Trapezoidal wave inverters?

[leesamuelm]

I was looking at some cheaper aliexpress "pure sine inverters" and saw feedback on one that showed a trapezoidal waveform and the buyer complained it wasn't pure sine.
As far as I knew there were pure sine and modified sine waves, but trapezoidal was new to me. Anyone else have feedback on if this might work for running a normal fridge? I'm more interested in the comparisons between MSW trapezoidal and pure sine wave.

 

[time2roll]

I speculate trapezoid is another description for modified square wave. link?

 

[leesamuelm]

 

[leesamuelm]

guessing this is just a MSW then? I ordered this https://www.aliexpress.com/item/1005002064389435.html?spm=a2g0o.order_list.0.0.21ef1802xNLE4S

and should arrive today or tomorrow. I'll try to test it this week on an oscilloscope and check for myself, but will let you guys know. I was just very surprised to see a trapezoidal wave form as I have never seen it (I have seen Modified stepped squares, pure sine, triangular, and pure square) I guess this might be a triangular, then shift to a square at the top?

I wonder if this would be close enough to a pure sine for most applications (compressor motor on my fridge)

 

[leesamuelm]

So I'll close out this thread. I tested the inverter I got and confirmed it is a pure sine wave inverter. I did not have the guts to max out and test how many actual watts it can pull, but had it tested with an oscilloscope and had a nice clean sine wave.

 

[leesamuelm]

so the "trapezoidal" curve may have been a red herring. The person who originally posted that picture may not have had their oscilloscope range set properly.

 

[solar8484]

That's a flat topped sine wave ... put a full load on the inverter and you'll likely see that waveform ... common for cheap inverters.

 

[leesamuelm]

good to know. Thank you for chiming in. Overall, I'm happy with the purchase so far. We'll see how long that lasts haha

 

[time2roll]

Some items such as microwave magnetron and motors like to see the peak voltage of the sine wave. Microwave may run at lower power if the peak is flattened, motors and other items may produce more heat.