Killswitch Failure at sea

[GuyC]

Originally Posted by beamishken

But if you think your system is better than most manufacturers then do it your way

I was putting my thoughts and justification down for comment. Having seen the comments and done some more pondering I'm going to change to a make to kill system.

Thank you for the input.

[GuyC]

Following on from previous posts.

It's a mechanical diesel inboard and operating the kill switch or engine stop switch makes a contact which energises the solenoid which pulls a lever and cuts the fuel supply off.

For the stop switch once you release the button after the engine has stopped it cuts the power to the solenoid.

Once the kill switch is operated, it energises the solenoid until it is turned off. It is generally not a good thing to leave a solenoid energised for long as they overheat and fail. If you've fallen out of the boat you might consider the burnt out solenoid as being a price worth paying but inadvertent operation with the engine off would be annoying and expensive.

The solenoid doesn't have a hold function so I can't get it to work that way.

The only solution I can think of is to use a timer relay that energises the main contacts for a limited period of time. This will hopefully be long enough to cut the engine but not long enough to burn out the solenoid.

Has anyone else come up against the same issue and how did they resolve it?

[beamishken]

You could wire a relay via an oil pressure switch so that when the oil pressure drops confirming the engine has stopped then the solenoid drops out
The oil pressure switch acts as a ground when it sees no pressure so should be fairly simple to wire in.
Only problem i could forsee is it may not allow the engine to start until oil pressure is built up

[GuyC]

Thank you for that and very interesting - you could use the oil pressure warning light as a trigger or the alternator charging light possibly.

Kill Switch (normally open) - 86
Earth - 85
Solenoid - 87
Power in - 30

This would be the normal operation and in the event of the KS being operated, the solenoid would become energised via the power source on 30.

Alternator Light / Oil Pressure Light - 86
Earth - 85
Output to KS Relay - 87a - it is using this terminal that makes it normally closed.
Power in - 30

This is a normally closed relay i.e. with the alternator light / oil pressure light off, the switch would be closed providing power to the KS relay.

If the KS is operated, the KS relay would be energised and the engine would stop. This would cause the light to come on triggering the Light relay and cutting the power to the KS relay de-energising the solenoid.

That is food for thought and certainly easier / cheaper than changing the solenoid and installing a power drive relay into the system.

[beamishken]

Not sure how the alternator warning light would work as the alternator acts as an earth when stationary to light the bulb but becomes positive out once charging to extinguish the light so relay may not work or may cause issues with the light.
Oil pressure is a straightforward ground

[GuyC]

Ah OK

A little knowledge is a dangerous thing...

I briefly considered a Voltage Sensing Relay but following what you say above, the oil pressure light is the way to go. I thought about your comment on not allowing the engine to start but in the scenario above, even if the oil pressure light is on, breaking the contact by resetting the KS will, I think, allow the engine to start.

The scenario where it might give you an issue is if your oil pressure light was to come on whilst you are driving, the kill switch wouldn't kill the engine, you would have to use the stop button or manually pull the lever....or just wait for friction.