>
>
>
>
> > Hi
>
> > I have a 12 v relay driving an large 220 volt AC relay . Across the
> > contact of the driver relay i placed one RC snubber circut (27NF with 10=
0
> R resisitor in series) to help with some spikes that were influencing th=
e
> low voltage driver circuits.
> > The driver circuit is able to detect =A0mains zero crossing and fire the=
> > driver relay at an angle i choose .
> > From what i read the best point =A0to switch off the power relay is at z=
ero
> crossing . I did that and i show a large spike up to 1 KV =A0at the rela=
y
> contact followed by a decaying 500hz waveform to 0 volts . After some
> > experimentation the best point came exactly when switching off at the pe=
ak
> of the mains voltage .At this point there is smooth decaying waveform =
=A0to
> 0 volt after 5 periods of =A0 =A0500 HZ =A0but no overshoot. The relay p=
resents
> no arcing. =A0If i remove the snubber and make the experiment the best p=
lace
> to switch is zero crossing but i also see large SHARP spikes up to 500
> > Volts Peak.
> > My question is
> > The switching with snubber must be made at zero crossing or at the peak =
of
> an ac voltage waveform ?
> > What is the behaviour of the circuit ?.
> > As i understand any large =A0spikes can harm the X2 capacitor i'm using =
so
> what is the best operating practise ?.
>
> > Any help will be appreciated
>
> > Michael
>
> Use a solid state releay and dont worry about it.
>
> Bob- Hide quoted text -
>
> - Show quoted text -
Right. If you have a resistive load for the final 220VAC load, a plain old solid state relay will work fine (be sure to heat-sink the SSR at about 1.5 watts per amp load). If you have an inductive load, you may want to spec a SSR made to switch these loads, which have back- to-back SCRs to eliminate the possibility of not being able to turn off the SSR).
If this is a class project, you won't lose any points by going for the simple solution, as long as it also happens to be the best one.
Good luck Chris