I have a question I am hoping one of the electrical gurus we have on the forum can help me with. I have a Charles isolation transformer and a charles batter charger in my 26' convertible. Mt elec panel is a Blue Sea.
There is a light on that panel that indicates if I have reverse polarity. Everything is fine until I turn on the battery charger. I notice the red reverse polarity glows on the panel, but not real brightly. Just noticeable.
Any ideas why this might be happening?

Also I am afraid to charge my batteries as I am wondering if I may be inviting corrosion issues. Would that also be a concern?

I am really stumped on this one.
As always, thank you guys....
Bob

Check to see if you have a bad diode in the battery charger. One that conducts both ways. --Ed

On a similar but different vein, I was fortunate to resolve my battery over-charging problem. To wit:

For several years, water levels in the batteries were too low, so much that I was putting water in every few weeks (and it cost me at least one battery). After hearing someone suggest that I turn the battery charger OFF when I leave the boat--a good idea!--the water loss was lessened. So I replaced the old charger with a new, reconditioned and guaranteed unit--and many thanks to who suggested it here.

Problem resolved.

Jeff

Agreed, but this was a carefully watched test.

For one thing, I had 3 fully charged batteries on line to run the bilge pumps. I know from monitoring the boat all summer, that it doesn't leak much (purely from the stuffing boxes), and my new rear cockpit deck is so water tight that the bilge below is dry for the first time in years!

Your point is extremely well made, however. Many an outdrive boat with a cracked bellows has gone down in the slip after the batteries gave out.

Jeff

Your isolation transformer has two windings, a primary (dock) winding, and a secondary (boat) winding. There is a shield wire as well.

There should be NO connection from the primary to the secondary. There should be NO connection from the shield to either the primary or secondary.

The primary connects to shore power black and white. The shore power connects to nothing else.

The shield connects to shore power green. Shore power green connects to nothing else.

The secondary connects to the panel hot (black) and return (white) inputs. The return (white) also connects to the panel ground (green), which is usually connected to the hull.

If these connections are made, then there is no reverse polarity.

I would look carefully at the connections to the isolation transformer. I have seen several that were wired with the shorepower ground connected to the panel ground, eliminating all the value from an isolation transformer. The SeaRay plant (about 200 yards from my boat) cranked out many such miswirings once thanks to a bad production procedure, and there was a brisk business fixing them for a while.

Connecting your 12 Volt return (not actually a ground) to the hull is something you are stuck with because the engine block is the return for all the engine circuits, and the block is connected to the hull. Most Marinettes seem to have a stud in the hull in front of and between the engines. Battery negatives go to the stud, and a heavy wire runs over to the block.

This is fine, but the preferred way is to run heavy wire from the starter directly back to the battery, eliminating the connection at the stud. In any event, the battery negative ends up connected to the hull.

You probably don't want to let the secondary of the isolation transformer (tranny?) just float. If the hot side shorts to ground (hull) then the neutral side will become hot and the breaker will not trip, both bad things. Most sources say to connect both the neutral (white) and ground (green) to the hull for proper breaker operation. This connects the metal frames of microwaves and stuff to hull for you via the green wire, and keeps the white wire near ground potential where it belongs.

Be sure that the dock power goes only to the primary side, with the green connected to the shield or frame. Be sure the dock power green is not connected to the hull. The whole reason to have an isolation transformer is so you don't have to have the dock power green connected to the hull.

Don't be concerned that the hull is being used for both dc and ac grounds. Just be sure that the connections are made at one spot only. For dc, that is probably the stud in front of the engines. For ac, it is the isolation transformer secondary white. The green to the outlets also goes to the hull.