Uninterruptible Power Supplies

[Axxel]

Thanks archangle... what would happen if you just plugged the power brick of the ResMed unit into the AC outlet off of this device or would I still need to get the DC converter?

http://www.sears.com/shc/s/p_10153_1260 ... ockType=G1

If you want to use it as a backup unit to be hooked up after the power goes out, in theory, it will work fine on S9 units. It's probably got a MSW inverter, so it might damage the humdifier on S8 or earlier units. You would probably get more run time if you used the ResMed DC converter.

The original poster asked about an uninterruptable power supply setup. I don't know if that particular unit will run the inverter and produce AC while it's plugged into the wall.

It seems to be intended as a backup device, not a full time 24/7 UPS device. Many such backup battery devices will slowly damage the battery if you leave them plugged into the wall 24/7. Reliability and lifetime may be unsatisfactory if used full time.

I'm also concerned about the using an inexpensive inverter intended for short term use in a long term application. If it's designed for use a few nights a year, is it extra likely to fail if used 24/7? Is it likely to fail in a mode that will damage what's plugged into it?

Inverters in general are prone to failure. I don't know how often they fail in a mode that could damage your CPAP. If you're only using it a few nights a year during power failures, the risk is not that bad vs. the benefits. Using them 365 days a year increases the risk.

If you're using an inexpensive inverter 365 days a year, I would also not be surprised if the inverter is likely to have more outages in a year than the power grid.

I did not know certain units would be damaged by the ups MSW. Other than the S9, do you know any other units that are ok with a ups?

I wonder what poses more risk of damaging a cpap. A brownout, or running it on a ups?

You make a good point about battery life too. Although my ups is 4 years old and still works fine, the battery only has enough life left in it to run for a minute to shut down my computer that I have on it.

[archangle]

I did not know certain units would be damaged by the ups MSW. Other than the S9, do you know any other units that are ok with a ups?

I wonder what poses more risk of damaging a cpap. A brownout, or running it on a ups?

You make a good point about battery life too. Although my ups is 4 years old and still works fine, the battery only has enough life left in it to run for a minute to shut down my computer that I have on it.

I'm not sure I really believe that the ResMed S8 humidifiers will be damaged by MSW, but ResMed warns about it. It's one of those things that's hard to evaluate if you're not the manufacturer. Someone could try it, but what would that really prove? If someone plugs an S8 with humidifier into a MSW unit and it doesn't burn out immediately, that's good to know, but will it burn out sometime in the next month? The next year? Will it work OK on one inverter, but blow up on another?

I do NOT trust ResMed in general. They've done a lot of things I consider sleazy like shipping their humidifiers with disposable humidifier tanks you can't open up to clean. Is it a real problem, Are they being overcautious, or are they trying to sell more of their proprietary DC converters?

I have not heard about a Respironics statement on MSW inverters. I have briefly plugged my PRS1 Auto unit into an MSW inverter and turned it on with no apparent problems, but I didn't actually use it.

I THINK units that have an external power brick and power both the CPAP and humidifier off of the brick are less likely to suffer a MSW problem than a unit with a 120VAC humidifier. Also, if MSW damages anything, it's most likely to damage the power brick, which is a lot easier to replace if it's an external brick. I can't guarantee your CPAP will handle it though.

In general, I don't think there's really that much risk to CPAP machines from MSW inverters, but there's a theoretical risk and the CPAP is expensive and difficult to replace. I do understand why AC powered humidifiers would have problems. They tend to use "Phase Fired Controllers" to regulate the power levels and they tend to have problems with non-standard waveforms.

A brownout shouldn't hurt a CPAP unless it's a really bad design. It might cause it to fail to operate properly, of course. However, brownouts are often accompanied by power surges, and that could kill the CPAP.