Tracy;
Well; the worry
is this. Safe wiring practice requires being able to protect the wire,
especially if it is in a bundle or close proximity with other wires, against
any failure which would overload the wire. Running the numbers says
that the maximum safe current for a 16 awg wire is 15 amps. If I
interpret you correctly; it is possible for my coil power lead to have to
carry 27 amps (for 3 coils) for a short time, which would trip a breaker, or
blow a fuse. Under these conditions one can not properly protect the
wire against a potential short – unless a much larger wire is used. My
wires run in a wiring duct, which isn’t exactly a bundle, but the analysis
says for 27 amps in a bundle you need about a #10 wire.
Further; I went
to great lengths to maintain the redundancy that you also strived for in the
ECU with the dual controllers and the isolation switches. I have the
engine critical bus connected to the dual battery system, and isolated by 40
amp diodes. I think you’re suggesting that it’s possible for the coils
to momentarily draw 54 amps (6 x 9), plus pump and injectors; maybe up to
nearly 70 amps. Ain’t
gonna work.
So what am I
misunderstanding here, or how do we get around this? Under what
temporary condition can this high current exist? Is there an
operational sequence to avoid this possible condition?
Thanks,
Al
Al, not Tracy,
but I think what Tracy is saying that in the milliseconds or so it
takes the EC2 to calculate the proper coil dwell time it is possible for a
coil(s) to draw up to 9 amps (or perhaps even 27 amps in your
case). The instantaneous power in
that case would be 27*12 = 324 watts IF that current
drain remained for as much as 1 second (actually probably less because when
cranking you probably would not have more than 10 volts). However, I
believe the duration of that surge is much shorter duration.
IF I am correct then I suspect your 16 gauge wire is more than adequate
because of the very short time interval in which this happens (I'm guessing
that situation does not last for even 100 milliseconds,
Tracy??).
If that is
the case then the power (which is what we are really concerned
about) per second would be 1/10*27*12 = 32.4
watts average power consumed during that time. The very conservative
Power transmission (bundled) for 16 gauge is 3.7 amps x 12 volts = 44.4
watts. Therefore, IF the surge is l00 milliseconds duration or less then it
would appear you wiring is more than adquate. Now if the surge
condition can actually last for as long a second then its a different
story.
Ed