UPS, PWM Sine wave or True Sine wave

[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.