Small AC motor won't start

Tomorrow I'm picking up an old drill press, somewhere in the 1/3-2/3 HP range to give myself something to tinker with over the winter. One of the things that will need addressing is the motor, according to the seller, it only starts if you give it some help. Where do I start on a problem like that? I'd rather not spend the cash on a new/used motor, especially if this one turns out to be the 1940s original.

It may well use a capacitor to start, and the capacitor may be bad.

If it has a capacitor, it must be internal, no capacitor housing on the motor like I've seen on the bigger ones.

start winding is bad then

you could TRY adding a Cap, even a 'sofstart' cap?

i dont know if these only apply to 480v motor's, but at work we use em to coax a few weeks out of an aging motor until a replacement arrives.

-J0N

In reply to jmthunderbirdturbo:

If you can walk me through how that needs to be connected, maybe. I'm going for ME and not EE for a reason.

I think I'll start of a build thread on this drill press, Atlas built Craftsman, its nicer than I thought, IT STILL HAS THE LUBE TAG ON IT.

Anyhow, its a 1/2 HP Craftsman 115.6962 "Capacitor Motor", dual output with a cast base w/ switch like you'd find on a bench grinder. I believe that interchanges to a GM Packard motor. When you flip the switch it growls and moans and moves slowly till you give it a spin. Then it runs fine. Put a new cap in it, right? Where the hell is it hidden? I hear the centrifugal start switch click off when you shut it down.

Could be the start switch. Is it a general purpose motor? If so look through the back endshield and push with a screwdriver to open the start switch. They usually open up with the centrifugal force, but if the endshield is worn where the bearing seats, then it might not work correctly. Post some pictures of the motor, I might have one you can use. Is it regular speed or a high speed motor?

I can look in there and everything looks clean and good, it makes an authoritative CLICK spinning down. Which indicates to me the switch is at least operating, maybe not contacting? I see no capacitor so it must be hidden in the base. I think I'll pull the motor off and check that, just on principle of it being a 60yr old cap. Its seems to be in good shape otherwise, I plugged the 2 prong, unpolarized, original cord in both ways and didn't get shocked.

Pics:

You can see two cords hanging because the press' switch is unhooked and whoever installed the motor opted to use the switch on the motor instead.

I was thinking the groaning at first is the motor running on the start cap only, the start switch is slow to engage, once it does then the run cap takes over. Sometimes the start switches don't engage right away (because of whatever reason)and that happens.

I have the exact same motor on a grinder. I can't remember if the capacitor is in the base in this model. Seem like a good motor. I don't think I was able to totally disassemble this motor as the wires are soldered. Pretty sure if you pull the motor off the stand you'll find a rectangular shiny metal box under the base, which is the capacitor. You can pull the bearing cover at the end of the dirve and relube if you want to just use bearing grease. I'd go at it with electric cleaner, hit the switch and play around with it.

Good luck, I love messing with old motors.

edit, the capacitor is indeed in the base of the motor, I just checked. Just pull the motor tilt on its side and pull the cover and you'll see what looks like a can of sardines, that is the cap. My motor's is of the 3450 variety but of the same vintage.

In reply to Slippery:

I don't see how it can simultaneously have a bad start switch and try to run off the cap/start winding. As I understand it the start cap's job is to give the motor a push one way or the other, so having to spin start would indicate a bad switch or a bad cap.

I'm gonna pull it off and ohm out the start circuit, if I get a reading besides open I'll try a capacitor.

Update: Pulled motor off. Start cap has a hole rusted in the case, its a thin rectangular one I'm having trouble finding on the net, only markings I can find on it are AUG 17 1945. Sears does not acknowledge the existence of this particular motor.

I ohmed between the cap wires with the cap soldered and got something like 10 ohms. So I think the start circuit and switch is ok.

Edit, found a manual here with part numbers http://vintagemachinery.org/pubs/detail.aspx?id=3331 Punching this into sears parts give me NLA.

Go to an electric supply house with the stuff written on the motor and get a cap for those specs. It ain't that critical. If it fits where the old one was, that's a bonus, but otherwise rigging it up would be acceptable for a shop, in my opinion.

Measure the capacitance and get a new one.

I am not saying the start switch is bad, I am saying it might be having a hard time engaging. Its basically a spring loaded mechanism that opens with centrifugal force.

By runs slowly I mean it barely even moved, like 3 rpm. I'm under the impression they are built to open at more like 80% of full speed.

Dr. Hess wrote: Go to an electric supply house with the stuff written on the motor and get a cap for those specs. It ain't that critical. If it fits where the old one was, that's a bonus, but otherwise rigging it up would be acceptable for a shop, in my opinion.

This.