Electronics > Power/Renewable Energy/EV's

Variable Voltage AC supply- Not a Variac

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I looked for this solution once before but came up blank. I currently have a large fan (pulls ~300W@120V), and I use a variac to regulate the speed. It does have multiple windings for low, medium and high, but even the 'low' is too high at times.

What I'd love to find is some electronically controllable variable AC voltage supply. I know UPS units do this, as I've rebuilt some of the 'stepped' ones although I haven't tested one of those.

I suppose I could also gear the knob in such a way that a standard IOT type device could control it- but with all the projects I still haven't completed...

Anything out there you are aware of ?

Thanks much-

I will soon have the attached fully ready for you. (LTspice sim)
It is 4 flybacks...acting together....a pair acts on the positive half sine, and another pair on the
neg half sine. And you end up with a controlled sine voltage on the cap.
You may have to swap the diodes for ones in your version  of LTspice.

As you can tell, it is superb, it allows you to have an variable output voltage sinusoidal mains inverter with very simple circuitry...and no software needed.
Just enjoy the variable sine...and enjoy your slower fan!

David Hess:
The all electronic alternative is a sine source driving a class-d amplifier driving a step-up transformer.  If only a limited output range is required, then the output of the transformer may be placed in series with the power line to produce an output, so only a fraction of the power has to be supplied from the class-d amplifier.

Today lower voltage class-d amplifiers of suitable power are trivially available in the form of class-d audio amplifiers.

A linear class-b or class-ab amplifier could so be used, but efficiency will be lower.

Replace the motor with a variable speed BLDC one? (They're known as "ECM" in the HVAC industry.)

That would take all the fun out of rebuilding the fan .. but I'll take a look at the HVAC surplus place near me

I'm going to have to read up on the class d amps. Apparently hardware at work uses them but I don't know nearly enough to be contact and certainly hasn't considered using them to drive this fan.

And I'll be reloading spice on this machine or sending it into work to try out.

Than you all.


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