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archangle wrote:... Another big problem with gasoline generators is that stored gasoline goes bad in short order ...You need to drain the gas tank of your gasoline generator or run it dry periodically. ...

archangle must have been hanging around my garage! Yup. I think that's what happened. I failed to use up the gas one time and the next month it would not start. Sigh! Finally more than a year later I got it to the shop for repair. Fortunately, no really bad storms since I first had the generator. And I hope it will be back from the shop when the next bad storm arrives.

On a another note, the pros and cons of running a MSW inverter, while I have several and use them for different things. They work by switching the voltage 150V approximately on and off positive and negative. While this works ok for motors and transformers, the switching power supplies in cpaps, computers, etc. have a hard time with this, the interaction between the two can cause instantaneous high current spikes between them. This not only causes lots of electrical interference that can be passed onto the cpap, but it also causes the efficiency of the power supply to drop considerably, so the power conversion could be as low as 40%

This is helpful information.

At first glance, I don't get how your machine would know to automatically switch off the humidifier if you drop to battery power only. Am I missing something?

Lee

Very interesting. I ran into noise problems with several of my telcom electronic devices where transformers were fine, but they did not like running off switching power supplies.

Apparently in some cases, newer is not always better!

So best to avoid running switching power supplies with an MSW inverter then?

And of course a direct DC adapter for the CPAP is the best choice! (I have the PR System One)

Also, when I get the chance to power up one of my MSW inverters and put a meter on the power output, what hertz will I find? I know normal US AC is 60 hertz.

Lee B.

lee_leses wrote:So best to avoid running switching power supplies with an MSW inverter then?

Yes, no, and maybe. It depends on what the power supply is designed for.

The first inverters were square wave inverters. They switch between +/- 120VDC. Light bulbs act like it's 120V AC, but to an analog power supply, these sort of look like 85V AC.

The "modified sine wave" inverters came next. They switch between -140VDC, 0VDC, and +140 VDC. (Some inverters may use a voltage other than 140.) To an analog power supply, this looks like roughly 99V and a lot more devices can handle it.

Many switching power supplies have an analog power supply before the "digital" part. Many of them can handle the effective 99V input they get from a MSW inverter. Some can't.

There may be some switching power supplies that do unconventional things and can't handle the strangely shaped waveform of a MSW inverter. A MSW inverter also generates a LOT of electrical "harmonics" and "noise" in the voltage it puts out. This can potentially "confuse" a switching power supply if it's not designed to handle it.

A lot of UPS backup supplies use MSW inverters and don't bother to warn the customer that it's not "real" AC power. A lot of uneducated consumers think "UPS" means "clean power." Many of the manufacturers probably feel compelled to "play along" because they don't want to have to explain to irate consumers that it's the UPS's fault, not their device.

A switching supply usually has "smarts" that allow it to adjust better to input voltage variation than an analog supply. Unfortunately, penny pinching is the name of the game. Manufacturers tend to squeeze every last penny they can out of the design. This may leave the switching power supply unable to handle the reduced effective voltage of an MSW inverter.

There's actually a third kind of "power supply". Some things use "dimmer" circuits. These are like the light dimmers in houses. They work by having an electronic "thyristor" that blocks the AC voltage for part of the waveform. It waits until the AC voltage reaches a certain voltage in the cycle and switches on. By varying the turn on voltage, you chop out more or less of the waveform and make a lower effective voltage.

Some CPAP machines use a "dimmer" type of circuit to control the AC voltage to the humidifier heater. I suspect these may not react well to a MSW waveform that jumps from 0 to 140V instead of ramping up slowly like a sine wave does. This is my best guess as to why ResMed says that a MSW inverter will damage an S8 or older model humidifier.

LOL!

I'm following about 80% of what you're saying, I really like this gem:

a MSW waveform that jumps from 0 to 140V instead of ramping up slowly like a sine wave does.

So are you an electrical engineer or a master electrician? One of the things I find interesting on this forum is how many of the afflicted folks are highly intelligent people. Maybe we are more willing to think though what our problems are and deal with them as best as possible?

