Broken Electric Motor? HOW TO Test If A Motor Armature With Commutator Is Damaged #ElectricMotor

When an electric motor is broken, one suspect is the armature with commutator of the motor. In this video, we show different tests (180 degrees test, bar-to-bar test, continuity "bar to stack" test) that can be completed to determine whether or not the problem with the motor is caused by the armature with commutator being damaged or having failed. Note that those tests apply to DC motors and universal motors that use a motor armature with commutator.

In my case, the armature, coming from an old circular saw, was found to be faulty. Was it a surprise? No. Other signs of the armature having failed included:
1) Motor not reaching full speed when using the circular saw
2) Smoke coming from the armature when using the circular saw
3) Motor not spinning at all when placing the motor brushes on A specific commutator bar (the one where the resistance drop in test #2 was observed)
4) Irregular film left by the brushes on the commutator bars

Cause of the motor failure? Short in the armature windings.
But ultimately because I'm an ass!
- Short in the armature windings was because the coils got too warm
- The coils got too warm because the tool had to draw too much power
- The tool drew too much power because I pushed an old saw (with possibly degraded winding insulation) into cutting off wood that was too thick, too fast and on a super-hot summer day, so ultimately, the tool failed because I'm an ass.

► To check the motor field coil / stator, see:

► DISCLAIMER
Always make sure you operate in a safe and secure manner.
For this project this means, make sure not to eletrocute yourself, even if you find it fancy

▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
▼ CONNECT!
▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
▼ MUSIC
► "That Part" by Diamond Ortiz
▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬▬
╔══╦╗╔╦═╦╗╔═╦╗╔═╦══╦═╦╗╔╦╗╔╗
╚╗╔╣╚╝║═╣║║═║╚╣║╠╗╔╣║║╚╝╠╗╔╝
═║║║╔╗║═╣╚╣╦║║║║║║║║║║╠╣║║║═
═╚╝╚╝╚╩═╩═╩╩╩═╩═╝╚╝╚═╩╝╚╝╚╝═

[jorma]

Straight to the problem, no bullshitting, watching the video solves all your problems. Thanks! ❤

[Markus.Cantor]

What an excellent find! I appreciate the pacing and just the right amount of information to get you going without being overwhelming. Extra props for being so active in your comments. I'm looking forward to checking out all you have to offer. Thank you, good job and keep up the good work!

[F.Krueger-csvk]

I was out driving my 1944 GPW ford jeep. I noticed the amp meter was not working, reading zero. I decided to head home as i became worried. The amp meter needle then moved into the negative side of the guage which indicaded the battery was been drained on energy. After a while the needle moved to show a positive charge. i thought ok, all good, jeep has fixed itself. 😅👌🏻👍🏻. As i continued along home, suddenly the amp meter went totally crazy. The needle was flicking from side to side, the higher i reved the engine, the more violently the amp meter needle flicked from side to side. 🤤😓😭😭. I made it home ok. My jeep has a 12 volt system. New external voltage regulator & battery installed 3 months ago. I didn't know what to do or where to start. I found your video, thank God. Removed the generator/stripped down. Generator internals were filthy/full of dried dirt/dust as if it was dropped in mud for 6 months, then installed in the jeep. Probably dirt from world war 2, 😅🤣. Completely cleaned the internals with contact cleaner aresol, housing/armature/commutator. Surprisingly the 2 brushes had probably 60 to 70 % left.. Cleaned commutator bars where the brushes make contact with 800 fine grit paper. Commutator bars came up like new. Filed the brush surface that contacts the commutator bars with a file, so it was flat for better surface contact with the commutator bars. Done 3 tests on the armature as per your instructions. 2 ohms & 1 continuity tests. Armature passed the tests with flying colours. I assembled generator/ installed in jeep, left the fan belt off the generator. To test the generator, i connected a wire between field terminal & armature/dynamo terminals on the generator . I then ran a 2nd wire from the positive side of the battery to the wire that connected both terminals on the generator. The negative lead must be connected to the battery. The pulley spun on it's own indicating it was working properly. Connected up wires, started jeep engine. Reved the engine to approx 700 to 900 RPM, amp meter needle moved across to the positive charge on the amp meter. Tested battery charge rate was 14.2 volts at approx 700 to 900 RPM. All the problems were caused by a gut full of dirt in the genny, 😅🤣😂 Thankyou for sharing your information, really got me out of trouble. 😂🤣😅👌🏻👍🏻👏🏻👏🏻👏🏻 Cheers from 🇦🇺

