mid-'50s shopsmith disassembling and cleaning -- help

JPG · Post by **JPG** » Sun Mar 15, 2009 1:42 am

mickyd wrote:So glad to have an electrical engineer in the group!

How come there is a capacitor on the motor? What's the relay do?

The relay is part of the start circuit. When the motor is first turned on, the start current(high) causes the relay to close the contact which connects the capacitor into the circuit. Once the motor is turning fast enough, the current drops and the relay removes the capacitor from the circuit. This is an over simplification, but is the general idea.

mickyd · Post by **mickyd** » Sun Mar 15, 2009 2:18 am

JPG40504 wrote:The relay is part of the start circuit. When the motor is first turned on, the start current(high) causes the relay to close the contact which connects the capacitor into the circuit. Once the motor is turning fast enough, the current drops and the relay removes the capacitor from the circuit. This is an over simplification, but is the general idea.

So the capacitor in effect is acting like an additional power source at startup to keep amperage down? I had no idea that a capacitor can store so much energy. Any idea how much it holds?

JPG · Post by **JPG** » Sun Mar 15, 2009 2:27 am

mickyd wrote:So the capacitor in effect is acting like an additional power source at startup to keep amperage down? I had no idea that a capacitor can store so much energy. Any idea how much it holds?

Actually it provides additional 'phase shift' in one of the windings which in turn increases the torque enabling it to start rotating. Once it IS rotating the motor does not need this additional phase shift to continue running. It all has to do with back EMF and slip speed(far deeper than either one of us wants to go this late in the week/evening).

mickyd · Post by **mickyd** » Sun Mar 15, 2009 2:37 am

JPG40504 wrote:Actually it provides additional 'phase shift' in one of the windings which in turn increases the torque enabling it to start rotating. Once it IS rotating the motor does not need this additional phase shift to continue running. It all has to do with back EMF and slip speed(far deeper than either one of us wants to go this late in the week/evening).

Thanks. I think I'll read up on it. I'm an ME but took enough EE to get a basic understanding.

etc92guy · Post by **etc92guy** » Sun Mar 15, 2009 7:03 am

JPG - thanks for the confirmation. When I pulled mine apart I thought the capacitor leads didn't matter, but wasn't going to take a chance. Next machine rebuild, I won't bother.

When I saw the capacitor I must have slipped into car stereo mode. "...You ain't bumpin' unless your thumpin'....."

dusty · Post by **dusty** » Sun Mar 15, 2009 7:48 am

etc92guy wrote:Edward - I apologize for the delay in this.....got hammered into the ground with work.

There should be 3 wires coming out of the motor: yellow, brown, and black. I may be off on the dark colors because I'm working in a shop area with one fluorescent fixture.

The colors for the power cord are from the original 1956 cord. Your new cord, I'm guessing, is white, black and green. White=tan, black=black, and green gets a spade connector and is attached to one of the bolts that hold the motor together.

When I pulled mine apart, I marked the capacitor lug that runs from relay connector 1 to the capacitor with a "+" sign. You obviously didn't do that. Since this is all AC, it shouldn't matter which capacitor connector is used, but I'm not a electrical engineer ( just know enough to be dangerous ). I'm calling on this forum to weigh in here and confirm this.

Promised diagram below.

[ATTACH]3531[/ATTACH]

And guess what? My Shopsmith is still in pieces.

Maybe an EE could modify the diagram here to show run windings and start windings complete with capacitor and centrifugal switch and then we would understand what is going on.

robinson46176 · Post by **robinson46176** » Sun Mar 15, 2009 8:23 am

dusty wrote:Maybe an EE could modify the diagram here to show run windings and start windings complete with capacitor and centrifugal switch and then we would understand what is going on.

I once read a story about a small boy who asked his father what made the light bulb on the ceiling work. The father gave him a full dissertation on power generation, grid management, relays, transformers and a full description of all of the relevant theories involved. The boy then wandered off.
A few minutes later the boy found his mother in the kitchen and asked her what makes the light bulb on the ceiling work. She told him "the switch on the wall". He said "OK, that is all I wanted to know..."

While we here tend to want all of the gory little details the general public usually just wants to know about the switch.

I remember that little story from about 40 years ago, just don't ask me what I had for breakfast.

dusty · Post by **dusty** » Sun Mar 15, 2009 8:42 am

robinson46176 wrote:I once read a story about a small boy who asked his father what made the light bulb on the ceiling work. The father gave him a full dissertation on power generation, grid management, relays, transformers and a full description of all of the relevant theories involved. The boy then wandered off.
A few minutes later the boy found his mother in the kitchen and asked her what makes the light bulb on the ceiling work. She told him "the switch on the wall". He said "OK, that is all I wanted to know..."
While we here tend to want all of the gory little details the general public usually just wants to know about the switch.
I remember that little story from about 40 years ago, just don't ask me what I had for breakfast.

Maybe but then some of us might want more detail. When this little boy (no longer a little boy) turns on the switch and the light doesn't come on - he thinks the only thing that could be wrong is "the switch on the wall".

robinson46176 · Post by **robinson46176** » Sun Mar 15, 2009 9:17 am

dusty wrote:Maybe but then some of us might want more detail. When this little boy (no longer a little boy) turns on the switch and the light doesn't come on - he thinks the only thing that could be wrong is "the switch on the wall".

In another 5 or 10 years they won't let him change his own bulb without a permit anyway...

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In a side note I just changed my signature line and was surprised to note that it was then changed on a message I made before the change. I wonder how far back it changes them (speaking of being curious about how things work)?

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I should probably go renew my amature woodworkers license.

dusty · Post by **dusty** » Sun Mar 15, 2009 9:28 am

robinson46176 wrote:In another 5 or 10 years they won't let him change his own bulb without a permit anyway...
-
In a side note I just changed my signature line and was surprised to note that it was then changed on a message I made before the change. I wonder how far back it changes them (speaking of being curious about how things work)?
-
I should probably go renew my amature woodworkers license.

I believe that these changes are made to ALL documents that are in the
"archive of documents" for that particular "user name".

I say this because I have changed avatars and I see the oldest of my forum documents with the later avatar.