Prior to any
discussion of fuses vs CBs; this issue needs some clarification. Is it
possible for more than one coil to be drawing this level of current at the
same time? I have 6 coils on my 20B; three on each circuit with a 16
AWG wire. This could be frightening!
Al
Don't think it
is a worry. All can be on for a short time (possibly long enough
to blow a fast acting fuse) but not long enough to heat a 16 ga wire
significantly.
Tracy
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
Oh darn,
I knew this would happen.
The
momentary 9A load on each coil only lasts in the range of 50 - 100
milliseconds under worst case conditions during start sequence. There
is no way to avoid it but FWIW, it just isn't a problem. The
16ga wire would not have time to get even warm. The specs you
are discussing relate only to long term events and do not address short
term transients.
Tracy