Main 12-volt Control Schematic Diagram

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S/V Nevermore MAIN 12-volt CONTROL schematic

!!!! NOTE: On 07 Nov 2010 the wiring of the two main battery switches
!!!! was changed (because tje ;pwer switch became unusable).
!!!! The  "..._rewire_12v_main_sw_ ..." sketch shows before and after versions of switch
!!!!  wiring.  These diagrams show ONLY the wiring for high-current battery switching, 
!!!! and power drive to Nav Station CBs.  There is also lower-current wiring to each 
!!!! battery for charging from shore power, and to power the automatic bilge pump.
!!!! NOTE: The "12-volt Control schematic diagram" has been removed 
!!!! (observed approx Sep 2010) because there has been significant 
!!!! rewiring during the period approx late-2009 and 2010. 
!!!! Therefore much of the walk-through prose of this document, below, 
!!!! is no longer applicable.
!!!! (Ed: We don't think a diagram was produced when these circuits got rewired;
!!!! M.Wall (and maybe T.Young) may have a new diagram.)      

(return to Systems Descriptions 3.3.1)
 Right-click [12-volt system schematic]
 to view diagram while reading description below...
 The walk-through below relates to 27Aug07 version of the schematic.
 There is also an electrical schematic for the Engine
 Its circuitry will replace the 12-volt schematic's "cloud of assumptions".


The drawing is mostly schematic but also approximates some 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 (120 VAC -to- 12 VDC converter) 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 and a ground buss connector located under the engine, Also shown are the starter and alternator 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.


  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.

See [test-and-reconnect task] since 12V ckt disconnected c.Sep07] 
    4.0 NOTE: the understanding of the circuit and its operation is
        a bit erroneous below when a "relay" is assumed in the "cloud
        of assumptions."  We don't have time right now (pre-splash June '08)
        to rewrite these subsections (4.3, 4.4, and 5.2 below.)
        The CORRECT concept has been expressed in our write-ups which
        link to this wiki page.  
        Specifically, the "relay" which provides +12V to the "blue wire"
        charge inhibition function of the charger is actually the fuel-pressure
        switch defined in the engine schematic.  
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 [but see 4.0] that we will 
find that 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 [see 4.0] 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  The 120-v AC power to the Converter is most likely controlled by the 
left-hand 110 volt switch on the bulkhead above and to left of nav station,
in addition to the switch on the Converter itself.

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.  [NOTE: (Jun08, looking at this
section quickly]: The non-back-flow function of the alternator diodes is
probably important, but the observations about, or the importance of, 
the multiple little wires to the regulator doesn't make sense to me right now...]  
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.  [NOT QUITE TRUE; SEE 4.0.]

5.3  I also expect to find a shunt for the ammeter somewhere in the
alternator/engine area in the CLOUD.  [Uhhh... we believe -- but aren't
double-checking our memory of walking thru the schematic -- that the
ammeter shunt is actually in the meter.  Therefore, the whole charge/discharge
current flows out of the engine wiring harness and through the instrument 
panel harness (there's a plug/socket to connect these two pieces of equipment.)

6.1  TODO: 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.  
[c. end-Sep07 ThomS finds it on common contact of 1 of the 2 primary battery 
switches; doesn't remember which one, but will find notes when redraws the 
12-V schematic.]