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Switch exploded?

#262252 by Jdalbs » Thu Aug 22, 2019 12:44 pm

I was using my shopsmith mark V today and went to turn it on at one point and the shopsmith didn't turn on. Then dark smoke started coming out of the enclosure.

Opened it up to find the switch had more or less exploded.
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Switch
fullsizeoutput_bc1.jpeg (357.04 KiB) Viewed 899 times

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fullsizeoutput_bc2.jpeg (374.73 KiB) Viewed 899 times


Anyone know what could have caused this?

I have been using it for several months with no real issues prior to this.

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Re: Switch exploded?

#262253 by bainin » Thu Aug 22, 2019 1:27 pm

A couple reasons why this might happen :

If the current draw was larger than expected - the switch has a power rating though I don't know what the rating on that switch might be. This would indicate some other problem downstream (motor, etc) which I hope isnt the problem for you.


Weak contact between wires and spades on the switch - this would lead to raised contact resistance/excessive heating and could cause the plastic body of the switch to melt. The spades in your image look clean - are these soldered connections or threaded screw?


Arcing/contact from switch spades to SS case/ground


Those are the things that come to mind for me.

I dont think I've seen a mechanical switch like that fail internally. I suppose it could happen.


b

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Re: Switch exploded?

#262254 by Jdalbs » Thu Aug 22, 2019 1:56 pm

Thanks bainin,

the spades are screwed on, and seem tight. The fourth spade is of course missing, I guess it got blown off.

I suspect it is the 3rd option. Looking at it again it seems that the spades were relatively close to the quill assembly, though I don't know what would have caused them to come into contact all of the sudden.

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Re: Switch exploded?

#262257 by john_001 » Thu Aug 22, 2019 3:09 pm

Was this the original SS switch? Replacement switches should have a specific horsepower rating for use with motors, not just the proper amp rating.

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Re: Switch exploded?

#262258 by jsburger » Thu Aug 22, 2019 3:12 pm

Jdalbs wrote:Thanks bainin,

the spades are screwed on, and seem tight. The fourth spade is of course missing, I guess it got blown off.

I suspect it is the 3rd option. Looking at it again it seems that the spades were relatively close to the quill assembly, though I don't know what would have caused them to come into contact all of the sudden.


If the spade contacted the quill or head stock casting there should be a burn mark at that place.

---

John & Mary Burger
Eagle's Lair Woodshop
Hooper, UT

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Re: Switch exploded?

#262260 by garys » Thu Aug 22, 2019 3:40 pm

This kind of damage to a switch to me indicates that part of the switch broke loose inside it and got across the hot and ground. An external short rarely will damage the switch internally as the damage will be externally at the point of the short.

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Re: Switch exploded?

#262261 by Jdalbs » Thu Aug 22, 2019 3:48 pm

thanks garys. That makes sense, the inside of the switch (I took it apart) is completely burned and broken into little pieces. Looks like something shot out of it, creating the hole in the picture.

Any idea if that is just something that happens every now and then from a bad switch? Or could there be external problems that cause that to happen?

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Re: Switch exploded?

#262262 by dusty » Thu Aug 22, 2019 3:59 pm

Obviously the hot wire became shorted to ground and drew a major spark Where that short occurred is hard to say but I would put money on "right there at the switch".

Is this a common thing? NO! I seriously doubt "just a bad switch". The switch brings power intentionally to only one thing .. the motor. If the motor runs now (after the incident) then suspect wires or switch contacts that "got together where they should not have.

Check the motor wires for continuity to the motor casing. There should be none.

---

"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

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