CPAPtalk.com

Nan:

I was looking at deep cycle batteries that had about 1400 amps, but the 100 amp-hour figure you mentioned is quite a decent amount to work with for a battery. Your amps are a little less, 750, but it sounds like a decent battery. Thank you for looking for me!

Archangle, thanks for explaining the adapter to me. Electrical stuff is sort of my "thing" since I was 12 years old, but I didn't know those things on there are for RF filtering!

I still need to figure out somehow how much better / longer lasting it is to run off of direct dc instead of inverting to 120 and then back down to 12 volts again. Certainly less to break!

Lee

Also thank you johnb!

lee_leses wrote:Nan:

I was looking at deep cycle batteries that had about 1400 amps, but the 100 amp-hour figure you mentioned is quite a decent amount to work with for a battery. Your amps are a little less, 750, but it sounds like a decent battery. Thank you for looking for me!

Don't confuse the "Amp" figure with "Amp-hours."

A CPAP machine will only draw a few amps at most. You want the battery to be able to supply that many amps for a long time. "Amp-hours" or "reserve capacity" are a lot more relevant than "Amps."

In lead acid batteries, deep cycle batteries tend to supply fewer maximum amps, but can withstand a deeper discharge without damaging the battery. A deep cycle battery of the same size and amp hours will produce fewer maximum amps than a starting battery, but will handle deep discharges a lot better.

lee_leses wrote:I still need to figure out somehow how much better / longer lasting it is to run off of direct dc instead of inverting to 120 and then back down to 12 volts again. Certainly less to break!

Lee

Some of us kicked this around several months ago with regard to battery backup for the S9. We did not come up with a definitive answer but the general consensus is that all three types of units, 12 to 120v inverter, 120 to 24v power supply, and 12 to 24v converter, are most likely on the order of 95% efficient. With the inverter/power supply combo you're probably looking at a net efficiency of something like .95x.95 or about 90%, or about 5% more efficient than a 12 to 24v converter. If the Respironics unit can use 12v directly from a battery then that should be 99%+ efficient.

You can't go by the watt rating of the power supply because the actual current draw depends on the humidifier settings and blower speed, or pressure. If you're running your CPAP at moderate levels it's probably drawing about 5 amps with the humidifiers. For 8 hours that's 40 amp-hrs total, or 120 for three nights. Resmed has a power consumption chart available. Don't know if Respironics does or not.

There's enough variables in CPAP power usage that the differences in efficiency really isn't a determining factor which way to go unless you are looking at a very tight power availability vs. consumption situation, like having to depend on a battery for 6 nights straight with no recharge possibility.

In my case I decided cost considerations were paramount. I already had an inverter, and the Resmed 12/24 converter costs more than a 125 amp-hr deep cycle battery. I bought a few more odds and ends and fixed up a connection to my pickup so I could use it to recharge the deep cycle battery. On a recent camping trip it worked OK but not as good as I had hoped. A deep cycle doesn't seem to take a fast recharge like a regular car battery will. One thing I do know, a well used car battery won't be good for more than one night with humidifier. I found that out last year when my pickup wouldn't start in the morning!

Also thanks to rested girl. And also to idamtnboy for great info.. Enough info from all of you to keep me interested and reading for days, maybe weeks!

Lee

Stupid me, I just realized when I said my CPAP machine was using 75 watts / 1 amp, that was running at 12 but I think the humidifier was on too. I have to re-test it to confirm if the humidifier was on or not.

Lee

It's only 20 watts, .3 amps, with the humidifier turned off...

I just saw this on Amazon (8.31.2011) for emergency power.
Looks like a GREAT price, but I bet it won't be this price for long, so I would hurry if this may be useful for you.http://www.amazon.com/Duracell-DPP-600H ... 398&sr=8-1

Vader wrote:I just saw this on Amazon (8.31.2011) for emergency power.
Looks like a GREAT price, but I bet it won't be this price for long, so I would hurry if this may be useful for you.http://www.amazon.com/Duracell-DPP-600H ... 398&sr=8-1

Can this battery be used with any cpap machine? Would I need to purchase anything else?

apneawho wrote:

Vader wrote:I just saw this on Amazon (8.31.2011) for emergency power.
Looks like a GREAT price, but I bet it won't be this price for long, so I would hurry if this may be useful for you.http://www.amazon.com/Duracell-DPP-600H ... 398&sr=8-1

Can this battery be used with any cpap machine? Would I need to purchase anything else?

