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RE: Another DIY 3 phase variable frequency drive for Papst motor update.

Posted by twystd (A) on July 20, 2016 at 22:56:51

In Reply to: RE: Another DIY 3 phase variable frequency drive for Papst motor update. posted by coffee-phil on July 20, 2016 at 21:33:49:

Thanks Phil, I think there is an error on both the phase generator and the tach. However, all things are relative, and since I can change the frequency 1/10hz at a time, I should be able to dial things in. 1/10hz should equal about 3 rpm on the motor.

I really don't care if I have to run the signal generator at 60.7 hz (or whatever) to actually get the correct speed. I do seem to get repeatable results when I power the motor and/or the generator on and off again, same with the tach. The plan is, once I get the TT built, to get something like the KAB SpeedStrobe to set the speed right at 33 1/3 and 45 rpm, then write down the correct settings for both the voltage and hz settings for the generator. I really don't care what the settings on the generator are, as long as I can get correct and consistent speed and voltage on the TT itself. So far it seems that is a realistic expectation.

Also I plan on running an external idler drive (single idler) on a ROK belt drive platter, as the belt drive platter is heavier than the internal rim drive platter of the idler drive ROK. The outer rim of the ROK belt drive platter is machined true for the belt, hence external idler drive. I have a mint belt drive platter and bearing that I'm planing on sending to Applied Fidelity, and get the "Full Monty" work over.

That means I'm going to have to machine down the capstan on the Papst motor, so there will probably be a slight error there as well. So the VFD should be able to be tweaked to get the speed where it should be. The way I see it the 1/10hz increments should translate to .0555 rpm @ ~ 33.333plater speed. I think that is more accurate than the fluctuations of 120V 60hz line frequency.

BTW, did you ever try those triple mica Voshkod tubes in your Little Bear? My bud bought a Little Bear, and we are running them in his, we think it sounds better than with the Chinese tubes. Here's a link to the signal generator.

twystd

• http://www.ebay.com/itm/NEW-3-Phase-Sinusoidal-Signal-Genera   (Open in New Window)

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