Why is it bad to use a square wave inverter with transformers and inductors?

Thread Starter

jlawley1969

Joined Feb 22, 2021
93
So basically I was writing down why a modified sine wave inverter or "pure" sine wave inverter is beneficial over a simple square wave inverter. I understand the fact that a square wave is comprised of many different and higher frequencies and these high frequencies cause more inductive reactance in the inductor. What I dont get is that it seems as though the inductor is seeing a constant voltage and current just for short amount of times and so is a constant voltage/current through an inductor a bad thing then? And if that is the case then why is a modified sine wave better than a square wave? because it spends less time at a non-zero voltage?

Building upon this I have read than transformers are less efficient and dissipate more heat when passing a square wave but I have to find a satisfy answer as to why this happens. I understand the power losses given the high frequencies present in a square wave and the formula for inductive reactance being dependent on frequency. what I don't understand is why more heat is created given that reactance does not dissipate energy as heat as resistance does.

thanks
 

crutschow

Joined Mar 14, 2008
28,158
if that is the case then why is a modified sine wave better than a square wave? because it spends less time at a non-zero voltage?
It's not the converter, transformer, or inductor that's the problem, it's the load.
Loads designed to operate from the main's sinewave, may have a problem or fail if fed a square-wave instead of a sinewave.
 

neonstrobe

Joined May 15, 2009
178
Is this homework? You didn't answer.
Schmitt - transformers are designed to reach a given magnetic field. Whether that is done by square wave or sinewave is generally not the issue but by design.
Many older inverters and some new ones work on square wave drive.
Getting a pure sinewave is actually tricky.
 

Audioguru again

Joined Oct 21, 2019
3,828
A squarewave that produces the same heating power as a sinewave has its peak voltages only 0.707 times the peak voltage of a sinewave.

Many electronic products rectify the sinewave and operate from the smoothed higher peak voltage of a sinewave. Most of the products will not work when a rectified squarewave produces only 0.707 times the required DC voltage.

if a squarewave inverter has its peak voltage the same as the peak voltage of a sinewave then heaters and many other products would burn out.
 

Ian0

Joined Aug 7, 2020
3,752
You can run any mains-operated device on a sinewave, because it's designed to be run on sinewave.
You can run some mains-operated devices on squarewaves, and modified squarewaves, but no manufacturer will tell you which ones, because they only have to design their product to run an a sinewave. Try it on a squarewave it you want to but if you damage it you won't get a refund.
Generally motors and transformers are bad - they buzz a lot and run hot. (core losses as @schmitt trigger said)
Anything that is a capacitive load might damage the inverter.
 
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