Relay connected to PIC fluctuating

[Aditya070390]

Hai everyone!!

I have connected a 30amps relay to GP4 of PIC12F508 through a bc547 transistor.The code is written to turn it on at certain input condition and turn it off at some condition. The logic is working fine. The relay turns-off perfectly but while turning ON it switches ON for a fraction of a second and switches OFF after a delay of nearly 1 0r 2 seconds it repeats lik this again and again.finally after 4 or 5 spikes like this, it rests in ON condition. I have attached the part of that code and also the circuit,i dont know where am wrong.Please help me out.

        bsf GPIO,4
	nop
	nop
	call	 Delay_30;delay of 30 seconds..
	call   	 Scan
	btfss	 currinput,1
	goto	 Full
	btfsc	 currinput,2
	goto	 run
	goto	 Back

 

[jayanth.devarayanadurga]

Use a capacitor across relay coil to stop relay chattering.

 

[paulfjujo]

hello


if you are sure about the software....
does it works fine with a Rsistor+led instead of the relay ?


Do you have a load driven by the relay contact ? or just the coil ?
because you can also get spike from the load , if 30 Amps in the driven circuit.
add RC accross contact.

You better have to add a resitor between Base and ground to fix the Vbe potential
when without commande from the PIC
and get the transistor in blocage status. .. 12V on collecteur , no IC current
This renforce noise immunity from spike comming from the coil.
and capacitor ,if you are not hurry to put relay ON ..
less DV/DT => less disturbance