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Thread: VFD stopped working
03-19-2017, 08:18 PM #1
VFD stopped working
I recently got a Teco Westinghouse VFD for my surface grinder and wired it last weekend. Everything worked great for about 3 days, then I try to start the machine and the motor clicks but won't start. I didn't have time to look very closely then so I unplugged it and left it alone. I tried to start it a couple days later and I got an error from the VFD "OC-A" which means Overcurrent trip. I don't have any ideas to try to resolve this. Is there something wrong with the VFD or my wiring?
The motor is a 220v 3/4hp 3 phase 3450rpm and the vfd is a 1hp 110v input, 3 phase 220v output.
03-19-2017, 08:37 PM #2
Disconnect the output wires from the unit. Turn on and make it start.
If it does NOT do the OC, then check your wires. Odds are there is a short from phase A to earth.
If it DOES do the OC, then look carefully for any stray wire strands inside, shake it out, and try again. If still does OC, it is as dead as Kelsey's nuts, so check your warranty.
03-20-2017, 01:44 PM #3
Other than that, your advice is dead on. Isolate the problem first to the VFD or the motor circuit. If the motor is unwired from the VFD and the fault persists, a transistor is fried and the VFD is a door stop.
(I had to look up "Kelsey's nuts", funny! I did some work at a Kelsey Hays wheel factory nearby in the late 70s, it's the same Kelsey. I however had never heard that expression before. Apparently it was a favorite of Tricky Dick Nixon back in the day, but he twisted the original meaning of "Tighter than Kelsey's nuts", referencing the lug nuts of his wheels. His saying "Deader than Kelsey's nuts" could only refer to an anatomical reference..., but he was the POTUS so I guess nobody argued the point with him!)
03-20-2017, 01:57 PM #4
yeah I did assume it was a phase reference. Plausible, useful, apparently not true.
I guess the ID as accel, etc could be useful, I'd suspect the phase ID to be more so, and perfectly possible to do. I figure operator would know what it was doing, but I suppose for an unattended conveyor, etc, it might not be otherwise obvious.
picked up the saying from a boss long ago.
03-20-2017, 02:25 PM #5
03-20-2017, 02:45 PM #6
I have a Teco that wakes up cranky sometimes. I'll get an over-load fault one day and not the next. When I get the fault, I have to increase the accel. time to get the motor to start. Some days 1 second is good, other days it takes 3 seconds. I am sure one day it will not start at all. I keep a spare.
03-20-2017, 06:19 PM #7
03-20-2017, 07:17 PM #8
03-20-2017, 09:03 PM #9
I can get the over-current fault when I try to start the lathe the first time in the morning. I will reset the VFD without changing any parameters. The lathe will start on the next try and be fine for the rest of the day.
I don't want to hijack this thread. I suspect the VFD as being faulty since this is the unit that got crunched about 4 years ago when the lathe fell on it.
03-20-2017, 09:47 PM #10
To the OP: Can you try spinning the grinding wheel manually in the correct direction, then engaging the VFD (with your other hand behind your back )? (Not as an ongoing operational mode, but for diagnostic purposes.)