Main 12-volt Control Schematic Diagram

S/V Nevermore MAIN 12-volt CONTROL schematic

 Right-click [12-volt system schematic]
 to view diagram while reading description below...
  
 The walk-through below relates to 27Aug07 version of the schematic.

LAYOUT OF THE DRAWING

 The drawing is mostly schematic but also hints at physical placement of parts.
 

On the diagram, circuit elements are placed in a few "compartments" (CMPT) separated by dashed lines; these sections are laid out to correspond approximately with their position on the boat, but are mostly placed to correspond to some of the ship's wiring shown on the diagram:

a. on the left of the diagram is the BATT CMPT which contains the 2 power switch bodies and the two batteries (#1 (aft) and #2 (fwd)); note that the switches are pictured as viewed from aft, i.e. when visible when the battery compartment cover is off.

b. in the middle of the diagram are the CVTR CMPT which is actually forward of the nav table, and a BILGE CMPT which actually implies part of the bilge some wires run through.

c. below the BILGE CMPT and to the right of the BATT CMPT is the ENGINE CMPT, containing battery #3, a ground buss connector located under the engine, Also shown are the starter and laternator in a CLOUD OF ASSUMPTIONS which shows functionality which I don't yet know how connects.

d. the lower right part of the diagram shows the 2 primary switches viewed from the front, so doesn't conform to the physical mapping of CMPTs discussed in a. - c. above; they're views looking aft from under the nav table.

WALK-THROUGH OF THE DIAGRAM

  discussing each device, connection, and wire in passing 
  as the functionalities of devices are listed.

1.1  Starting in the BATT CMPT, the "+" (HOT) power of batteries #1 and/or #2 
are connected by thick red wire to the "1" and "2" terminals of the 
top main switch, flowing from the switch's COMMON terminal by thick black wire 
(color not noted on schematic) to the COMMON terminal of the bottom switch, 
thence directly (without any switching by the bottom switch) by the 
red thick wire under the sole in the battery compartment to [we allege]
a starter relay in the ENGINE CMPT.

1.2   The "-" side of batteries #1 and #2 are jumpered together, and connected
via a big black wire out the sole to a ground buss bolt under the engne.

1.3   The alternator's charging current [apparently] comes to the batteries
through the same thick red wire that the battery starting current follows.
[We think this is why this wire is colored red, not black.]

2.1   Battery #3's "+" (HOT) is routed from the ENGINE CMPT to the bottom main
switch's "1" terminal in the BATT CMPT, thus allowing battery #3's "HOT" side
to be connected through the bottom switch's COMMON terminal to the
thick red wire (i.e. the same one as in 1.1 above) going under the sole 
to the STARTER "HOT".

2.2  Battery #3's "-" goes to the ground bus connection under the engine.

3.1  Hummm... what to make of the thick black wire between the top main switch 
COMMON  terminal to the bottom switch "2" terminal?   
Hypothesis: Because driving the starter through the cascade of two switches 
adds a "splice" at the bottom switch's  COMMON terminal, a slightly lower 
resistance at the bottom switch's COMMON cable lugs MIGHT occur if we 
position the bottom switch to its "2" position, thus letting the COMMON
terminal's bolt give current to the wire lug..

4   The 120 VAC -to- 12 VDC converter is diagrammed in the CVTR CMPT.
On the boat, this unit is located in a compartment under the port bunk,
and directly forward from the nav center.

4.1  Charging current at approx +13.5 V pass through three isolation diodes
and are connected to the "1" and "2" terminals on the main switches
where batteries are connected.   
Two pieces of 2-wire "Romex-like" wire contain these 3 +13.5 volt
drives (2 whites and 1 black, where the black color has no different
drive characteristics than the white wires).  
The two white wires drive batteries #1 and #2, while the black drives battery #3.

4.2  The other black in one of the "Romex" wires from the Converter is the 
common for the 3 charging circuits, and is connected to the ground buss
under the engine.

4.3  The blue wire from the converter is used to turn off charging by the
converter  whenever the engine is running.  We allege that we will find t
hat this wire will get alternator voltage through an isolator or relay
which decouples the battery "hot" from being sent to the blue wire
when the engine isn't running, as sketched in the CLOUD OF ASSUMPTIONS.

4.4  The above isolator/relay function is also needed to power the engine 
oil-pressure annunciator, and is shown as the same circuit in the 
CLOUD OF ASSUMPTIONS driving the Converter and the oil-pressure gauge 
(and maybe other gauges?)

4.5  The 120 VAC circuit is not shown for the Converter.  There is an 
on/off switch on the unit, and a variable resistor (internal, not expected 
to be "tweaked") which sets the output voltage to all three isolation diodes
in the unit.

4.6  I believe there's another on/off switch for the converter to the left 
of the nav station.             TODO: check this...

5.1  The alternator and isolation diodes in the CLOUD OF ASSUMPTIONS are
there to show part of the functionality needed to use the same wire
with battery "hot" from the main switches for sending the alternator's
charging current back to the batteries.  
The alternator has -- in addition to its medium-thick red wire for its output --
a number (3 + 2 or 3 + 3) tiny wires from it going back to a rat's-nest
of intersections of wiring harness, which I didn't want to split apart.  
This plethora of little wires from the alternator hints at finding that the
regulator is separate from the alternator.

5.2  The "ignition key" function which would have turned on engine instruments
must use a relay that activates them when the engine is running,
i.e. driven from the alternator.  

5.3  I also expect to find a shunt for the ammeter somewhere in the
alternator/engine area in the CLOUD.

6.1  I just realize that I don't know where the "hot" of the distribution 
switch  panel at the nav station connects into the ship's 12 V main.  
I'll betcha Ted will know by now?