Single Phase Motor Problem

T

tryan

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The 3hp single phase AC motor on my lathe has developed an issue that I am having trouble finding a match for online. When I start the lathe, the motor will turn, but it buzzes or vibrates significantly and if left on for more than a few seconds, it trips the breaker. The odd thing is that it doesn't do this every time. If I pulse the start button, I can get it to run normally. I pulled the belts off to confirm it is the motor and not gear train related. When the motor runs normally, it is smooth and quiet. I pulled the starting caps and plan on replacing them, but both were holding a charge and there is no obvious deformation of the body or and leakage.

Any thoughts?

Thanks,

Tim
 
The motor on my lathe started doing the same thing a while ago. I think it has something to do with the centrifugal switch that is supposed to disengage the start winding. Makes a god-awful noise on startup (occasionally), trips the breaker if I let it continue, but if I switch it off then back on again it runs up fine. I’m not real confident with my motor diagnostic skills though, so I’d wait until some of the more savvy folks offer up a better analysis.

-frank
 
weakened or rusted centrifugal switch springs, stuck/sticking flyweights, or friction in the sliding mechanism can cause faulty starting
 
When the motor does this does it take longer than normal to come up to speed? If so then it's like John and Mike said, the start switch is flaky OR there's an intermittent fault in one of the capacitors. It's possible too (although less likely) that one of the windings is shorting somewhere inside, but lets not think about that for now :faint:
-Mark
 
Sometimes, small metal shavings can find their way inside the motor and get into the contacts on the centrifugal switch. Does your motor have any shields protecting the cooling air intake area?
 
I replaced the bearings on a grinder motor a while back and it did the same thing after I put it together. A local motor shop sorted it by
adjusting the centrifugal switch.
 
I pulled the centrifugal switch off the motor. I am no expert, but this doesn't look right.
centrifugal switch.jpg

There aren't any markings on the switch. The motor is a late 80's Taiwanese import. What do I need to know to find a replacement?
 
In our city, we have an electric motor shop. If you have someone like that in your area, take that switch in, along with a clear picture of the motor label. They may be able to get a new one for you.
 
tryan said:
I pulled the centrifugal switch off the motor. I am no expert, but this doesn't look right.

There aren't any markings on the switch. The motor is a late 80's Taiwanese import. What do I need to know to find a replacement?
Click to expand...
i have some solid state switches used in single phase meat slicers, they effectively take the place of a centrifugal switch
if you would like to keep the old motor and go this route, i would be happy to help out in the conversion
send me an email if interested
ulmadoc@gmail.com
 
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