UPS, PWM Sine wave or True Sine wave

[mike31154]

Originally Posted by theokie

Mike,

I was unsure if a PWM sine wave was square or a bit closer to a true wave form, but it appears, I'm just going to have to bite the bullet or rather cut in to my coral budget for the next month or two.

Yeah, I've never heard a manufacturer of inverters use the term PWM sine wave. I know that the cheaper inverters with 'modified' sine waves have 'chopped' peaks, so not really a true square wave either, as they try to time a bit of a slope into the wave to make it more sinusoidal. To me PWM can mean many things, including a modified square wave with different frequency and all kinds of nasty permutations. In other words, not only can the amplitude of the wave vary from one wave to another, but also the 'off' time between waves, i.e. the width between pulses, which is a sort of frequency modulation. I would hope that something PWM designed to emulate an AC sine wave would very closely mimic such sine wave, but it's still not a pure sine wave, so probably not the best option to run an AC motor. I could be wrong & they've figured out how to time the pulses to make a pure sine wave, who knows. More research required....

[banditpowdercoat]

High dollar Inverters I work with all the time at work, Industrial Electrician, All use PWM, not a true sign wave. We control speeds via frequency from 3Hz up to 400, All PWM. So no worries on a induction motor. The motor itself, The coils that its built form actually smooth the Pulsed waveform into more of a sign wave. And AC/DC supplies transform the power lower first through a transformer, a coil, then rectify to DC so no worries on PWM inverters for them either. Like I said, Only thing I ever noticed was small powerheads were a bit noisier. The PWM makes them chatter kinda like. Nothing bad. Just smaller motors with the high impedance coils.

And most all UPS run direct off the mains when the power is on, Only after the Mains is out, they swap over to battery. So, only running PWM when the power is out. Will be direct off the house sypply, bypassing the UPS electronics when the power is on

[KrazyKuch]

all inverters use PWN to generate the sine wave, Just more expensive ones do a better job...From what i have found in the past is motors need to be rated for ups use, you will find when the motor is running off the batteries it will sound funny, but shouldnt burn out your pumps...

[mike31154]

I guess it comes down to 'efficiency'. I can remember when inverters were 'motor-generators', before there was such a thing as an electronic inverter. They were large, noisy & needed periodic maintenance... replacement of brushes, bearings etc, but they produced the purest sine wave out there. The purest sine wave is still produced by something like this, a DC motor attached on the same shaft as an AC generator, which essentially rotates at the desired frequency & produces the desired voltage amplitude. Not unlike a common generator that uses a gasoline or natural gas fueled combustion engine to spin an AC generator. And remember that your household AC is a pure sine wave. Hence, most of the equipment, as in motor(s), you wish to run off the 'inverter' will run best & most efficiently on a pure sine wave. I'm sure there are newer AC motors out there these days that are optimized to run well on modified sine waves or PWM signals, but I would wager most of the AC motorized equipment used in our hobby prefers a pure sine wave. I think DC motors will increase in popularity in our hobby, since they are much easier to control and a lower voltage around water is always a good thing. So if you have a DC power supply & DC motor/pump, you don't need an inverter! One less piece of gear. Every time power is converted from one form to another, you lose some efficiency in the conversion process. Not a big deal necessarily, but for something that runs 24/7, like a return pump or powerhead, the more efficient, the greater the savings. That can be applied to your back up as well, run a DC motor off your 12 volt battery instead of using an inverter with a funky wave to run an AC motor and you'll probably get more running time during an outage.