XPost: sci.electronics.basics, sci.electronics.components, sci.e   
   ectronics.design   
   From: jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net   
      
   michael nikolaou wrote:   
      
   > 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   
   >   
   WHen you say relay, I assume you mean a mechanical contact?   
      
     if so, It takes time for the contacts the release. If you turn it   
     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 .   
      Many contactors are fast but not fast enough to open before current   
   can get a charge going.   
       That's just my evaluation of what you're doing.   
      
      By you signaling to turn off the relay at a peak, the contactor will   
   most likely not open until it gets near the zero crossing point.   
      
      
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