Can I use the PLC output to directly control a magnetic contactor?
Yes, you can directly connect a PLC output to the coil of a contactor to control it, but there are some important considerations:
It needs to vary the voltage of the Contactor Coil and also has two types of PLC Outputs.
The normal voltage of the contactor coil has to be the same as the output voltage of the PLC.
Ex: Available power range are 24V DC or 120/240V AC.
In the case of the PLC output, sufficient current supply must be given to the contactor coil. It should be noted that the presented reference contactor coils are designed for a typical current consumption of 0. 5-2A.
The output module in use should therefore be PLC’s Output module that is rated for this load.
Wiring Diagram
The Positive terminal of the plc output has to be connected to the A1 terminal of the contactor coil.
Join the A2 terminal of the coil to the negative side of the control voltage whether as the DC common in a linear supply or AC neutral.
Pipe the three phase power to the L1, L2, L3 of the contactor terminals.
Screw the T1, T2, T3 Contact terminals to motor terminal.
An auxiliary contact (NO) may be taken from the contactor to PLC input in order to inform a PLC that it had energized.
Function
Eventually contactors can create electrical noise when they are in the process of energizing or de-energizing.
It is advised that a snubber circuit or an arc suppressor should be connected across the coil to avoid the problems on the PLC input.
Contactors are used with a motor horsepower, which is limited according to the manufacturer. Make sure that the contactor used is capable of handling the motor used so as to avoid breakdowns.
In order to protect the motor from any over current situation an overload relay should used. The overload can be connected in series with coil of the contactor or it can be connected with PLC input.
Therefore, you can directly control a contactor with PLC output signal if the voltage and current ratings of contactor will match with the PLC output.
As long as the contactor wiring is correct and the issue of electrical noise is taken care of, along with proper contactor sizing and overload protection, you should not encounter any problems.
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