Has anyone tried the Ryobi 18v inverter to power their CPAP?

[chasmm]

Home Depot has an 18v Ryobi inverter for $70. I've got several of the 3a and 4a batteries. On a lark, I purchased the inverter in advance of this past weekend's snowstorm just in case. Fortunately we didn't lose power...so I haven't tried it yet, but before I do, I was wondering if anyone else has attempted to use this as a battery backup system for their machine? If so, what's your experience? Run time with various batteries, etc.

Using the forum search, I did find a thread from over a year ago, but there didn't seem to be a resolution to it, so I thought I'd ask in a new post rather than resurrect a zombie thread...

I'll add that I'm not an electrical engineer by any means, but I do have a technical background. I know that inverters are an inefficient tool and that I would likely be better served by purchasing a dedicated battery/power system. That said, I do have a bunch of the Ryobi batteries, so my "new" cost would be just the inverter...

Also, this inverter is a "modified sine wave". I'm not sure exactly what that entails as opposed to a "pure sine wave", but my concern would be if it is safe to use to power my CPAP (Dreamstation 2).

Any advice and/or suggestions would certainly be appreciated.

Thanks!

[LindanHotAir]

The power bricks used for CPAPs are auto ranging switching power supplies originally designed for laptop computers. Their nominal input range is 100 to 240 volts AC, 47 to 63 Hz, to work with commercial power worldwide. Japan is 100V and much of Europe and Asia is 240V. The input filter is designed to filter out odd harmonics. A modified sine wave is created by adding together different shaped square waves, and the filtering will handle that wave shape. The input of a switching power supply charges a capacitor, and the output is an inverter that provides the required DC output. The input waveform doesn’t affect the output power quality.

[JJJ]

I have a ton of Ryobi tools, both 18v and 40v, plus a dozen batteries of each voltage, so when I suddenly noticed the inverters for sale I bought the 40v one. I tried it with a 6 amp-hour 40v battery, and it lasted for about six hours. I used it for my Resmed S9 BiPAP, set to 15-25cm, but without even having the humidifier attached, and an ordinary non-heated hose. But bear in mind that the inverter changes the 40v DC from the battery to 120v AC ('cause I'm in North America), so there's a lot of power loss. Instead of the inverter if you used a simple DC-to-DV stepdown transformer to the voltage that your xPAP machine needs, a 6AH battery should power your machine for twice as long. But if you're using 18v batteries I think the biggest ones available are 4AH.

Most of my batteries are third-party, not genuine Ryobi, because you can get them online for half the price of the Ryobi batteries. Yes, my setup is horribly inefficient, but it was also dirt cheap because I already had the batteries. All it cost me was the price of the inverter.

And don't worry about the sine wave; my inverter ran the PAP machine flawlessly.

[chasmm]

Thanks for the replies...

JJJ - you had posted in the old thread that I was referring to above, and that's what led me to the Ryobi inverter, so thanks for that.

Have you used the 18v inverter? I know you posted about the 40v one. 

Just to be clear, the 18v is a modified sine wave, the 40v is a full sine wave. It sounds like that doesn't matter, though.

Regarding the 18v batteries, they're available in (4a or larger):

4a
4a High performance
6a
6a High performance
9a (although this is out-of-stock locally and online, so not sure if it's available anymore)

I'm also not sure if the "high performance" batteries would be worth the extra cost. I'd certainly be willing to give one a shot to see. I already have several "regular" 3a and 4a that I could use for testing.

[Crimson Nape]

chasmm - Based on your intended use as a source for the CPAP power supply, I don't believe there will be any problem. The CPAP's step-down power converter is very tolerant of fluctuations.

[JJJ]

JJJ - you had posted in the old thread that I was referring to above, and that's what led me to the Ryobi inverter, so thanks for that.
Have you used the 18v inverter? I know you posted about the 40v one. 
Just to be clear, the 18v is a modified sine wave, the 40v is a full sine wave. It sounds like that doesn't matter, though.
Regarding the 18v batteries, they're available in (4a or larger):

4a
4a High performance
6a
6a High performance
9a (although this is out-of-stock locally and online, so not sure if it's available anymore)

I'm also not sure if the "high performance" batteries would be worth the extra cost. I'd certainly be willing to give one a shot to see. I already have several "regular" 3a and 4a that I could use for testing.

