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06-26-2011, 02:22 AM #1
Does Anyone Have Wiring Diagrams For GE Motor Starters?
Something came up where I have a need for my big table saw. It has a 5HP 440-0nly, two speed motor and a GE CR7108C 100R dual magnetic starter, as well as a "Shortstop" electric brake.
I'd asked some questions in the past about the best way to run this thing, so I could start planning and obtaining whatever I need. I decided that in this instance an RPC feeding a step-up transformer was my best option.
I picked up a big autotransformer, and a few months ago I made my first RPC, a 3HP self starting version for use at another location. It works great. I got the RPC , the transformer and the saw in the same room and spliced everything together. To my amazement, the saw started, ran, and cut wood. The spindle was even turning the right way!
But there are hints of trouble in paradise. The low speed does not run. Nothing happens when that button is pushed (no attempt at pull-in, no noise, etc.) And when the Stop button is pushed, the motor spins down as a normal installation (w/o brake) would, except the 440/110 control transformer hums loudly until the motor speed approaches zero. I'm assuming this has something to do with the non-functioning Shortstop brake.
I poked around inside and could find no glaring defects. I have come to the conclusion that this saw had some issues when removed from service. The PO's comments confirm this. It looks to me like they disabled the low speed side by denying power to the pull-in coil, possibly because of the Shortstop brake.
Now, the saw runs, and high speed is probably the more useful option. I can live with this, especially in the sort term. But I don't know what that Shortstop brake is doing when nobody's looking. I don't want to burn up a very special (not easily replaceable) motor. I'm thinking that the easiest and safest alternative may be to restore the controls to their original configuration, especially since the Shortstop brake doesn't work anyway.
The problem is, this is a very complex starter, and I'm not sure what's supposed to go where. I'm used to two wire momentary start/stop switches, and these things have five. there is very little intuitive about this setup, although I think the added function of these switches is to provide an electrical interlock, disallowing simultaneous engagement of high and low speeds. (This is in addition to the mechanical interlock at the contactor.) This setup is very similar to a dual, reversing contactor, but more complex. I made up a truth table listing the various conditions at each pair of start button terminals when buttons are pressed and not pressed (the stop is a simple two-wire break) and I am confuseder now than I was before.
So, here's the question:
Does anyone have any literature on these starters, showing wiring connections? I'm pretty sure I could figure it out eventually, probably with a little trial and error, powering up only the 110V control circuit, but there's no substitute for the real thing.
The motor and controls, with the exception of the brake, appear to be original to the saw, which dates from 1955. I did an internet search for that GE contactor and came up dry. Any help will be welcome.
06-26-2011, 04:49 AM #2
"The motor and controls, with the exception of the brake, appear to be original to the saw, which dates from 1955. I did an internet search for that GE contactor and came up dry. Any help will be welcome."
Perhaps a "special".
Oliver built a very good wood lathe, really a patternmaker's lathe for turning cores, which had FOUR speeds.
It was a direct drive headstock with an integral motor which had two "consequent pole" windings of the ∆/YY type.
Even had four separate sets of overload, one for each speed.
The whole deal was lashed together with a sliding selector switch which was of the "break before make" type.
Made interposing a VFD rather easy going.
06-26-2011, 09:51 AM #3
I have a GE book of control wiring for mags and other devices...your CR number seems to be way off base, are you sure that isn't a number of a assembly or something. What number is on the plunger of the actual mag itself?
I have a Shortstop electronic brake in an enclosure. On the inside of the cover is a wiring diagram for the unit, does your brake not have this info.
06-26-2011, 12:02 PM #4
Peter and Stuart,
Thank you for the replies. The number I sent is the only number on the starter unit, but it is located on a tag on one of the contactors, so it may be the number for the contactor not the whole unit.
Fortunately, though, the point is moot. After posting the initial message I decided to button the thing up for a while as I worked on other aspects of the current project. But I decided that first I'd poke and pry just a bit more. I discovered a little round disc capacitor, fried and lying in the bottom of the brake's case.
That's enough for me. I removed the brake completely from the circuit, and now high speed runs fine (as it always did) but the mysterious hum at shutoff is gone. I then started looking at the start/stop circuit again. I decided that the #5 wire was the most likely candidate to engage the low speed contactor coil. Where did it go when it got back into the starter case?
To an unused terminal. This confirmed my idea that someone had disabled the low speed portion. I relocated that wire to the high side of the coil, and now i have both speeds functioning properly. At some point in time I may come back to the brake, and try to repair it, but for now I'm off to saw some white oak!
Thank you again,
06-26-2011, 02:16 PM #5
YAHOO.........onward and upward! Good Job Steve.
06-27-2011, 01:42 AM #6
FYI, the Short Stop brakes were made by a company called Ambitech, but they were bought out by TB Woods, who then sold that division off to Vacon USA, who sold off the old Ambitech product line to a company called Saldet.
The reason the Low Speed was disabled is that you would have to have 2 separate brakes if you used two speeds, because each brake would have to be adjusted for the kinetic energy in the load at the different speeds. So if you want to use the bake again, you will need to sacrifice one speed, or buy another brake.