Originally Posted by daveNZ
Svlamorocha, no I haven't checked the whole engine loop; but I have got a small (.2 ?) drop from alternator
+ve to battery +ve so will add a direct cable (or two) soon.
That is not bad on the positive side (assuming you are measuring from house battery, which is what matters) but IMHO the killer is usually the negative.
In the average BVI bareboat
with Yanmar/Hitachi setup the drop between alternator negative and battery negative is more than 1V (just the negative) when the alternator is pushing only 25 or 35 amps. Consider all the steps:
- Drop in wire from battery negative to negative battery switch (not bad in carter boats because this wire is fat).
- Drop across terminals negative battery switch. I have measured 0.3V once, but it got better after "exercising" the switch.
- Undersized wire from switch to Common Ground Point bolt in engine with associated rust, grease, etc.
- Terribly undersized wire between Common Ground Point and alternator.
This sounds bad and kills batteries but saves alternators. With the usual machine sensed alternator, the additional drop keeps battery voltage down , which then limits current
that in turn saves the alternator from burning.
I bet that MarkJ´s alternator would not have lasted that long if he had cleaned all the connections, upgraded the wiring
and connected AO direct to the house battery positive (instead of going through the cheapo relay they have in those Moorings boats, which can have 0.2V drop when old)and alt negative with fat wire direct to the switch or battery negative.
If you have one of those cheap
Hitachi lookalikes without the Hitachi thermal cutback be prepared because after you improve the wiring
you will increase the absorption current and that may fry the alternator. Have an extinguisher ready!