alternator technical question

[pappaecho]

Fitted a diode splitter today.. problems caused by wiring loom. When connected to the "alternator" pole on the splitter, the ignition circuit sounds an alarms because there is not enough voltage etc. Connecting back to the +ve on battery system starts ok.
The wiring loom is such that a 60 amp brown cable comes form the alternator to a pole of the starter motor relay and then onto the back of the boat to the battery. A second cable again 60 amp goes forward to the ignition switch and to the ammeter. There is a very much higher current cable connected to the other pole of the starter solenoid probably 150 amp. A thrid pole connects the solenoid to the starter. There is a fourth connection a 6mm Lucar, when comes for the ignition switch and activated the relay causing the starter to activate.

The alternator seems to have two 6mm lucar connectors, one marked on the wiring "exciter", and the other "aux". A much bigger 12mm lucar connector is connected via 60 amp cable to the solenoid, and then on to the battery.

If I disconnected the 12mm lucar connector at the alternator and connect a new 60 amp lead to the diode splitter, will this direct the alternator output to the splitter and thence to one of two battery banks, dependant on their relative charge? By doing so will I be causing any "excitement" problems?

Finally I seem to recall working on BMC series cars in the 1970's when power from the alternator and power to both starter and ignition circuit came down a single heavy duty cable when ended up as one pole of the starter relay. If that is the case can I do similar on the boat providing power to the ignition switch from the heavy duty cable already connected at the solenoid, using th existing brown 60 amp cable to connect from alternator to diode splitter?

If alternators have exciter circuits why dont SWMBOs

 

[VicS]

A diagram of what you have would be a lot easier to follow.

What engine .. may be able to find an original diagram to help

However the alternator output must go directly to the common terminal of the diode splitter. Then the other two terminals to the batteries.

The main heavy feed from the starter battery to the starter motor solenoid remains.

The feed to the engine control panel should be taken from the above terminal of the solenoid.

The feed to the domestic switch panel should come from the domestic battery.

Separate isolator switches of course for each battery ( and a third to parallel them in an emergency if you wish)

Ammeter I think will have to be rewired according to what you want it to read.
Total alternator output, current to/from domestic battery or current to starter battery.
Ideally it would be a meter using a shunt.

Basic idea like this. But how did you charge the battries before you fitted the diode splitter.

 

[pappaecho]

The output from the alternator/+ve to ignition switch brown 60 amp lead was wired to the "common" side of the 1-2-all-off switch, and clearly charges either the starter battery switch set at 1, domestic at setting 2, or both when at all. This works fine but does not charge the lowest discharged battery in preference, hence the splitter which actually is Mosfet not diode.

I have three different wiring diagrams for 3 different alternators on old Ford engines, but the actual wiring is essentially the same. Clearly such items as splitters did not exist so it was quite OK to connect the alternator output to the ignition circuit, using one cable to perform two completely different functions

 

[Bosun Higgs]

I've attempted to draw a diagram of your wiring to try and help you but as you have described it, the wiring is far from clear. For example - the brown wire which goes to the battery. Is it the battery positive or negative?

 

[VicS]

The output from the alternator/+ve to ignition switch brown 60 amp lead was wired to the "common" side of the 1-2-all-off switch, and clearly charges either the starter battery switch set at 1, domestic at setting 2, or both when at all. This works fine but does not charge the lowest discharged battery in preference, hence the splitter which actually is Mosfet not diode.

I have three different wiring diagrams for 3 different alternators on old Ford engines, but the actual wiring is essentially the same. Clearly such items as splitters did not exist so it was quite OK to connect the alternator output to the ignition circuit, using one cable to perform two completely different functions

Using a 1,2, both, off switch you can charge whichever battery you wish.

Select the battery to use for starting and start the engine. Allow that battery to recharge. Then switch to both then to the other battery if that's the one you want to charge. ( or leave it on "Both" until you stop the engine)
Just don't go to the "Off" position while the engine is running or you are likely to blow the alternator diodes.

A splitter is not really necessary if you have the 1, 2 ,both off switch but
if you do fit a splitter it is more sensible to do away with it in favour dedicated starter and domestic batteries with individual isolators.
I will not suggest any circuitry involving a splitter and a 1,2,both,off switch

With a diode splitter you really need to convert the alternator to battery sensing to overcome the volts drop. Presumably that's not necessary with a mosfet device.

Slightly amended version of my previous diagram, taking the starter battery output from the splitter to the starter solenoid terminal:

 

[pappaecho]

The splitter is Mosfet and the drop is less than 0.1 volt on 12 volts. The splitter works three ways as I have also a bow thruster battery, which gets no charge at all, unless there is a splitter involved, which is why the system was designed. As you say the 1,2 all off switch does the job nicely except for the bow thruster battery, which also works the windlass.

The previous owner had separate isolators for 4 batteries which is fine but there was no possibility of crossing over the batteries in an emergency, if the starter battery was flat.

I think that today I will look at the starter motor relay and move wires around and replumb what is probably more than 30 years old.

Thanks for your advice, it help a lot to get he logic right. ( A a retired Chemist I spent much of my time getting engineers to get their logic right!)

 

[pappaecho]

I've attempted to draw a diagram of your wiring to try and help you but as you have described it, the wiring is far from clear. For example - the brown wire which goes to the battery. Is it the battery positive or negative?

The brown wire 60 amps rating twins with the main +ve feed from battery to starter motor relay. It is +ve, and I think I can use the main feed to provide power to the ignition circuit, moving the brown wire to connect the output of the alternator to the splitter input. Most "old car" circuits seemed to use the main feed to the starter relay, as a point to pickup power to the ignition circuit, as well as return for output from dynamo or alternator back to the battery.

Clearly in this loom they have decided to use a dedicated wire for connection to the ignition circuit and for output from the charger to the battery, which works fine until you are the wrong side of a Mosfet, which means effectively no power to the ignition circuit or to the starter motor relay initiation circuit.

I hope that a bit of replumbing of the wiring to the starter motor relay will do the trick