Puzzling Motor Problem

I have a Jet 2HP 230V 8" helical head jointer. The motor won't start on a seemingly random basis. Since the jointer is still under warranty (for a short time yet), Jet is replacing the motor so I'm not complaining. However, I'm troubled by the problem and am concerned that it might not be the motor.

More details - I can use the jointer repeatedly with no start/stop problems but the very next time I use it the motor won't start. Then it won't start for awhile until one day, it just starts again and the problem persists for a period of time until the motor starts again.

Here are a list of things which have been eliminated as the cause:

1. Consistent, adequate power - The power company has verified that 240V is available into the house and I have further verified via a tester that there are also 240V at the outlet. Jet has indicated that the motor requires a minimum of 208V to start. Since the measured power has not been below 240V when the motor won't start, this is not the cause.

2. Jointer Power Switch - Jet previously supplied a new switch which I installed. The jointer worked for about 5 uses then again wouldn't start. I bypassed the switch at Jet's request and the motor wouldn't start when plugged into the outlet.

3. Capacitor - Jet previously supplied me with a new capacitor and this was installed at the same time the new switch was installed. Jet indicates that, in their opinion, it isn't a bad capacitor because there is silence when the switch is turned on rather than a humming sound (which would indicate a bad capacitor).

4. Motor Plug-In - A cord from the motor plugs into the cord from the switch. I have tested this plug-in connection by unplugging and replugging several times and/or holding the plug end securely together. Only once did the motor start, but the random starting of the motor is the actual problem. Right after that it wouldn't start again.

Any suggestions of other causes besides just a bad motor? I would hate to have the motor installed; then have the same problem. Thanks in advance for any suggestions.

The only thing left is the centrifugal switch inside the motor. It’s either dirty or damaged.

This may sound stupid, but have you checked the cord? I had a new machine, (blower motor), not a Jet, that had a bad place on the cord. I could wiggle the cord, or sometimes just move it a little and all was well. Do it again and it wouldn't budge.

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Originally Posted by Randy Heinemann

Jet indicates that, in their opinion, it isn't a bad capacitor because there is silence when the switch is turned on rather than a humming sound (which would indicate a bad capacitor).

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The silence also makes it unlikely that the centrifugal switch is at fault. No hum is a strong indicator of no power to the motor.

Some possible causes, in order of likelihood:

1. Connections
2. Switch
3. Cable
4. Motor

You've already replaced the switch so, while you could have gotten another bad one, it's probably not at fault.

For the connections let's start at your power outlet. You've verified power there. The next point is the power connector on the power cable. If it's a molded connector about all you can is bend the cord tightly where it enters the molded part while running or trying to run the motor. Otherwise open it up and make sure everything is tight. Next are the connections to the switch which you have just replaced so presumably those are good. The molded connectors breaking the cable from the switch to the motor can be checked the same way as a molded connector on the power cord. Last, and a resonable probability, are the connections at the motor. With the power cable unplugged open up the connection box on the motor and make sure all of those connections are secure.

Finding an intermittent open in a cable can be difficult although Steve's technique can be useful. Using your tester to verify power at the motor in that cramped space and with a motor that could start up at any time is not something I would recommend.

If you've gotten to this point and the only things left are the cables and the motor it might be worthwhile to have Jet send you a new set of cables to try before trying to replace the motor.

David did an excellent job, but I just want to add. Depending on who wired your house or shop the cheap 49 cent outlets are junk. I would replace the outlet with a good grade heavy duty one. Plan on paying about three bucks or so for good one. Who knows when you open up that box to replace the outlet you might find some loose wires.

So motor replacement then.

No damage to the cord either from the motor to the switch or from the switch to the plug (which I wired myself anyway).

I wired the shop and the 220V outlet later. I don't know about cheap outlets but I didn't shop for the cheapest. However it's what they had. Wouldn't the outlet show there wasn't power when tested if it was bad though?

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Originally Posted by Randy Heinemann

I wired the shop and the 220V outlet later. I don't know about cheap outlets but I didn't shop for the cheapest. However it's what they had. Wouldn't the outlet show there wasn't power when tested if it was bad though?

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From my experience in the electrical field since 1962, I have seen things that checked for good voltage even when they are bad. It only takes a very thin wire to show the voltage. It takes a good solid connection to supply the amps needed. If its 220 volt outlet more than likely its fine, but checking the connections might not hurt. Even the ones in the circuit breaker panel.

Sounds like you know a lot more about motors than I do. Opening up the motor is a difficult problem. The motor is mounted so that there is only access on one side inside the enclosed cabinet below. That's one of the reasons I wanted Jet to send service out to deal with this. To this point, I wasn't even able to get at all the motor mounts to get the motor loose or out of the cabinet. I tried when Jet Service wanted to assign installation to me. I will ask the service people when they come out to install the new what their experience with Jet is as they have been Jet service in my area for awhile. So, if any checking is being done, they will need to do it before and after the new motor. Problem is random and intermittent which means it might not show up when I want it to.