I didn't know that the 18v batteries were available as big as 9AH; thanks for mentioning that. All of my 18v batteries are 4AH. And yes, I bought only the 40v inverter. I remember reading customer questions, answers, and reviews on the U.S. Home Depot website from people who used the 18v batteries and inverter to power PAP machines, and no one mentioned any problem. And they reported that they got a full night out of one 4AH battery, which is better that I get out of a 6AH 40v battery. But their PAP machine may have been more efficient than mine, and/or their pressure was lower. Lots of variables that make it difficult to make precise predictions.

[chasmm]

Crimson Nape - thanks for the input...

[/url][url=http://www.apneaboard.com/forums/User-JJJ]JJJ - well, I'm going to give it a shot with the 4a batteries and report back.

Here's hoping...

[chasmm]

Okay, I used the Ryobi 18v inverter last night. I didn't change any settings on my Dreamstation 2 prior to using it.

Humidity - 3
Heated Tube - 3

I tested the following batteries, all of which had been charged within the previous 24 hours:

4a (2 of them) - each ran the machine for ~2 hours (+/- 5 minutes) for a total of 4 hours
3a (2 of them) - each ran the machine for ~1.5 hours (+/- 5 minutes) for a total of 3 hours
2a (1 of them) - ran the machine for ~ 1 hour (+/- 5 minutes) for a total of 1 hour

It was unpleasant to wake up so frequently to swap out the battery. There was no noise from the inverter during usage (I had read it might buzz), and it's certainly possible that the battery died earlier, and I didn't wake up. However, given that I used two each of the 3a and 4a batteries, and each one seemed to last about the same times respectively, I'm fairly certain that I was waking up soon after the battery died.

So in total, I got about 8 hours of sleep from the 5 batteries. I could therefore use this setup to get a full night's sleep, but it would be even more interrupted than usual (I typically wake up 1-2 times each night). One thing that is annoying about the inverter is that there is a dedicated power light on the top of it that glows a BRIGHT GREEN while the inverter is in use. Easy enough to mitigate by sliding under my nightstand...

I guess I could try to go with zero humidification and maybe tweak the settings, but I wanted to see if I could make this work with my current settings.

I don't have any of the high-performance (h-p) batteries at present to see if there is a difference in how long they last versus the regular versions. The marketing of the h-p batteries says up to 4x/6x runtime for the 4a/6a respectively. I'm not sure if that has to be paired with a corresponding HP+ tool, or if it also means extended runtime in the inverter.

My next step will be to pick up a 6a h-p battery and see how long that will last. It seems from my test that each amp is worth roughly 30 minutes of usage. If I could get 3 hours from a 6a battery, then a couple of them could get me through a night with my "normal" wake-ups.

I suppose I could also try the 9a version. I've found it on Amazon. There are also several 3rd-party versions on Amazon, but I think at present I'm going to stick with the genuine Ryobi batteries.

Hope this helps someone else.

Again, I know that the best way to do this would be to avoid the inverter or to use a dedicated CPAP battery setup. I'd like to make the Ryobi setup work because I already have several of these tools and batteries. Buying 1 or 2 more batteries for this would be something I wouldn't mind.

[YoSpiff]

I haven't done it yet, but I had a discussion on that topic recently in the Ryobi user group on Facebook. Since we could have another power grid failure here in Texas, I wanted to see if I could run one all night on a battery.

What I determined is that there are many variables and I'd have to try it to know for sure. But I could probably run my travel CPAP (An HDM Z1) off the 4AH 40 volt battery with power to spare. With the 18 volt battery and inverter, I could run all night with a 9AH battery. The biggest 18v I have now is a 4AH, however.

I am looking at the usage of my travel unit because it should draw less power, partially because there is no water tank and heater to run. If you turn off the water heater and use an HME device in-line on the hose, you can probably get much more run time.

Added: Didn't see all the responses and your test until after I posted. But it looks like the results are in line with what I expected.

[chasmm]

Since we could have another power grid failure here in Texas, I wanted to see if I could run one all night on a battery.

Here's hoping your power is still on!

FYI, I've picked up two (2) 6a high-performance batteries and will be giving them a shot tonight...