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# 12v DC to AC 2000W inverter mod into -> variable frequency drive? Answered

I wondered if anybody could guide me in the right direction. I'm trying to make a variable frequency drive by adding a square wave signal from a signal generator to the set of transistors within the inverter itself. The signal generator is putting out a 8v square wave to the outputs.

Also, this is the inverter i was looking at "http://dcacpower.com/index.php?main_page=product_info&cPath=1&products_id=5"

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You don't do it by varying the drive FREQUENCY. The usual topology is a PWM, of fixed frequency.

The magnetics in the inverter are always designed around a fixed excitation frequency, since the rate of change of flux is directly proportional to it.

+2

You are better off just taking the signal from a function generator, amplifying the signal to provide enough current, and running the signal through a transformer.

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| Function generator |
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| Amplifier |
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| Transformer |
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No, not if you vary the frequency !!!

If you're not careful, you'll saturate the core, and then it'll destroy the driver stage.

Thank you, so if i were to take the 60 cycle frequency and run it through a NST, which is rated for that frequency anyways, how would i modulate the high voltage signal with signal generator?

You need access to an oscilloscope to do it, and a signal generator.

Steve

Actually what i meant was i am having trouble finding a circuit diagram for a high voltage capacitor and transistor bank for controlling the frequency. Basically working the same way as an audio amplifier, but amplifier caps aren't exactly rated for 5kvac @ roughly 10-15A.

I didnt realize that formula was so simple.
So excuse me, lets say 3.3A 900VAC from the transformer at 60hz.

I dont know what capacitance to look for in order to get full discharge at frequencies up to 20khz. Or how to wire the transistor, resistors, diodes, etc.

I haven't seen an NST rated at more than 10mA. What are you using ?

If it would be cheaper and easier to make the inverter from scratch let me know, I found a diagram to follow.

All i need to know is how to wire a 1 1/8" audio jack to the unit without affecting the excitation frequency of the drive. And get a 900v square wave AC output.
Maybe a voltage pot would be nice

http://dcinverter.blogspot.com/2011/04/3000w-power-inverter-circuit-12vdc-to.html

I think a center tapped will do, I changed my mind about the NST since the voltage has changed.

Also will it naturally be an easy task to change the modified sine wave into the square wave the generator emits?