[CJWarlock]

Best presentation of this kind I've seen on YT. Congrats! :)

[firststep]

So I switched on my vacuum and it began to smoke. I checked the commutator bars with the lowest resistance and in the four of the tests the resistence couldn't settle on a reading: it would spikes and even show "OL". I didn't need to test given the smoking issue but wanted to know where the problem was. Thanks for the this lesson. It was straight to the point.

[dawnninorvince]

One of the Best Tutorial DIY because he was Clear, non monotone, and easy to understand, and to the point without any bull.
I would like to know: if I purchase a motor followed hooked up wiring as per direction from rear ran fine for about one 1 min then slowed down, this is to a compressor that has ben running for 16 years so power to the power switch is more than fine. Help me. Ps this is the second motor in two days from harbor. Freight Smith and Jones 3hp

[peterx]

Excellent video. Going step by step....again....again.
Most youtube videos skip basic steps like setting multimeter before each test and you have to go back to beginning to see what is the multimeter set to
. Same thing with measurements....taking two measurements after each other is perfect and enough to show roughly the same reading. Nice work, LabOtomy
! :-)

[onCover]

Thank you SO much for posting this video. I have an vintage sewing machine that is not starting up when I plug it in. Hopefully it's a short in the wires or wires not connected properly and not the commutator/aperture.

[realvanman]

To perform this test properly, a four lead, low ohms meter is required at minimum, and much better to use a growler. To properly test for grounds between the windings and the Core, a megger is really required, or at very least set your meter to the Highest ohms setting, Not the lowest. The insulation test need only be performed between ONE commutator bar and the armature Core, because All commutator bars are connected together!

[johnfreeman]

Thank you very much for the video It is a very good demonstration.
1) Could you please confirm though an easy way to measure correctly /accurately 180 degrees on the part indicated.
2) In the 2nd test are you checking comparing the 1st with 2nd (and) the 2nd with the 3rd and so on OR the 1st with the 2nd (and) the 3rd with the 4th and so on.
I look forward to your reply
From a Learner
Thanks

[brianconcannon]

To test continuity to ground wrap a braided copper wire around the comm then measure from braid to stack ( ground) it is much faster.

[markrainford]

Before you bin it though. Try scraping out the slots between commutator segments with a piece of sharp metal that fits the gap.

[weldmachine]

Good video.
Mostly when i see the Armature of an electric motor ?
Is when my Angle Grinder stops working.
IF the bushes are worn replace them.
If Not worn, and the commutator is worn.
Then in the bin it goes and off to buy a New Angle Grinder, LOL.

[angelnoheart]

..my utmost thank you to you.. I have a gbh 4-32 that has been broken for a long time and I was thinking of throwing it away but after watching this video and a few other related videos on your channel, the machine is now working.. i subscribe..

[powertoolsrepair]

very informative video and very good edited. Thank you

[garrygemmell]

Excellent tutorial I have learned something new today - always a good day!

[herberar]

The format, the graphics, the contents and even the music is very clear and amusing, great !

[westinthewest]

If you measure no bar to stack leakage on the first bar, shouldn't that conclude the test? Any leakage from the windings to the stack would show up on all of the bars.

[danoid]

I have this exact looking motor on a drill press. When I power it on it hums a little at 0 speed but if I try to increase the speed it shuts my whole press off due to some kind of over temp protection.

[amseek]

awesome track man. it's killin me tho. was a dj for close to 20 years (tribal house, breaks, dnb, later some dubstep -i dislike joining bandwagons when they're in full swing). anyways, I stopped paying attention to the video itself and am now lost in good feelings and love of times past. thank you :) ..oh yeah, I'll make sure to watch the video again to learn some electronics :) -Art (djseek/ASF, Santa Cruz, CA)