Background:
    The Kisae charger is central to our new system.  It's connected to
    the vehicle battery, to "solar" (optionally, either real or fake),
    and to the house battery.

    In addition it has two wires that can connect to a temperature
    sensor, and it has a power switch that has been hacked so that the
    power can be switched on externally.

    The Kisae will charge the house battery if either of the charging
    inputs has enough "juice":
	- the alternator is raising the starter battery voltage above its
	    normal "resting" voltage by a sufficient margin, or
	- the "solar" input meets the right voltage and current requirements.

    If both are present, the Kisae will choose the alternator.  (The
    alternator will usually be the stronger charging source.)

    It will stop charging if:
	- neither of those charging inputs is available (e.g., when
	    boondocking), or,
	- if the temperature sensor leads are connected together (in order
	    to intentionally cause an E07 error), or,
	- the internal or external power switches are opened up.
    When it stops charging, it goes into "deep sleep" mode

We have two relays in the system.  They are "normally" in Idle state.

    - Relay R1 switches house loads between the house battery and house PSU
	Idle:
	    Caused by:  default
	    State:  house loads connected to house battery
	Energized:
	    Caused by:  house PSU is live/has power
	    State:  house loads connected to house PSU

    - Relay R2 acts as an external Kisae power switch, overriding the
	internal power switch, which is always left "off". 
    	Idle:
	    Caused by:  default
	    State:  external Kisae power switch is on (closed)
	Energized:
	    Caused by:  house PSU is live/has power
	    State:  external Kisae power switch is off (open)

There are three use scenarios:

    1) Driving.
	The Kisae's external power switch (relay R2, in its default
	state) will be "on".  The Kisae will sense that the alternator
	is running, and will charge the house battery.

	Relay R1 (in its default state) will connect the house loads
	to the house battery.

	The alternator will charge the vehicle battery.

    2) Boondocking.
	The relays are unchanged from "Driving", but the alternator
	is no longer providing power.

	The Kisae's external switch (relay R2) will be on, but there
	will be nothing to charge from (usually -- solar would change
	this), so there will be no charging of the house battery. 
	(Unfortunately, the Kisae itself will drain the battery by
	roughly 1.25Ah/day in this state.  To prevent this, we can
	either use the manual "Charger Disable" switch (see below), or
	we can purchase a solar panel.)
	
	Relay R1 will connect the house loads to the house battery.

	There will be no charging of the vehicle battery.  (No
	alternator, and no 110V for the vehicle battery charger.)

    3) Shore power.
	When we plug in, the relays both become activated by the 12V
	house PSU:
	 - The house loads are diverted to the house power supply
	    unit (by relay R1).
	 - The Kisae will be turned off (by relay R2).
	 - The vehicle battery charger becomes operational, because
	    its 110V plug is now live.  This is why we turn off the
	    Kisae -- otherwise it would be confused by the vehicle
	    battery charger supplying juice to its vehicle
	    battery/alternator input.

	So the normal shore power state is that:
	    - the Kisae is off
	    - the house battery is isolated (not charging, and no loads
		draining it).
	    - the house loads are all powered by the house PSU
	    - the starter battery is being charged by the vehicle charger.

	There are two manual switches to adjust the above behavior:

	    When we need or want to disable the Kisae completely, for
	    instance if we're boondocking or parked in the driveway
	    for weeks without plugging in, there will be a "Charger
	    Disable" switch (SW1) which will turn it off completely.

	    Conversely, If we absolutely need to force the Kisae to
	    turn on while on shore power, perhaps to do emergency
	    house battery charging from a solar panel or power
	    supply, we can use the Kisae's internal switch, which will
	    turn on the Kisae regardless of relay R2 and switch SW1.
	    (Normally the internal switch would be left off.)
	    BUT!!  We would need to unplug the vehicle charger before
	    doing so!!!  So we might want a warning label near the
	    Kisae's internal switch.


There are two more controls:

    First, it can damage the house battery to charge it when
    temperatures are below freezing (32F).  It's okay to draw power
    from it at those temperatures, but no charging.

    The BMV battery monitor (the round display up on the wall) will
    have a temperature sensor attached to the house battery.  It also
    has a tiny relay within it, which will be connected to the
    temperature sensor input of the Kisae.  (That it's a temperature
    sensor input is just coincidental, since all we're doing with it
    is faking a fault to get the charger to shut down.)

    We will program the BMV so that if the temperature falls below 33F
    (say) that it should close its relay, which will in turn cause an
    E07 error on the Kisae, and shut it down.  The BMV will be
    programmed to keep its relay closed until the temperature has
    risen to 40F (say), at which point the charger will be allowed to
    operate again.
	
    Second, during the winter we will likely remove the house battery,
    to avoid the risk of it being exposed to damaging temperatures
    (-10F or below).  When we remove it, the house loads will no
    longer have a power source.  So there's a switch (SW2) which will
    connect the house loads to the vehicle battery.  We just need to
    avoid using high power loads in this mode (i.e., no fridge).