will work with a 12-volt, 3.42 amp sustained output battery. A converter connected to the battery will convert from 12 to 24 volts, and must be rated to draw 3.42 amps and supply the S9 with the current it needs at 24 volts of EMF. The S9, when not used with its h5i humidifier, can connect to a 30 watt output power supply. 30 watts is the same as 30 amp-volts. The maximum designed current draw for the S9 is, therefore, 30 watts / 24 volts = 1.25 amps.
Another faulty assumption - the CPAP pump has a startup current draw of somewhere around 3-4 amps, and actually cycles on and off on every breath. The total average load depends on the pump pressure, and for a setting of 20 will be about 1 Amp. At a more typical pressure of 12 it will be about 0.65 Amps. But the issue for the battery pack is whether the startup load of the pump will trip a current limiter in the battery and shut it down - this has been a problem with some packs that have the same "26000 milli-amp-hour" rating. This can only be determined by experimenting.

Oobie wrote:The battery, rated for 26 amp-hours, will drive an s9 drawing 1.25 amps for 20 hours. 26 amp-hours / 2* 1.25 amps = 10.4. Around 9 hours for a 90% discharge. 8 hours to allow for inefficiencies because there would have to be a converter also in the circuit dissipating some heat. Presumably that would be 8 hours at 30 watts, or, 240 watt-hours, which is below the rating for the battery. Working only from the data sheets, the battery should last for most of a transatlantic flight.

Now, if we assume that 1.25 amps is the power draw for 20 cm of pressure, then it seems reasonable that 70% of that is a good fudge-factor for 10 cm, allowing for the dynamic features of the S9. That would mean the battery would last for 11 hours at least. Probably more.
All built on a bogus assumption - though I agree that it will probably last a night, if it works at all. That's because at pressure 10 the draw is 0,55 amps or say about 5 amp-hours for a night, and the pack is actually about 8 amp-hours at 12 volts.
Oobie wrote:Li-polymer batteries, I'm told, are very lightweight. 1.5 pounds is not impossible.
Yes, it is, with the current commercially available cells. If you try to find the "energy to weight ratios" for current cells you get numbers around 500 kJ/kg, which is about 140 watt-hours per kilogram or about 100 watt-hours for 1.5 pounds. Or you can search available LiPo cells and you'l find that a 2200 milliamp-hour (at 3.7 volts) cell weighs 48 grams, so 12 of them is 26400 milliamp-hours at 576 grams or 1.26 pounds for the raw cells.
Oobie wrote:Whether they'll let it on a plane is another question. The official guidance is actually a little bemusing; Delta seems mostly concerned with the mass of lithium found in the battery and whether it's packaged safely. I can't see any information about that, but there are reviewers on Amazon discussing its use on a plane.
Yes, it is hard to figure out the regs and each airline interprets it a bit different. The basic guideline is 8 grams of lithium in lithium-ion packs. A 2200 milliamp-hour cell has 0.66 grams of lithium, so 12 cells is 8 grams. This means that 26400 milliamp-hours at 3.7 volts, or about 98 watt-hours is the practical limit for carrying on a plane. Some airlines use this as the limit, other calculate a bit differently, but since there are a number of packs with this identical spec, it would seem they are all designing around the same guideline.

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Re: Homegrown battery packs for a Resmed S9

Post by Oobie » Sat May 30, 2015 9:53 am

CapnLoki wrote: WRONG!!!
A rhetorical coup de grace, to be sure. Keep persuading me like that, because it really works! (I've been using kirchoff's law for 30 years.)

Anyway, you also supplied the data. If what I have to do is consider the "natural cell" voltage rather than the output of the battery pack in order to understand the specification, then sure. That's a 100 watt-hour battery pack.

That means it's roughly equivalent to the C-100 on offer at cpap.com. That suggests that it's still worth a try.

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Re: Homegrown battery packs for a Resmed S9

Post by CapnLoki » Sat May 30, 2015 10:37 am

Oobie wrote:
CapnLoki wrote: WRONG!!!
A rhetorical coup de grace, to be sure. Keep persuading me like that, because it really works! (I've been using kirchoff's law for 30 years.)
Sorry about being so harsh, but I did try to explain it twice in this thread already. And I've mentioned it a number of times just in the last few months. And what does kirchoff have to do with it?
Oobie wrote:Anyway, you also supplied the data. If what I have to do is consider the "natural cell" voltage rather than the output of the battery pack in order to understand the specification, then sure. That's a 100 watt-hour battery pack.

That means it's roughly equivalent to the C-100 on offer at cpap.com. That suggests that it's still worth a try.
Yes its worth a try; feel free to get one and report back. But virtually identical units have been tried by a number of forum users with mixed results, just make sure you can return it after its been used. (Search for poweradd or 32000 for several other threads on this type of pack)

And yes, there's a reason why this is similar to the C100 - its because it uses essentially the same cells in a similar configuration. For instance, in the specs it says "Equivalent Lithium Ion Content: Less Than 8 grams" just as I predicted. The C100 has the advantage of having been setup to run cpaps, and comes with the proper cords, etc. but the premium paid is pretty stiff.

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Re: Homegrown battery packs for a Resmed S9

Post by Oobie » Sat May 30, 2015 3:52 pm

CapnLoki wrote:
And what does kirchoff have to do with it?
You get 12 volts from four Li-poly packs in series.
CapnLoki wrote: But virtually identical units have been tried by a number of forum users with mixed results, just make sure you can return it after its been used. (Search for poweradd or 32000 for several other threads on this type of pack)

And yes, there's a reason why this is similar to the C100 - its because it uses essentially the same cells in a similar configuration. For instance, in the specs it says "Equivalent Lithium Ion Content: Less Than 8 grams" just as I predicted. The C100 has the advantage of having been setup to run cpaps, and comes with the proper cords, etc. but the premium paid is pretty stiff.
Nah, if it doesn't work for the CPAP, then it stands to reason that the C100 will also not suit me. At that point I'll be building something out of a deep cycle battery. And I'll just keep the thing as a laptop charger. Or I buy two for the same amount of money as a C100

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Re: Homegrown battery packs for a Resmed S9

Post by Oobie » Fri Jun 12, 2015 3:44 pm

I bought the battery. It works very well with just the pump and a slimline hose and mask. It does not work at all with ClimateLine and the heated humidifier added.

The first test used the full kit, humidifier and heated tube included. The pump shut down after the pressure adjusted past 8 cm or so. It only took about three minutes to stop altogether.

My second test was with a fully charged pack, the voltage converter (12-24V), and a three hour nap. The charge meter still lit up "full" after three hours. It will be sufficient for the plane rides. Which is about where I thought it was going to end up.

Rob

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Re: Homegrown battery packs for a Resmed S9

Post by palerider » Fri Jun 12, 2015 4:08 pm

Oobie wrote:My second test was with a fully charged pack, the voltage converter (12-24V), and a three hour nap. The charge meter still lit up "full" after three hours. It will be sufficient for the plane rides. Which is about where I thought it was going to end up.
we'd be most appreciative if you'd use it and see how long it will actually run the thing... whether it goes from full to empty at 5 hours, for instance.

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