O/T Question for electric Gurus

Blackhole49 · Dec 27, 2012

I have an older FMC 6101 Wheel Balancer with a 3hp 240v single phase motor. I am trying to understand how the contactor is drawn in to put power to the motor. Right now, when I hit the start button there is a slight humming. If I physically push in the contactor, the motor will start. I do use the machine to balance tractor tires?

Paul from MI · Dec 27, 2012

I assume you have a magnetic motor starter on the machine. You should hear a "clunk" when the motor starter coil pulls in the armature to close the contacts and start the motor. Sounds like you may have a tripped overload coil, or other "open" in the starting circuit. Using a voltmeter, check to see if you have voltage across the coil contacts when the start button is pushed. If so you have a bad coil. If not there is and open somewhere in the start circuit. You'll just have to start tracing to find it. Hope this helps.

Blackhole49 · Dec 27, 2012

Can you tell me 120v is used to pull in the contactor?

John T · Dec 27, 2012

Since its a single phase motor that is NOT self starting, to get her turning the seperate slightly out of magnetic phase orientation "start winding" must be temporarily activated (and via relay terminals if a magnetic starter is used, unlike an internal centrifugal switch activation circuit).

It sounds like that part of the motor (its start winding) is okay and works WHEN YOU PHYSICALLY PUSH IN THE CONTACTOR.

THEREFORE, it looks like theres a problem in the starter (relay) and/or its wiring and terminals and connections BECAUSE THE STARTER WINDING CONTACTOR isnt working electrically, ONLY by manually activating it...

It should self engage electrically and pull the contacts in (to activate start winding) and it has control circuitry and connections and wiring, so either some of that is bad or simply the starter relay itslef is just baddddddd

John T My very first job as an EE was for Century Electric Motor Company but that was over 40 years ago and Ive slept since lol so no warranty, see what the more current and practicing engineers and electrical techs have to say

Paul from MI · Dec 27, 2012

Starters(contactor) can be had with various voltage coils. It should be plainly marked on the coil itself with the voltage. 120 volt is very common, but full voltage(240 in your case) is also, along with 24volt. Check your coil.

JF in MI · Dec 27, 2012

Dynamic balancing tractor tires? Just how fast does this tractor go???

David G · Dec 27, 2012

The coil in the contactor can be most any voltage, you need to pull it out and read the label. I would suspect it is bad.

John T PS · Dec 27, 2012

PS Just FYI Forgot to mention, those magnetic starters have "heaters" or "thermals" to protect the motor from over current and overheating and burning up by opening but those are for the RUN winding NOT the start portion. As most of us agree the start relay coil/winding could be bad/open so a simple ohm meter or continuity test can verify that. It needs to be a closed continuous loop/coil to conduct current to create a magnetic field to pull the contactor in

GET YOUR METER AND VERIFY CONTINUITY IN THE COIL OF THE RELAY if its good then look for wiring or connection or mis wiring problems

Again, Im rusty on this so listern to the fine electricians and techs here

John T

buickanddeere · Dec 27, 2012

Since the motor will run. It sounds like an old dry stuck and dirty contractor with a weak coil.

Geo-TH,In · Dec 27, 2012

JohnT,
I had an old wheel balancer and the motor had brushes. A iron wheel on the motor rubbed against the wheel and would spin it at about 120 mph. Motor needed to be a universal motor to get the torque

It is possible someone used oil on the contactor, oil dried out and is now sticking.

Besides what you said, Rust will make them stick too.

Happy New Years to all,
George

old · Dec 27, 2012

Been since 1992 since I messed with that type of stuff but sounds like the contractor is going bad and by holding you are making the contact get warm so then they make and the motor starts up. I know when we ran into that on machines in the factory I worked at we simply replace the control box as in the contactor

Walt Davies · Dec 27, 2012

The main question here is why are you balancing tractor tires. What kind of tractor anyway.
Walt

John T · Dec 27, 2012

My buddy has one of those wheel balancers and youre right THEY REQUIRE A SUPER TORQUE TO SPIN A HEAVY WHEEL N TIRE.......Yep besides a bad coil, the contacts may well be burned and pitted and carboned up, Id say a new contactor will get him going......

John T

Ozlander · Dec 27, 2012

(quoted from post at 11:27:46 12/27/12) The main question here is why are you balancing tractor tires. What kind of tractor anyway.
Walt

This is a tractor forum. If he is balancing tires, they have to be tractor tires is stay on topic, or some one will complain.

John T · Dec 27, 2012

Yep and he said and I quote....

"I do use the machine to balance tractor tires"

Maybe the tractor and speech police will allow the post to stand, ya reckon???????? lol

John T

O/T Question for electric Gurus

Blackhole49

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Paul from MI

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Blackhole49

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John T

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Paul from MI

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JF in MI

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David G

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John T PS

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buickanddeere

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Geo-TH,In

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old

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Walt Davies

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John T

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Ozlander

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John T

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