motor starter question- any electrical types out there?

[mrhinsjc]

My saw has a 5hp, 26 amp 220 single-phase motor with a separate motor starter. The on/off switch and motor starter are original (50 years old). The motor starts immediately when the on button is pushed, but you need to hold the stop button down about 5 seconds or so to shut it down. I have disassembled the switch and glass-beaded the internals. I understand the principle behind a motor starter but know nothing about the internals. Any thoughts?

 

[Ddaddy]

The starter motor is a high torque low speed device to spin the main motor up to sufficient RPM to operate on its own on a single phase circuit.

It needs to be shut off so that the main motor drops below its operational RPM in order to disengage, hence the hold time to disengage and allow the main motor to wind down.

What part are you confused on?

 

[pishta]

that part......

 

[mrhinsjc]

that part......

The starter motor is a high torque low speed device to spin the main motor up to sufficient RPM to operate on its own on a single phase circuit.

It needs to be shut off so that the main motor drops below its operational RPM in order to disengage, hence the hold time to disengage and allow the main motor to wind down.

What part are you confused on?

What I'm calling a motor starter is a separate box with solenoids in it which are triggered by low current 110v circuit so you don't have 26 amps going thru your on/off switch. What you are saying is there is something inside the housing of this 5hp motor to spin it up to running speed, like a commercial jetliner using APU gases to spin the turbines? Never heard of that.

 

[67Dart273]

What I'm calling a motor starter is a separate box with solenoids in it which are triggered by low current 110v circuit so you don't have 26 amps going thru your on/off switch. What you are saying is there is something inside the housing of this 5hp motor to spin it up to running speed, like a commercial jetliner using APU gases to spin the turbines? Never heard of that.

This is simply a glorified relay/ contactor. They usually have overload protection. Might be as simple as the stop switch gone bad, or the actual solenoid is sticky.

To troubleshoot break the "stop" contact wiring and add a temporary test switch so you KNOW the stop circuit is broken and retest. The stop switch will be "normally closed" that is when not pushed the stop switch is closed. When you push it, the open breaks power to the contactor relay coil

 

[Keystone]

Put a voltmeter on the coil of the starter (btw, if it doesn't have an overload attached, it's just a contactor) and verify that the voltage to the coil is removed as soon as you press the stop button. If that checks okay (my guess is it probably will) then the contactor is faulty. The motor is going to be connected to the Normally Open contacts and what's happening, I think, is that the contactor isn't immediately returning to its "normal" state when the coil is de-energized.

I never tried to open one up to service it, in my line of work components like that are always replace if defective. Since you have nothing to lose, try taking it apart to inspect the internals.

 

[67Dart273]

Put a voltmeter on the coil of the starter (btw, if it doesn't have an overload attached, it's just a contactor) and verify that the voltage to the coil is removed as soon as you press the stop button. If that checks okay (my guess is it probably will) then the contactor is faulty. The motor is going to be connected to the Normally Open contacts and what's happening, I think, is that the contactor isn't immediately returning to its "normal" state when the coil is de-energized.

I never tried to open one up to service it, in my line of work components like that are always replace if defective. Since you have nothing to lose, try taking it apart to inspect the internals.

X2 but you may not be able to easily do that as some switch covers are interlocked mechanically

 

[Unconventional]

I always left those mag starters to the professionals. A couple of different times due to a starter failure I had to wire "around" the starter and switch the machine with the main breaker. The electrician would just shake his head at me when he got there . 20 guys waiting for concrete or asphalt aren't going to be happy waiting for an electrician at the plant. Wear gloves and don't stand directly in front of the main breaker when attempting this stunt.