Join Date: Aug 2006
Location: Arlington, VA
Thanked 11 Times in 9 Posts
Rep Power: 10
The preferred method of wiring alternators these days is to connect it directly to the house batteries (only), using an appropriately sized fuse located near the batteries.
Then, the start battery is maintained using a voltage-follower device (EchoCharge, DuoCharge, etc.) or a battery combiner. Some installations use battery isolators, but I don't like them and they're not recommended these days. I just removed a (new) isolator from a client's boat yesterday; it had failed and wasn't putting any charge at all into the batteries. But, mainly, they involve an undesirable voltage drop.
For most cruisers, a Xantrex EchoCharge is all that's needed. Easy to install and totally automatic. I like these voltage followers better than battery combiners, since they have no moving parts (no relays to fail) and they don't combine deeply discharged batteries with near fully charged batteries, causing an undesirable in-rush current.
RE: your alternator switch on the panel, it is NOT a good idea to place a switch in the alternator output line; this could cause an almost immediate destruction of the diodes in the alternator. It may be that the switch is instead wired to cut off the field current (that's OK) or to reduce the output of the alternator, depending on the type of regulator used. Some external regulators, like the Balmar MC-612, 614, etc., have provision to wire a simple toggle switch which will cut the alternator's output in half in situations where that may be desirable (e.g., overheating, less drag on engine, etc.).
Good luck with sorting out the PO's wiring mess. That's not a job I enjoy!