Re: Lighting questions

[Tony Lum <tlum@flash.net>]

At 09:43 AM 8/8/98 PDT, you wrote:
>Hella suggests relays with resistors and diodes on the control circuit 
>to avoid voltage spikes up to 500 volts produced by the relay closing.  
>I noticed the resistor and diode are on the control side.  So now my 
>relays will blow my brittle headlight switch, I can't win! ;)
>
>Scott Miller
>'90 200tqw  (Chinese built?)
>
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Hi Scott,

Its standard practice in ATE (automatic test equipment) which use hundreds
of remote contolled relays to place a backwards diode (cathode side to
+12V) in parallel with the relay's coil to suppress the inductive spike you
get when you cut the power to the relay.  Many relays have this suppression
diode built in since the spike can take out your solid state driver.  Don't
have any idea how much reduced life a mechanical switch design to switch
10A or so.

 
-Tony
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Tony Lum  (tlum@flash.net)                  1987 5000CS Turbo Quattro
Berkeley, California, USA                    1985 4000CS Quattro
Audi Owner/Driver/Mechanic by Necessity ;^)   1980 5000S Sedan
                                               1987.5 Coupe GT (new)
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