Thermal Overload Device w/ VFD and PLC
Thermal Overload Device w/ VFD and PLC
(OP)
Good Day,
My guestion is: can you use a thermal overlaod relay without subsequent contactors on the load side of a vfd? Then use the signal from the relay to a plc to shut down the system. The system being multible motors with acme screws in a lift (non-personnel) application.
My guestion is: can you use a thermal overlaod relay without subsequent contactors on the load side of a vfd? Then use the signal from the relay to a plc to shut down the system. The system being multible motors with acme screws in a lift (non-personnel) application.





RE: Thermal Overload Device w/ VFD and PLC
But the overload protection built into the VFD is generally going to be better than an external OL relay that was not designed for the harmonic current and PWM waveform it will be seeing.
There will be some VFD experts along shortly with better opinions.
RE: Thermal Overload Device w/ VFD and PLC
RE: Thermal Overload Device w/ VFD and PLC
You should use external thermal overload devices into a VFD when using multiple motors. The in-built 'electronic' thermal overload in most VFD's will not be functional in this case as the drive will not know which motor is overloaded.
You should be able to connect all therm-overloads into the VFD to shut down the system if one of the motors goes into overload. Presumably you would want the complete system to shut down if just one motor trips (sometimes you wouldn't want this). So contactors on the output should not be necessary, use the logic into the drive to provide a shut down assuming the drive can do this. Some drives will provide a NC circuit that can be esed as an 'external alarm' and register a specific fault so that you know what has caused the drive to shut down.
RE: Thermal Overload Device w/ VFD and PLC
RE: Thermal Overload Device w/ VFD and PLC
RE: Thermal Overload Device w/ VFD and PLC
RE: Thermal Overload Device w/ VFD and PLC
RE: Thermal Overload Device w/ VFD and PLC
I will rap my brain around your comments.
As far as the last few comments, I will incorporate them into the design. Make's good sence.
Thanks again.
RE: Thermal Overload Device w/ VFD and PLC