When my JET band saw was new the motor had issues. They finally sent a new one, the wrong one! Had to box up and send back. The one I got then was perfect, and install was not easy but it got done.

Lack of humming really seems to indicate a power supply issue.

Can you measure the voltage AT THE MOTOR when it SHOULD be on, but isn't? I bet you'd see no voltage.

Lack of humming could also be a dead spot on the armature

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Originally Posted by Dan Friedrichs

Lack of humming really seems to indicate a power supply issue.

Can you measure the voltage AT THE MOTOR when it SHOULD be on, but isn't? I bet you'd see no voltage.

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^+1

Randy, this is a great place to apply 'law of halves' to trouble-shoot electrical problems. Test in the middle of a given system and determine which 'side' is bad. Test again in the ~ middle of that bad half and isolate the bad half of that half ...... repeat as necessary. The problem's possible location gets narrowed down quickly.

Test when the motor won't start*:
- If you have power at the output side of the controls (= approx middle?) , then the problem is in the last half of the system (wiring to the motor, or in the motor). First half is fine.
- - If you measure the voltage at the motor and there is rated voltage, then the problem is in the motor. (All else is fine.)
- - If you measure the voltage at the motor and there is no voltage, then the problem is in the wire between the starter & motor.
- If you have no power at the output side of the controls, then the problem is in the first half of the system (power supply or starter). Second half may be fine, but is yet to be determined.

....repeat until you find the 'break' in the system.

(I use 'half' loosely, pick convenient spots to test voltage that have accessible points (terminals, wire nuts, etc).
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* Please remove the belt and use good judgement when the controls/JBs/peckerhead are open!

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Originally Posted by Jerome Stanek

Lack of humming could also be a dead spot on the armature

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AC induction motors do not have armature and brushes.

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Originally Posted by Malcolm McLeod

^+1

Randy, this is a great place to apply 'law of halves' to trouble-shoot electrical problems. Test in the middle of a given system and determine which 'side' is bad. Test again in the ~ middle of that bad half and isolate the bad half of that half ...... repeat as necessary. The problem's possible location gets narrowed down quickly.

Test when the motor won't start*:
- If you have power at the output side of the controls (= approx middle?) , then the problem is in the last half of the system (wiring to the motor, or in the motor). First half is fine.
- - If you measure the voltage at the motor and there is rated voltage, then the problem is in the motor. (All else is fine.)
- - If you measure the voltage at the motor and there is no voltage, then the problem is in the wire between the starter & motor.
- If you have no power at the output side of the controls, then the problem is in the first half of the system (power supply or starter). Second half may be fine, but is yet to be determined.

....repeat until you find the 'break' in the system.

(I use 'half' loosely, pick convenient spots to test voltage that have accessible points (terminals, wire nuts, etc).
________
* Please remove the belt and use good judgement when the controls/JBs/peckerhead are open!

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Problem is intermittent and he can not gain access to the motor connections when its installed.

Thanks for the suggestion, but I already did check them all. In fact, since I could turn the power off to the sub-panel, I just redid them all. The other thing is the jointer operated for 3 1/2 years with no problem on that circuit. While I realize things can change and I did check it to make sure, it seemed unlikely that the connections would be the problem. It's a 20 amp breaker with #12 wire run through conduit; no junction boxes anywhere, just continuous wire from the box to the outlet about 25 feet. Thanks again.

I appreciate all the help although that last few have been a little beyond my electrical capability and knowledge. I will definitely discuss with the service people when they come. I'm really fortunate in that this company is very good and knowledgeable with a lot of experience in the stationary power tool business. Either Jet vetted them, found them by accident, or they are one of the only companies in the area qualified. Anyway, your responses gave me some issues to discuss when they replace the motor because motor replacement at this point is a given whether it resolves the problem or not.

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Originally Posted by David L Morse

...Using your tester to verify power at the motor in that cramped space and with a motor that could start up at any time is not something I would recommend.

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There is a safe way: turn off the power, connect the meter with a alligator clips or other gripping probes, then turn on the power. If needed, clip on and run several insulated lines out and tape the ends to the outside of the equipment, turn on the power and probe those lines.

JKJ

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Originally Posted by Bill George

Problem is intermittent (:: test when it wont start) and he can not gain access to the motor connections when its installed (:: where there's a will, there's a way) .

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.........:)

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Originally Posted by Malcolm McLeod

.........:)where there's a will, there's a way) .

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That is easy to say, hard to do if you need to do it. He has experts coming, they will get it done.

I can't help but wonder if the machine has some sort of thermal overload protection..... perhaps built into the motor itself. Does this motor have a time rating? Does this have a temp rating?

Really, it does help to have a meter (VOM or DVM) along with some knowledge to narrow down the issue rather than assuming and unnecessarily replacing parts on the machine until the problem is resolved.

Have you tried giving the motor a good smack when it doesn't start? Just wondering.

No, but it doesn't seem like that would be the best solution when Jet will replace the motor. A motor which requires a "good smack" is not the preferred motor.