Hi,

Thanks for all your suggestions..

The motor is single phase AC (240V) rated 1.5HP.

I can do the switching at zero crossing but I think the relay's response
time might have an impact here. (coil energising time, mechanical
delay..etc) This response time might vary for every relay and the problem
might show up is some of the boards. (board to board variation)

I tried adding a few more caps (470uF and a 220uF) but still can't get it
any better.

The power supply for the PIC and the relay is not 100% isolated. They are
inductively coupled. The mains transformer is center tapped. I am using the
first half of the secondary winding for the PIC and the other half for
driving the relays. This is done for cost / enclosure space  reasons. May be
I should try isolating this. Your ideas are welcome.

Thanks,
Ismail


On 4/8/06, Vasile Surducan <piclist9@gmail.com> wrote:
>
> On 4/7/06, Mohamed Ismail Bari <izmile@gmail.com> wrote:
> > Hi guys,
> >
> > I have designed a circuit with a relay to turn ON/OFF a 1.5HP motor
> (250V
> > AC). The relay is energised with 6V and is wired to an opto isolator
> > (MCT2E). The other side of the isolator is driven by PIC16F877. The
> problem
> > is - when the relay is energised, the relay contact archs. This happens
> may
> > be once in 5 times. "Sometimes" due to the arching the PIC gets reset.
> > (Eventhough there is opto isolation!)
> >
> > I was thinking of trying a snubber but never seen one used for AC
> circuits.
> > Furthermore, the load is inductive and it might cause damage to the
> > capacitors. Any ideas on how to realiabily control it?
>
> Let's go backward: 1HP = 746W (always talking in metric units system,
> that's why have been invented)
> So 1.5HP = 1.1kW
> If you're runing on one phase 220V + nul is one way to solve the
> problem (because your motor circuit should have a false phase
> generation using either capacitors either inductors), if you're using
> a tri-phase supply would be another way.
> So what kind of motor do you have?
>
> greetings,
> Vasile
>
> >
> > Thanks,
> > Ismail
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist