On 4/8/06, Mohamed Ismail Bari <izmile@gmail.com> wrote:
> Hi,
>
> Thanks for all your suggestions..
>
> The motor is single phase AC (240V) rated 1.5HP.

Not enough informations. It has brushes or it's squirell type ?
Do you have any huge capacitors near motor ?
If it's with brushes you have to dig much more...

greetings,
Vasile


>
> 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
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