Audio inverter ???

[Downunder35m]

I am still pondering on a nice way for off grid cooling.
And while reading up on some Danfoss info in regards to their DC compressors I started to wonder....

The motors used in our small refrigeration compressors are all single phase.
But their speed is not Voltage controlled but a result of the mains frequency and motor configuration.
Resulting in around 3000RPM as the average here.

Why can't we use a nice sine wave audio signal and run it through a powerful enough audio amplifier?
I was thinking in this direction:
Simple signal generator that is limited to an output between 40 and 70 or 75Hz.
With the mains frequency being the default.
Fed into a 12V audio amplifier with enough power to spare as those low frequencies always great more heat.
To make it work a transformer with 4 or 8 Ohm on the amplifier side and a secondary winding providing main voltage with the amp sitting at around 50% capacity.

Sine it obviously can't be THAT simple based on the total lack of inverters based on this.....
What are the obvious flaws here?
Does the magnetic cores of the transformer matter much for the amp and how it performs?
According to the WWW the average amp provides about 14.4V on the output, so 28.8V peak to peak.
So with the amp being adjustable and all and winding ration of 1 : 20 or 22 to cater for losses should be fine.
Which brings the question of what size wire on the primary side with how many turns will provide the best magnetic flux?
From there we at least can guess how many turns on the secondary we need, but...
The secondary needs to be able to provide 150 to 200W for quite a while without any part of the transformer getting too hot....
Heat means efficiency goes down the drain....
Considering there is motor with start capacitor on the output:
How badly does this mess up things through the transformer for the amplifier?
Can we keep it somehow clean and efficient?

Is it possible?
Is it FEASIBLE?
Or is it just totally unefficient even if it could work?
Seems to easy to actually work....

[Downunder35m]

I did some crappy test with a 12V transformer and a dirt cheap 20W amp.
The output was surprisingly nice until I added a tiny load.
Next was adding about 6 ohms worth of copper wire onto an old ring transformer.
This worked MUCH better and a resistive load of about 15W did not do any harm.
Then I decided to hook up a small 10W filter pump from my fish tank.
Clearly the inductive load messed up things as the amp was getting really hot really quick.
In all fairness though : I could not crank the amp to full as then the output from the transformer would go over 250V...

Something to level the playing field was required to keep the load on the amp more natural.
A resistor to limit the current and a little AC capacitor from my spare parts box made a good difference.
I clearly upsets things a bit in the transformer with the current and voltage getting out of sync a bit but under an inductive load it all evens out better.
Upscaling for a resistive load is pretty easy.
Use a bigger transformer and more powerful amp to match.
But catering for changing loads while keeping the amp stable isn't as easy as it first looked.
Unlike a forced inverter the amp is not designed to deal with high flux rates and load changes on the output.

But what about a dirt cheap UPS that still has a transformer inside?
Shouldn't it be possible to salvage one and to modify it so we can use and adjustable output frequency?

[autonomous]

Hello,

Your idea is interesting, but there are some obvious flaws in your proposal. Using a sinusoidal audio signal to control the speed of a refrigeration compressor is not a common method. Also, it could lead to overheating and overloading your audio amplifier, as low frequencies generate a lot of heat. However, cryptocurrency technology is often used to control the speed of computer processes, which could include controlling the speed of a refrigeration compressor.

[Downunder35m]

Really ?
What a long way of adding crytpo crap to something totally unrelated.
But since my idea is so badly flawed you wouldn't mind explaining to me how how crypto tech can be used to control my compressor - would you ?