[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] homebrew VFD?



I've run a pretty well loaded 1/2 horsepower synch motor from a 65 Hz square wave inverter without problems. Have others had different experiences?

Ed

William Noble wrote:

square waves will cause significant heating of the motor as well as some really nasty harmonic effects - this is why VFDs go to some significan effort to make sine waves

Date: Mon, 10 May 2010 15:56:38 -0700
From: evp@xxxxxxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] homebrew VFD?

OK in principle but a practical problem will be in supplying enough current to get the motor started. I've used a similar device to power telescope drive motors but the total power was only 5 watts and they don't draw more on start. You could start the motor off the power line and then switch to the VFD and it would certainly work for frequencies less than power line.

The motor will be perfectly happy with square waves so no need to filter. In fact, the capacitor on the secondary could screw up the inverter or make it take a lot of excess power. You didn't specify what you planned to use but it does have to put out a PERFECTLY SYMMETRICAL square wave. In my case I used a '2 X' multivibrator oscillator feeding a divide by two circuit to guarantee that.

Ed

Scott Bogard wrote:

Greetings all,
While my intentions with this are completely off topic, the information could be extremely helpful for those running asynchronous rotaries, and I know of nobody else to ask this question, thus I fell no guilt putting it here. I want to know if it is possible to essentially build a variable frequency drive, this is what I had in mind. Get a mot, remove the windings then make your own to take 36V to 120V. Drive the primary with a variable flyback type inverter, designed for 1-120 Hz. So we have a DC square wave entering the primary. On the secondary put a capacitor sized to take a square wave and make it nearly sinusoidal (so perhaps a cap resonate with about 90 Hz?). And then feed your secondary into your induction motor winding. It seems to make sense in my head but it seems a bit too simple, perhaps the square wave will not really drive the mot core correctly because of saturation in which case I don't know what to do. Any thoughts or should I just abandon this.

Scott Bogard.
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla


_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
		 	   		  _______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla



_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla