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MMD > Archives > July 2002 > 2002.07.25 > 09Prev  Next


Relay As Power Switch Replacement
By Craig Brougher

For those who need a switch to prevent arcing (which is particularly
bad in dc circuits with inductive components like solenoids and
magnets), I suggest using a small Radio Shack relay with at least two,
preferably four dpdt switches.  By wiring its switches up in series,
there is no way that switch is able to arc anymore.

The problem has been the close proximity of most relay contacts and
their silver content.  When the contact breaks (opens), any inductive
kick at all will cause a big spark and the silver in the contacts will
form a bright green plasma.  It will then sit there while open and melt
completely down to a plastic blob, using the inductor's back emf to
fire the oscillator circuit.  A radio tuned to a weak station or no
station will usually detect this trying to get started.  You will hear
a static burst that lasts for a longer time than just a "click."  Then
pretty soon, off it goes steadily.

If you can find a relay with tungsten contacts, you will have no
problem.  It's just that they will strictly be surplus if you can find
them at all.

Craig Brougher


(Message sent Thu 25 Jul 2002, 14:38:43 GMT, from time zone GMT-0700.)

Key Words in Subject:  As, Power, Relay, Replacement, Switch

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