How to diagnose/fix a motor?

[chopnhack]

Any pointers on how to do the above. I am trying to keep as much of the "magic smoke" in the motor! My second hand 20+ year old Jet 6" planer, that I have hardly put more than a couple of boards through, has developed some vibration and then creates smoke under very little load. I thought maybe the belt was loose, so I put more pressure and tightened the belt, but while I was under there and got to see it in action I saw the source of the smoke was from the motor itself. And boy does that stuff stink! The motor still runs, but seems to overheat very quickly? What do you think?

[Tom Slick]

it's toast. the motor windings are now shorted making heat and smoke. smoke and smell is the easiest was to troubleshoot motors.

[master53yoda]

it's toast. the motor windings are now shorted making heat and smoke. smoke and smell is the easiest was to troubleshoot motors.

agreed Tom, once you let the smoke out of a motor it is done. the reason it is still running is that you have only shorted a few of the windings but the longer you run it the more windings short together an then it lets out all the smoke. notice you did not blow the breaker yet .........

[Daryl]

Is the motor coming up to speed? If not it may be your starter circuit has dust packed in it preventing the centrifigul switch from working, basically keeping it in "start up mode" and causing the windings to overheat.

[chopnhack]

alas, my tool gloat from not too long ago, is now a tool regret. I hope the price of copper has gone up some.

[cabinetman]

Have you tried blowing the thing out. Maybe there's a dead critter in there.
.

[chopnhack]

Nah, I smoked him out C-man

Anyone have ideas where I can find a replacement motor on the cheap. It was a 120v, 1phase, tefc, 3/4hp 3400rpm motor. I have looked online and they mostly want over $100 and with shipping......

[LCHIEN]

did you try HF?

[master53yoda]

if you can't find a 3450 go ahead and get a 1725 and double the motor pulley diameter and it will run the tool at the same speed

[Uncle Hook]

I don't want to high jack this persons thread, but I have 50 year old 1/2 HP AO Smith motor on my dads old Shopsmith and I keep blowing capacaters when a load is put on the motor. Is such a motor shot and or worth repairing? What would cause a capacaters to blow?

[LCHIEN]

I don't want to high jack this persons thread, but I have 50 year old 1/2 HP AO Smith motor on my dads old Shopsmith and I keep blowing capacaters when a load is put on the motor. Is such a motor shot and or worth repairing? What would cause a capacaters to blow?

there should be a centrifugal switch the engages the starting cap when the motor is not turning and disengages when the motor gets to speed.
If the switch is stuck closed, the motor will start, but the capacitor wil keep shunting current the whole while the motor is running, probably burning it up. If the switch is stuck open, the motor won't start at all, maybe just sits there and hums.
When you start a capacitor start motor often you can hear a click as the switch disengages after about a second or so, depends on the motor.

Yor switch is probably stuck closed. you may find this switch on one end of the motor shaft, some cleaning and WD-40 may bring it back to life.

[chopnhack]

did you try HF?

I did, the one I found on their was roughly the same, if not more in price and it was turning at 1800rpm, I dont know if the 200rpm increase will be a bad thing or not. As Masteryoda pointed out (which is awesome and completely overlooked) doubling the pulley size will make this motor turn at 3600 rpm whereas the old motor was turning at 3400.

I will check around to see what other motors may be available. Thanks for the info!

[LCHIEN]

I did, the one I found on their was roughly the same, if not more in price and it was turning at 1800rpm, I dont know if the 200rpm increase will be a bad thing or not. As Masteryoda pointed out (which is awesome and completely overlooked) doubling the pulley size will make this motor turn at 3600 rpm whereas the old motor was turning at 3400.

I will check around to see what other motors may be available. Thanks for the info!

There's really no difference between 3400 and 3600 in an induction motor. The 3600 is the synchronous, no load speed. When they quote 3400, they have taken into account speed slip of about 5-10% under load, all induction motors will behave the same, so they'll really perform the same at speed.

A 2-pole, 60Hz induction motor claimed as 1800, 1750, or 1700 are all the same
A 1-pole 60 Hz induction motor claimed as 3600, 3500, or 3400 are all the same.

[chopnhack]

Ah...cool. Thanks Lchien. Also, if I have a hard time finding a 3/4Hp can I substitute a 1/2 or 1hp motor? This is for a 6" Jet jointer. Thanks

[LCHIEN]

Ah...cool. Thanks Lchien. Also, if I have a hard time finding a 3/4Hp can I substitute a 1/2 or 1hp motor? This is for a 6" Jet jointer. Thanks

as long as it fits. I would not go smaller. A bigger motor can produce up to 1 HP, but if doing the job only requires 3/4 then it will only produce 3/4 HP. A smaller motor will stall and bog down if overloaded (with a load that required 3/4). If the original machine had a 3/4 i would not put less. You would stall or bog down on heavier jobs your old motor would have done fine.
You might feed slower or go with a finer cut depth with the smaller motor and get by, but I'd really go with the original.