How To Protect Digital Circuit From Inductive Kicks

Hi .. Everyone
I am Using Micro controller Based Digital Circuit To Drive Contactor For AC motors and Electrical Appliance.
When Contactor is Get Energies then Micro controller and whole circuit is get hang or out of order.
Plese Guide How To over come the problem in reliable way.

How are you driving the AC motor from the micro-controller? What does your interface look like?

Hi .. Its Like That ..

|MCU |---->>>|Opto-Coupler|---->>>|Relay Driver Circuit|---->>>|Relay|---->>>| AC Contactor |


For MCU and Relay i use different power supply with different Two Transformers
The Power Supply for MCU and Optocoupler is +5v.
For Relay +12v.

Did you include a diode over your relays? It should be included to prevent inductive kickback.

yes I have used ...in reverse direction ...
but still response is not obtained

Is your MCU EM-shielded from the AC part?
Don't use the same ground plane for different parts of your circuit.

"Don't use the same ground plane for different parts of your circuit"

can u explain it ..
u mean same ac source point .. ??

Try to keep analog and digital circuits separated. Try to minimize loop areas in your circuits, this will keep down
inductive coupling in your circuits and thus reduce the noise.

Hope I am being helpful. You can upload circuits/photos/layouts etc. then more of us can see your circuit and help,
solve your problem.

Is your problem that the microcontroller stops when it switches the relay on or off?

Yes Micro-controller is get out of order and change there input and output pin state and sometime stop working ..

Try placing a capacitor over the Vdd and gnd of the micro.

Amardeep said:

Yes Micro-controller is get out of order and change there input and output pin state and sometime stop working ..

Click to expand...

From your description and without a schematic, you say your microcontroller switches an ac contactor on and off. The contactor's switch has an inductive load on it: a motor. But you don't mention any zero-crossing circuitry.

* Your posts are a big too vague for me to be sure this is the problem you're having. But if it is... *

Even with a suppressor across the contacts, I have seen then opening of a relay driving an ac motor cause a nearby microprocessor to stop executing instructions and freeze. Our relay had around 80V ac across its contacts when it opened. The microprocessor was a foot away and on the other side of an earthed 4mm-thick large steel plate. This processor crashed often in all test six machines during a major testing operation. We recreated the problem with a static discharge gun. We solved it in the cheapest and most reliable way for us. We added a Solid State Relay (SSR) with zero-crossing turn-off in series with our ac relay and ac induction motor. Control logic switched on by enabling the relay, waiting longer than the relay's contact travel time then enabling the SSR; we switched off by disabling the SSR, waiting 20 ms (50Hz half-wave is 10ms, adding tolerances and margin) then disabling the relay.

Baas Rietrot asked if you had EM-shielded you ac section from the microcontroller section - please look into this. Try moving the microcontroller circuit far away from the relay/contactor circuit. If they're all on the same PCB, you'll have difficulties. If they're separated by wires, extend them and move them six feet apart and try it.

Let us know how you get on. Please post a schematic with your next post

Here is an Video In which same effect is seen without contactor and AC motor .. Please watch this video ..

https://www.youtube.com/watch?v=UM4uYLGUBDY&feature=youtu.be

In my view you need to try free wheeling diodes to opto-couple output terminal ....second is try using snubber circuit for high voltage rate of change of voltage problems...

refer the following -
**broken link removed**
**broken link removed**
http://www.irf.com/technical-info/designtp/tpap-5.pdf


I hope your problem will be solved with this

Good Luck

@TonyM You mean On-off switching of contactor with ZCD output at zero level of AC voltage will avoid suppressors .. and large distance between Micro controller and load is necessary.

Referring to the initial post, the main problem is created by contact arcing of the power contactors rather than inductive kickback of relay coils. Inductance of e.g. AC motors will increase contact arcing at switch-off, but the problems may be present with large resistive loads as well.

There a basically three ways to reduce contactor related interferences:

- reduce contact arcing, e.g. by snubbers or varistors. It's not common or suitable for large (kW range) contactors.

- separation of logic/processor and power interface circuits. According to your reports, you have optocouplers providing the separation. To be effective, you also need separated grounds and power supplies. Without inspecting your actual setup, I won't guess about effective implementation in your ciruit.

- "hardening" of the logic/processor circuit against interferences. Involves solid ground planes or at least meshed ground nets for the processor board, power supply filtering with surge arrestors, usage of common mode chokes for external cables, input filters for external input signals, protection (z-diodes, varistors) for output signals.

Amardeep said:

@TonyM You mean On-off switching of contactor with ZCD output at zero level of AC voltage will avoid suppressors .. and large distance between Micro controller and load is necessary.

Click to expand...

Referring only to the problem we had, the symptoms we saw and how we solved it...

As you know, a mechanical relay is far too slow to switch on and off at zero-crossing. So we used an SSR in series with our ac motor. Our ac load current was only a few amps so we could do this economically. As you're using an ac contactor for your ac load, instead of a relay, what is your maximum ac load current? An SSR may be impractical or too expensive anyway, depending on how large the load current is.

We found that suppression wouldn't stop the problem in our application and neither did our free large earthed metal screen. Screening would have been costly for us - we chose to spend less money on an SSR and control circuitry. This had the benefit of designing out our problem, rather than letting it happen and trying to get rid of it again. We then made 5000/year of this office machine for at least ten years with no problems.

You may have a completely different problem to ours. I suggested distancing the microcontroller circuit from the ac switching circuit just as a *test* of this theory. But try it if you can and let us know how you get on. Good luck