> Hi
>
> > I have a 12 v relay driving an large 220 volt AC relay . Across the cont=
act
> of the driver relay i placed one RC snubber circut (27NF with 100 R
> > resisitor in series) to help with some spikes that were influencing the =
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 pre=
sents no
> arcing. =A0If i remove the snubber and make the experiment the best plac=
e to
> switch is zero crossing but i also see large SHARP spikes up to 500 Volt=
s
> Peak.
> > My question is
> > =A0The switching with snubber must be made at zero crossing or at the pe=
ak 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
>
> > =A0Michael
>
> WHen you say relay, I assume you mean a mechanical contact?
>
> =A0 if so, It takes time for the contacts the release. If you turn it
> =A0 off at what you detect as the zero crossing point, the contacts most
> likely will not actually release until some where in some mid point .
> =A0 =A0Many contactors are fast but not fast enough to open before current=
> can get a charge going.
> =A0 =A0 That's just my evaluation of what you're doing.
>
> =A0 =A0By you signaling to turn off the relay at a peak, the contactor wil=
l
most likely not open until it gets near the zero crossing point.
>
> --- =C1=F0=FC=EA=F1=F5=F8=E7 =EA=E5=E9=EC=DD=ED=EF=F5 =F3=E5 =F0=E1=F1=DC=
=E8=E5=F3=E7 -
> - =C5=EC=F6=DC=ED=E9=F3=E7 =EA=E5=E9=EC=DD=ED=EF=F5 =F3=E5 =F0=E1=F1=DC=E8=
=E5=F3=E7 -
I observe all signals with a scope . I see actually the "driver relay" signal .So all my observations about timing are correct . My notion was different though .I expected to turn off at zero crossing voltage and have no arc .Actualy when the transition happents at the peak of voltage then i see only a decaying waveform ,no overshoot, for which i suspect since i know the capacitor and measure the frequency one could calculate the total inductance value (cables+relay coil). Since its clear that V(emf)=3D-L*di/Dt as pointed out by your emails also then the correct point to switch off the driver relay is at peak voltage since current lags voltage by 90 deg in any inductor. Now i only have to find out how much can a relay type deviate from the measurements i have made. Thank's for all you help guys