Single Phase Speed Controller Weirdness - Page 1
Forum section: electronics / general

author: Morberis
author_rank: Newbie
timestamp: June 11, 2019, 04:03:10 pm
content: Sorry this is a first time post and this looks like the correct forum. Long time EEVblog watcher.I have here a single phase AC 120/208v motor speed controller for fans. It takes a 0-10v signal and uses it to control a triac, Q6040K7 fromLittlefuse.Now the manufacturer recommends putting relays, contactors or another control device on the output of the device if staging or on/off control is desired. Sure enough I do that and I get problems. The motor will hum and not rotate and is fact resistant to rotating. The output waveform of the controller messes up but if I wobble the speed around a little bit everything corrects itself. By a little bit I mean 5%. I can use electro-mechanical relays, Solid state relays, or solid state with zero-crossing. The motor here is only a 1/4hp jobby that pulls 1.2 Amps.This also when I stop it, let it coast to a stop, and then starti it from a stop. Though the same thing happens if I stop and start it before it can stop. I can also coast the speed down to the minimum and then try to stop it and that also causes problems. Putting the control device on the input also causes the same problems. I've also tried switching 1 phase, or both phases of this 208v motor.Unfortunately I'm an electrician by trade and training and I only dabble in electronics. So I was wondering if this is a common problem with triacs or if it's something weird with their control board. I did do some searching but didn't find any answers.Here are the pictures from our oscilloscope.Correct Waveformhttps://drive.google.com/open?id=1UxvwieSKOsUgdYrNJ4WBRkyGQq_9DpKGhttp://i65.tinypic.com/2m7vwia.jpgIncorrect Waveformhttps://drive.google.com/open?id=1Xdfm0h-F0EYN55AVfn1RzlqvljxVkFDKhttp://i66.tinypic.com/2ihwh92.jpgBoard image just because. Don't worry about the bare wires you see there, everything is powered off and it's just a cable that got tossed onto it. I didn't realize it was in the shot until I looked now. This is meant for controlling 2 fans with individual speed control. The slave connection is for connecting to one of their devices that can control it over a communication bus. There are some jumper pins for selecting different acceleration curves depending on the motor used and they are correct. But even trying the other curves result in this problem.https://photos.app.goo.gl/aT29V1teXEWxoPGv5Sorry I can't seem to embed the images.Yes the motor is meant to be speed controller. It's actually one they recommend but it is I think a shaded pole? motor by Exacon.I have talked to the company and one of their 'engineers' but they're baffled by it. They are also unconcerned because the problem

author: duak
author_rank: Super Contributor
timestamp: June 24, 2019, 12:31:32 am
content: The triac based, shaded pole motor controllers that I worked with had integral manual speed controls that started at max speed and then turned down. I seem to recall that if the speed control was set too low and then AC power was applied, the motor would not start turning but would hum.Since your control has an external speed input, one would expect it to start at any setting. What happens if you set the speed higher and cycle the AC power off then on?These controllers should also work as incandescant lamp dimmers. Could you try wiring a small lamp of 10 to 40 W in parallel with the motor and see what happens? It could be that because of the inductance of the motor, there is insufficient resistive load on the controller and because it's probably wired in series, it just can't get started properly.