On Feb 26, 7:14*am, "sycochkn" wrote:
"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

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