Thank guys for your replies .Some of them i have to study first

Let me make some things clear about the circuit and values chosen

1. I've measured turn-on , turn-off delay at 3.3 ms for the driver relay.All
results are
after calculating this delay .So what is see on the scope is at the moment
i'm explaining
2. the arc is across the driver relay .The power board is inside a control
unit box so
i have to leave with small distances and cpu disturbances.Its actually a
microcontroller
having the problem .Driver relay contact current rating is 5A at 220V
..Power relay coil is rated is 6
watts consumption at 220V.
3. Using large value capacitors over 33 nf was causing sometimes latch of
the power relay so i have
value limitation here
4. The capacitors i've chosen are X2 self healing 275VAC. With no ZC control
they are blown
to 0 nf value (some of them) after 10-12 months of operation.
5. I don't have the space or budget to use large sized capacitors rated at
higher voltages or SSR .
The idea was to use ZC to avoid using expensive and large size protection
snubber
So the question is .

Does the relay On/OFF time differs with time .If it's 10% it's not a
problem since again
the arc will not be so high .Since its the current break that causes the
arc i must switch off at Peak of the
ac voltage .This is what my reading confirmed .In this case switching a
resistive load must i change the driver
algorithm ???

Any helpful comments will be apreciated


"Fred Bloggs" wrote in message
...


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 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 mains zero crossing and fire the
driver relay at an angle i choose .
From what i read the best point to switch off the power relay is at zero
crossing . I did that and i show a large spike up to 1 KV at the relay
contact followed by a decaying 500hz waveform to 0 volts . After some
experimentation the best point came exactly when switching off at the
peak of the mains voltage .At this point there is smooth decaying
waveform to 0 volt after 5 periods of 500 HZ but no overshoot. The
relay presents no arcing. If i remove the snubber and make the
experiment the best place to switch is zero crossing but i also see large
SHARP spikes up to 500 Volts Peak.

WTF are you talking about, the arc across the driver relay contacts or the
arc across the "large 220 volt AC relay?" It gets reall aggrvating when
you don't make yourself clear...

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 spikes can harm the X2 capacitor i'm using so
what is the best operating practise ?.


Your whole idea is dumb anyway, you're working with relays and pull-in
times that are a substantial fraction of line voltage period and vary with
age and operating conditions. Snubbers are spedc'd around worst case and
not timing. They are only an approximation, the inductance of the "large
220 volt AC relay" is non-linear and may differ by 10:1 between pulled in
and out. And some relays require an arc for contact longevity. You let the
relay manufacturer take care of the switching and just work out a better
12V drive circuit immune to the dV/dt current from that HV ringing,
usually means lower impedance drive.