"Greg Mayman" bravely wrote to "Roy J. Tellason" (05
Oct 03  07:49:00)
 --- on the heady topic of "VEHICLE LED'S"

 -=> Roy J. Tellason said to George White
 -=> about "VEHICLE LED'S" on 09-30-03  04:05.....

 RJT> Even though it's been *ages* since I've actually seen one of those,
 RJT> now that you mention this I can remember that a couple of the coils on
 RJT> those things (the 3-coil units) were wound with some *really* thick
 RJT> wire.  :-)  Those must be the "current" windings.

 GM> Yup.

 RJT> The other thing that just comes to mind with those is that underneath
 RJT> the mounting base were wire-wound "resistors",  maybe 2
or 3 of them.

 GM> Usually wound on mica strips. IIRC they were connected across the
 GM> "buzzing" contacts of the voltage and current control relays to
 GM> minimize arcing.

That's not the right thing to do however because the capacitor causes
the spark energy to be dissipated into heating the contacts thus making
them burn or wear out faster. The proper way is to add a certain amount
of resistance in series with the capacitor to safely dissipate the emf
energy while keeping the voltage low enough so there is no arcing. The
value of resistance is found by dividing the voltage limit by the peak
reactive current. The other advantage to adding a series resistor is
that the capacitance can then be a lot smaller than before. Sony
equipment in the 70's always had this combination of
resistance/capacitance across switching contacts.

 Mike
 ****

... Resistance Is Futile!   (If < 1 ohm)
--- Blue Wave/DOS v2.30