Santos

Hey guys, new member here.

I have a flocculator control panel run by an ASI Robicon 454GT VFD drive. This drive runs 3 flocculator motors.

Thursday (raining and windy)
One of the doors to our VFD panels opened and got wet. The front board of the VFD was wet along with the contactor and 3 starters. I immediately shut the power off, hand dried the most I could and connected a heat lamp and let it sit overnight hoping it would dry.

Friday
Everything looked pretty dry, no signs of wetness to the visible eye. Turned the power on and VFD display doesn't come on. I know for sure the VFD is going to need some parts replaced but that is not my concern at this moment.

We have the option of bypassing the vfd and running straight across the line but when I do that and start one of the motors, I get a humming noise coming from the main contactor that feeds the 3 starters (only 1 starter is sucked in). Motor runs fine. Amp readings are ok (2.4, 2.7, and 3.4). Let it run for about 10 minutes and shut it off.

Turn the next one on and now the humming noise is louder. This time I notice that both the starter and the main contactor are making the noise. Again, this motor runs fine. Amp readings are (3.1, 3.2, 3.6). Let it run for about 10 minutes and shut it off.

I checked the cabinet right next to it (same setup) and it was not making this noise

Why are they making this noise?

JTMEYER

Any electromagnet (starter coil) working on A/C power would hum at the frequncy of the A/C power applied without a small portion called the shading coil. It holds the core in place while the main magnetic feild falls with the voltage. If the laminated core has been wet it will rust, disrupting the magnetic feild, causing the hum. At least thats how it was explained to me. I have removed the rusty laminates from old starters and wire brushed them back shiny and stopped the humming. However, any water left in the starter may be causing problems as well. I'm sure someone else will explain this a little better if you wait a while.

MDShunk

I've never heard of running a floc stirrer on a VFD, but that's another matter. I think it's safe to say that since the "regular" starters have not run in so long, their either rusted (common in waste treatment) or were never wired properly in the first place. Confirm proper voltage going to each starter coil. If the proper voltage is present, dismantle each offending starter coil and clean it with a brass-bristle toothbrush.

__________________
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John Valdes

Thats right. These are bypass contactors and may have not been used for years. Take them apart and clean them up.

ATSMAN

The noise (hum) is caused my the 60HZ magnetic field of the contactor coil vibrating the armature (core.) Some noise is normal.
Very loud noise can be caused by dirt, grease, rust on the core surfaces
that mate when the contactor is closed. Shut the unit down and clean the two surfaces with Scotchbrite or fine sandpaper and see if that helps. Run the unit and take a stick and push on the contactor forcing it in the closed position. If the noise decreases then the surfaces are not making good contact. If it gets real bad, running the motor for a long time may overheat the contactor and burn it up. Contactor may have to be replaced.

Tony