Hi.
To convert DC into 120V / 60Hz pulsing AC and then by LC circuitry, make it near sinusoidal for a couple of hundred watts to power a blower fan motor ?

(Instead of using a typical inverter) How would you make one ? For 12, 24, 36, 48 VDC input to 120VAC output ?

 

It's not a best idea to convert a rectangular voltage into a sine wave using an LC filter. If the load current changes rapidly, the LC filter gives strong voltage spikes.
You can also use a ferroresonant transformer; I've seen a 10kW industrial UPS made that way. The input was 3x400V AC, the battery was 120V, the output was single phase 230V. However, this transformer is big, heavy, and noisy

 

Blocking oscillators are very simple but also very inefficient. For the simple reason that to oscillate the transformer has to be driven hard into saturation.
Not only does that increase the core losses significantly, but core saturation means that the core material loses most of its permeability, meaning high current spikes that the switching transistor must carry, which causes additional losses.
For those reasons, blocking oscillators are used for low power, usually 5 watts at most.

 

why not use fan made for your desired DC voltage (you mention 12, 24, 36, 48 VDC) and forget about using AC fan?

 

A Universal motor can run on AC or DC. As long as you got the voltage right.

"Couple hundred watts" isn't very small. How big is the motor you want to run?

The devil is in the details. Help us help you.

200W (assumed) divided by 120VAC = 1 2/3 amps.

 

1 horsepower is equal to 745.7 watts. 200 watts is equal to 0.268 horsepower. So you're talking about roughly a quarter horsepower motor. It should be easy to find a DC motor that runs on the voltage you want to start with - without having to spend a lot of money making a not so easy build to run your motor.

why not use fan made for your desired DC voltage (you mention 12, 24, 36, 48 VDC

PM said it first. Makes sense to me too.

 

A simple inverter with adequate capability will be te best way to drive an AC induction motor. The second choice is a switching type voltage multiplier scheme. I have seen those circuits but I can't supply any help with them.
The big concern is to not have the frequency too farfrom the motor design frequency. Driving a motor above its intended frequency will run it faster, driving it much below the rated frequency will result in running hotter and at a lower speed.

 

Baxandall inverter (resonant Royer).
This type of inverter produces sinusoidal voltage. They were widely used to power CFC lamps in monitors and TV's, just their frequency was much higher, around 20-30kHz.
It would be possible to recalculate such an inverter for a lower frequency.

Royer oscillator - Wikipedia

 

To convert DC into 120V / 60Hz pulsing AC and then by LC circuitry, make it near sinusoidal for a couple of hundred watts to power a blower fan motor ?
(Instead of using a typical inverter) How would you make one ? For 12, 24, 36, 48 VDC input to 120VAC output ?

Simple use UPS.

 

Is the concern that "A typical inverter" is not so efficient?? OR is this thread intended to explore alternative schemes?

 

For a blower motor, the most simple inverter should do: idle - positive - idle - negative. A filter should not be required - I'd expect the motor to have a sufficiently high inductance to create something like a sawtooth current form the voltage steps input.

 

For a blower motor, the most simple inverter should do: idle - positive - idle - negative. A filter should not be required - I'd expect the motor to have a sufficiently high inductance to create something like a sawtooth current form the voltage steps input.

I've read reviews that water pump motors work poorly if the power supply voltage is square-shaped. The motor hums loudly and gets very hot.

 

The applied volt-seconds of a square wave is 11% larger than a sine wave of the same amplitude. You have to reduce the amplitude by the same amount ti avoid magnetic saturation.

 

The applied volt-seconds of a square wave is 11% larger than a sine wave of the same amplitude. You have to reduce the amplitude by the same amount ti avoid magnetic saturation.

You may as well reduce the on-time of the "squares" (that's what the "idle" was meant to indicate).

 

Exactly! You either reduce the volts or the seconds.