Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Vinyl Asylum ]

---

[ Alert Moderator ]

---

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

Posted by twystd (A) on July 19, 2016 at 19:33:45

I took a long break from my motor drive project due to burn out, spending a whole lot of time on a new puppy, and cutting the cord on my TV (streaming TV is very cool). I can't tell you how happy I was to say good blank'n bye to the greedy satellite folks (no Time Warner Cable either)! Both are time consuming and very worthwhile projects, and like I say, I needed a break.

I got back into it, and started to do some real testing. First, let me say this isn't an elegant solution to VFD, but appears to work none the less. Also this is well within the skill range of your average DIY guy.

Just when I started to get serious with measuring RPMs and the amount and degree of adjustment, the cheap laser tachometer I bought crapped out. I have another one, which I hope is better, coming in the next few days, so should be able to post specific readings soon.

Just before the tach crapped out, I got a reading of 1780 RPM @ 60hz with 120VAC to the motor. With a perfect 60hz, should have been 1800RPM, but close to the accuracy range of the tach (1%). I also ran the motor at 81hz, which would be pretty close to what I'd need for 45s, but since the tach quit working, can't confirm the actual RPMs, but the motor obviously sped up.

When I had the same voltage output from the generator section at 60hz, and went to 81hz, the voltage to the motor increased significantly. The little 3 phase generator has variable voltage output, as well as variable frequency, so I was able to decrease the voltage from the generator to get 120VAC output to the motor @ 81hz as well. However, this was at the very low end of my adjustment range. A final tweak on my impedance network between the three outputs of the generator, to the three power amps, are in order, to get the output voltage range in the sweet spot, to accommodate a range of 50 to 90hz. This will be done by the time the new tach shows up.

I still had an instrument at my disposal that gave some good observations about the project, namely the index finger of my right hand. I have a second Papst motor and had it wired for single phase with the faking capacitor. I ran both motors at the same time, and held my finger in contact with the shafts. The 3 phase supply had WAY, and I mean WAY, more torque than the single phase motor, before bogging down. Also when I put the finger to the face plate of the motors, I could feel some slight vibration from the single phase motor, and none from the 3 phase motor. I'm also told that the Papst motor, when run on 3 phase, runs cooler than when running on single phase. I didn't measure that, but feel that is a reasonable expectation.

Everything seems very stable, there is no feedback loop or automatic control of RPM, but if you are okay with manually setting speed changes (frequency and voltage) this seems to be a viable option. From what I can see, once you have the output frequency and voltage parameters worked out, the settings are repeatable. I can change frequency and voltage in less than 30 seconds.

This is kinda the Jethro Bodine, brute force, low tech solution, to motor drive. As a matter of fact, I think I'll call it Jethro. I'm using a potential 600 watts to control a 30 watt motor. I think that overkill factor makes it very stable, and hopefully long lasting as well. Certainly is cheap enough at around $175 in parts, and with as little as 1/10hz adjustment on frequency, should be able to dial it right in.

Seems like a worthwhile project with the benefits of VFD, less motor vibration, more torque, and lower motor temperature. I know this isn't a DIY forum, but if there is interest, I can post a bill of materials, sources, and instructions if folks might be interested.

twystd

Edits: 07/19/16

This post is made possible by the generous support of people like you and our sponsors:

Signature Sound

[ Signature Sound Lounge ]

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---