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Tris

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Evening all,
I need to pick the brains of those who know more about this than me (not difficult I know).
Earlier this evening my lathe started making a nasty hum whilst running and seems to have lost power. It's a Jet 1442 and has 2 capacitors, I suspect the run capacitor is fried so I've opened it up to get access. The fitted run capacitor is 30uf but the manual states 25uf. Motor is 750w and I just want to check if it will cause problems to run with the lower rated capacitor?
Thanks
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CHJ

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These type of capacitors can have a fairly wide tolerance band so I doubt you would notice any difference unless either or both of them were at the opposite ends of their tolerances.
motorcapacitor.jpg
 

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Myfordman

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Either will be fine but make sure the working voltage of the new one is equal or higher.
However excessive hum suggests to me that the starting capacitor might not be being switched out once the motor is up to speed. Is the motor running hotter than previously? If so that would support this theory.
 

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Thanks for the replies, I don't know if the motor is running hotter than usual as it is rare to ever need to get close enough to feel it.
As they are not expensive components is it better to replace both or should I be looking further?
 

Myfordman

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A failed run capacitor usually means reduced output torque and no change in noises.
A failed start capacitor usually means it won't start without manual help and will buzz/hum a possibly blow a fuse.
A fault, failing to switch out the starting capacitor after it has got up to speed, leads to buzzing and increased heat and possibly eventual fuse blowing.
Analysis is better than scatter gun replacement of components but as you say is a cheap first step before calling in knowledgeable face to face help.
 

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Thank you, that is useful. I don't recall hearing the usual click of the centrifugal switch so a fault may be more likely. I will have to pull it out and head for the local rewind shop.
 

Myfordman

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If the contacts have welded shut, the characteristic click would be muted/modified and give the symptoms you are seeing.
 

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It looks likely that something has stopped the weights from throwing out. They are moving now and the switch opens/closes but it was tight when I first checked. Would the switch contacts show signs of arcing if they'd been stuck shut?
 

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Well the switch contacts were clean so I went round the mechanism of the centrifugal switch with a small brush. This removed a small amount of gunk but I couldn't see any damage so I reassembled the motor. Plugged in, switched on and everything ran smoothly.
I finished turning the bowl I'd been working on and roughed out another with no further issues.
Thank you for the help
 

Myfordman

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Glad you are up and running again. General advice on these centrifugal mechanisms is to resist tempation to lubricate with anything but it sounds like you just gave it a clean up and that is spot on!
As a suggestion, get to know your motor. Listen subconciously for the click as you switch off and get a feel for how much it heats up after a good long turning session. If is is not a totally enclosed fan cooled type(TEFC, most are these days) then a blow out of accumulated dust every now and then is a good precaution.
 
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