TractorJeff
Well-known member
Neighbor got a 3 phase lathe, his son got an electrician to wire in a motor driven Converter. The lathe didn't seem to function, maybe from when it got damaged in shipping? Anyways I went down to look at it, found a wire loose on the motor connection of the Converter, easy fix.
Now the lathe would attempt to start but the starter contactor would drop out (chatter). I used the min/max feature on a Fluke 87 to capture the 3 phases when attempting to start the motor. A-B was 270v, A-C was 254v, B-C was 240v, when the contactor was pushed in manually the voltages dropped by a half on A-B and A-C phases while B-C stayed at 240v. Using this information I found the control transformer was wired across A-B causing the 120v to drop to 66v hence the coil chatter. Moving the one control wire from phase A to C allowed for the 120v to not drop under the motor startup load.
Now the lathe would attempt to start but the starter contactor would drop out (chatter). I used the min/max feature on a Fluke 87 to capture the 3 phases when attempting to start the motor. A-B was 270v, A-C was 254v, B-C was 240v, when the contactor was pushed in manually the voltages dropped by a half on A-B and A-C phases while B-C stayed at 240v. Using this information I found the control transformer was wired across A-B causing the 120v to drop to 66v hence the coil chatter. Moving the one control wire from phase A to C allowed for the 120v to not drop under the motor startup load.
