We use an SB560-E3/51 diode on the master contactors, which you
can get from digikey or mouser. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=SB560-E3/51GI-ND
Or it is included in the Vertical Power wiring harness kit.
From: Tom Gourley
[mailto:tom.gourley@verizon.net]
Sent: Friday, April 17, 2009 5:44 PM
To: lml@lancaironline.net
Subject: Re: [LML] Re: spike suppresion diodes
Just as a clarification - the "spike suppression
diodes" do not protect the electrical system from high voltage spikes;
they protect the switched device, which in this case is the solenoid coil of
the relay being turned off, and the switch itself. The coil really
doesn't care, and the switch is designed to tolerate the resulting arc.
The normal wiring (I'm no good at putting graphics in an email so I'll do
it "verbally.") Goes from the battery and all your expensive
electronics to the switch, to the relay coil, and to ground(return). The
high voltage spike exists only between the switch and relay coil, no where else.
Gary
is correct. When current to the relay coil is interrupted the inductance
of the coil will cause a voltage spike at the coil. How big depends on
the inductance of the coil and the amount of current that was flowing when the
switch was opened. Whether or not the switch will tolerate this depends
on the switch. Personally I think a diode across the coil is a good
idea, just be sure it's installed the right way. I don't see the need for
anything fancier than a diode, something like a 1N540x (where x is 4, 5, 6, 7,
or 8). If you want to protect larger parts of your electrical system
against voltage transients you will need something fancier than a diode.