Ask Me Help Desk - Shop Fox Motor not running right

A fellow scrounger rescued a Shop Fox W1685 Dust Collector from the garbage man recently and passed it on to me. The report from the original owner was that the motor was bad, but it could have been a switch. When I got it, the switch cover and the motor wiring cover had been removed and the start capacitor was missing.

The parts list in the manual on the Shop Fox website called for a 200 uF 125 V capacitor. The place I went didn't have an exact match so I got a 189-227 MFD start capacitor and wired it up. When I plugged it in, the motor started slowly and picked up speed. Within about 30 seconds I smelled smoke and saw a few wisps coming up from the motor housing where the wires come out.

I took it apart and blew the dust out to get a better look. Two things looked possibly wrong.
1) On the spindle end of the housing is a switch(?) that looks black around the electrical contact. I assume this is what is supposed to open/close the start circuit.
2) On the motor shaft there is a mechanism that shuttles back and forth, and it looks like this is what actuates the switch. When I took the motor apart I found a small piece of plastic that broke off this mechanism.

After I cleaned it out I put it back together and tried again. This time I couldn't get the shaft to spin with no load on it (might not have aligned the end housings perfectly). It did start when I gave it a turn to get it moving just before I gave it power.

So... What I need help with is figuring out what is wrong and if it's something I can fix. It seems to me like the motor is not getting up enough speed to actuate the switch to open the start circuit. Maybe that makes it draw too much current and that heats something up causing the smoke?

http://img.photobucket.com/albums/v2...ng/DCmotor.jpg
http://img.photobucket.com/albums/v2...king/black.jpg
http://img.photobucket.com/albums/v2.../DCspindle.jpg

The contacts in the second photo need repaired, or replaced, the plastic piece that broke may be important. Try to see where it came from and repair or replace.

Thanks for the quick response. You can see where the plastic piece came from in the third picture - look for the break just under the spring. To fix the contacts, can I just try sanding them with ~400 grit sandpaper, or do I need to find a way to remove and replace them?

I sanded the contacts today and put the motor back together. It starts now, but I don't hear the centrifugal switch engaging/disengaging. I didn't leave it plugged in long enough to heat up and make any smoke, so I'm not sure if that still a problem. I can move the centrifugal switch manually and it seems OK, so I'm not sure if that means my capacitor is undersized or the motor is just shot.

Maybe its working and can't hear it switch?

Tell you what:

Wire an external switch in series with the cap/switch combination for testing.

Let the motor start and then turn off the added switch. If it behaves, you may be set.

Also if you can bring out two wires across the switch and monitor the voltage across it. Initially it will be zero and then probably near line voltage. This should, at least give you an idea that things are working.

If they are, then, I think you have the basis to to try a permanent fix.

You don't want the contacts to stick and that's what they are doing. Fixing the contacts would be difficult, if not impossible.

Move the voltmeter to the winding. Note the back EMF. Your going to probably want, to know this value and maybe subtract 20%.

The centrfugal switch for a dust collector, I guess has it's uses primarily because the dust collector is constantly turning on and off and you don't want the starting winding to be engaging while the motor is running.

Usually you can hear the centrfugal switch cut in as the motor slows down. It's difficult to hear when starting up.

What you want to do is replace the centrifugal switch with something like this:

http://www.magnecraft.com/library/se...831_Series.pdf

in 120 V.

http://www.alliedelec.com/Search/Pro...DESC=831VS-120

You'll need a piece of DIN rail to mount it. Another $10.

Monitor the voltage across the start winding and the contacts of the relay would go where the centrifugal switch is. See: http://www.achrnews.com/Articles/Fea...00f932a8c0____

This is a 5 terminal version. Contacts, sensing and power, rather than two.

This would gives years of trouble-free service. You'll just have to get the adjustments right. Measuring motor current could help. If it's engaged too long, then the current would be higher.

Then you should also be able to remove the centrifugal guts as well.

References:

Reversing and Repair of Electric Motors

Potential Starting Relay Voltage Specs - Editorial Archives - Air Conditioning, Heating & Refrigeration NEWS

Kickstart®Hard Start Devices - Contractor FAQ's

What you're seeing in the cap value is the tolerance, which is/can be very sloppy for this application.

There is useful stuff here, but I hate the diagrams. http://www.supco.com/images/pdfs/Man...20-%20supr.pdf

Have no idea what the functionality is.

KISS - Thanks for the idea of putting a switch inline with the capacitor. So simple - I wanted to smack my forehead when I read it. I tried it out tonight and am pretty sure the motor is toast.

With the capacitor off, when I applied power for a second and the motor hummed but didn't spin. Then I kicked the capacitor on and the motor took right off. A few seconds later, I cut the capacitor power. The motor slowed a little, and maybe 20 seconds after that the smoke started.

The way I see it, the centrifugal switch not engaging tells me the motor is not hitting full speed and I'm guessing that there is a problem in the run windings. I think that also explains the smoking after it runs for a while. So, it's time to price out a options for a motor rewind and a replacement motor and weigh that against setting it back out for the junk collectors.

Thanks Stratmando and KeepItSimpleStupid for your input.

The centrifugal switch is not disengaging, not engaging.

Now that you understand the reason for the centrifugal switch: i.e. It's not good to start a running motor

The design is going to be a problem no matter how you cut it especially if your dust system starts and stops with the power tools.

I think your dx is correct at this point.

A single to 3 phase converter with a 3 phase motor might even be better, but not cheap.

Quote:

Originally Posted by KeepItSimpleStupid

A single to 3 phase converter with a 3 phase motor might even be better, but not cheap.

Yeah, I wired up a VFD with a 3 phase motor on my lathe, and it works great. However, in this case the dust collector is a lower end model with a comparable one selling new for $250 + shipping. It's hard to justify putting too much money into it before just moving on to a new one.

Like I said, I don't like the design.

Either move the contactor outside of the motor. Use the contacts to drive a contactor, solid state or whatever.

Use the potential relay of a 3 phase motor.