Date:         Wed, 6 Feb 2013 04:34:03 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: No Start Cause: Relay Failure. PICS, Thoughts.
Comments: To: Dick Wong <sailingfc@DSLEXTREME.COM>
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At 02:44 AM 2/6/2013, Dick Wong wrote:
>With my old Scirocco, the fuel pump relay will get hot to the touch and has
>actually melted the side of the plastic case.  After filing and cleaning the
>contact, it typically runs cooler.  I also keep a spare fuel pump relay.

Dick, we used to use a "point file" on ignition contact points to get
rid of the "mountain" deposited on one side by the arc, but those
points are made of tungsten.  Relay contacts are typically silver and
may or may not be a thick solid piece of same -- either way they're
very soft.  Rather than a file I'd suggest using 1500-grit or even
finer wet-or-dry paper to do the cleanup.  I'd also suggest tracking
down why it's running hot.  Bad contact in the socket maybe?  A relay
should not run hot unless something is wrong.  If the contacts are
pitting rapidly because it's switching an inductive load, try adding
an old-style ignition condenser from the load side to ground, or put
a reverse-polarized 4004 diode across the supply and load
terminals.  If the diode fails, use a higher voltage rating.  I think
a 4007 has a 1,000 V PIV (peak inverse voltage) rating, which ought
to be enough. 4004 IIRC is 200 V.  4001 is 50 V, probably not
enough.  In general terms, a one-amp or better power diode with PIV
at least 200 or 400 volts should do.  Hook up with the marked end
facing the supply.  If the marking is an arrow pointing to a bar,
hook the bar side to the supply.

Yours,
David