Battery Backup Design

John, that's a fantastic design and very thorough write-up. Being an engineer (industrial and systems), I know that a great design with horrible documentation can break a project just as easily as horrible conceptualization. I love the safety measures you've included as well (the safety factors and the preventive measures in the design).

I've got an S9 with an H5i (with climateline, generally at 70-73F - below the 27C/80F on the table). According to the ResMed battery tables, I need 49AH or so for an 8-hour night. Now, having been here 6 years in central NY, we've not lost power more than 4-5 hours at a time. (and only one of those was when I needed or would have needed to turn on my S9). I'm willing to go without the humidifier if need be. For 2 nights, though, I guess I'm looking at 100AH.

Anyway, if I only needed 1 night, I figure $220 for the battery, 40 for the tender, 9 for extension cables, and 13 for the battery box. Looking at around 150 for the 150W pure sine wave inverter as well. Additional for the hardware, wingnuts, post covers, etc.

Am I really looking at over $400 to run this? Is my cost calculation really that far off?

Thanks!
Roman.

Roman, look in the battery guide for your S-9 , It can be run on a modified sine wave inverter. The modified sine wave can be purchased for around $40. This is from the battery guide Resmed has put out, page 2. FYI, john


The S9 with H5i will operate with a modified
sine wave inverter. A minimum continuous
power rating of 150 watts or higher is required.
Refer to the following pages to confirm your
exact battery and inverter requirements

Roman, thanks for your thoughts on the design. During the upcoming year, I will finish a Wiki article about this design. It will make it easier for folks to refer to one source. I will also go a little more into the power calculations for folks with non-Resmed systems. And I may add some of this into it as well.

jlk has it right about the S9 and the ability to use the modified sine wave inverter. It will make it cheaper.

Of course, running the humidifier will take more power than if you run without the humidifier. Thus you would need a MUCH bigger battery if you intend to use the humidifier. In upper NY, you may well need to run the humidifier, since the cold dry air can be a bear.

I was able to find a sizeable battery (for an ASV unit, so the power demands were considerable), for much less. I think it was from a Batteries Plus store. But you can find a good AGM battery for a reasonable price. Still, there's no doubt it is a pricey proposition.

And as an engineer, you will know the task I will set you ... you need to develop a cost-benefit analysis. The benefit may well outweigh the cost.

Figure that a deep cell battery will last four years (though I often get six years from them). Figure that you will spend $300 (your $400 less $140 for the pure sine wave inverter plus $40 for a modified sine wave inverter). So, the cost will be about $75 per year.

Now, how bad do you need the xPAP device? Do you have to drive to work? When you sleep poorly does it impact your driving? It did mine (due to a neurological issue, I no longer drive). What happens if you can not think clearly? I was a trouble shooting engineer. When everyone else in the company had no idea, I would be brought the problems. So, when I was dealing with problems we were typically talking about millions of dollars in lost revenue for my company or for our customers. Either way, being "foggy" was NOT an option.

In my case, the $75 was a simple decision.

I have since gone on disability (due to my neurological issue). However, since the neurological issue now includes severe central sleep apnea, even proping myself upright is not an option. I just stop breathing without my ASV unit. And trust me, it's a horrible feeling to awaken when I've stopped breathing for a minute or two. So, though I no longer face those issues with work, the physical and psychological benefit far outweigh the $75 per year cost.

Anyway, that's how I tackled the question of cost. My wife saw me go through the calculations, chuckled and told me that I was such an engineer. She said I should just go get the stuff and be done with it. She said I was a good deal at $75 per year!! Glad she thinks I'm worth it!!

Hope that helps.

Oh, I'm not questioning the cba, John. And yes, it IS worth it. Just tough to swing that kind of money around Christmas and "property tax season.". We don't escrow. (Why should someone else make a buck off me like that? Especially banks?)

Roman
My 12 volt marine battery and modified sine wave inverter only came to $170 canadian...in U.S. bucks it should be less than that. I get up to 4 nights
8.7 hours per night..without the humidifier. I keep it on a little hand trolley and put a charger on it about once a month to keep it at the ready in case of power outage. The trolley I bought so I could haul it in & out of my motorhome in the summer.
And YES, no matter the cost, its worth the bucks to have "just in case"
.
Nan

First off, thank you for the great write up, John. Now that the S9's DC/DC converter is available, I'm in the process of following your solid design for creating my own setup, albeit with no inverter.

When I picked up the Resmed converter last week, I noticed a warning (amongst the many) about not using the converter from a battery while the battery is connected to main power. While I realize that this a bit of a loaded question since you probably don't have one of the new converters in hand, I was just curious as to your thoughts on that warning. I can't help but wonder if it's based on a real practical concern or if it might be there just from a catch-all liability standpoint. With a low-amp float charger that won't allow overcharging, I can't for the life of me see a real danger with running it while the charger is also connected to main power. Almost 3 decades have come and gone since my last EE course, so I naturally distrust my first thoughts when it comes to power safety.

In all likelihood, I'll leave it in my heated garage except when power goes out, so it probably won't be a concern, but it would be nice to have a better understanding of why that warning may have been included.

BernieRay wrote:... First off, thank you for the great write up, John. Now that the S9's DC/DC converter is available, I'm in the process of following your solid design for creating my own setup, albeit with no inverter. ...

Glad you find it helpful. I use my backup battery (whether I need to or not) at least once a month. It helps preserve the life of the battery.

