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David Beierl wrote:
<blockquote cite="mid:4bcb868a.292ce50a.39f5.ffffaea6@mx.google.com"
 type="cite">At 11:39 AM 4/18/2010, Janne Ruohom&auml;ki wrote:
  <br>
  <blockquote type="cite">Isn't this something what the diodes
installed in parallel with the
    <br>
relay coil are for, in transistor controlled circuits ?
    <br>
  </blockquote>
  <br>
Hi Yanne -- yes, that's what the diode is for.&nbsp; It's reverse biased
against the coil drive voltage, so it doesn't short out the coil; but
when the circuit opens the collapsing magnetic field in the coil drives
its input terminal negative trying to keep the current flowing.&nbsp; The
diode is then forward biased and discharges most of the stored energy
in the coil.
  <br>
  <br>
A capacitor would lower the voltage of the spike, but store the coil
energy which would then pass back and forth, stored as an electrical
field in the cap and as a magnetic field in the coil as it gradually
used up the energy.&nbsp; This is how the old Kettering (points-type)
ignition system works, and why the points burn up rapidly if the
capacitor fails open or is missing.
  <br>
  <br>
Yours,
  <br>
David <br>
</blockquote>
<font size="-1">David. The whole thing (above). Well-written. Probably
too technical for most -- they will blank well before the second
paragraph -- but tight and accurate. There's a lot to unwind in those
sentences. </font><br>
<br>
<pre class="moz-signature" cols="72">--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR

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