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?
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Soft Start
- Thread starter bowmaned
- Start date
It chops the incoming ac wave to effectively act as a reduced voltage starter. Current into the motor is reduced and this reduces the voltage drop caused by the motor starting.
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.
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.
Are you saying that it does NOT reduce the voltage to your motor right now, as in you are not sure if it is working? If that is the case, how are you determining this? A fast acting non-RMS digital multimeter may not allow reading of the true RMS voltage going to the motor. You need to use a true RMS reading voltmeter or an old iron vane analog meter.
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.
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.
Or, to say it another way, your ability to soft start is entirely determined by the breakaway torque of the load. If the load requires high torque to start then the motor will require high current to start, as well. Just that simple.
Unless you install an inverter. Then there is only the amps required to develop the synchronous torque which is generally much less.
Unless you install an inverter. Then there is only the amps required to develop the synchronous torque which is generally much less.
controlsdude
Electrical
SMC has a boost torque feature, if starting torque is the issue, just remember on an SMC, more torque less speed.
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.
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.
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