F/R Switched While Running, Single Phase Motor

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sailfish-007

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Dear All,

I'm NEW and happy to have found this site.

I'm just getting started with a barely used Mill Drill machine. 2HP. Single phase 240V motor.

Issue: While it was running, the F/R switch was flipped by accident from F to R before the motor comes to a complete stop. After that, it won't run in either F or R. Power is live at the outlet 240V. No burnt smell.

Is there a chance that the US Motor was burnt? Could it be a Capacitor? Is there an overload switch that got burnt? No fuse was found on the machine.

Thank you in advance
J
 
There’s the possibility that the thermal switch has been compromised. It is internal of the motor.
The on/off switch could have been compromised as well
The capacitor could be open
The centrifugal start switch could be burnt
Wire connections could be faulty
 
Probably a loose wire, possibly from the power cord, in the F/R switch. If the motor hadn't slowed enough to re-engage the internal
start switch then you can rule out the capacitor and the internal switch as culprits- they'd still be open circuit at that moment.
As flipping the switch was the last thing you did, I'd look there first
Turn off power of course before opening anything up
The thermal button or the F/R switch itself could also be faulty as Mike mentioned
 
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Greetings J and welcome to HM!

The motor itself is likely OK. You are getting great advice so I'm sure you will determine
what went wrong. Good luck.
 
If the motor was reversed while still above, the cutout speed, the motor should have just kept running in the same direction. The capacitor and the centrifugal switch would never have come into play. However if the rpm was low enough that the switch was closed, there would bean excessive current load in the start winding as the motor tried to reverse direction. Start windings are designed for short duration use and wire is usually undersized. But the duration of the overload would probably be insufficient to do damage to the winding.

While the momentary current was excessive, I don't believe that a single occurrence would have fried the centrifugal switch. There may be a an overload fuse in the motor which could have blown though.

Best bet, when the motor was reversed, the start capacitor would have seen a higher than normal voltage as in addition to the line voltage, there would be a back emf from the start winding and the capacitor could have shorted out.

Can you start the motor by spinning by hand? Remove the belts to allow the motor spin freely. If it starts and runs normally, the the problem would be limited to the start winding circuit. A visual check of the centrifugal switch plus an ohmmeter check will validate its condition. Perhaps the easiest way to check the capacitor is with a substitution. The capacitance value doesn't have to be identical for this purpose. The start winding can be checked with an ohmmeter.
 
Some good advice already posted. I am a little confused about the sequence of events. Do you have a forward / reverse two position switch and an on / off switch or a single three position switch; "forward, off, reverse"?
 
RJSakowski said:
If the motor was reversed while still above, the cutout speed, the motor should have just kept running in the same direction. The capacitor and the centrifugal switch would never have come into play. However if the rpm was low enough that the switch was closed, there would bean excessive current load in the start winding as the motor tried to reverse direction. Start windings are designed for short duration use and wire is usually undersized. But the duration of the overload would probably be insufficient to do damage to the winding.

While the momentary current was excessive, I don't believe that a single occurrence would have fried the centrifugal switch. There may be a an overload fuse in the motor which could have blown though.

Best bet, when the motor was reversed, the start capacitor would have seen a higher than normal voltage as in addition to the line voltage, there would be a back emf from the start winding and the capacitor could have shorted out.

Can you start the motor by spinning by hand? Remove the belts to allow the motor spin freely. If it starts and runs normally, the the problem would be limited to the start winding circuit. A visual check of the centrifugal switch plus an ohmmeter check will validate its condition. Perhaps the easiest way to check the capacitor is with a substitution. The capacitance value doesn't have to be identical for this purpose. The start winding can be checked with an ohmmeter.
Click to expand...
Yes Sir! I will start checking with a meter and trace it back from the power supply to the F/R switch and then to the starter capacitor and then the centrifugal switch. I biggest fear is the motor itself. It's a 2HP motor, Single Phase from U.S. Motor. Replacement cost is between $800 to $1,200.00. I hope it's just something simple. Thank you so very much.
 
den-den said:
Some good advice already posted. I am a little confused about the sequence of events. Do you have a forward / reverse two position switch and an on / off switch or a single three position switch; "forward, off, reverse"?
Click to expand...
It's a R O F rotary switch configuration. I believe it was in F and then rotated to R, while motor was running
 
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