I think "obscure egg-headery" was the phrase you were searching for, Rocky.
: )

 

Cya,

Robert

 

 

From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Mike Rocket J Squirrel
Sent: Sunday, April 18, 2010 7:13 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: The alternator issue

 

David Beierl wrote: 

At 11:39 AM 4/18/2010, Janne Ruohom�ki wrote: 

Isn't this something what the diodes installed in parallel with the 
relay coil are for, in transistor controlled circuits ? 

Hi Yanne -- yes, that's what the diode is for.  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.  The diode is then
forward biased and discharges most of the stored energy in the coil. 

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.
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. 

Yours, 
David 

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. 

--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR