Help from Motor Experts!

[Peter Aeschliman]

Hi all.

I recently acquired a 1950's DeWalt model GA radial arm saw with a 3hp single phase motor.

The wiring in the motor was pretty tattered, so I carefully replaced the wires that I could replace, and added shrink tubing to the wires going into the motor (which can't be replaced without re-winding the motor from what I could tell).

I added a new magnetic switch from grizzly (http://www.grizzly.com/products/Magnetic-Switch-Single-Phase-220V-Only-3HP-21-25A/T24101).

I started it up without a blade installed (still waiting on it from Forrest). It starts and runs fine from what I can tell without a blade, except that there is a loud clicking and electrical arcing sound coming from the box on the motor. I opened it up to take a look, and there is visible arcing occurring at what I believe is called the centrifugal switch. Here is a video of me shutting down the motor:

https://photos.app.goo.gl/y0QiZPlUegjYshc53

My question is: Is this arcing normal? If not, what can I do about it?

Thanks in advance for your help!

Peter

[Rod Sheridan]

Hi Peter, it is not a centrifugal switch, it is a starting relay.

When you start the motor, current is very high and this high current in the relay coil causes the relay to close, powering the starting winding.

Once the current drops as the motor reaches near synchronous speed, the relay drops out, de-energizing the starting winding.

That slight toggling on shut down shouldn't hurt anything...........Regards, Rod.

P.S. Watching the video with the sound on I now realize that you have a voltage sensing relay, not a current sensing relay.

In your case the relay coil is probably connected in parallel with the run winding, as the motor accelerates to near synchronous speed the voltage rises and the relay disconnects the start winding.

When you shut down the motor, the run winding voltage will drop however the winding will attempt to maintain current flow, so its voltage will rise momentarily, closing the relay again.

It's not something I would worry about............Regards, Rod.

[Peter Aeschliman]

Thanks Rod. Sounds like you know your stuff, because the only part that I understood was your last sentence. lol. As long as that's the case, I'll carry on as usual. The electrical zapping sound was just a bit surprising to me since none of my other machines do that.

Thanks again for your help!!