Troubleshooting washing machine pcb. Triac input 120v, output 30-60v. Is this normal?

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
Greetings

I’m in the process of troubleshooting the control board on my whirlpool washer. The AC motor is having trouble starting - and when running is louder than it should be. It has two windings and I’ve found that one is getting 120v while the other is moves in the 30-60v range.

Each winding is supplied current via its own triac on the board. I’ve confirmed that both have 120v at MT1 - however MT2 is lower (30-60v) on on of the triacs when the motor is running.

I have no formal electrical engineering training and have been doing crash course research for this project. Is the lower voltage output a symptom of a failed triac or could it be intentional as a way of controlling the speed of the motor?

Thank you very much - I appreciate any help.
Charlie
 

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
Thanks Dave! I'm going to be away from the washer for a few days so I can't check the exact motor model. I do have a wiring diagram that I will post here. There are 4 wires going to the motor - 2 hot (one for each winding, one is referred to as the CW and the other CCW) a neutral and a ground. The voltage I'm seeing is the same at the motor wiring harness as on the control board. The motor does have a run capacitor, that I've tested and is OK. I also replaced it to be sure, and still get the same results. This motor was actually pretty simple, and I disassembled it completely and didn't see any physical damage + the resistance of both windings were exactly within spec according to the technician's manual.

Here is the wiring diagram: https://www.dropbox.com/s/2rcuckhy6ek2y3e/washer_wiring.png?dl=0

Looking at the wiring diagram - I'm beginning to wonder if perhaps only one winding is directly energized at a time and the other is only partially energized via the pass through current from the capacitor? If that's the case, my reading of 30-60v at the MT2 triac terminal is voltage coming up through the wiring harness rather than voltage being let through the triac. Unfortunately this is where I'm venturing into speculation because I don't know enough about how the circuit should work.
 

MaxHeadRoom

Joined Jul 18, 2013
21,639
As the schematic says, that is a PSC AC induction motor, the cap is in circuit all the time and just swaps windings for start and run as they are identical.
Each is fed by the cap in turn.
Only one triac would be on at any one time.
Max.
 

MisterBill2

Joined Jan 23, 2018
7,327
You need to measure the Voltages across the motor wires to be sure, one set will be the Brushes, will be the Field windings, which are in series . Take pictures of it, also model number.
It is not likely that this washing machine motor has brushes. Mostly they are induction motors.
 

MisterBill2

Joined Jan 23, 2018
7,327
Many current washing machines have service information stashed someplace in the enclosure. That may possibly be in the controls console. My guess is that there is a run capacitor someplace and it may have partly failed, or else there may be a poor connection. If you take the belt off the motor it may start OK.
 

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
Thanks everyone. You definitely answered my question - if only one triac is open at a time then what I’m seeing isn’t the issue. The motor is getting 120v on one winding and the cap is good (I tested it and also replaced it to be safe). I’m suspecting a motor issue despite the simplicity of the design. I did find one small cap that was swollen on the control board and have since replaced it. Since then the motor has not failed to start - but it does make a louder than normal humming while it runs.

Thanks again
Charlie
 

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
Thanks maxheadroom. I believe this is a 2 speed, reversible motor. There are two triacs, one connected to R and the other to S. So it reverses by just turning one on instead of the other. They have a shared
To test a PSC motor, referring to the L.H. Single spd pic. It reverses by taking L1 to S instead of R.
Max.

View attachment 161057
common neutral. I don’t understand how the speed is controlled but I’ll do some research.
 

MisterBill2

Joined Jan 23, 2018
7,327
Thanks everyone. You definitely answered my question - if only one triac is open at a time then what I’m seeing isn’t the issue. The motor is getting 120v on one winding and the cap is good (I tested it and also replaced it to be safe). I’m suspecting a motor issue despite the simplicity of the design. I did find one small cap that was swollen on the control board and have since replaced it. Since then the motor has not failed to start - but it does make a louder than normal humming while it runs.