I believe so, it's complete, but I have not bought one. Gumby may very well be the best qualified here to answer that question properly.

Oh- Gumby! ......

In the event that Gumby doesn't respond right away, I did this search:

search.php?keywords=black+and+decker+jump+starter

apneawho wrote:

Vader wrote:I just saw this on Amazon (8.31.2011) for emergency power.
Looks like a GREAT price, but I bet it won't be this price for long, so I would hurry if this may be useful for you.http://www.amazon.com/Duracell-DPP-600H ... 398&sr=8-1

Can this battery be used with any cpap machine? Would I need to purchase anything else?

If you want to use the 120 VAC, it's probably a modified sine wave (MSW) inverter. Your S9 machine will theoretically work just fine on AC from the battery pack. ResMed says MSW is OK for S9 machines with humidifier. ResMed says a MSW inverter will damage the humidifier for S8 machines. ResMed says S8 machines without humidifiers are OK. I haven't seen a statement from Respironics.

I would not be surprised if it apparently works OK if you try it with a "non-MSW compatible" CPAP machine. Just because it doesn't immediately burst into flames doesn't mean it won't do damage later.

You'll probably get more time out of the battery if you use the 12V DC instead of the inverter, but you'll need a DC power cord. PRS1 machines use a DC cord that's just a cord and will power the humidifier off of DC.

Unfortunately, ResMed says all of their CPAP machines require an expensive ResMed DC-DC converter to run on DC. S9 machines will run the humidifier and heated hose off the DC adapter. Other ResMed's won't run the humidifier off of DC.

Unfortunately, ResMed says all of their CPAP machines require an expensive ResMed DC-DC converter to run on DC. S9 machines will run the humidifier and heated hose off the DC adapter. Other ResMed's won't run the humidifier off of DC.

For me, just another reason not to buy ResMed machines.

That IS a very nice looking box on Amazon Vader!

Here's my question and comments about it.

First, while it looks neater and better packaged than something you make yourself like from johnb's plans (although his setup is a close second in neatness), I think you can build something more modular with more AMP hours for a similar budget. You could buy an inverter for $50, a Costco deep cycle 125 aH battery for about $80, and a battery tender jr to charge the mess for about $25 on Amazon.

And, if the inverter, charger, or battery goes bad, they are not all in one package and are easily serviced without having to take it apart and the parts are easy to find and get.

The Duracell unit only has a 28 aH battery in it, and my question about many units like that is I don't think they're telling you if it is a deep cycle battery, or not? I guess it would have to be, but I'm not sure?

Lee

Gee, I don't have the Duracell yet.... I'll have to see about getting one. It certainly looks heavy duty. You could pick up a B&D for about $100 @ Walmart if that helps anyone. Edit: Or Home Depot

lhpangler wrote:I got this one.

http://www.homedepot.com/webapp/wcs/sto ... reNum=2502

Les - You would need to buy a DC cable to fit your machine.... Or make one. You could use the AC inverter on it but I wouldn't. Let's look at it, all of the machines made convert the AC to 12 volts, well except Re$med. So they ALL do convert back to DC in any case. AND DC will last much longer, period.

Someone with an S9 needs to step up to the plate and find out what the 3rd wire goes to so we can ALL benefit.

GumbyCT wrote:Gee, I don't have the Duracell yet.... I'll have to see about getting one.

It was $115 this morning for about two hours. It's now $149.
I've never really had to learn about these things because I have a Generac whole house generator, powered by natural gas (or propane) in the event of an emergency. I don't use it a lot, but OH....WHEN I DO!