Let me cut to the chase. One of the things I'm trying to understand is what causes the damage in devices that can't handle the MSW interters, and how to best predict which devices will have a problem? The manual from the Power Bright Corp. mentions only a short list of devices that will have a problem. It's too long to quote here, but this seems quite thorough:

http://www.powerbright.com/pdf/PW900-12 ... french.pdf

It starts on about page 4 if you want to check it out. I'd be interested to hear any thoughts you have on what they say.

I also wanted to comment, I've powered several laptops plugging their adapters into an inverter in the car, and I haven't had a problem or seen any damage so far, that I know of...

Lee

decided to post this here in a newer thread
not sure if anyone has talked about this elsewhere but this seems like the it battery
its Lithium ion so no charge memory
its light at 4.5 pounds
and it can put out 15A and looks like it will run most CPAP machines for 3 or 4 nights

http://www.bestcpapprice.com/Compact-Po ... p_516.html
i'm not a seller i'm a soldier that will be getting this battery as part of my cpap deployment pack.

One important point I haven't seen mentioned is that wall outlets have a ground connection. The output of an inverter is not grounded, unless you attach an external ground wire. Lots of the inverters tell you to do this, but nobody does it. On a USA wall plug, two of the wires are grounded.

For various reasons, this isn't as dangerous as it sounds at first, but there is some additional risk.

lee_leses wrote:One of the things I'm trying to understand is what causes the damage in devices that can't handle the MSW interters, and how to best predict which devices will have a problem?

I haven't seen enough devices actually damaged to know percentages on damage. I think most things will work fine. I just can't tell you it WILL work. Most of the things that don't work will probably not be damaged. Just don't blame me if it fails.

I'm guessing that the most damage will be from the low effective voltage. You'd think a device would simply not work on low voltage, but some things do actually damage themselves with low voltage.

The noisy and spikey nature of the voltage would be my guess for the next most common problem.

I suspect a number of manufacturers are concerned the inverter will fail in some way and produce a damaging voltage, the wrong frequency, etc.

I think so many people use laptops with inverters that the manufacturers feel they can't get away with a power supply that can't handle it. They also like to have a worldwide capable power brick for laptops for travelers and to have fewer parts to inventory. A "voltage nimble" power supply can probably handle the effects of MSW power.

SGTDGUN wrote:decided to post this here in a newer thread
not sure if anyone has talked about this elsewhere but this seems like the it battery
its Lithium ion so no charge memory
its light at 4.5 pounds
and it can put out 15A and looks like it will run most CPAP machines for 3 or 4 nights

http://www.bestcpapprice.com/Compact-Po ... p_516.html
i'm not a seller i'm a soldier that will be getting this battery as part of my cpap deployment pack.

Yup. It is one of the options that people use. Another set of battery options is:

https://www.cpap.com/cpap-battery-power ... attery.php

I have a LP powered generator that kicks on within 30 seconds of a power outage and this handles things in my country home that just have to have power (sumps, water pump etc) and a few rooms. I lose power all the time, flickers and days on end sometimes. I can plug my machine into a socket that gets juice from generator and no problems, my question would be what type of UPS or like device should I get for the S9 AutoSet with heated humidifier? It only has to have enough juice for a few minutes, something to handle the power until the generator kicks on. Thanks in advance!

Cuda wrote:I have a LP powered generator that kicks on within 30 seconds of a power outage and this handles things in my country home that just have to have power (sumps, water pump etc) and a few rooms. I lose power all the time, flickers and days on end sometimes. I can plug my machine into a socket that gets juice from generator and no problems, my question would be what type of UPS or like device should I get for the S9 AutoSet with heated humidifier? It only has to have enough juice for a few minutes, something to handle the power until the generator kicks on. Thanks in advance!

Since the S9 Autoset is one of the models that handles MSW power OK, almost any UPS will probably work just fine for the few minutes you need it. The S9 needs 120VA to run so get a UPS that will handle that for long enough for your generator to kick in.

Thanks, I appreciate it.