Posted by Neil Wyatt on 19/02/2014 11:25:19:
There are four ways of 'stopping' an inverter powered motor.
1 An e-stop button before the inverter. This makes the motor coast to a stop and kills all power. It can damage the inverter, but is 100% guareanteed to cut all power.
2 Use the coast to stop function of the inverter. This works exactly as an e-stop but leave the inverter live. It can be wired to work from a 'break' switch so existing e-stop buttons can be used as well as limit switches etc. I have impemented this and it works. The stop is very sudden with my setup.
3 Fit a resistive brake to the inverter. This will more or less short the motor and it will stop dead. This is MUCH faster than with an e-stop, especially for machines with a lot of rotational inertia. It will leave the inverter itself live. This can be wired to be operated by e-stop and limit switches. I have not implemented this.
4 Use normal soft-stop buttons. This causes the motor to slow down gently to a stop over a preset period.
My approach is to use 4 for normal working as gentle stop/start helps avoid motor overheating and is less fraught. I use approach 2 for e-stop as it is very fast with my machine. The cautious would take approach 1 and in indiustry i'm sure they would use number 4 – active braking – to get the fastest stop possible.
Neil
Don't forget DC Injection Braking, an option available on many good drives which although not as fast as using a braking resistor is still quick enough to require positive retention on screw-on chucks to ensure they don't go on safari