View source for Main 12-volt Control Schematic Diagram

= S/V ''Nevermore'' MAIN 12-volt CONTROL schematic =

::::::::(return to [[Ship's Systems Descriptions#3.3.1 12-volt DC | Systems Descriptions 3.3.1]])

  Right-click [[http://home.att.net/~t-e.spettel/nevermore/schem-12v-P1090654-bw-72p-070827.jpg  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 schematic dgm|Engine]]
  Its circuitry will replace the 12-volt schematic's "cloud of assumptions".

= LAYOUT OF THE DRAWING = 
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.

= 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.
 
 See [[http://sailing.mit.edu/mediawiki/index.php/110v_charging_system_%28task%29  test-and-reconnect task]] since 12V ckt disconnected c.Sep07] 
 
 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  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.
 
 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?