Solenoid question - genset stop solenoid

[igatenby]

I finally got around to rewiring the genset engine - a Lister STW2 of indeterminate vintage (they were built '79-'91 IIRC, not sure which century though) after a minor fire at the genset end (a chip of wood created by a previous owner had bridged two of the transformer terminals - which then got wet when a hoseclamp failed, which.... smoke, small fire, no damage.

The engine wiring was a real mess - most wires changed colours about three times - pink was joined to blue which was joined to yellow. Anyhow, I logged it all and replaced it with new tinned cable. Then I rebuilt the starter (last done 5 years ago) as it was full of salt.

So now it starts, runs and generates power - but it won't turn off. The solenoid stays energised - and I have checked that the wiring appears to be as it was (minus lots of splices and colour changes).

If I turn the key off - the starter light comes on - which I'm assuming isn't good for the alternator, so I didn't keep it running like that. I can manually push the solenoid out to kill the engine. If I commence starting the engine but switch it off before it gets going properly, the solenoid kills the engine properly. This makes me think there may be some sort of problem with the alternator - is this likely, and if so, what is it?

Thinking this through, I might try pulling the alternator out and seeing what happens???????

Any thoughts?

Ian

[Tylerdurden]

My first thought is you have the ignition switch mis-wired. You really need to have a volt/ohmeter to be able to diagnose. A lot could be happening. Get a print for that engine if possible to work your way through it. First off see if you are getting voltage to the solenoid, if so check to see if the windings are open. If not go back through the harness to find the mistake.

[igatenby]

You really need to have a volt/ohmeter to be able to diagnose

Agreed - I actually had three of them down there today - but only myself and I think this is a two-person job. The key is too far from the solenoid.

I'll leave it for the weekend and will shanghai a crew.

Thanks
Ian

[Hwyl]

I agree with TD, it should be easy to see if the stop solenoid is energised when the switch is "off", if it is, then you have to find where that current is coming from and your problem is solved. If it's not you have a sticky solenoid, and it should be replaced.

I long for the days of stop cables and levers.

[Canoeyawl]

You are probably “back feeding” current from your alternator to the shut down solenoid. Often this problem is caused by a wiring error at the ignition switch. If it is an automotive type switch, all connections except the ignition and the "Hot" must be wired to the accessory side of the switch. The ignition wire must stand alone.
There are other scenarios that can cause this problem and another remedy is to install a diode or a relay in the charging regulator circuit, but without a schematic to reference, I recommend first checking the switch wiring.

[Gary E]

Is your engine a Diesel? If it is, maybe the solinoid is suposed to be energized to close the throttle rack so no fuel is delivered, anotherway of looking at it is that it pulls the idle position stop screw to a even lower position so the engine stops.

[Tylerdurden]

Agreed - I actually had three of them down there today - but only myself and I think this is a two-person job. The key is too far from the solenoid.

I'll leave it for the weekend and will shanghai a crew.

Thanks
Ian

Get a roll of primary wire and unthread the end in the spool a couple of feet, Attach aligator clips to both ends and make your self a set of extra long jumpers. Buy a set of regular jumpers too.
Sometimes when working alone thats what I need to get the job done. Or if you have an extra pull nearby you can disco that and use it.
If you are concerned about broken or corroded wires on a run, make up a 9v battery with a clip and ring out for voltage. if you find a drop (in voltage) you have found your culprit. Of course sometimes you need a megaohm meter for such things (like insulation breakdown) but way too much money for the simple stuff.

[Ken Hutchins]

Keep it simple, toss the solenoid und use a simple push/pull rod to stop the engine.