Circuit Breaker labeled APS?

#1 SWAG,
Active Protection System

Do you have Barnacle Busters or Cathode protection in/on/under your hull?

#2
Auxiliary Propulsion System
Uh,,, Not on an Egg

#3
Ah, I know. It don't make sense but trust me..
You owe us a beer..

BTW
Welcome to Yacht Forums.
There are a few Post Kids in your hood.
I can not remember any Egg owners but I know a few are close to you also.

APS = Automatic Power Selector

Sounds like you have multiple battery banks (probably 2?) which are connected as inputs to this unit. There should be a single output feeding something important, possibly house loads in your case. The APS simply selects the input with highest voltage to supply the output.

SShhhh
I wanted a beer

Sorry!

So is this APS system basically just a load sensing relay? Draws from one bank then if voltage drops to a point it switches to the other? If the main engine batteries are powering house loads I wonder if it also has a set point where it drops the house load entirely to ensure enough power to start the engines?

Yes.

No.

Not likely. My guess is engine batteries are on one input, genset battery on the other, so output is from whichever is showing a charging voltage. Basically an auto-select switch for running vs moored.

OP should provide specs or make/model for further info.

There's usually a reason for that

Geeez..
He just asked what APS stood for.
And your guessing also.

I look forward to what your further investigations find.
Is there anything in the prints, manual or logs?

True. Hopefully I made that clear.
At least he knows where to look now

Could be Auto Pilot System.

I have an APS breaker on my 24v panel. It's the Auto Pilot Solenoid. Activate the hydraulic steering pump, and the pilot steers by solenoid.

I think that transformer is just to knock down voltage for lights.

It's apparently quite common (on twin engine U.S. made boats) to have a bank for each engine and approx. half the house each. Not a horrible set-up; have to do cost/benefit analysis to decide whether a separate house bank would be worth the effort. Yes, there's that potential voltage drop thing; don't turn on your electronics before starting your engines.

The headline on your link says AC input, DC output... so maybe it would keep your Furuno stuff ON if (when) you have shore power or genset power feeding the transformer. ??? The way that product is described in the table, I'm guessing there are several versions, one each for 120 or 240VAC input, and one each for 12 or 24VDC output. Four versions??? Or maybe feed it either 120VAC or 240VAC and get either (both?) 12VDC and 24VDC output. Two versions???

If you try that RS "find similar products" option, then filter by Acme and buck/boost transformers, you'll get 50 results... so presumably each of the individual products (numbers) does something slightly different...

Our isolation transformer is by Acme, and I just yesterday learned in another forum that Acme has become part of Hubbell. You might ask them...

-Chris

Not correct.
That is ACv in, ACv out.
It is a transformer, not a power supply.
My lights on a vintage Pequod worked this way.
Hatterass has this still.

That's consistent with their description in that link:

"The most common example is boosting 208 volts to 230 volts, usually to operate a 230 volt motor such as an air-conditioner compressor, from a 208 volt supply line."​

I don't quite see how to translate their product headline that way:

"...1-Phase, 60 Hz 120 X 240 V Input 12/24 V Output, 0.05KVA"​

???

-Chris