I have had some occasions using a solid state relay to switch a large
contactor. We found that a random turn-on relay was as good as a zero
crossing turn-on (and cost a bit less too). Turn-off with a solid state
relay will be at the next zero *current* crossing regardless of the type of
SSR used. As to snubbing, I found that a snubber across the contactor's coil
was more significant than one across the SSR. A secondary snubber can be
applied across the SSR if still needed.

The main purpose of snubbing with a SSR is to control the slew rate and peak
voltage across the SSR's switching element (traic or scr) to keep it below
the point of causing a spurrious trigger/conduction cycle. You should also
be mindful that triacs are more sensitive to triggering in certain quadrants
and may lead to an asymetrical output conduction (aka a net DC component)
which can cause inductive loads to saturate.

Oppie

"michael nikolaou" wrote in message
...
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 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.
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 ?.

Any help will be appreciated

Michael