"michael nikolaou" schreef in bericht
...
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



The best moment for switching off, highly depends on the load. As long as
the load is resistive, the zero crossing point of the voltage is best as
switching is done at minimum voltage and current. As soon as the load has a
reactive component, zero crossing of the voltage differs from zero crossing
of the current. It is the breaking of the current that causes the voltage
spikes.

petrus bitbyter