Single phase motor fault finding.

[pennychew]

Looking for some help with motor fault finding.

I've got a small woodworking router that i broke a couple of years back, given that we've just been covering very basic motor theory at college i want to see if i can either fix it or at least understand what's wrong with it if its terminal!

This is the router.


When i stripped it down i could see visible damage to the rotor windings and also marks on the housing where the windings have touched it. This has resulted in two individual strands being broken.





Im not sure if this is enough to write the armature off or not?

After a bit of googling and watching some youtube vids the tests i could find to carry out were to check the resistance at the two field windings (4.27ohms and 4.22ohm so i think they are ok) and to check the resistances across the opposite bars on the rotor.

There are 24 bars on the rotor shaft and they all but one read around 24ohms when testing the two bars 180degrees apart on the rotor, the last bar has no continuity to any of the others but as expected has continuity to one of the broken wires on the rotor winding. There is no continuity between any of the bars and the rotor shaft itself.

The carbon brushes need replacing as one wont touch the armature as its only half the size of the other brush, not sure if this indicates a fault or not? there is also some burning on that brush housing..


The bearings are fine and i think the physical damage to the windings has happened as i was pushing the router hard on a job it was nowhere near big enough for possibly distorting the housing a little.

I can pick some brushes up monday morning if this can be repaired, the router has been discontinued and you cant buy a replacement armature anymore so if its that i'll just scrap it!

Stu

 

[telectrix]

scrap it. then buy one from aldi.

 

[pennychew]

Good thinking mate, might be able to pick up some 'aldidas' trainers when I'm there!

 

[telectrix]

aldidas.. like it. seriously, though, some of those workzone tools are OK. i bought the 10.8V multitool the other week. cracking tool.

 

[Marvo]

If you want to try and fix it because you like tinkering and have lots of time then go wild. If you're doing it to try and recondition the router to save money then rather buy a new one.

The winding damage looks very much like it's mechanical rather than electrically caused. Possibly you distorted a bearing housing causing the winding to contact the brush holder or the chassis. If the distortion was caused by heat then the machine is probably scrap, if it was caused by the case separating or twisting during use then it might be salvageable. I'd investigate the reason first before attempting an armature repair.

You could repair the armature, you need to clean the shellac or varnish off the last few millimeters of the broken wires and tin them very quickly with solder. You may need to carefully raise them a little off the rest of the winding to make some space. Then get some wire of a similar gauge or even a little bit thicker will be okay. Bridge the breaks in the winding wires by soldering in an extra short piece, don't worry if it stands a few mm proud. Once it's repaired you can apply several coats of varnish or lacquer or even paint as long as it's rated at over 100 Celsius. Finally once dry just press the joint flush with the rest f the winding and apply another couple of coats.

The carbon brush you can cut yourself, Repco will sell you either a generic replacement or the raw carbon blocks and you cut your own. Maybe there's a similar supplier in the UK, I'm not sure, you could try RS Components who have some off the wall stuff like this.

 

[pennychew]

Yeah I quite often pick bits up when I'm in there, I'm selling most of my woodworking gear off as I don't do much of it anymore though

 

[pennychew]

If you want to try and fix it because you like tinkering and have lots of time then go wild. If you're doing it to try and recondition the router to save money then rather buy a new one.

The winding damage looks very much like it's mechanical rather than electrically caused. Possibly you distorted a bearing housing causing the winding to contact the brush holder or the chassis. If the distortion was caused by heat then the machine is probably scrap, if it was caused by the case separating or twisting during use then it might be salvageable. I'd investigate the reason first before attempting an armature repair.

You could repair the armature, you need to clean the shellac or varnish off the last few millimeters of the broken wires and tin them very quickly with solder. You may need to carefully raise them a little off the rest of the winding to make some space. Then get some wire of a similar gauge or even a little bit thicker will be okay. Bridge the breaks in the winding wires by soldering in an extra short piece, don't worry if it stands a few mm proud. Once it's repaired you can apply several coats of varnish or lacquer or even paint as long as it's rated at over 100 Celsius. Finally once dry just press the joint flush with the rest f the winding and apply another couple of coats.

The carbon brush you can cut yourself, Repco will sell you either a generic replacement or the raw carbon blocks and you cut your own. Maybe there's a similar supplier in the UK, I'm not sure, you could try RS Components who have some off the wall stuff like this.

Thanks for that, if I can get it working I'm going to use the motor on my test rig as I'm messing around with some basic motor control stuff.

Never even thought about making my own brushes, I'll look into that!