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Old 06-27-2020, 04:00 PM   #21
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Here is a coil with a broken interpole coil aka pole face coil or shading ring coil.

http://2.bp.blogspot.com/_uVIqG8v-4n...ading+ring.gif

It’s definitely one of the things that is easy to miss if you aren’t looking for it. Smaller contactors don’t have them. It’s used either to manipulate the shape of the magnetic field or the strength so it drops out faster. Interpole coils are also used in DC motors to help shape the pole magnetic fields.

In a contactor with a missing one the T-bar rides the edge of the magnetic field instead of pulling in tight so it chatters because it isn’t quite closed in. The coil runs excessive current but usually there is enough give in the contacts that the first thing to fail is the coil itself. In any MCC over 10 years old there is almost always one.
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Old 06-27-2020, 04:35 PM   #22
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Originally Posted by paulengr View Post
https://www.retekool.com/HOW-IS-A-ST...id3097364.html

Electrolytic capacitors. On DC types you can get away with making one side of the aluminum the insulator. Not on AC.

It is filled with an electrolyte such as glycol. Hence the name...electrolytic. No confusion here. NOT used for run caps.

So the issue with single phase is there is no rotation. We just have North and South magnetic poles swapping places. But if the pole energizes with the rotor at an angle since the rotor has an induced current it will pull the rotor around again. During voltage bulls the rotor coasts past the “dead spot”. But when the motor starts there is nothing induced out of phase. So you can “pull start” a motor with a bad start circuit but it won’t start on its own.

We then add an auxiliary coil 90 degrees offset from the main coil. If it’s smaller we could just wire it up. This is called permanent split pole coils (PSC). They work but since one coil opposes the other all the time efficiency is rotten and torque is not great.

We could just switch off the starting coil. We just need to know when. The off signal can be a timer, a mechanical centrifugal switch, or a voltage relay that triggers when the main coil voltage drop changes as the motor comes up to speed. Modern starters lean towards the potential relay because it’s more reliable.

Thing is it’s a highly inductive load so we can offset some of this with a power factor correction capacitor. This one is energized continuously so it is typically oil filled and sized to match the motor power factor, The motor can run without it but you lose some torque and efficiency. These often look like a big bulge on the side of the motor,

The second issue is starting coil starting works but torque is limited. On motors not designed to start this way it won’t even start. It would be nice to get plenty of torque. Enter the starting capacitor. It is about 10 times bigger but only energizes for a few seconds so it isn’t as big as it would be. Voltage is greatly increased by 2-3 times normal line voltage as seen at the motor. If the switch that disconnects it fails they explode. If they dry out they arc and explode. So they don’t last very long.

There are dual caps that contain both capacitors in one can.

Personally I hate single phase motors. They are poorly labeled. You spend half the time just figuring out what everything is and whether the last guy just put in the wrong parts or wires it up wrong. They are always on the verge of not working. Every manufacturer tries to make the sizes nonstandard to charge you more for very cheap parts. Everything you need to see happens in about 2 seconds. And everything costs $20 except the motor. Three phase motors are just so much higher torque, smoother running, higher efficiency, and very easy to work on. It’s so cheap often the best way to “fix” one is just test the motor itself and the contactor, then just replace both capacitors and the potential relay (or change to one) and call it a day. My shop doesn’t even stock the parts because there’s no money in it. I have to go to the competitors to buy repair parts.
There. You see? That's the type of quality post we've come to expect from you!
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Old 06-28-2020, 11:08 AM   #23
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Quote:
Originally Posted by paulengr View Post
Here is a coil with a broken interpole coil aka pole face coil or shading ring coil.

http://2.bp.blogspot.com/_uVIqG8v-4n...ading+ring.gif

It’s definitely one of the things that is easy to miss if you aren’t looking for it. Smaller contactors don’t have them. It’s used either to manipulate the shape of the magnetic field or the strength so it drops out faster. Interpole coils are also used in DC motors to help shape the pole magnetic fields.

In a contactor with a missing one the T-bar rides the edge of the magnetic field instead of pulling in tight so it chatters because it isn’t quite closed in. The coil runs excessive current but usually there is enough give in the contacts that the first thing to fail is the coil itself. In any MCC over 10 years old there is almost always one.
All true, but in this case by changing out the starter and the problem still existing, he eliminated all of that from the list of probable causes.
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Old 06-28-2020, 12:09 PM   #24
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All true, but in this case by changing out the starter and the problem still existing, he eliminated all of that from the list of probable causes.
He changed the bucket and we do not know where he works so he hasn't really eliminated anything. A used starter is a damp/dusty non air-conditioned space would probably be worse than a starter that has been in use.

Taking a voltage reading on the coil and field stripping a starter isn't a heavy lift (especially if you work at a place where pulling the bucket live is no longer allowed). Im to lazy to be a parts changer and im defiantly to lazy to do it with used parts.
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