[dohenyboy]

I have a charging problem that I just cannot figure out. Everything has been working fine for two years and something broke.

I am on a mooring, so except for a wind generator that keeps the batteries topped off, and running the engine, my main source for electrical power is a Northern Lights 6kW genset. The genset is wired to produce 120V AC.
I have two chargers on board, an older (2003) Xantrex inverter charger (2500 W inverter, 140 amp charger, for the house bank ), 7 Lifeline AGM batteries with 105 amp hours each) and a Xantrex True Charge 20 in the bow for the anchor windlass batteries.
The big charger is one of those with transfer switching. While AC is input, up to 28 amps is used for charging. However, any AC demands from the ship take precedence and reduce the current available for charging. I have it set up for 1 AC input and 1 AC output. (there are two AVAILALBE inputs and two AVAILABLE outputs but I don't need that complicated of a set up) If there is no AC input on the unit, it acts as a pure inverter, supplying 120v AC from the battery bank.

The genset AC goes through a ship/shore switch then, the neutral wire goes to a small AC neutral bus, and the hot wire goes to the two breakers-one for the big charger and one for the bow charger.

The bow charger works great.

The big charger does not. When there is no AC input, it inverts just fine. It will not charge, and when there is AC input, no AC comes out the AC output (no "pass through").

I took out the charger and had Xantrex look at it. It tested good.
Then I bench tested it at home, using house current for the input, a vacuum cleaner plugged to the output, and a marine battery hooked up to the DC outputs. The charger did work perfectly. It charged, and passed through the AC to the vacuum cleaner.

So, there must be something wrong with the boat. It has to be either (a) my house batteries, (b) bad AC from the generator, or (c) something wrong on the AC panel or further downstream.

I took the big charger, the marine battery and the vaccum cleaner to the boat. I connected the charger input to the ship shore switch, and connected the same marine battery to the DC outputs. I did not connect the AC output. In other words, the same as at home except for the AC input.
It did not work. No charging and no pass through of AC (I tested with a digital multimeter) I was getting 120v AC from the generator. I could hear the transfer switch inside the charger click and the charge light came on. But voltage at the battery was unchanged. I took the ship shore switch out of the circuit, wiring the generator directly to the charger, no difference. I then connected the generator line to an outlet box I made up, and the vaccum worked.
The Xantrex repair people are flabbergasted.
Anyone out there have an idea?
A new Xantrex is over $1000. I may get one of the Iotas but I would rather not have to spend any money