Motor, Starter and Switch Question 36-812 Unisaw

[Brandon Mitchell 777]

I've read much on this forum but haven't seen a clear answer to what I'm looking for. My uncle owns a 36-812 type 1 Unisaw. He purchased it used, the previous owner had replaced the motor in 2005 or 2006 with a Marathon 3HP model: 145TBFR15506. Also, the saw was wired with a single pole switch and appeared to have been used this way for a while. So one leg was on a switch, the other was continuously energized. No overload protection is present on the motor or remotely located, and the switch is obviously the wrong switch.

A couple of questions. I've removed the switch and hardwired the motor for testing purposes. The motor now trips the breaker shortly after being turned on (2-5 seconds). I took the motor completely apart, and cleaned out all the sawdust. I found one spot where one of the leads from the start capacitor had shorted to the cover. I fixed this and replaced both capacitors. There does not appear to be a centrifugal switch. The only switch is one connected to the two capacitors. Everything in the motor looks fine, nothing looks or smells burned. There are no contacts to be cleaned up that I can find. I can only guess that something is wrong with this "capacitor" switch or a winding is toast. The motor still trips the breaker as before. I've checked all plug and outlet wiring and the breaker is good. Anyone have any thoughts on this? Can these capacitor switches be replaced, or are they known to anyone to be a problem? Or do you think it's most likely a winding? I have no place locally to take the motor for testing.

My other question is regarding the new switch/starter setup. In one scenario, I'm considering installing a switch like the Delta part number: 438013170154. I believe this would be okay for use with this 3hp motor and would provide the benefits of a magnetic starter as well as some overload protection. As a second scenario, I was wondering what some of you would suggest in terms of a specific magnetic starter (brand and model in your experience) and remote switch. One issue I worry about with a mag starter is the potential for it to become accidentally activated by bumping it or something dropping against it, which I've read has happened. So I'd want an extra disconnect switch wired in ahead of the starter. I was thinking the grizzly switch H8243 for the remote switch for the starter, and then maybe just a basic heavy duty 2-pole switch for the disconnect prior to the starter. What do you guys think? Thanks.

[Rod Sheridan]

Hi Brandon, the motor you have does indeed have a centrifugal switch inside the motor.

Carefully check the wiring diagram for the motor and verify that
- you're using it on the correct voltage
- there isn't a wiring error in the terminal box

The motor obviously should run without tripping the breaker after a few seconds. It sure sounds like a wiring error in the terminal box.

I would use a magnetic starter for that motor, and either unplug the saw when changing blades, or add a disconnect switch.

My home shop machines have a small locking disconnect switch from the manufacturer, very convenient.

If you have a local electrical supplier, go to them and look at IEC rated enclosed disconnect switches, compact and cost effective, far nicer than the North American NEMA devices.

regards, Rod.

[Brandon Mitchell 777]

Thanks Rod. I have checked the wiring, I believe it is all correctly connected and on the correct voltage. I'm contemplating pulling the bearing and if I can get the part, replacing the centrifugal switch.. I hope this will fix it and provide a few years of additional service. I can't think what else the problem could be. Whether I can fix this or I get a new motor, I do plan to install a starter as you suggest. Can you suggest one or two specific device models to look at that are the IEC rated devices, switches or disconnect, and starter if possible?

Does anyone else have any additional thoughts to add?

Thanks again..

[Charles Lent]

The centrifugal switch is most likely your problem, but it's more likely the switch actuator than the switch itself. On the motor shaft there is a plastic collar that moves along the motor shaft when some governor type weights swing out away from the motor shaft as the motor comes up to speed. They drop back toward the motor shaft as the motor slows down. Frequently this collar sticks on the shaft due to rust, sawdust, etc. This collar must be free to slide on the shaft so that it can actuate the centrifugal switch. If it fails to move or move far enough the centrifugal switch won't open and the start capacitor and start winding of the motor will remain connected, causing the breaker to trip. Usually, cleaning this area of the motor shaft is all that is needed. Lubrication may cause more harm than good as it will collect debris and cause additional failures, but I would use a few drops of WD40 or equivalent carefully wiped on very thin to prevent rusting.

Charley

[Brandon Mitchell 777]

Hi Charley, Thank you for the info. I'm going to try this.. The actuator seems to move on the shaft okay by hand, but I think I will pull the bearing if I can remove the actuator and clean the shaft.. It looks like I can order a new actuator if that were the problem, but I'm not so sure I can still get the stationary part of the switch, which I also have not yet identified.. But perhaps getting the shaft clean and if I can find any contacts to clean while doing so, maybe I'll get lucky..

[Charles Lent]

The switch contacts should be mounted to the inside of the end housing of the motor. When the motor is assembled the plastic collar of the centrifugal part on the shaft should be very close to it so that the collar can push on it to open the switch contacts as the motor comes up to speed. The contacts should be normally closed, and open when pushed by the collar. A piece of emory cloth folded lengthwise can be slid back and forth between the contacts to clean them, but be careful not to bend or in any way change the spring tension of the switch when you do this.

I wouldn't try to remove the centrifugal part from the motor shaft. You would likely damage it in the process. Just clean the shaft where the collar moves with emery cloth. If you are careful, you can remove the springs and slide the plastic collar out of the way for the cleaning and polishing, but be sure to remember how to put it back together, and be careful with the springs as they have significant tension.

Are you certain that the wiring to the capacitors is correct? One capacitor should be connected to the centrifugal start switch. The other terminal on the capacitor should be connected to the start winding of the motor. The second capacitor should be in the run circuit of the motor and not wired through the centrifugal start switch.

Charley

[Brandon Mitchell 777]

I'm 90% sure the wiring is correct on the capacitors. The start capacitor has a wire that goes to the switch, and a wire that goes to the run capacitor. The run capacitor has three wires, one is the one from the start capacitor, one to the switch, and one to the winding. The switch has what looks like a little balloon/air bag, which appears to stay connected on both sides, I don't know if that's supposed to be that way, but I assume so. The switch looks good, no visible burning or charring or dirty looking contacts. I went into everything again yesterday and cleaned up the shaft, etc. Put it back together and wired it up to test. The breaker trips the first time after about five seconds. The second time and thereafter about every two seconds. Probably I'd guess because the breaker gets warm too and trips sooner. I flipped the breaker probably eight to ten times for a cumulative run of the motor of about 30-40 seconds I'd guess. Maybe a bit longer. The motor was so hot I couldn't hold my hand on it comfortably. Also I noticed after each breaker trip, about two seconds later I'd hear a faint click from the motor, which I assume was the centrifugal switch disengaging as the motor slowed down, but not sure. So I'm thinking perhaps the switch is working. The bearings appear to be in good shape. I don't know what else to think, aside from maybe windings. Nothing looks burned, all of the windings I can see look fine. But for the motor to get that hot that quickly, I'm assuming it's abnormal? I think I'm looking at a full replacement motor unless you or anyone else can suggest anything else to check out. I don't know if there is a way to test the windings myself.. nobody locally services electric motors, so I'm limited to what I can do or replacement. Thanks again for your help and time..