Solid state contactor???

[gerard]

Hi,

I am using the relays of a control panel to switch on a single phase contactor. This contactor then turns on a motor. The relays are 24V dc rated and inside this control panel there is electronic circuitry. I am worried that the back emf created by the contactor coil might damage the relays or even worse, damage the electronics inside the control panel. Would it be better to use a solid state single phase contactor rather than the conventional contactor to prevent this?

 

[pmac10]

i wouldnt bother, i dont know your exact apllication but i dont think the back emf produced by a collapsing 24v coil will cause your electronics much bother. if it helps you sleep better connect a diode in parallel and in opposition with the coil

 

[sbrown2]

Solid state relay - Wikipedia, the free encyclopedia

agree with the previous post in most cases. But check the application as above, I've never used solid state relays by calculation but by necessity.

Regards

 

[mechelec]

To prevent arcing accross contacts and to dissipate the back EMF safely a free wheeling diode is connected in parallel (anode on minus) to the coil. This way it doesn't conduct normally. When the coil is switched off, the voltage across the coil reverses to maintain the current's direction. Then the diode carries the current until the energy is consumed by the coil's inner resistance.

This can be used for DC only. For AC use resistor/capacitor (RC) network

 

[gerard]

Hi,

Thanks for that. I'm pretty sure these surge suppressors can be easily purchased so I will do as you say!!

Thanks for that.