Mark, et al;
I don't believe Hypothetical #1 is a possibility at all. Electric current
doesn't just
generate a shower of sparks because the circuit path has been
opened...especially
not at 14volts DC. An alternator can be run at full speed with the positive
power lead disconnected with no adverse affect on the alternator. The
only place any possible spark might happen (by hitting the kill switch)
is briefly across the opening gap of the kill switch between the internal
switch contacts within the kill switch itself.
Remember too, the intensity of any such momentary spark across/between
the kill switch contact points will be relative to current flow at the time
the
kill switch is hit. That being the case, the current flow should only be
a few amps for a race car (ignition, gauges, electric fuel pump) unless
the battery in the vehicle is heavily discharged. That's one reason
switches
have current ratings....to indicate the maximum current the switch is
designed to turn on/off.
If I were wiring a race car setup, I'd use a single-pole-single-throw (SPST)
kill switch with a current rating sufficient to handle ALL the cars
electrical
current flow EXCEPT for the starter motor current. I'd then run two leads
from the positive battery terminal (negative if positive earth car) as
follows:
(1) Lead one (starter current cable to starter solenoid)
(2) Lead two to Kill switch with the other side of the kill switch then
connected to the cars electrical system (fuse block, dash switches, etc).
Someone else suggested putting the kill switch in the ground path of
the battery, but that then requires a switch capable of handling ALL
the current flow, including starter motor current which can be pretty
high. Additionally, from a purely "worst case" safety perspective,
if the car was in an accident and ended up with the battery dislodged
or otherwise with some part of the cars metal (sheetmetal, frame, etc)
coming into contact with the ground terminal of the battery, then that
would render the kill switch useless since the switch would then be
bypassed by the battery ground termional making direct connection
to the car's ground itself as a result of the accident.
Cheers,
Bill Sohl
----- Original Message -----
From: "Mark J. Bradakis" <mjb@autox.team.net>
To: <fot@autox.team.net>
Sent: Sunday, April 24, 2005 11:29 PM
Subject: Re: Kill Switches
> Hypothetical situation #1: You wired in a simple two post kill switch in
> a car running an alternator. The tech inspector requests that you
> demonstrate
> that the kill switch works, so you fire up the motor, he flips the switch
> and
> your alternator explodes in a shower of sparks because the current
> generated
> by the still spinning alternator has no place to go.
>
> Hypothetical situation #2: You wired in a simple two post kill switch in
> a car running an alternator. You just got punted off turn 2, you're
> sitting
> there with the motor still running and a ruptured fuel line soaking your
> Nomex in gasoline because the fuel pump is still running, and the corner
> worker reaches for the kill switch...
>
> mjb.
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