Washing machine motor controller, tacho feedback.

[dr pepper]

I have built a couple of washing machine motor controllers that were used with hotpoint motors, both designs were just fancy phase angle light dimmers and ran open loop, as most washer motors are universal brushed ones.

I was thinking of modding one to run closed loop with a pic micro, so the rotor speed remains constant on and off load.

I doubt its the kind of thing that people mess with often but was wondering if anyone knew anything about the tacho's found on the back of washer motors, are they a voltage o/p, so many v per 1000 revs, or are they a frequency o/p so many pulses per rev.

Last time I looked at this I considered a tda1085, but they are obsolete now, so it'll be a pic.

 

[Mike odom]

Here's a constant speed Fan controller we built for LABCONCO back in the 90's. Uses the firing pulse as feedback to hold the motor at constant speed under varing loads. Speed Control is via pot.

Don't worry about © copyright infringement, AMT went out of business in'03 (the circuit designer and owner sold AMT in '98 and I left in 2000 to start Avatar Engineering, Inc. I have the circuit board foil patterns (gerber and PDF) I could forward to you and can extract a BOM also. The board is about 4" x 5" (with corners cutout).

The owner and I talked about the intricate workings of the circuit many times while in development, but that was 20 years ago and I don't know if I could dig that out of my brain. While I have the circuit reproduction documents, I don't have any notes or other development documents. Would be a good practice in circuit theory if you'd want to try and figure out how the damn thing works. Also, if you do want the circuit patterns, I could also make any changes you'd want on them. The source files (binary) still load into my current CAD system.

View attachment 69164

 

[Mike odom]

oh wait, you're 50Hz not 60, so I don't know if this would work w/o major modifications...

 

[picbits]

The last washing machine motor I controlled had a simple magnet / coil arrangement for the tacho - it gave a sine wave output with a frequency proportional to the speed of the motor.

 

[dr pepper]

Interesting circuit mike, I was thinking of using a micro rather than discretes, that said I might be able to borrow some of your ideas from that for the feedback and firing circuits.
I've never seen anything like that before, I can see your filtering the mains into a triangle and then using a comparator to compare that with a dc ref from the pot, working out how you got feedback is gonna take a bit more staring at that and more coffee.

Bits: I found a company that sells a controller for washing machine motors aimed at the model making industry, as a cheap source of power, I think they use the tda 1085, like I said I want a pic, however their instruction manual says that the tacho is a freq out, whatsmore you can solder on more poles to increase the o/p freq, interesting, if I were to use timer0 or timer 1 with ext clock I'd be able to get a better resolution and lower speed without loads of code.

Edit: looks like I was wrong, the motor circuit looks as though its part of the oscillator.