Electromagnetic Interference when Actuating a Contactor 1

[gustavosilvano]

Hello there!

I've made an application at my factory where I had to assemble an electrical panel. There we have two contactor that is disposed near a PLC. I've noticed that when I actuate the contactor, it creates an interference with the PLC. In fact, when I unplug the cable that connects the coil of the actuator with the output of the PLC, I don't have this interference.

The interference is noticed because I have a timer connected directly with one input. When the contactor activates, the input kind of deactivate, resulting in the timer reseting.

The coil of the contactor is 24V DC.

Do you guys had gone through something similar? Is there an easy solution?

Best regards.

Gustavo

 

[waross]

Back in the day of Solid State Logic Control, some systems were sensitive to a step change in voltage.
If for some reason there was a step change in the power supply voltage, some or all of the memories, flip-flops, timers and sealed Ands would reset.
Do you have a capacitor across the contactor coil?
If so, it may be causing a transient voltage drop that is resetting the counter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Compositepro]

Do you get sparking at the contacts? Spark gaps were the original radio transmitters. A small capacitor across the contacts can suppress the sparking. Try disconnecting the load from the contactor to determine if the problem is due to the coil or the contacts.

 

[itsmoked]

That contactor had better have a freewheeling diode across its coil!

You also may be mixing the PLC field-side power wiring with the PLC CPU side power. They are always to be strictly isolated in all respects. If something on the field side is causing disruptions to the CPU it sounds like they're sharing power - which is asking for problems like this. Correct design requires two separate power supplies.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

For whatever brand of contactor you used, go to the mfr and order a coil surge suppressor for it based on your control voltage. You can "roll your own" too, but the ones they make will be designed to attach to the contractor very easily.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Peter_nominal]

Hey Gustavo,
You might want to look into high current DC output solid state relays, they do not interfere.

http://www.nominalcontrols.com