In article ,
Engineman1 wrote:
In article , Rick
writes:

Do you know if the fuel solenoid is engergized to run or to stop?

Rick

The solenoid has to be energized to stop the engine.

I may not do anything to my friend's boat but just as an exercise in elementary
circuit logic I'm using Turbocad and trying to design the simplest circuit to
allow an engine to be controlled entirely by the key switch.
My parameters a no modifications to the fuel injector or engine, no solid
state components, IE no 555 chips, nand gates, and gates ETC. I'd like my
device to be just an add on, keeping the kill button active and using the
existing key switch.
My circuit would consist of dpdt relays and time delay relays. Since the boat
may not be used for a month or more at a time, the system cannot have any
devices which would drain the battery during nonuse without any extra switches
to turn off. So far this last requirement has been my biggest hurdle.

Hmm ... I would opt for a solenoid which had to be energized to
allow fuel to reach the engine. I'm presuming that when the engine is
running, there is a generator to keep the batteries charged. Under
those circumstances, the relay and solenoid power consumption is less of
a problem.

Turning on the key should pull in the solenoid valve (with or
without the help of a relay, depending on how much current the solenoid
valve happens to draw.

Anything with a time delay relay to turn off the fuel with a
apply-power-to-shut-off solenoid valve would either need a continuous
power drain for at least one relay, or a mechanically latching relay to
*hold* it off once the time delay is past. (There are old time delay
relays which operate with a heater and a bi-metalic strip in a vacuum
envelope if you *absolutely* want to avoid solid-state devices. But
they draw *lots8 more current than a well-designed solid-state timer.
If you want a minimum current way to operate the solenoid, I would go
for a power-to-fuel-flow solenoid, and a logic circuit (including
counter-timer) build around CMOS logic, which can draw *extremely* low
power at slow clock speeds -- except for the driver to a solid-state
relay, which is why the apply-power-to-flow option is preferred.

Of course -- there is the problem of making it survive the
electrical glitches which are often present in motor systems.

Good Luck,
DoN.
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