I have been looking into having an inverter & battery backup supply to power my home chest freezers.
I really like the look of Mean Well's NTU-1200 inverters, particularly as it has a built in "by-pass" facility. I have heard however that you have to be a bit careful when using inverters with things with motors in as the high frequencies from the inverter can cause over heating (?) and I really don't want to shorten the lifetime of my freezer!
Anyone have more experience in this?

 

To drive an AC motor it is best to have AC power, close to a sine wave. That is possible to do, BUT it is less efficient and more complex. But I have seen designs that come close. The circuit will look more like an audio amplifier with a transformer output. And just like audio amplifiers the trade is efficiency versus low distortion.

 

Possibly you could obtain information from the Mean Well company as to how suitable their inverter is for powering induction motors. Of course I am guessing that your freezer has an induction motor for the sealed unit compressor. If it has a BLDC motor then there should be no problem because those systems rectify the mains voltage first.

 

The NTU-1200 appears to be a true-sine-wave inverter, so will be compatible with any refrigerator or freezer. I lived off-grid for many years and ran a number of refrigerators and freezers without problems, using Outback and Selectronic inverters.

I think your concerns are based on the problems with using 'modified sine wave' inverters, which are essentially square wave output and hence not compatible with inductive loads.

 

If you have an older freezer with a compressor with a capacitor-run induction motor that is switched on and off using a thermostat, then you get an inrush current every time the motor starts, which will be three or four times the running current of the motor. Make sure that your inverter can provide that without shutting down.
Newer freezers with variable-speed compressors will be easier on the inverter, and also more efficient, which means that they would run longer off the battery when there is no mains. Neither batteries nor freezers last for ever, so a new freezer will save you money on batteries!

 

I think your concerns are based on the problems with using 'modified sine wave' inverters, which are essentially square wave output and hence not compatible with inductive loads.

An inductive load won't be bothered by a squarewave, because dI/dt is limited by the inductance. A capacitive load would be a problem, and freezer compressors are capacitor-run motors.

 

The NTU-1200 appears to be a true-sine-wave inverter, so will be compatible with any refrigerator or freezer. I lived off-grid for many years and ran a number of refrigerators and freezers without problems, using Outback and Selectronic inverters.

I think your concerns are based on the problems with using 'modified sine wave' inverters, which are essentially square wave output and hence not compatible with inductive loads.

Thanks boostbuck!

 

An inductive load won't be bothered by a squarewave, because dI/dt is limited by the inductance. A capacitive load would be a problem, and freezer compressors are capacitor-run motors.

Well there you are, I stand corrected - the starting caps are the issue, not the motor induction. All I can say is that the original modified-sine-wave inverter I had gave me untold grief, and once I switched to pure-sine-wave units I had no further issues.

Essentially, the NTU-1200 will be fine.

 

Well there you are, I stand corrected - the starting caps are the issue, not the motor induction. All I can say is that the original modified-sine-wave inverter I had gave me untold grief, and once I switched to pure-sine-wave units I had no further issues.

Essentially, the NTU-1200 will be fine.

I use Victron inverters which are sinewave, and give no trouble with motors apart from the inrush.
I also think that the motors are not good on squarewave (euphemistically called "modified sinewave") inverters because they are motors, and not simply because they are inductive (or capacitive). The current is the difference between the input voltage and the "generating" voltage divided by the impedance. The generating voltage will be sinusoidal at a steady speed, but the shape of the input waveform isn't and the difference between them will be an even worse waveform than comes out of the inverter.

 

At least some of the "modified sine wave" inverters implement steps rather than a plain square wave. So that may have some impact. And it still may be good to question the freezer manufacturer, who may have some good advice.

Aside from that, I see that some industrial motors are rated "inverter compatible", which in their case means variable speed drive inverters. So there is another hing to consider.