Hi
im using a microcontroller for On and Off AC (230V) motor (its a fuel pump actually ) , the AC motor control through a AC contactor ( contactor connect through 5v relay and 5v relay interface to microcontroller through optocoupler for additional protection) , but when the motor ON and OFF randomly the microcontroller freeze , i made some decoupling capacitor and snubber circuits , but no one was successful. can anybody help me to solve this issue.
Thanks

 

Do you have a R/C snubber across the contactor coil?
In the case of an AC coil this can be the cause, as I had the same condition, the snubber corrected it.
The better option is a DC coil with a rectifier across it.

 

Do you have a R/C snubber across the contactor coil?
In the case of an AC coil this can be the cause, as I had the same condition, the snubber corrected it.
The better option is a DC coil with a rectifier across it.

yes , i already tried with RC/snubber , it was not successful in my case , there is a RS485 chip to read the level sensor , when this freezing happens MAX485 chip also burnt due to EMF.

 

Did you try bonding the DC supply commons to earth GND?
I assume your AC is not isolated?
Do you have a earth referenced supply where you are?

 

Can you post a schematic of your setup. There's no way a MAX485 should be 'burning up'.

 

There are two main ways this could happen. When the contactor opens or closes, there will be a large voltage transient generated on the AC supply.
If you are using a mains fed power supply for the microprocessor, the interference on the AC line could be getting through the power supply and resetting the circuit.
The second way is by means of radiation from the power conductors. Long unshielded wires between the motor and sensing circuit could pick up the EMI from the switching transients and cause problems.