AC motor controller

[Pfenning]

The mechanical aspect seems pretty easy to me. I can figure out how to build the drive wheel, bearing, and platter, but I'm lost when it comes to electrical design, and motor specifications.

Pfenning

[Grainger49]

I have had a bookmark to Pabst Synchronous motor.  I'll find it and get back to you. 

I'm assuming you can make the idler wheel and calculate the circumference versus motor RPM.  Right now I couldn't.

I'm smoking a turkey today and am on and off line.

[Grainger49]

It is hard typing now, I was scalded moving the turkey on the fire.

Here is a link to a motor manufacturer you can buy synchronous turntable motors from.

http://www.hurst-motors.com/papbdirectdrive.html

[Pfenning]

Thanks for the link Grainger. I hope your ok from the scalding, I know how easy accidents can happen when working around the grill. On the motor, how do I regulate the speed to dial it in? I can calculate the idler diameter, and build it (i think) to a high precision diameter, but how do I make slight adjustments in the speed to get it exact? How close will the motor run to the specified rpm? There has to be some tolerance on that, but how much? I hope your feeling better today.

Pfenning

[galyons]

snip...On the motor, how do I regulate the speed to dial it in? I can calculate the idler diameter, and build it (i think) to a high precision diameter, but how do I make slight adjustments in the speed to get it exact? How close will the motor run to the specified rpm? There has to be some tolerance on that, but how much?

Pfenning

The speed of an AC asynchronous motor is driven by the line frequency.  In an ideal situation, you get 60Hz at the outlet and the motor runs at the specified RPM. It is up to you to determine the motor pulley/ platter diameter ratio to generate the desired speed. In reality there are slight frequency deviations at the outlet and motors don't always run quite to spec.  Additionally, bearing friction, wear , ambient temperature and lubrication will impact the delivered speed.

A good TT AC motor controller will synthesize a "perfect"  60Hz sine waveform.  You can adjust the frequency of the regenerated sine wave to speed or slow the motor allowing for fine adjustment to the platter speed.  Simple to describe, much harder to design, manufacture and keep costs reasonable.

It is also beneficial to reduce the voltage once the initial torque to bring the platter to speed is achieved. This will reduce vibration in the motor for quieter operation.

Cheers,
Geary

[Grainger49]

Exactly, what Geary said.  All AC tables made today that do not include a speed controller rely on the power department to keep the frequency stable.  I don't think it stays off frequency for long but has periodic wavering.

The benefits I see from a dedicated speed controller are as Geary says.  First, you get a stable 60 Hertz with no wandering or wavering.  Second you get the voltage drop after startup.  The motor torque that brings the platter to speed in a revolution or two causes hunting, dither, once the platter is at speed.  Dropping the voltage drops the current and the current causes the torque.  So once at speed less torque gives a steadier speed.

[Pfenning]

Ok, so I understand the motor speed is set based off the 60 hertz. How do I build a speed controller like you and Geary mention? I follow you on the torque reduction idea.  Can I rob the design from an existing TT (TD124 or )? I'm confident in my ability to build the mechanical items, but I'm pretty lost on the motor controller stuff. I need a pretty clear path to follow.

Pfenning

[Grainger49]

I think that Dan and the Bottlehead crew is going to come up with a kit.  I hope so.

[galyons]

Ok, so I understand the motor speed is set based off the 60 hertz. How do I build a speed controller like you and Geary mention? I follow you on the torque reduction idea.  Can I rob the design from an existing TT (TD124 or )? I'm confident in my ability to build the mechanical items, but I'm pretty lost on the motor controller stuff. I need a pretty clear path to follow.

Pfenning

I would not considering designing and building your own controller.  It is a sophisticated device that requires considerable electronics and microprocessor expertise.  There was a DIY design, short lived, Mark Kelly Synchrotron AC-1 Drive Controller. Mark sold a basic board. It worked well, but, IIRC, was difficult to build and maintain.  They occasionally pop up used, but I would be wary as to why!

