bench grinder motor burns when shaft is vertical 2

[downwash]

i am building a machine witch has a bench grinder motor mounted verticly because its most practical for the apllication. the first motor ran and smoked and died. it was replaced the new motor makes noise and starts to burn i shut it off. i then put it on the bench it ran fine i picked it up while running and held it verticly it made noise and started to stink like a burning motor it is ac brushless if that matters the smoke and smell seem to come from a wond coil device mounted near the on off switch. i took the old one apart because it was the same one to see the configuration and found no machanical damage. im still scratching my head any one have any idea whats going on thanks

 

[waross]

What kind of bearings does it have?
Is there a lot of end play in the shaft?
respectfully

 

[downwash]

i would expect they are radial contact made to support no axial load. witch in my case they are needed to support the axial load of the hub assembly. the bearings are mounted between wave type washers meaning the shaft has some axial yeild

 

[MikeHalloran]

Electric motors don't ordinarily come with thrust bearings, so you have to special order them for vertical shaft orientation.

You might be able to adapt the grinders you've been buying; just don't run them with the shaft vertical until you've got a thrust bearing in there somewhere.



Mike Halloran
Pembroke Pines, FL, USA

 

[JERRYROBINSON]

Vertically oriented machines have a bearing to maintain centering of the laminations of the stator and rotor. Also as this is a small grinder hp, this could be a capacititor start or permanent split capacitor or a combination which might have a starting winding centrifugal switch.

If the lamination gets too far out of position it could prevent the starting winding cent. switch from operation and causing high current draw on the windings.

 

[ACY]

Agree with jerryrobinson. The slightest movement of the rotor will affect the internal cent switch. If it infact does have one. The motor will either struggle to start, or most probably in your case, start, but run hot, and burn out. The switch unable to open will cause this prob.
There are couple of diferent possibilites. I would assume all of them will revolve around there being a mechanical prob with the motor, eventually causing an electrical prob.

 

[electricpete]

regarding the last two posts... maybe the original poster can clarify whether in any of these cases the motor was started horizontal and turned vertical?

how long did the motor run before these symptoms were observed?

is there an air flowpath that you blocked when you turned the motor vertical?

how much does the shaft move axially under the weight when turned from horizontal to vertical?

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[waross]

Have you taken the motor apart to see the internal arrangement?
respectfully

 

[dV8r]

Use pullies and a belt to eliminate this problem.

 

[downwash]

the motor burns up in about an hour probably less. there is no ventalation blockage caused by position. the original bearing arangement didnt apear to allow for any accurate axial shaft allignment, meaning the shaft could float if pushed because bearings are mounted between wave washers, with this type of arangement i would think axial alignment isint inportent. also i replaced the bearings with opossing angular contact bearings now the shaft has no axial movement. tho problem is stil not fixed ,there is nothing inside the motor that looks like a sensor.

 

[stardelta]

I dont think the mounting position is the root cause of the problem. The fact it takes an hour to burn-out suggets to me it could be being overloaded or that the winding is not rated for continual use.

 

[itsmoked]

Wavey washers are not thrust bearings. I'm sure the one being ridden on is getting hot and annoyed.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MikeHalloran]

Is this by chance the cheapest bench grinder you could get?

If so, you need to trade up. Better bearings, better ventilation, more copper, continuous duty, etc.





Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

It is possible that you are just overloading the motor. It may be the duty cycle rather than the physical position that is doing the damage.
respectfully

 

[downwash]

its the most expessive one 180$ we use identical ones that run for full shifts for years. the only diffrance is this one is to be mounted verticly. i have a hard time beleving that thrust induced drag is the problem

 

[edison123]

downwash

Could you possibly post photos of your motor in horizonatl and vertical positions here ? That could give us some clues.

Keith has posted the following useful faq on how to post photos in this forum.

faq238-1161


*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[ACY]

Even though once power is applied the rotor should pull into alignment with the stator, perhaps in your particualr set-up, there are some causes which will not allow the rotor to correctly allign itself. IE - Downward load pressure, coupled with gravity. You mentioned there is end play, therefore - there will be movement of the rotor, once mounted vertically.
This will have an effect on the motor, and the current it draws. As for an electrical explantaion, and or equation, i will need to leave that up to the engineers of the forum.

 

[badservo]

Downwash mentioned "a wond coil device mounted near the on off switch" in the very first post, is it possible that this might be a current sensitive relay (I have seen this on a radial arm saw motor before) for the start winding? and if tilted it can't operate properly(ie no return spring, uses gravity to open contacts)?

 

[downwash]

"a current sensitive relay" uses gravity to open curcuit you are 100% correct we discovred this today, exactly what you said. i mounted the relay rite side up within the frame. no shudder no smoke altough i think the motor is already dammaged from running the wrong way i say this because the motor gets extreamly hot.thanks everybody for your help

 

[edison123]

That was a 'good' catch, 'bad'servo.

A LPS for you.

*Nothing exists except atoms and empty space; everything else is just an opinion*