ac 3 phase motor spikes with uC

[garg29]

Dear friends,
i'm working on a project in which i have to run a motor with a 89c51 microcontroller. the microcontroller counts the rotations on 4 digit display. i'm using a 12v relay. when the realy starts the motor the microcontroller gets reset or hangs up. Please help me. thanku

 

[Nigel Goodwin]

Unless you post the complete circuit, with power supply, decoupling capacitors etc, we don't know how your circuit is already designed to prevent it?. I'm presuming you have a diode across the relay coil?.

 

[garg29]

thanks for replying. i have already put a diode 1n4007 across the relay. i think when the motor starts there is a mains voltage drop for a second, which causes the microcontroller to hang up.
i have put 0.1uf 250 volts capacitor"s" across the power supply and input pins of microcontroller, but still no use

 

[pop]

One suggestion would be to have a delayed power-on the microcontroller so that it turns on after some time during which the motor has finished starting up.
Anyway like Nigel said it be good if you post your schematic and also tell us what kind of motor (type and power rating) are you using.

 

[garg29]

thanks for replying. i have to run a 3-phase 220 volt A.C and 2 hp, motor.
i have to start the motor from microncontroller-relay interface. please suggest any solution

 

[Nigel Goodwin]

thanks for replying. i have to run a 3-phase 220 volt A.C and 2 hp, motor.
i have to start the motor from microncontroller-relay interface. please suggest any solution

As we've already said, post your circuit and we can make suggestions.