How to fault find DC motor speed controller?

It could be a build up of carbon dust around the brush holders.

+1.

Used to happen quite frequently on industrial DC spindle & servo motors when these were common. Sometimes the semiconductor fuse would blow but, more often with earlier drives, the thyristors would often blow to protect the fuse.

Before stripping the motor down, try removing all the brushes, take the motor outside & blow through the brush holders with dry compressed air. This frequently ejects the build up of dust (hence the "take it outside" bit !) - replace the brushes & you are good to go. Couldn't do this with spindle motors with external blowers though - usually a build-up of coolant residues would cause the brush dust the adhere to the brush holders & required the use of solvents to wash out the conductive gunk. Most of this type of motor had removable access plates at the brush gear end, so access was not usually too bad. It was usual to find bright "splash" marks on the brass brusholders where the tracking had taken place.

Nigel B

Ha! I've been fooled by the double grub screw or long grub screw into recess before! Not this time.

In bits now. The brushes are in very good condition and it is really clean in there. Dates from 1978 but not a huge amount of use

It does have a supressor so maybe I will try a new one:

Can somene point me to a suitable replacement?

Edited By jaCK Hobson on 04/11/2016 13:05:25

Shouldn't be difficult, for example Maplins sell a similar delta suppressor for £3.49

Dave

..and before condemning the motor, try running it on the speed controller.....just in case it is the filter caps that are the culprits....more likely the one going from Live to earth.....

Hi John,
You'r forgetting that this is a DC motor. Both motor connections will be connected live for half of the time via the bridge rectifier in the speed controller.
Jack, The supppressor that Dave suggests look to be a suitable replacement.

Les.

Les, you are correct.....(I've been busy repairing my collection of Bridges drills that are universal motor powered with a similar suppressor arrangement..) Notwithstanding my excuse, just try the motor without the filter.....lol...

Note to self.....Pay attention at the back!.....

Edited By John Rudd on 04/11/2016 16:35:47

Got a new supressor but a little too big to go in motor housing. Now I just need to remember how it all goes back together:

Hurrah! It seems to be fixed. 30mins af full speed. Thanks for the help.

I thought I'd resurrect this thread! I have a similar setup to the examples above, but after less than 10 minutes my Parvalux motor slows down and then stops (in the space of about 30 seconds).

I sent the motor to a re-winding company who checked it and said it was fine, so I'm investigating the controller. Electrics aren't my primary field of excellence (!) and I haven't done the lightbulb test as described above. I figured that I could connect one of the wires for the bulb holder to the wire that should go to the field windings, but where should the other wire from the bulb holder connect? Earth? This is why I haven't done this yet!

My motor will only run with the switch in the "Reverse" position- it won't run at all in the "Forwards". I can get around this mechanically so I'm not too fussed about this. When the motor is running, the speed can be varied quite happily.

I disconnected one cable to the large white cylinder and the motor wouldn't run, so I guess this is the start capacitor?

Are the two blue cylinders the run capacitors?

I'm also curious as to what the black discs with white plastic circles in the centre are. They have a bit of white oxide-y type powder on them so could be the problem?

It would be really great to get this working as I made all of the mechanical fixtures to drive a positioner and only when I tried to use it properly did it become apparent that it won't run for very long.

Edited By SillyOldDuffer on 03/09/2022 09:13:30

.

Those are pre-set potentiometers, Paul … and yes, they should be clean

At the very least; give them a spray of Servisol and move them around to clean the track [returning to the same position]

MichaelG.

After rotating Paul's photo of the motor I was able to read the label: 200/220V DC SHUNT, 55W OUT, 3000rpm.

As it's a DC motor, there are no Start or Run capacitors. (They're a thing on AC single-phase induction motors.)

That the speed controller and motor work OK in reverse, and the motor is confirmed to be in good order, suggests a simple fault. There's a good chance the Forward/Reverse switch has failed and needs to be replaced. Looks like a common 2-pole 2-way switch like this example on Amazon. (Check physical fit) If the designer did a 'proper job', the switch will have a centre OFF position, in which case it's a 2-pole 3-way switch like this one.

Dave