electrical problems

[Frank mellin]

Hi, recently purchased a westerly centaur fitted with a Nanni 3.75HE diesel engine.
As is often the case with boats a previous owner has spent some time butchering the electrical circuits for the engine and am trying to put right in stages.
I have recently had the alternator checked and it is fine in all respects.
My problem is that I cannot get the ignition light to go out.
The red + wire from the alternator which has a built in regulator goes to a multi battery isolator,the middle terminal.
Both of the other terminals on the isolator are live all the time but the middle terminal to the alternator is dead irrespective of whether the ignition is on or off.
My question is should this terminal be live to the alternator at any time?
Should power be feeding to the red + terminal in order for the alternator to operate or is it only live when the alternator is running?
The engine runs fine and starts well.
Any help in understanding this problem would be appreciated

 

[PaulRainbow]

The two outer terminals are live because they are connected to the batteries. The centre one is not live because the split charge device is stopping that, it will be live when the alternator starts to charge.

Simple check, remove the middle cable and fit it to the outer terminal that goes to the engine battery. Start the engine and see if the light goes out. If it does, the split charge device is stopping the alternator from getting it's excitation current.

What make/model of split charge device do you have ?

 

[knuterikt]

Having problem visualizing your wiring diagram.
The wire from generator to separator should be live when engine is running.

 

[Frank mellin]

wow....am impressed at your speedy reply!!
Will check on make of isolator and let you know.
I have tried connecting the thin wire that comes out of the alternator which I assume is the "exciter" wire to the live terminal on isolator but the ign light remains on.
The alternator has 4 terminals neg . positive. tachometer. ign light. as mentioned there is a small wire that comes out of the alternator which was connected to the positive terminal but as this was not live I was told to connect it directly to a live point which is why I used the battery connection on the isolator.
Many thanks for your prompt response.

 

[knuterikt]

Have you confirmed that there is no charge from generator?
One possibility is problem with charging lamp.
Using a voltmeter you should be able to measure charging voltage on both sides of the separator.

 

[peteK]

This thin wire on most engines is connected via the ignition warning light to the ignition switch.

 

[VicS]

This thin wire on most engines is connected via the ignition warning light to the ignition switch.

The OP separately mentions an "IGN" terminal, which will be the warning light connection.

The alternator has 4 terminals neg . positive. tachometer. ign light. as mentioned there is a small wire that comes out of the alternator which was connected to the positive terminal but as this was not live I was told to connect it directly to a live point which is why I used the battery connection on the isolator.
Read more at http://www.ybw.com/forums/showthread.php?497380-electrical-problems#UD34Tpv1dQQsyoWh.99

This thin wire sounds more like the modification for a Sterling alternator regulator or a battery sensing connection. If I understand the OP correctly it is in addition to the warning light connection.

 

[PaulRainbow]

The OP separately mentions an "IGN" terminal, which will be the warning light connection.



This thin wire sounds more like the modification for a Sterling alternator regulator or a battery sensing connection. If I understand the OP correctly it is in addition to the warning light connection.

That was my first thought Vic, if it is, they are usually yellow.

To the OP, If it battery sensing it will need to be connected to the battery side of the split charge device, as close to the batteries as possible, preferably at the battery.

If the split charge device is a diode and by-passing it cures the problem, the easy solution is to fit a Victron FET based battery isolator or a VSR.