So one of our plants has been trying to upgrade the VFDs in one of their machines after some shorted wiring allegedly ruined a couple of the old ones. They were struggling as they are not electricians but plant maintenance guys so over the course of a couple weeks I was consulted by phone several times. The machine was designed with several 2hp SEW Eurodrive gearmotors and Hitachi SJ200 drives about 20 years ago, brakes powered by a separate circuit. Upgrading to Hitachi WJ200 drives. A couple of the motors were replaced at some point with Baldor brake motors and various gearboxes from different manufacturers.
Anyway, to make a long story short, the drives that were feeding the Baldor brake motors would trip after a few seconds. I don't remember the specific fault. They were having some other tangentially related issues as well so I was asked to go there and get the machine running again. Most of the issues were mis-programmed drives easily solved. I left the two tripping drives for last. Checked all parameters, no improvement so I open the conduit box on one motor to find only four wires, T1, 2, 3 and ground with the brake connected directly from there. Huh? Checked the other end of the LFMC.....yup, six wires going in. So six conductors in, four out, both motors identical. I correctly wired the brakes back to their original circuits, everything works like it should.
To say nothing of the wires left hanging in the conduit, it has always been my understanding that there is no way a drive can reliably power a brake. I got to the airport and opened up my computer, checked our purchasing records. Those motors were bought in 2010 and were working just fine off of the SJ200 drives for probably that whole time. Those motors had clearly not been opened in a long time. I asked one of the techs who admitted to installing them that way all those years ago, claims it was the only way he could get it to work.
Can anyone explain this?
Anyway, to make a long story short, the drives that were feeding the Baldor brake motors would trip after a few seconds. I don't remember the specific fault. They were having some other tangentially related issues as well so I was asked to go there and get the machine running again. Most of the issues were mis-programmed drives easily solved. I left the two tripping drives for last. Checked all parameters, no improvement so I open the conduit box on one motor to find only four wires, T1, 2, 3 and ground with the brake connected directly from there. Huh? Checked the other end of the LFMC.....yup, six wires going in. So six conductors in, four out, both motors identical. I correctly wired the brakes back to their original circuits, everything works like it should.
To say nothing of the wires left hanging in the conduit, it has always been my understanding that there is no way a drive can reliably power a brake. I got to the airport and opened up my computer, checked our purchasing records. Those motors were bought in 2010 and were working just fine off of the SJ200 drives for probably that whole time. Those motors had clearly not been opened in a long time. I asked one of the techs who admitted to installing them that way all those years ago, claims it was the only way he could get it to work.
Can anyone explain this?