Potential electrical problem with DC Lathe Motor

[markba633csi]

The potentiometers on many KB controllers DO have line voltage potential on the terminals, one of the reasons they usually are supplied with
nylon shafts to help mitigate shock hazard

 

[GeoBruin]

Okay, I've got some testing to do but as for grounding the motor (sorry for the stupid question) this is the wiring diagram for the controller:


Trying to interpret the little diagram, is this suggesting the Armature should somehow be grounded or does this just mean to ground the case?

 

[markba633csi]

Case, and it's a good idea to run a separate wire or strap from the motor case to a bolt on the machine

 

[Jeff.64]

The potentiometers on many KB controllers DO have line voltage potential on the terminals, one of the reasons they usually are supplied with
nylon shafts to help mitigate shock hazard

In the original post, he is getting shocked by touching the knob of the pot. So the pot is using a conductive shaft. A good quality pot should have the wiper well insulated from the shaft. I've used Minarik drives and found their supplied pots to be of low quality. So, I've replaced them with high quality pots. The low quality pots don't seem to last long in an industrial environment.

But, just to be safe, a good quality pot with a plastic shaft, as you said is very good advice.

 

[Nigel123]

In the original post, he is getting shocked by touching the knob of the pot. So the pot is using a conductive shaft. A good quality pot should have the wiper well insulated from the shaft. I've used Minarik drives and found their supplied pots to be of low quality. So, I've replaced them with high quality pots. The low quality pots don't seem to last long in an industrial environment.

But, just to be safe, a good quality pot with a plastic shaft, as you said is very good advice.

In the original post he took a reading from the controller case to the lathe and read 40 volts
He said the case has a ground hooked up
That would indicate voltage from the motor unless his ground on the case is bad
I would check for voltage from the motor case to a good known ground
rabler gave a list of checks to do which is good advice
I assumed this problem occured after hooking up the DC drive but
It might have been present before you bought it
Other wiring on the lathe maybe at fault so work carefully

 

[GeoBruin]

In the original post, he is getting shocked by touching the knob of the pot. So the pot is using a conductive shaft. A good quality pot should have the wiper well insulated from the shaft. I've used Minarik drives and found their supplied pots to be of low quality. So, I've replaced them with high quality pots. The low quality pots don't seem to last long in an industrial environment.

But, just to be safe, a good quality pot with a plastic shaft, as you said is very good advice.

In the original post he took a reading from the controller case to the lathe and read 40 volts
He said the case has a ground hooked up
That would indicate voltage from the motor unless his ground on the case is bad
I would check for voltage from the motor case to a good known ground
rabler gave a list of checks to do which is good advice
I assumed this problem occured after hooking up the DC drive but
It might have been present before you bought it
Other wiring on the lathe maybe at fault so work carefully

So I just double checked. I'm getting 38 volts from a screw that goes through the motor case to the ground wire/screw on the controller. I checked the pot and I'm not actually getting anything there, but the pot knob is plastic so that makes sense. Also, the case is anodized so I'm not getting anything when probing the case itself, but everything else on the surface of the controller (including the power switch, the mounting screws, and the little cap that fills the hole where the FBR switch goes are all energized - reading the same 38 volts. I must have brushed something else on the face of the controller when I originally felt the voltage.

 

[Nigel123]

So I just double checked. I'm getting 38 volts from a screw that goes through the motor case to the ground wire/screw on the controller. I checked the pot and I'm not actually getting anything there, but the pot knob is plastic so that makes sense. Also, the case is anodized so I'm not getting anything when probing the case itself, but everything else on the surface of the controller (including the power switch, the mounting screws, and the little cap that fills the hole where the FBR switch goes are all energized - reading the same 38 volts. I must have brushed something else on the face of the controller when I originally felt the voltage.

This is strange
The switch and screws mount on the same plate as the ground screw so no voltage should show
With the power off check ohm reading from the plate where the switch is mounted to ground
should be close to zero ohms