Author Topic: Will replacing armature and brushes of a totally burned out motor fix it?  (Read 473 times)

J Boogie

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So I have a circ saw that totally smoked out and stopped running. The motor is burned out to the point where nothing happens when you press the switch. No melted plastic or anything though, it didn't get that crazy hot and I ran the blade without load for 15 seconds or so before it stopped working to try and air it out. My hunch is that the motor would either need to be rewound or replaced along with new brushes. I am not considering rewinding it.

The saw is 355 new, and I can get replacement brushes (8 bucks) and armature ($58) relatively inexpensively. I've seen vids of people replacing armatures and brushes so it doesn't seem too challenging.

But I don't do any significant electrical engineering so I'm not sure if this is throwing good money after bad or being a good steward. I just want confirmation that replacing the armature and brushes should be enough to bring it back to life or vice versa. Thanks in advance!


BDWW

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I would guess not, if it actually started smoking, it's like the insulation/epoxy between the windings has burned up and the windings have shorted. But wouldn't be able to tell without digging into it.

 

J Boogie

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I would guess not, if it actually started smoking, it's like the insulation/epoxy between the windings has burned up and the windings have shorted. But wouldn't be able to tell without digging into it.

It seems the armature assembly I am planning on buying includes new windings. I figured I was replacing all the burnt up components (commutator, windings, etc) with this part. Is there anything else I would need to replace after buying new brushes and this part?

https://www.partswarehouse.com/Makita-Armature-Assembly-115V-SP6000K-513676-9-p/mk-513676-9.htm?gclid=Cj0KCQjwuLPnBRDjARIsACDzGL2tSIvA3yJv_z-HbejWoccu6zo2yvm6weZ68OlAdmFvgi98UAv6M8oaAvLeEALw_wcB&Click=365719

BDWW

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Sorry, trying to dig through cobwebs of last time I worked on motors.

Yes, It looks like a permanent magnet DC motor, so the case holding the permanent magnets is the stator, and the windings are part of the rotor. As long as the case is fine, replacing the rotor (armature + commutator) and brushes is essentially replacing the whole motor.


Edit: that's not to say that something outside the motor couldn't actually be the problem. You could supply voltage directly to the wires connected to the brushes to verify that the motor itself doesn't run.

Further edit:
Jeremy Fielding on youtube has a good series on motor basics that I reference when I need a refresh. Here's a link to the first one.

https://www.youtube.com/watch?v=onjFFoOC_yk
« Last Edit: May 28, 2019, 11:22:36 AM by BDWW »

J Boogie

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Sorry, trying to dig through cobwebs of last time I worked on motors.

Yes, It looks like a permanent magnet DC motor, so the case holding the permanent magnets is the stator, and the windings are part of the rotor. As long as the case is fine, replacing the rotor (armature + commutator) and brushes is essentially replacing the whole motor.


Edit: that's not to say that something outside the motor couldn't actually be the problem. You could supply voltage directly to the wires connected to the brushes to verify that the motor itself doesn't run.

Further edit:
Jeremy Fielding on youtube has a good series on motor basics that I reference when I need a refresh. Here's a link to the first one.

https://www.youtube.com/watch?v=onjFFoOC_yk

Thank you!! That is very valuable information. Much appreciated.

Next time I rip hardwood on my (hopefully soon to be fixed) tracksaw, I'll either get a dedicated ripping blade or do it in 5 passes or more.

Wrenchturner

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Might want to change out the bearings while you're in there.  Make sure to put the seal on the same side.  Should be off the shelf bearings.

lukebuz

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Might be smart if you aren't experienced to take it to your local shop.  Our factory does it all the time.  Repair cost vs Replace; maybe 30%, plus 2 days vs weeks for a new one.

BTDretire

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Sorry, trying to dig through cobwebs of last time I worked on motors.

Yes, It looks like a permanent magnet DC motor, so the case holding the permanent magnets is the stator, and the windings are part of the rotor. As long as the case is fine, replacing the rotor (armature + commutator) and brushes is essentially replacing the whole motor.


Edit: that's not to say that something outside the motor couldn't actually be the problem. You could supply voltage directly to the wires connected to the brushes to verify that the motor itself doesn't run.

Further edit:
Jeremy Fielding on youtube has a good series on motor basics that I reference when I need a refresh. Here's a link to the first one.

https://www.youtube.com/watch?v=onjFFoOC_yk

  I don't see enough information to convince me it is a DC motor.
What do you see that makes you think it is DC?

BDWW

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You're right, told ya I had cobwebs. It's probably a universal motor (as opposed to a permanent magnet motor), so there's probably a field assembly that could be fried too.

Maybe boogie will let us know how its going.

J Boogie

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You're right, told ya I had cobwebs. It's probably a universal motor (as opposed to a permanent magnet motor), so there's probably a field assembly that could be fried too.

Maybe boogie will let us know how its going.

I received the parts but haven't replaced yet. I see there is a field assembly replacement part offered, so I'll check my field assembly and check for signs of damage and overheating.

Thanks for commenting! I might have been really frustrated if I just replaced the armature and found it still didn't work.