Internet PLC Forum

General => Technical support => Topic started by: jonsoderberg on November 22, 2003, 03:05:40 PM

Title: md-exp1616r relay
Post by: jonsoderberg on November 22, 2003, 03:05:40 PM

I need to switch on a 120vac relay control loop on a soft start thyristor board.  Will I have to install a varistor/ bypass diode used for induction loads?? The load is minimal as its just a control circuit.

Title: Re: md-exp1616r relay
Post by: support on November 24, 2003, 01:40:03 PM

What is the coil voltage? Is it a DC 24V or AC voltage? If it is DC 24V coil and driven by the solid state output from the PLC then no need to add diode as there is built-in flyback diode. But if you use relay output of the PLC then you should add a diode to absorb the inductive kick.

However, if your coil is 120VAC and you are using the PLC's relay output (that's the only choice) then you can use a varistor to absorb the inductive spike. But if the current to drive the coil is low then use of varistor is not necessary.