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Electrical help

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
So I have a 10ft 1/4" cincinnati mechanical shear I bought used 11 months ago. It had older electrical mismatched garbage on it with no cover on a some of the boxes. I was running off a cord into a 60 amp 3 phase welder outlet, until about 8 months ago when I finally got around to painting it and upgrading the electrical/wiring. I bought a new surplus 30 amp combination starter on Ebay with a max 7.5hp motor rating on the starter. Ran it on a 40 amp 8 ga wire circuit.
It had a 5hp motor on it that took almost a full minute to get to operating speed.
Fast forward to 2 weeks ago.... I started it up and it was cold in the shop, 35 degrees or so, as I had just gotten there. I noticed it was taking longer than normal to get to speed so I walked over and saw the motor was smoking a little. Turned the switch off and walked away.

After my shop warmed up I tried to run it again and it was seized up. After doing some research it seems most of these shears came with 7.5 hp motor. Last week I found a new Baldor 7.5hp with the same frame size locally at a surplus place still on the shipping skid. Motor hooked up and worked fine to test. I just got around today to putting the pulley, and new belts on and running it. It ran for 5 seconds and tripped the 40 amp breaker. Tried a few more times and same results. Hooked up and my clamp meter and some how it's drawing 130 amps! Took the belt tension off and ran with just the pulley on the shaft and it runs fine pulling 18 amps on start up then drops.
I'm not an electrician but know enough from researching and wiring new to me machines to get most things done, but I'm not understanding this at all. First, I don't know why my overload protection didn't save my 5hp, also why is this running such a high amperage? It never gets to speed before it trips the 40 amp breaker. Also it's not blowing the fuses in the disconnect.
Any thoughts????
I
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Sounds like your shear is so hard for your motor to pull that it is near stalling the motor.
Maybe the machine is too tight someplace.

QT:. Ran it on a 40 amp 8 ga wire circuit.
It had a 5hp motor on it that took almost a full minute to get to operating speed.

That is odd... Does the motor run Ok when disconnected from the machine?
 

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
Yes, motor runs great with no load, and just the pulley. Pulls 18 amps at start then goes down to 13
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
How does that shear get the drive from the motor to the blade?

Does it have a flywheel and a "trip", so that the motor is always running, and the shear only strokes when the "trip" is triggered?

Does the motor just fail to get the flywheel system spinning?
 

Just a Sparky

Hot Rolled
Joined
May 2, 2020
Location
Minnesota
If the new motor is pulling 140 amps at full speed when loaded and 13 amps unloaded then there is a mechanical problem with the shear.

If it's not reaching full speed when loaded then you need to invest in a soft starting arrangement. 9-lead motor with VFD, 12-lead motor with star-delta starter, autotransformer starter, electronic soft starter, etc.


A motor should never take a full minute to get up to speed unless starting in a reduced voltage state. 10 seconds maximum under normal conditions. This also tells me that your motor is not fitted with adequate overload protection, as that should have tripped about 10 seconds in if fitted with properly sized Class 10 heaters.
 

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
There's no mechanical problem. All the motor does is spin the flywheel until I trip the blade. I can trip the blade and spin the flywheel by hand and the blade will move up and down. I can do this with the belts hooked up or not. Also the new motor does not get to full speed before it trips the 40 amp breaker in the panel
 

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
Also a 5hp was standard on 3/16x 10 foot shears. And the 5 hp did the job for who knows how long. The shear was made in 1945. Granted I know that it wasn't the original motor.
There are no heaters it's a newer square D solid state overload with a dial.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
Is the motor having to spin the FW too fast? too high a drive ratio, or too fast a motor?

Seems I recall many of those having slower speed motors.
 

joebass

Aluminum
Joined
Apr 3, 2005
Location
NY
UPDATE.....
I checked all the connections in the disconnect starter enclosure and found a lead going from the starter to the motor that pulled out by hand. I then went through and made sure every other connection was tight.
Fired it up and it got to full speed in under 10 seconds without tripping the breaker in the panel.
 

BT Fabrication

Hot Rolled
Joined
Nov 3, 2019
I was going to say you are loosing power somewhere and something isnt right and probably loosing voltage if its taking that long, like a burnt set of contacts etc.
but glad you found it. resistance is a B****. remember V=IR voltage=current X Resistance. the resistance was the loose connection.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Same. I was reading down the page and got to the part where he said the motor worked fine unloaded and that he could freely move the flywheel by hand. I said to myself: "there's a wiring issue somewhere." Good that you found it. That's the kind of thing that could cause a fire.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
"Resistance"...Heh.....

It pretty much needs to be an "open", because "resistance" at motor start current levels will result in red-hot connections very quickly. There was no mention of smoke and smells, so....

But an open connection is a good call. And, sometimes a motor will start single phased. Usually it just hums, but it can start, as apparently this case.
 








 
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