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Subject: Re: [LML] Re: spike suppresion diodes
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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.
Tom Gourley
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<DIV><EM>Just as a clarification - the "spike suppression diodes" do not =
protect=20
the electrical system from high voltage spikes; they protect the =
switched=20
device, which in this case is the solenoid coil of the relay being =
turned off,=20
and the switch itself. The coil really doesn't care, and the =
switch is=20
designed to tolerate the resulting arc. The normal wiring (I'm no =
good at=20
putting graphics in an email so I'll do it "verbally.") Goes from the =
battery=20
and all your expensive electronics to the switch, to the relay coil, and =
to=20
ground(return). The high voltage spike exists only between the =
switch and=20
relay coil, no where else</EM>.</DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Gary is correct. When current to =
the relay=20
coil is interrupted the inductance of the coil will cause a voltage =
spike at the=20
coil. How big depends on the inductance of the coil and the amount =
of=20
current that was flowing when the switch was opened. Whether or =
not the=20
switch will tolerate this depends on the switch. Personally I =
think a=20
diode across the coil is a good idea, just be sure it's installed =
the right=20
way. I don't see the need for anything fancier than a diode, =
something=20
like a 1N540x (where x is 4, 5, 6, 7, or 8). If you want to =
protect larger=20
parts of your electrical system against voltage transients you will need =
something fancier than a diode.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Tom Gourley</FONT></DIV>
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