Inverters - modified and pure

[dgadee]

Trying to understand the implications of buying the different types of inverter. Want to run an AC induction motor (cap start and run). Some sources say using modified sine wave is not a good idea and pure needed. Others say modified ok. Which is it?

 

[lw395]

'modified sine' covers a range of sins.
What you can get away with will depend on how heavily the motor is loaded, among other things.

 

[dgadee]

I was looking at a Sterling one. 1800 watt, I think. I emailed them but no reply.

 

[jiris]

AS per post #2: not all "modified waves" are equal and some signs of deficiency may appear under only a certain conditions. In general: there are very few devices that would be grossly unhappy with the modified wave. On my boat I am running a huge array of 240 V AC appliances from a MW inverter for years. I am still to find one that wouldn't work.

 

[matthewriches]

Have been using modified sine on the tug boats since way before I took over one of the contracts and they've always been ok from what the crews tell me. One boat has a Samsung microwave oven that makes a high pitched noise when not actually doing anything so suspect some noise off an internal component as it doesn't do it when plugged in shoreside. They just unplug it when not in use. Apart from that everything seems to function as expected.

 

[Norman_E]

I was looking at a Sterling one. 1800 watt, I think. I emailed them but no reply.

I have that model. It runs my mains fridge compressor with no problems. Sterling inverters are good quality and I think you will be perfectly OK provided you buy one big enough to cope with the starting current of any motor you plan to run from it, and that applies to pure sine wave models as well as the modified sine wave ones. Some motors need three times as much current on start up as they do running at full load.

I would avoid the cheap Chinese inverters sold on Ebay, as I suspect that many are not as powerful as claimed, and may not even have anything better than a square wave form.

P.S. Remember the vital rule: Start the inverter before connecting any load.

 

[William_H]

I would suggest that the OP needs a pure sine wave inverter to run an induction motor. Now it is likely that a modified sine wave or even square wave output inverter will run the motor but will probably be less efficient with heating from the harmonics of the 50 hertz present in modified sine wave inverter. In other words a pure sine wave inverter should run the motor with less DC input current than a modified sine wave or square wave inverter. olewill