Thanks again
Charlie
Once again, the capacitor may no longer have adequate capacitance. Add a few MFD in parallel and see if that helps.
 

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
Once again, the capacitor may no longer have adequate capacitance. Add a few MFD in parallel and see if that helps.
Thanks MisterBill2. The run cap is rated for 50uF and tested at 46.4. I ordered a brand new one that also tested at 46.4 - so I assumed that the cap was fine. Last night I wired the second one in parallel and starting torque is significantly higher - it now chirps the drive belt when the motor starts and gets up to speed in about half the time.

In short, it runs great - but there is still a loud humming sound during operation that my wife swears wasn't there before (this occurs with or without the second cap). Is there any danger or problem with continuing to run these two caps in parallel?

The motor has not failed to start since I replaced the smaller cap on the control board (it was 1000uf 6.3v) and I'm not sure it has any relation to the drive motor or if it had another function.
 

MaxHeadRoom

Joined Jul 18, 2013
21,639
Have you tried the motor OFF the machine?
I would not run a PSC motor with that large, i.e. a (double) cap, obviously the manufacturer selected the optimal value.
You could also connect directly to the AC to test, i.e. by-pass the triac.
Max.
 
Last edited:

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
I haven't tried it off the machine, but I plan on removing it this evening to double check the windings resistance and also double check for any winding shorting out to ground.

At the moment the only problem I'm experiencing is the excessive humming coming from the motor. Based on the help/info that you have all provided I'm convinced the Triacs are working fine. The motor is receiving 113-120v on the run winding and 30-60v on the start winding via the capacitor. At this point the only thing I can think of is that the motor is failing for one reason or another.

For those curious, here is a short video of the washer spinning up without the extra cap:

https://www.dropbox.com/s/yotdbcfmhgf9zsp/washer_motor_without_extra_cap.MOV?dl=0

and then another video with the extra cap. In both videos you can hear the humming:

https://www.dropbox.com/s/wsgi5zlttiya8hn/washer_motor_with_extra_cap.MOV?dl=0
 

MaxHeadRoom

Joined Jul 18, 2013
21,639
Couldn't preview the files.
If the motor is under triac control I would expect some humming from the triac switching.
I would remove the belt if it has one or remove the motor and try it on straight AC for a conclusive test.
Max.
 

MisterBill2

Joined Jan 23, 2018
7,327
And I would agree with Max that using double the capacitance is too much. But adding a bit is probably OK. And, about the humming, there may be some short-circuited turns Those will cause a hum. So one test is to run the motor for a normal wash load and then feel both the motor and the capacitor to see if either is excessively hot. Also, check the circuit wiring to see if there is excess resistance at some point in the motor power circuit, especially in the capacitor circuit. Also, if it fails to start fast enough after running a while, substitute the new capacitor for the old one, since failure with internal temperature rise is a common failure mode.
 

Thread Starter

charlieaf92

Joined Oct 4, 2018
10
For those interested - I removed the motor and ran it directly wired up on my workbench this evening. Here is a short video. I believe that the noise it is making is not normal and louder than it should be. When power is cut, the noise goes away immediately, which rules out a bearing. I'm not completely sure why it would be making the noise, but I'm going to order a replacement and run it the same way to compare.

https://www.dropbox.com/s/clknme0onw7y66h/washer_motor_bench_test.MOV?dl=0
 

MisterBill2

Joined Jan 23, 2018
7,327
Motors can fail, and short circuited turns is one of the modes of electrical failure that does happen. And the current circulating in those short circuited turns will often cause a loud hum. Bad news for the motor, but probably cheaper to replace the motor than the control circuit board.
I hope that the replacement motor is an exact fit, sometimes it does not happen that way.
 

MaxHeadRoom

Joined Jul 18, 2013
21,639
I do not find anything that drastic in the sound of the motor, my guess is that it is lamination noise, also confirmed when power cut.
A current check would confirm if any thing amiss.
If it is not a loose rotor bar but the stator lamination's, judiciously painting the lamination's with shellac may stop it.
Max.
 
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