Until BH does a controller kit, I would focus on building the TT, (no small task!), with plans to pair it with a commercially available AC controller.  A used VPI PLC can be had for about $300, the much more sophisticated SDS , used for $800-900.  You can source a new unit for about $380 from Phoenix Engineering , the Falcon PSU Turntable Speed Controller.  There are probably a few others of which I am not aware.

I think Doc realizes that there is a DIY market for the controller, but it may well morph into the same manufacturing issues that the DAC faced. Not a small undertaking!

Cheers,
Geary

[fullheadofnothing]

The TD-124 uses a shaded pole motor. It's speed control involves moving the idler on a stepped pulley that is connected by a belt to the motor. Fine speed control is done by putting drag on the pulley with a magnet with a moving shield to control the magnet's field. The motor speed is, so far as I can tell, immune to fluctuations in frequency, but sensitive to changes in voltage. DIYing this design, would be an incredible pain (and cost way more than buying a 124)

There are a lot of pages about DIYing tables. This looks pretty comprehensive:
http://www.altmann.haan.de/turntable/

Reading pages by people who have actually built these things is probably more useful than forum postings by a bunch of people who switch up cheap beer and motors. Also, I'd focus more energy on the bearing than the motor. The motor will be swappable and tuneable if you're unhappy with the results. A lousy bearing will create all kinds of problems, and be way harder to change.

[galyons]

...snip

Reading pages by people who have actually built these things is probably more useful than forum postings by a bunch of people who switch up cheap beer and motors.

This comment bothers me.  I realize that it is hard to judge intent on the web, so hopefully this was meant to be funny?   Pabst is a well known German motor manufacturer.  About ten years after Thorens discontinued the TD124, they chose Pabst to provide replacement motors.  So I don't think Grainger is switching up "cheap beer and motors".


Pfenning was quite clear that he is reasonably confident in his mechanical abilities regarding the build.  Perhaps more so than the author of the DIY turntable site referenced.  Pfenning  was specifically asking for input on the electronics and motor.  That was the focus of the responses.

Cheers,
Geary

[fullheadofnothing]

There was never a _Pabst_ motor for the TD-124...

[galyons]

There was never a _Pabst_ motor for the TD-124...

I consider the Analogue Department one of the authoritative sites regarding Thorens.  Perhaps you'll take a look.

http://www.theanalogdept.com/papst_aussenlaufer.htm

"   

back to the TD124 dept.

A Papst in a Thorens?

The story goes something like this:

In 1977, ten years after the TD124 had been discontinued, Thorens management worried that it could no longer supply new replacement motors for their once top-of-the-line player.  The solution turned out to be the subject of this article.  Thorens contracted with Papst to adapt one of their "Aussenlaufer" motors to function in the TD124.

Above photo: A 60 hz version of the Papst Aussenlaufer motor designated by Thorens for use in the TD124.  It stands on chassis sn # 13943, which has been chemically stripped of its paint in preparation for a complete restoration.

 

About the Papst:

Thorens Service Bulletin Nr. 22, October 1977

In German

Service 22_pge 1a.jpg (311073 bytes)pge 1

Service 22_pge 2a.jpg (401314 bytes)pge 2

(roughly)Translated into English:

THORENS -- Service Information Nr. 22 Oct. 1977

Replacement Motor for Thorens TD 124

The continuing popularity of Thorens turntable TD 124 has led us to search out a solution for the replacement motor. We are therefore very pleased to finally introduce adequate replacement in the form of a motor manufactured by Papst.

Unfortunately, due to the completely different type of construction, and an alternative electrical suppressor circuit, the motor can only be operated with one voltage option.

To order, it is important to specify which kit:

3805-200 Kit for 200-240 V at 50 hz (with C = .47 uF) or

3806-110 Kit for 100-125 V at 60 hz (with C = 1.4 uF)"

Cheers,
Geary

[fullheadofnothing]

Yes. Steve Clarke knows his shit. He knows what a Papst motor is.

[Doc B.]

I do think Josh is getting a little revved up here, but c'mon Grainger, Pabst is beer. The company that makes the motors is Papst. Finding a link for a mispelled search word on Google doesn't automatically make it the American spelling - yet.