Hi people I need help.
I have a mill that has what looks like a KBIC-240 speed controller in it. Lately the mill motor has been playing up and getting really hot. Also when I try to run anything over 70% speed there is serious arcing coming from the motor's brushes the arcing lights up the roof of my workshop.
I took the motor into a motor specialist who told me that the armature was ok but it needed new bushes, needed the commutator to be skimmed etc. Long story short I finally got the motor back but the arcing is still there so I am feeling somewhat burnt at the moment.
I opened up the speed controller today and I cant seem to see anything wrong with it, I removed and tested the SCR's and they seem fine.
One thing that bothers me is that when I put the output of the controller on my oscilloscope I see that when I approach the 70% and above power figure the waveform has as much negative voltage on it as there is positive which concerns me. At lowest setting I have the normal wedge shaped waveform peaking at about 190V but the bottom of the wave drops to about -19V. At full power the positive wedge is still about 190V and wider, but there is a bottom almost square wave that is about -170V. I have been doing these tests with a 60W lightbulb connected to the output of the KBIC so this negative voltage is not back EMF from the motor.
There seems to be a few experienced people on this board when it comes to the KBIC controllers so I was hoping to bounce this off them. For starters is this waveform normal? If not where should I look on the board to fix it up.
I am currently living in South Africa so getting another controller is costly and will take time.
Thanks in advance
Anthony
I have a mill that has what looks like a KBIC-240 speed controller in it. Lately the mill motor has been playing up and getting really hot. Also when I try to run anything over 70% speed there is serious arcing coming from the motor's brushes the arcing lights up the roof of my workshop.
I took the motor into a motor specialist who told me that the armature was ok but it needed new bushes, needed the commutator to be skimmed etc. Long story short I finally got the motor back but the arcing is still there so I am feeling somewhat burnt at the moment.
I opened up the speed controller today and I cant seem to see anything wrong with it, I removed and tested the SCR's and they seem fine.
One thing that bothers me is that when I put the output of the controller on my oscilloscope I see that when I approach the 70% and above power figure the waveform has as much negative voltage on it as there is positive which concerns me. At lowest setting I have the normal wedge shaped waveform peaking at about 190V but the bottom of the wave drops to about -19V. At full power the positive wedge is still about 190V and wider, but there is a bottom almost square wave that is about -170V. I have been doing these tests with a 60W lightbulb connected to the output of the KBIC so this negative voltage is not back EMF from the motor.
There seems to be a few experienced people on this board when it comes to the KBIC controllers so I was hoping to bounce this off them. For starters is this waveform normal? If not where should I look on the board to fix it up.
I am currently living in South Africa so getting another controller is costly and will take time.
Thanks in advance
Anthony