Lathe Electrical Issue - Thoughts please

Hello,
I don't know much about wiring of electric motors etc so I thought I would post here and see what wisdom I get.
I have a ~1963 Colchester Dominion 13x36" lathe that was working 100% fine until about 10min ago. I have a dial/rotary switch in the main casting for Off-Forward-Off-Reverse (closewise). The motor is a 3hp single phase 230V (North America power - Canada).
What happened: I wasn't paying attention and switched it from forward to off (the motor clicked off as usual) but I must have not hit a 'notch' in the dial as it then started to go in reverse. I clicked it back to Off on the dial and thought nothing of it while I changed tooling. I the turned it on to forward and all it would do is humm. Turned it off (no click from motor) and tried reverse (just to see). It rotated the spindle at about 1/10 speed then the breaker went. Now all it does is humm or/and click the breaker.
It's a PITA to get to the motor/wiring as I have things right now so I am not going to look at it until tomorrow but I have a bunch of work I would REALLY like to get done on the lathe (wife away for weekend so I have all the time to work on projects! :))
Anyone have any ideas what I should look at/for when I get in there tomorrow?! I assume there is something in the box on the side of the motor I need to look at?!
Thanks, Jeff
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Sounds like you have either lost your starting switch (which is inside the motor) or a starting capacitor.
tim
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Your comment that the starting switch is inside the motor is more applicable when the motor doesn't have a reversing switch. A fair amount of the wiring to the starting winding is now outside the motor and that's where I'd start. Check to make sure that the wires to the starting winding are energized when you put the thing into the "forward" position. Do you have a VOM? Check continuity with the outfit unplugged rather than trying to put power to the motor. If the starting winding isn't energized, you'll just keep tripping the breaker.
bob g.
TSJABS wrote:

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    The rotation (you meant "clockwise" I presume) of the switch doesn't really matter much, other than how the problem happened. Mine is operated by a lever, and has (from left to right) FWD, STOP, and REVERSE. The switches all do the same things.

    My first guess is that the reversing without pausing zapped the starting capacitor, since it is a single-phase motor. Lack of the starting capacitor leaves the power going to a single winding which is not enough to start the motor spinning. You could possibly start the motor spinning by hand and switch it on and it would work -- until you switched it off again.

    There is indeed. The motor starting capacitor. It will be a cylindrical object, perhaps 2" diameter by about 5" long (maybe a bit larger, as what I have seen has been for a 1.5 HP motor.) It will have two terminals at one end, and the odds are that the end with the terminals will have been blown out of the can and will be hanging loose.
    There should be some values marked on the side of the capacitor, something like "150 uF 250 V". Write down whatever it says (or bring the old capacitor with you) to a shop which rebuilds motors. They should have some in stock, and they are quite inexpensive. (Probably less than $5.00 each at a guess.) I would (and did, when mine blew) pick up several spares, just in case it happens again.
    Obviously, unplug the lathe before you go in to work on it.
    It could be some other problem, but this I consider to be the most likely.
    Probably the next most likely thing is that the centrifugal switch, inside one of the bell housings on the motor's ends, is stuck open, or a bit of insulating material has gotten between the contacts. This will have the same effect as the failed capacitor, but is more likely to be fixable without extra parts. Be prepared to file the contacts with an ignition file if they are too badly pitted to make good contact.
    Good Luck,         DoN.
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Don has the idea. The massive Inductive voltage punched through the cap.
The cap might be oval or round. It might be under a can lid.
Don speaks from physical experience - I'm speaking of other motors...
You may have a start and a run cap. Take a grease pencil or crayon or such and mark the values next to the placement - so you don't mix them up.
Replace both at this time if two are there. a. start and run cap might be zapped b. you might not know which is which and this insures.
I mention this in case a different motor was used.
Martin
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Hello,
Thanks for the reply. Once I posted last I decided to try to get to the motor tomight. Well I can now get to the wiring box and there are 2 capacitors in there. I assume they test the same as small electronic ones so I connected up the multimeter on 300Kohm and connected them to the capacitors. They both showed zero then a higher number then back to zero as I would expect for a capacitor (or I have seen on small capacitors)? There was no smell or black marks on the capacitors and they looked fine. Maybe I will go find replacment ones anyhow to be sure if they aren't expensive.
I did some reading on the net and also found an item where the stator could be blown and toast the motor?
Anyhow I can't get to more than the wiring box tonight as I need rig up a way to move this beast away from the concrete wall. Ran fine for 2 years with no need to get behind it so I moved it (about 2 months ago) right up to the concrete wall *sigh*. Tomorrow I guess I'll try to get to the motor and look for the start switch.
I assume the start switch etc will be at the non-shaft end of the motor?
Thanks, Jeff
DoN. Nichols wrote:

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Jeff Williams wrote:

On an analog ohmmeter, the needle should at first show something like zero (initially there is a large inrush of current and it looks like nearly a dead short) but then the needle should swing towards infinity and stay there. No way it should go back to zero. If it does, they are bad. An ohmmeter forces a DC current and reads voltage across it. DC current should not flow in steady state through a capacitor, it should charge up and then stop.
I'm quite positive about this, also I happen to have a degree in electrical engineering ..
Grant Erwin

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The capacitors can be "bad" and still appear ok on an ohmneter test. That's because the battery voltage from an ohmmeter is quite low compared to the working voltage of the capacitors. Electrolytic capacitors have the strange ability to partially "heal" themselves to the extent they will test more or less OK with an ohmmeter. For a quick and dirty test, disconnect the leads from the caps and attach replacements via clip leads. On a scale of 1-to-10 the chances of your problem *not* being the caps is about a 9.
Bob Swinney

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    Hmm -- if it is a digital multimeter, it should display "-OL-" (perhaps flashing) or something similar when the leads are touching nothing, or after the cap charges from the multimeter's test voltage. At the moment of first contact, it should read something close to zero for an instant, and then run to progressively higher readings. If it has a real meter movement instead of a digital display, it will probably start at 0 (which is infinity on the resistance scale), and kick up to a higher reading (lower resistance) and then go back to the infinity mark (at the zero end of the scale).
    If both are behaving the same, they are probably good. With two capacitors, it is probably a cap-start, cap-run motor -- one is in the circuit full time, and the other is used to kick it to start. (Though it may be that they paralleled two capacitors to get the value needed to start that motor.)

    It never hurts to have spares.

    It could -- but that would be more likely to happen if the motor was overspeeded somehow.

    Ouch! I'm glad that I put mine so I could get to the back, something which turned out to be quite handy when it came time to add the taper attachment, and later, when I had to replace the motor's cap.
    Some of these days I will be putting a three-phase motor in there, with a VFD driving it.

    Most often, yes. Check which end the wires from the box go into, as that is probably where the centrifugal switch will live.
    Just in case you don't know -- it is good practice to use a center punch to mark the bell and the frame next to each other, so you put the bell back on in the same orientation. That can make a difference in the running of the motor.
    Good Luck,         DoN.
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<SNIP>

DoN, That's good advice about match marking the end bells. I learned long ago, by mistake, that motors will sometimes have much more drag if the end bells don't make it back on just like they were when the factory put them there. Some motors have the bearings mounted so they can swivel. After years of use the bearings can be kinda glued in place by thickened oil on the outside of the bearing. These bronze bearings will have worn in and will work best if not moved in relation to the shaft, And the old oil on the outside does no harm. Unless a motor is really grunged up and full of dirt it's best to just make sure the bearings have oil and to clean or replace any wicks if clogged. Clean the contacts of the centrifugal switch if there is one and make sure it moves freely and works when it's supposed to. Which means it should turn off at about 85% of the running speed. I've taken motors completely apart and cleaned everything out real well only to have to mess with the bearings to get it to spin freely. ERS
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There's a trick to getting motors to spin freely when the bearings are mounted as spherical balls, the way some oilite bushings are done.
Once the end bells are tightened up, take a wooden or plastic mallet, and whack the end bells and the main housing good a few times.
This serves to settle and align the bearings and it's quite amazing to see a motor that will hardly turn over by hand come free and spin like new, just 'cause it got walloped by a hammer a few times.
Jim
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Before you get too deep into the capacitors, check the mechanics and the wiring on the switch that you were operating.
I have done exactly what you did, tried to deliberately plug-reverse a single phase motor, and it did no harm to the start capacitor or centrifugal switch at all.
Always check first, the last thing you touched. In this case, the switch and associated wiring.
Jim
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Hello,
Well I know I have a dead start capacitor as the first motor place I was at tested the run and start caps for me. The bad part of the story is that no where open on Saturday has one in stock and the 3 surplus places I get stuff from doesn't have this size of cap either.
Oh well, guess it's a sign I should do house work instead of project work.
Thanks for the answers, TTYL, Jeff
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