Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Best waveform for an AC motor
Best waveform for an AC motor
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd January 2018, 06:38 PM   #1
Golear is offline Golear  United States
diyAudio Member
 
Join Date: Dec 2017
Default Best waveform for an AC motor

There are a few drive systems on the market, and one project here, which seek to drive a turntable's AC motor better than if it was just plugged into the mains. There are some differences in how they do this.

However, it seems to me that they all create a sinusoidal wave (or multiple sinusoidal waves).

What's the ultimate, best-est waveform for a turntable's AC motor? Is it possible that a square or triangular, or a wave of complex shape will be better than a sinusoidal wave?

If so, can one produce such a wave on a PC- or Mac-based signal generation program, have it do an endless repeat, send the wave to the headphone output jack, amplify that signal to the required wattage and then send it into the motor?
  Reply With Quote
Old 3rd January 2018, 07:42 PM   #2
diyrayk is offline diyrayk  United States
diyAudio Member
 
diyrayk's Avatar
 
Join Date: Aug 2012
Location: Traverse City, MI
Duh, a sine wave?

Ray K
__________________
If more is better, then too much is just right.
  Reply With Quote
Old 3rd January 2018, 09:14 PM   #3
globalplayer is offline globalplayer  Germany
diyAudio Member
 
globalplayer's Avatar
 
Join Date: Oct 2014
Location: =)
Click the image to open in full size.
__________________
◢◣◢◣◢◣◢◣◢◣
  Reply With Quote
Old 3rd January 2018, 10:35 PM   #4
sq225917 is offline sq225917  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917 Best waveform for an AC motor
Quote:
Originally Posted by diyrayk View Post
Duh, a sine wave?

Ray K
Assuming a perfectly wound motor with symmetrical stator cutouts and lots of other perfect assumptions. Probably a slightly skewed sine might be better.
__________________
Paradise Pre-reg PSU PCBs
  Reply With Quote
Old 3rd January 2018, 10:51 PM   #5
diyrayk is offline diyrayk  United States
diyAudio Member
 
diyrayk's Avatar
 
Join Date: Aug 2012
Location: Traverse City, MI
Quote:
Originally Posted by sq225917 View Post
Assuming a perfectly wound motor with symmetrical stator cutouts and lots of other perfect assumptions. Probably a slightly skewed sine might be better.
Perhaps if you have detailed design information about the motor and know what you are doing you might be able to pre-distort the waveform to compensate for these imperfections, but in almost all cases you don't and you can't. IME with the application of pulse width modulated variable frequency drives on motors as large as 5500 horsepower in industrial environments, the motors operate cooler and with lowest vibration when the VFD output is closest to a pure sinewave.

Ray K
__________________
If more is better, then too much is just right.
  Reply With Quote
Old 4th January 2018, 12:11 AM   #6
davidsrsb is offline davidsrsb  Malaysia
diyAudio Member
 
Join Date: Dec 2005
Location: Kuala Lumpur
I have seen using the motor as a generator suggested to find the actual pole and field structure. It won't be sinusoidal.
  Reply With Quote
Old 4th January 2018, 12:12 AM   #7
kaputt is offline kaputt  Germany
Banned
 
Join Date: Sep 2011
Location: Berlin
+1. Use another motor to drive the one in question and measure the output waveshape with an oscilloscope.
  Reply With Quote
Old 4th January 2018, 12:20 AM   #8
Pyramid is offline Pyramid  United States
diyAudio Member
 
Pyramid's Avatar
 
Join Date: May 2006
Location: Behind the Cheddar Curtain
Quote:
Originally Posted by Golear View Post
What's the ultimate, best-est waveform for a turntable's AC motor?
Define "best-est". Are you looking to maximize torque, minimize vibration, maintain constant impedance, constant phase angle between windings, reduce power consumption, maximize efficiency?
  Reply With Quote
Old 4th January 2018, 01:20 AM   #9
Golear is offline Golear  United States
diyAudio Member
 
Join Date: Dec 2017
Quote:
Originally Posted by Pyramid View Post
Define "best-est". Are you looking to maximize torque, minimize vibration, maintain constant impedance, constant phase angle between windings, reduce power consumption, maximize efficiency?
I don't think we'd mind if it took a longer time to reach the desired speed if there are other advantages to be had. And perhaps reducing power consumption and max efficiency are very low down on priorities. Reducing vibration might be a consideration though this may already be addressed by other things on the turntable.

I suppose the high-level question is: what sort of waveform could make the music sound better? We're not, for example, talking about what's required for a train or a cooling fan. So perhaps controlling things like.... cogging?
  Reply With Quote
Old 4th January 2018, 11:58 AM   #10
Pyramid is offline Pyramid  United States
diyAudio Member
 
Pyramid's Avatar
 
Join Date: May 2006
Location: Behind the Cheddar Curtain
Cogging creates vibration and it is a function of the drive frequency, the strength of the magnet and the power being delivered to the motor. It can be reduced by proper alignment of the phase between the coils in AC synch motors and reducing power (at the expense of available torque), but is never completely eliminated. As far as waveform, a pure sinewave will give you the lowest noise.

AC synch motors are not the optimal drive solution for turntables IMHO. 3 phase motors produce more torque, are more efficient and have little to no cogging, but require 3 phase sinewave drive to achieve the best results.
  Reply With Quote

Reply


Best waveform for an AC motorHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Compact Disc Motor and Turntable - Advices for Replace and Motor Service wanted tiefbassuebertr Digital Source 8 21st September 2018 04:39 PM
Replacing a Brushed Motor with a Brushless Motor - Advice needed. Salar Digital Source 14 17th August 2015 10:40 PM
Belt driven Synchronous Motor vs. DC Motor for Record Players tiefbassuebertr Analogue Source 11 27th September 2013 05:38 PM
Lambda motor vs. XBL^2 motor vs. any other motor Thinkcat Subwoofers 16 23rd December 2008 06:23 AM
DIY TT: motor, motor PS, platter speed measurements dice45 Analogue Source 52 9th May 2006 01:07 PM


New To Site? Need Help?

All times are GMT. The time now is 07:51 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki