troubleshooting perplexing AC shore power/inverter set up

hello - I'm troubleshooting an AC power problem with a new-to-me 2000 era sportfish, where all of the circuits that are powered by the inverter will not function on shorepower. They function on inverter power, or on generator power, but not shore power.

I believe the culprit is a failed low voltage transformer, but, before I simply replace it, I'm trying to figure out why the transformer is there in the first place.

Here's how the boat appears to be wired:

• 240v/50A black/red/white/green shore power comes into the engine room and goes up to the main panel in the saloon.
• Before the AC power switch on the panel, a 3-wire, 240V power feed (white hot/black hot/green) splits off and goes to a low voltage transformer (5kVA, 240 primary/120 secondary - ACME T253014S) with two outputs. I have not been able to find where this power feed split occours, but I know it is before the main panel because the circuit that feeds the transformer with shore power is hot even when the main panel showe power AC switch is off, or set to genset power, provided the boat is connected to shower power and the pedestal feed is on.
• One output of the transformer goes to a genset/shore power automatic transfer switch. The output of the automatic transfer switch goes to the 120v input of the charger/inverter, and the output of the inverter goes to an inverter bypass switch.
• The other output of the transformer also goes to the inverter bypass switch, presumably allowing you to power the circuits normally powered by the inverter with shore power.

Does this routing make sense? It seems needlessly complicated. If the point is to feed the inverter with 120v shorepower, why send 240v shore power to a transformer, which then knocks it down to 120V? Why not just skip the need for a transformer, and route one phase of the 240V shorepower directly to the genset/shore power automatic transfer switch?

It’s more than this - the inverter also needs AC voltage to charge the batteries when they are not needed for supplying power.

The transfer switch, as far as I can tell, doesn’t function off a discrete signal - it switches automatically based on which input circuit is energized. Which in turn begs the question of what happens when both the genset and transformer are sending it power. I don’t know the answer to that..

i understand what you are saying. For the “automated transfer switch” to be “automated” it has to have a controller that has some sort of logic implemented. My point is that, the reason I suspect the transformer, and not the transfer switch, is because the transformer is not outputting any voltage to the transfer switch (whereas the genset does).

here’s pics

One pic is the automated transfer switch, inverter, and the bypass switch (mounted on the bulkhead)

Other pic is the transformer, with the access cover removed

in the foreground of the image with the inverter there’s a black box - “southwire automatic transfer switch”

In the background of the same image is a box mounted on the bulkhead. It has an inverter (output) on/off breaker and a 3 way switch - on/off/bypass for the inverter

If you are inclined to zoom into the images, or if you can even zoom in that far, you may see I’ve labeled the wires with sharpie. But the basic AC flow is

shore power to transformer (and separately to main panel)
transformer to transfer switch and bypass switch (2 outputs)
Genset to transfer switch (and separately to main panel)
Transfer switch to inverter
Inverter to bypass switch
Bypass switch to main panel

Also google answered my question about what happens when both shore power and the generator are feeding the transfer switch - apparently it is preferential to the generator

https://www.southwire.com/power-man...r-switch-50a-hardwire-model-40100/p/40100-001

Eh..what’s not to trust? The question is what happens when it gets input from both the genset and shore power, the companies website says it preferentially selects genset, similar to dockmaster’s RV. in fact, it may be the same unit

No…I’m just saying I now know how that particular box is supposed to work

Relative to your suggestion to get a “real tech” out to the boat, that may well be where I end up. But my experience is that hiring someone to work on your boat without actually knowing what needs to be done is a recipe for large bills and bad outcomes. And it also doesn’t help you understand the boat any better for when the time comes you are in a situation where something breaks and no one is around to help

Unfortunately no help from the PO - no contact with him at all. And nothing in his limited logs or records. I did have it surveyed - this same problem was happening when at the dock where it was surveyed. It was explained by the seller as a pedestal problem. Then, it worked fine when we overnighted in palm beach - which I thought confirmed the original “pedestal problem” diagnosis. Then, when we arrived in Melbourne, we saw the same problem we saw at survey - no power to inverter fed circuits unless on generator or inverter power.

I could get an electrical survey done by Ward’s. It would be very expensive and I’d have to pay 4 hours of round trip travel but they are the only ones I know of who I’d trust to dive into something like this. It would be nice if I could narrow it down a bit more so I could fix it myself or at least get it to where I can hire someone local and know enough about what needs to be done to make sure it’s done right. I still don’t know whether this is a “fix what’s broken” situation or a “rip everything out and start all over” situation