BernieRay wrote:... When I picked up the Resmed converter last week, I noticed a warning (amongst the many) about not using the converter from a battery while the battery is connected to main power. While I realize that this a bit of a loaded question since you probably don't have one of the new converters in hand, I was just curious as to your thoughts on that warning. I can't help but wonder if it's based on a real practical concern or if it might be there just from a catch-all liability standpoint. With a low-amp float charger that won't allow overcharging, I can't for the life of me see a real danger with running it while the charger is also connected to main power. Almost 3 decades have come and gone since my last EE course, so I naturally distrust my first thoughts when it comes to power safety. ...

I suspect they put such wording on in the event of someone hooking up a high power charger. That would overload the entire system - including the converter. So, yes. I suspect it's just a liability issue. Still with the battery backup design it's a simple matter of unplugging the charger whenever you use it.

BernieRay wrote:... In all likelihood, I'll leave it in my heated garage except when power goes out, so it probably won't be a concern, but it would be nice to have a better understanding of why that warning may have been included. ...

A heated garage is a great place to store it. My garage is not heated and a cold garage is a great way to kill the life of the battery. The way it is covered and vented, it should not pose a problem if it is in the house. Mine is. I check the inside every now and then to be certain there is no corrosion (a sign of problems). Of course, having said that, there is always the first time. And a heated garage is a better / safer location when the battery is not in use.

I'll be interested in hearing how this works out for you!

I appreciate your thoughts, John. I knew I'd need to protect it from extreme cold to maximize life, but the sales guy mentioned that folks up north keep them off of concrete floors as well. I hadn't thought of that before he mentioned it.

As soon as I get the setup completed, I'll post some pics and let folks know how it works.

BernieRay wrote:With a low-amp float charger that won't allow overcharging, I can't for the life of me see a real danger with running it while the charger is also connected to main power.

It depends on the design of the "float" charger.... modern switching mode, multi-stage charger designs (which will automatically look after a connected battery that is "off-load") employ some fairly sophisticated approaches to determing the state of the battery they are connected to. If you add a load to the battery while that sort of charger is connected to the battery, it can change the charger from a low current maintenance mode to other modes on an unpredictable basis..... with unpredictable results.

Cheers,

Bill

Great point, Bill, and it definitely applies with the PulseTech XC100-P that I'll be using. Just a little more thought and that should have occurred to me. I did think about just everything else (I think):

Review Resmed Battery guide, extrapolate expected current needs for my 95% pressure, EPR, and humidifier under best and worst cases - check
Research and select a top line sealed AGM spiral cell battery of appropriate capacity - check
Research and select a solid, reasonably priced multi-stage float charger - check
Order good surge supressor, 25 ft SAE extension, Powerlet connector, battery box, and Magna Cart - check
Verify that everything will plug in easily and correctly - check
Verify that everything can handle my expected current needs - check

In fact, excuse me while I go grab a 2x4 to hit myself with...

I have been running my cpap directly ( continuously ) from a marine battery for the last year. The float charger is connected to the battery all the time. The float charger has three modes, on fast charge, battery voltage is around 13.7 volts, top off charging is about 16.2 volts, and float the voltage is at 13.3 volts. The cpap doesn't seem to mind the float charger at all. With the cpap on the charger will either be in the fast charge, or the float mode, it won't go into the top off mode unless the cpap is off. I keep the battery right in my bedroom under my night stand in a standard battery case which I put in a plastic dish pan for extra acid protection. I have a voltmeter hooked up so I can monitor the battery voltage all the time. I check the terminals for corrosion every two months and top off any cell that needs water, none yet. In the past year we have lost power five times at night while I was using cpap, so for me it is money well spent. You only have to wake up once gasping for breath because of a power outage to know that it is worth it.

John:
Check out the Super PWRgate PG40S at http://www.westmountainradio.com. This unit lets you power a 12 volt device by a power supply, charge a gelled or AGM battery, and switch to the battery upon power failure. The Super PWRgate is $139.95 and an AGM 79 Amp Hour battery is $199.95. Cables are listed under RIGrunner & PWRgate Accessories. There is also a battery box and power supply available. Since most xpaps can now be run from 12 volts (including the S9 with the DC to DC converter), this would make a good setup for those subject to frequent power outages.


Sleep Well,

Steve

The last piece of gear for my backup system, a surge supressor, is being delivered today. I've already installed the Powerlet port on the battery box, so all that's left is to cut some 3/4" plywood to provide a better barrier between my battery and the concrete floor, replace my old surge supressor, and run the power line from the supressor to where I will keep my battery backup cart in the garage.

I've posted pictures of my setup in Resmed S9 Battery Backup Using Resmed DC Converter.

OMG - - Most of these posts are great, but I missed where someone warned about using lead-acid batteries in the house. Or any confined space for that matter...and probably where the warning for using a charger while running an xPAP came from. Yes, I have an EE degree, but working on cars should be enough to heed this warning. LEAD-ACID batteries give off EXPLOSIVE HYDROGEN GAS WHEN THEY ARE charging, and is not breathable. That is why they come from the factory with that warning on them. Also why Battery Backups come only with sealed GEL cells. The hydrogen gas is not leaked into the air, but contained in the sealed GEL CELL unit. That was what they were designed to do. Oh and if your wondering, yes, I have had a small explosion occur because of a battery. No major damage, probably because it was in the garage, but I can just imagine the effects in a bedroom. Also, I am a CPAP user since Nov. 2001, eleven years and can not stand it without my humidifier. And believe me when I say, without heat it might as well not be there at all. PLEASE - PLEASE - PLEASE *****DO NOT USE LEAD ACID BATTERIES INSIDE THE HOME*****!!!!!!!!!!

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