" I still get about 5-8 of these "I passed through off." events each year, despite the battery switch warnings that are clear as day and written right on them."
A proper 3 way rotary switch has field terminal cut offs built in for the last 3-4 decades or so.
In all my years of working on boats I can count on my hands the number of times I have seen the AFD feature being utilized.
Of those times where it was being utilized it was wired
incorrectly in 98.5% of those situations.
The key word is alternator
FIELD disconnect. This means it must interrupt the field (power from regulator to slip rings) & be inserted between the internal regulator and the brush.
Cutting the "excite" wire, which I see all to often, with a powered up alternator, does not protect the alt from a load dump because once excited they self excite..
Only breaking the field (brush) or the B+ power wire to an external regulator will do this. It should be noted that cutting the
ignition wire to most external regulators is not fast enough to save diodes and it must be either the field wire or the regulator B+ wire. Most regulator manufacturers, or more accurately the electrical engineers who designed the regulator, would prefer the reg B+ to be cut over the field wire.
Of course, back on the initial subject, an AFD switch does nothing to prevent a transient caused by an internal BMS open circuiting while while the alt is producing or to prevent a transient by a charger or inverter while it is producing..
The best course of action is to route an alternator to the house bank, where you can now have accurate voltage sensing (not just at the "C" post) and the high performance charging you've paid for.
The field is usually under 6A so the wiring is cheap to install.
It's not the cost of the wiring. Heck you can just snip the B+ feed to a Balmar etc. install two ring terms and away you go. The problem is that many folks interrupt the ignition feed to the alt or reg and don't fully comprehend how to properly wire an AFD. I have seen excite wires connected to AFD's, regulator ignition wires, and even a few AC tap wires interrupted by an AFD. It is extremely rare when I see one wired correctly.
An AFD will work fine provided you are breaking the
field or B+ of an external regulator. Some internal regulators are very tough to tap into and break B+ but the brush wire can often be more easily be interrupted. Again, nearly every AFD switch I have seen wired, to use AFD, has been wired
incorrectly. This defeats the entire purpose of it. If you've wired yours correctly this is great and you're in the top 1.5%.
Best course of action, for charging performance, is to direct wire the alternator to the house bank and let charge management devices (ACR's, Combiners, Echo Chargers or DC to DC battery to battery chargers) take care of the start & windlass or thruster banks....
Folks stuck with one wire alts , built for start batts, should consider wiring in the proper 3 way rotary when installing 3-4 stage V regulators to charge a house set..
Folks installing a high performance charging system should ideally wire the alt direct to the bank in order to get the best performance from the system.
D'oh......
