b393capt wrote:
On my 39 foot Beneteau 393, I have a zinc fish connected to engine
ground via a stud I installed in my cockpit.

When I place an analog meter between the fish and the boat's ground, I
read 50 mA with most of my electrics off (except Link20, galvanic
isolator monitors, bilge pumps), 70mA with some DC power on, and 100mA
if I also connect to shore power (I have galvanic isolators, unsure
why the current should change)

Where is a reference I can go to, to learn is this is acceptable ?
E.g. where do I cross the line between this providing evidence I am
getting intended galvanic protection vs. evidence there is a problem ?

Thank,


Several things come to mind. First, is
the fish your only zinc anode?

Assuming it is, and assuming you are
measuring DC milliamperes (not AC), then
50 mA is probably high, depending on the
surface areas, distance from the fish,
and composition of the underwater metals
you are protecting. A direct current of
50 mA will typically consume a pound of
zinc in about 3 months.

I also assume you are in sal****er.

Applying DC power to various appliances
should not change the current through
the fish. The only thing that I can
think of to explain what you are seeing
is if the switches are switching both
positive and negative wires. Of maybe
something is wired "backwards" and sets
up a galvanic cell.

You should see no significant difference
with AC power connected if your isolator
is working properly. It is not clear how
this would be related to the increased
fish current when DC appliances are
switched on.

I'm having trouble imagining what could
cause all the symptoms you have
reported. And coincidental multiple
problems are usually suspect.

The best references are probably the two
12 Volt Doctor books by Edgar J. Beyn.
Remarkably lucid and useful.

BTW, when measuring the current, was the
negative lead connected to the zinc or
the engine stud? And was your reading +
or - 50 mA?

Good luck.

Chuck


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