I have a small cat (Tobago 35) with two 2GM20s. When acquired from the charter
company, the field sensors from the two alternators were connected to the diode block, on the upstream (current-wise) side of the diodes. Of course, this means the alternators do not sense the voltage of the batteries, and therefore tend to put out fewer amps at a lower voltage (measured at the batteries).
I found that when either sensor was switched to a battery
, either singly or at the same time, the buzzer at the starter(s) would sound. Since the buzzer does not sound after the engines are running, I rigged a switch to route
the wire around the diode block, so that the alternators' built-in regulators would see the true voltage at the battery
and cause the alternator
to send out a higher voltage to compensate for the diodes. I have heard this causes the alternators some extra stress. I often use a jumper with alligator clips to bypass the diode block from time to time to better charge a particular bank.
As I rely more on solar
for most of my house bank, this is more of a curiosity than a problem, but in those uncommon moments when eveything else is fixed, I often turn my mind to it.
How are they wired on a monohull
? How would they be wired when there were not two battery banks, like on a shore vehicle or machine? Wouldn't they buzz all the time?
So, what is so unique about my situation that they buzz whenever they sense a 12-volt battery?