Why did my power tool burn out?

[GullyL]

I am a mechanical engineer with very basic understanding of electrical motors.

I was working with a brand new drill the other day and it burnt out. It caused a lot of smoke. When I opened it up I noticed that the insulation around the coils on the stator and the armature are burnt off, but the armature seems to rotate freely in the stator. I had originally thought that there must have been some friction between the two causing overheating, but this doesn't seem to be the problem. I replaced it under warranty, but was interested in how this could have happened.

Any ideas on what may have caused this? Bear in mind this is a brand new tool and died 5min into use. I wondered whether it may have been a short between the coils of either the stator or armature?

Thanks

 

[jraef]

Probably. Most home power tools are marginally constructed to begin with. Any minor error can result in rapid failure.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[rbulsara]

Could be just a bad unit (shorted windings, bad insulaton etc) to begin with... (most likely reason)

Home tools are not intended for continuous use..or they can easily overheat..Not sure if you used continously under load.

May be the way it was used, it caused it draw excessive current.

 

[ScottyUK]

5 minutes of doing what? Driving a 6" core drill into concrete, or just a [¼]" bit into wood? There are many ways to kill a drill even if it was perfect when it left the factory. Was it a reputable brand? Take it back and get a refund if you haven't abused it.


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Your body might be a temple. Mine is an amusement park...

 

[Skogsgurra]

It could just as well have been the bearing. To my great surprise, I once learned that bearings for hobby tools have an L10 life of around 30 minutes. That means that one bearing out of ten will fail after half an hour of use (at rated load and speed).

Perhaps is there a similar specification for the winding?

Gunnar Englund

http://www.gke.org

 

[ahung]

Probably the insulation burn due to an excesive current. I agree with rbulsara about home tool are not designed for continuous use. If you need to do a heavy work you must use an industrial drill for example.

Regards

Alberto J. Hung C
Caracas Venezuela

 

[itsmoked]

Ah heck, they may be junk but if GullyL wasn't abusing it then it was just ol'infant mortality, given he only used it for a couple of minutes.

 

[GullyL]

It was a reputable brand, and I wasn't using it constantly or abusing it. Only drilled a couple of holes, so it might have been some sort of wiring issue. It is under warranty no problems.

I had thought it could be wiring or coils shorting in armature or stator, but wondered if there are any other things that would cause this?

Thanks for your help guys.

 

[edison123]

Was your voltage different from the one stamped on the drill ?

* If you have never succeeded in anything in first attempt, skydiving isn't for you. *

 

[SteveKW]

Extension cords used?

 

[bklauba]

Good Q, SteveKW. If a long extension cord with skimpy gauge was used, the motor would struggle to produce torque, and could overheat if put thru normal useage.

We have been seeing some hand power tools with reputable names on them (we are an industrial distributor) with both skimpy power cords (like 18 AWG for a device that pulls 10 - 12 amps), knowing that in the field a 25, 50 or maybe even a 100 foot extension cord would likely be added. Some of this stuff is made in China, and the quality of the internals and the sizing of wire gauge vary a good deal.

BK

 

[GullyL]

All good stuff to know, but it was used with correct voltage and no power cord.

I guess I am gonna have to go with the shorted wire answer. Thanks heaps for your help here guys.

 

[waross]

Heat is the culprit. Whether from over-use or to much line loss, a normal person will usually notice the heat build up and ease off.
However a shorted turn in the motor will often lead to progressive heating and failure as long as the drill was energised, regardless of the load applied.
All the posts are reasonable, but I think you have the correct answer here, GullyL.
"I had thought it could be wiring or coils shorting in armature or stator, but wondered if there are any other things that would cause this?"