Soft Start
Soft Start
(OP)
After the installation of a new grain leg on our country elevator, the larger 100 hp motor has a greater start up demand on our lines and dims the lights of surrounding houses. We're installing an Allen-Bradley SMC Flex Controller for the soft start feature. It doesn't reduce voltage to initiate the soft start and I didn't know how it works. Any help, does it effect the frequency or what?





RE: Soft Start
But starting torque is also reduced, so if this is running a bucket elevator or screw conveyor, you need to make sure it provides adequate starting torque to accelerate the load. You may not get as much benefit from this as you expect if your starting torque requirements are high.
RE: Soft Start
Other than that, if the device seems to be working properly but you are not seeing a reduced voltage, it is probably set too high (or the ramp time is too short). This would most likely be explained by what dpc posted above. At setup, someone may have discovered that reducing the torque cause the motor to stall, so they kept increasing initial torque until it no longer did. But in increasing it, they essentially removed the soft start effect altogether! That would be an example of someone not understanding the limitations of soft starters.
If what dpc said is the case, a VFD may be your only choice. By altering both the frequency AND the voltage at the same time, the motor can be slowly started, but with full torque from the outset.
RE: Soft Start
Unless you install an inverter. Then there is only the amps required to develop the synchronous torque which is generally much less.
RE: Soft Start
I have used the SMC3 and these were simple devices compared to your soft start flex controller. These used dip switch settings on the front of the smc. Not sure what it is on yours?
Just look at the documentation that came with the soft start flex controller.