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post #27 of Old 12-04-2008
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Fishfinder :

Sounds like you know your alternator fairly well.

Go into the back of the alternator, and find the field wire. The field wire accepts the current from the regulator to energise the rotor of the alternator. It is this field current that the make-before-break battery master switch is supposed to disable before it swops over the batteries. It looks very much like it is NOT doing that, as you have noticed the loads being switched off as you turn the switch.

When you find the field wire, you are going to cut the wire close to the alternator, and join a length of conductor to that wire. lead the length of wire up to your instrument panel and fit a wee switch for it, then lead the wire back to the alternator regulator again. Effectively what you are doing is allowing a manual interrupt to the field wire via a big loop.

MANUALLY, you must throw that loop switch to disable the alternator field wire before you move the alternator switch. Then after moving the switch, you enable the field wire again.

This is my set-up, and has been for years.

You simply remember to throw the disable switch each time.

It works too, and you can see the effect on your ammeter, if you have one. Don't trust that battery switch of yours. The loads must not drop out when you turn it. Your alternator diodes will not take that for long. It is possible to put a "snubber" at the back of the alternator to give you some defence, but mine fell off.

My alternator is the US-supplied Ample Power 100A, small frame model. It is a damn good alternator, now 16 years on, and still running.

You don't need fancy monitors and read-outs and flashing lights. One big storm in open water and the whole show will be soaked anyway. Man, getting soaked in seawater sorts out the junk from the necessary, I can tell you. A simple manual switch and a wee ammeter will do fine.

Last edited by Rockter; 12-04-2008 at 05:46 AM.
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