CPAPtalk.com

tisket wrote: ↑

Wed Aug 10, 2022 11:28 am

From what I can glean, older ResMeds had this thing where the power supply converted AC to DC for the circuitry but also passed AC directly through on another line for use by the humidifier. As a result you had to use a clean sine wave source for these because it was just passing the AC right through to the humidifier. More recent models seem to be all DC inside, and the power supplies are not finicky, so the requirement no longer exists. That's my impression anyway.

I am looking at two different scenarios for myself.

1. Power flickers/brownouts. My computer UPS often clicks during bad weather. I assume it is switching to battery for a moment during a brief power drop. Due to problems I documented in another thread I think these brief interruptions may be messing with my Airsense 10 if they happen in the middle of the night. So I want something I can leave plugged in all the time to protect the machine from these momentary power drops. Minimal battery capacity needed.

2. Hurricanes. It doesn't happen often but once a decade or so here we can lose power for a few days or even weeks due to hurricane damage. For this I think I would need a different device that could power the machine all night. Last time after the first day or so, they got power back at one of our offices so I had a place to recharge my phone. If such a scenario happens again it occurs to me that a big battery pack would be useful since I would be able to recharge it at work during the day. The lithium ion ones are more expensive but much lighter and easier to carry around than the lead acid ones. It's hard to size the lead acid ones because I am not sure what the power draw is for an Airsense 10 with heated tube and humidifier off. However the big ones are fairly expensive so I am not sure if the lithium ones are really that much more now.

Somewhere I got the impression the large lithium ones (like Jackery, Goal Zero Yeti, etc) were not meant to be left plugged in all the time and used like a UPS, but I am not sure.

Ray4852 wrote: ↑

Wed Aug 10, 2022 7:54 am

if you think my post was spam. I want you to study how electrical equipment works.

Ray4852 wrote: ↑

Wed Aug 10, 2022 7:54 am

all circuit boards in medical equipment run better and cooler with pure sine wave.

Ray4852 wrote: ↑

Wed Aug 10, 2022 7:54 am

all motors with oxygen,

Ray4852 wrote: ↑

Wed Aug 10, 2022 7:54 am

and c-pap need pure sine to run.

Ray4852 wrote: ↑

Wed Aug 10, 2022 7:54 am

if you try to run them on modified, your equipment won't last. they burn out from excessive heat. listen to any motor that runs on modified. it hums and runs hotter. look at lights. they flicker. all computers need pure sine wave to run the right way. all medical equipment needs pure sine. if you don't believe me. look in your owners manual. if you want to run modified. its ok with me. I care less what you do. I'm going to tell them the right way. look for pure sine.

Grumpy48 wrote: ↑

Wed Aug 10, 2022 2:42 pm

A brief overview of the basic operating principles of modern switch mode power supplies.

Grumpy48 wrote: ↑

Wed Aug 10, 2022 2:42 pm

Presuming that most all CPAP power adapters are of the same kind that are used for a laptop (such as those for a DS2 and AS10), these are what are called switched mode power supplies. A switched mode power supply takes the incoming 120-240vac, 50-60hz and immediately rectifies (changes to DC) the voltage and is then filtered/smoothed to take away most all of the AC component that may be left. This rectified DC is then 'switched' on and off at a high frequency through a transformer by a semiconductor device. This transformer feeds another rectifier that changes the output of the transformer back to DC at a low voltage that is usable by the CPAP machine (12vdc, 24vdc, etc). Another piece of the circuitry regulates the DC output voltage by telling the semiconductor 'switch' driving the transformer at what voltage it needs to be. There may be circuitry that protects the power adapter from overload as well. Depending on what the adapter is used for the DC output voltage may be filtered more or less. Some of the DC connecting cords may have ferrite beads to reduce or eliminate RFI (radio frequency interference) from getting into the electronics of the CPAP.
Unless otherwise indicated most all switch mode power adapters will not care if the incoming AC is sinusoidal or non-sinusoidal since the first step in the adapter is change the AC to DC and the rectifier doesn't really care what goes through it. It may be slightly less efficient with non-sinusoidal.

The importance of a pure sine is when using a device with a 'real' transformer (iron and copper) or an electric motor. A pure sine wave has no harmonics (just fundamental 50 or 60hz). A non-sinusoidal AC source may have harmonics (even or odd multiples of the fundamental frequency) components. Transformers and motors are usually designed for specific frequencies to function efficiently. The harmonics in a non-sinusoidal AC source may cause heating of copper windings and iron which eventually may damage them. A transformer supplied with a non-sinusoidal source may emit some noise due to harmonics.
If not sure what you're powering, it's best to err on the side of using a pure sine wave power source.
A pellet stove will likely use a conventional transformer (copper and iron) on its control board and the pellet feed and blower motors all should be supplied with a clean pure sine wave.

In the schematic below of a typical switch mode PS the Mosfet device IRF840 is switching the rectified DC on and off to the transformer.

turbo wrote: ↑

Fri Aug 12, 2022 3:56 pm

As I mentioned earlier. I've been using modified sine with AS10 for a few years now with no issues. I'd post what battery I'm using, but I don't want to spam the board.