YSB-8 alternator opertunity


12 Mar 2011
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My first post I lay before you my opportunity to solve before I can even get sailing.

Bought a seamaster 815 and it has a YSB-8 engine in it which has a hitachi alternator (LR135-31). I noticed that the charge light wasn’t illuminating so check the voltage across the batteries, which were approx 12-13 volts, so not charging then. I then took the alternator to an auto electrician whom bench tested it and he then said that the Alternator stator was done. He then stopped any further testing as in his opinion it was beyond repair.
So I now have to get a new alternator!!!!!!!!!!!!!!!!!! Simples........
One of the things that the auto electrician said was that the alternator was isolated return, but I cannot find a replacement alternator that is isolated return the only kind I can get, which is sold as a replacement for mine is earth return. Which I have purchased.

So the billion dollar question is how one connects it up then???I will not be the only person to have hit this wall then, there has to be others.

Earth return
Dead easy alternator goes to earth through the casing of the alternator, through the block and the battery negative will be connected to the engine block. More chance of a spark with this system.

Isolated return
There is an actual wire coming out the alternator going to an earth point and the battery negative will go to a central junction as well. I.e. it will eventually get back to earth as in the previous example.
So why if there is a difference when at the end of the day both systems will get earthed eventually, I realise that the isolated return is done as a safety feature ie less chance of a spark in that one billion to one odds of you having petrol fumes down in the bilge and on that day there just happens to a spark and boom, even although it is a diesel and the chance are even more remote. Is that the only reason for the difference.

So can anyone help me please.
1. Can i just wire up the new earth return alternator even although my electrical system MIGHT be isolated return. I will check this at the weekend, billion miles from the boat too
2. Or do I have to completely rewire my electrical system to negative earth (earth return).
3. Is there a third option.

Insulated return connections from rear of alternator
1. Battery
2. Live
3. Earth

Earth return connections.
1. blue wire for rev counter, not needed
2. Battery connection
3. ‘T’ connector top of ‘T’
4. ‘T’ connector vertical of ‘T’ connection
5. there is also an earth attachment point on the casing.

Regardless of what I do as its a seamaster there is not a big electrical system on board, it comprises of:-

1. cabin lights
2. nav lights
3. vhf
4. chartplotter
5. engine electrics.
6. wind gauge and depth

Think this is going to a long one...help please.....................