Noise problem

[dginbuffalo]

Hello- i have 200Hp compressor that is operated with a FW Murphy controller. As the unit ramps to speed, the input lights start to flicker and the whole unit goes down annd into alarm. The inputs are tied to ground to complete their circuit. This machine ran for years with no problems. We also burned out 2 controllers in the last 8 months and now can't get the machine to ramp to speed without tripping. the 24V supply has been changed and no fix. Also put a Fluke 87 on Min hold and it seems stable through this occurence. Seems like a ground problem-any ideas??

 

[Mickey]

Is this Murphy controller skid mounted along with the compressor? High vibration?

Get your screw driver out and check all connections for tightness.

 

[dginbuffalo]

yes-skid mounted-checked all connections.

 

[Fropitar]

Is there a ground running back to the electrical distribution panel? I know a lot of people love to add a ground rods for individual pieces of equipment. However, creating a difference in potential like that (a ground loop), you can have another piece of equipment in the facility using your compressors ground, and perhaps it is effecting your controller?


Had this problem a number of years ago with a company that had a DC speed control that would go out every 2 months, and they'd replace it with a new one. Turns out there was a ground loop, and a small heating element in another piece of equipment was using that path to leak current to ground, somehow it was effecting the speed controller.

This most likely isn't your problem, but I figured I'd throw my 2 cents in.

Best of luck! Let us know what you find.

 

[dginbuffalo]

Thanks for the replies. it turned out to be loose RTD wiring inside the head that was messing with the 24V. This in turn was affecting the controller performance. Weird part was the 24V wer enever sagging? O well-it's fixed and i'll store that one in the brain somewhere!