Dev Emch
01-29-2006, 4:56 PM
Here is a new one for you guys. What happens when a machine turns itself on but will not turn itself off? My old martin recently developed this problem and I thought it was just a defective off switch. Since I installed a brand new Allen Bradley IEC main line disconnect switch in the electrics box, I was using that to turn the machine off. I know, not a good idea.
Here is what I found. The pull in coil of a magnetic starter has two side sections on either side of the actual coil made from transformer like laminations of steel. After all, a mag starter is a type of transformer called a solenoid. But it has only one coil and the core can move.
The switch contact assembly that moves has a bar on the bottom also made of the same magnetic steel lamina as the two sides. When the coil closes the starter, this moveable bar of magnetic core material moves inward and contacts the side sections of magentic steel lamina on the left and right side of the coil.
Now, this magnetic core is coupled to the coil by virtue of the electromagnetic field created by the coil. Thus you have eddy currents flowing within this magetic core material. But it is not connected directly by copper wire to any actual electric circuits. Its entirely magnetic field coupled. The coil on the other hand is.
Where the cross bar contacts the two sides of the magnetic core, you have a tight contact connection. Almost like a set of points but to aide in moving magnetic flux about within the core.
What was happening was that these points had gotten dirty and the constant on and off pounding of the cross bar to these points had created a condition where the cross bar was sticking. Sorta like eggs sticking in an old scratched up pan.
The solution was simple. I used an old engine points file and stuck the file up into each point, closed the starter with one hand and filed with the other. Just a few strokes. By closing the starter, the file took a bit off on both sides of the point. Repeat process on the right side of the coil pull in arm.
Now the off circuit works like a million bucks. Being that I mostly use Allen Bradley NEMA class starters like the old 709 and newer 509, I have never run into this condition. The martin uses a european design that looks like a NEMA version of a starter made by ABB. It works great but this one threw me for a loop.. at least for a few minutes. So now you guys know what to look for if your machine refuses to shut down when the job is done. Now if we could only find humans that just want to keep on working like this.:D
Here is what I found. The pull in coil of a magnetic starter has two side sections on either side of the actual coil made from transformer like laminations of steel. After all, a mag starter is a type of transformer called a solenoid. But it has only one coil and the core can move.
The switch contact assembly that moves has a bar on the bottom also made of the same magnetic steel lamina as the two sides. When the coil closes the starter, this moveable bar of magnetic core material moves inward and contacts the side sections of magentic steel lamina on the left and right side of the coil.
Now, this magnetic core is coupled to the coil by virtue of the electromagnetic field created by the coil. Thus you have eddy currents flowing within this magetic core material. But it is not connected directly by copper wire to any actual electric circuits. Its entirely magnetic field coupled. The coil on the other hand is.
Where the cross bar contacts the two sides of the magnetic core, you have a tight contact connection. Almost like a set of points but to aide in moving magnetic flux about within the core.
What was happening was that these points had gotten dirty and the constant on and off pounding of the cross bar to these points had created a condition where the cross bar was sticking. Sorta like eggs sticking in an old scratched up pan.
The solution was simple. I used an old engine points file and stuck the file up into each point, closed the starter with one hand and filed with the other. Just a few strokes. By closing the starter, the file took a bit off on both sides of the point. Repeat process on the right side of the coil pull in arm.
Now the off circuit works like a million bucks. Being that I mostly use Allen Bradley NEMA class starters like the old 709 and newer 509, I have never run into this condition. The martin uses a european design that looks like a NEMA version of a starter made by ABB. It works great but this one threw me for a loop.. at least for a few minutes. So now you guys know what to look for if your machine refuses to shut down when the job is done. Now if we could only find humans that just want to keep on working like this.:D