MJM Yachts 34z Express - Manual (Page 22)

CHAPTER 6 ELECTRICAL SYSTEM
- 22 - 34z
6.1 GENERAL
The 34z’s electrical system is probably more advanced than to what you may be accustomed. It
combines DC and AC power. An understanding of how the system works will aid you in your
ownership.
12 volt DC power is stored in your batteries. This power is replenished either by an engine-driven
alternator or by a battery charger converting AC power to DC power. Most of the electrical
components on your boat use DC power.
120 volt AC power is what is typically found in homes. It is supplied to the boat in 3 ways: (1) via
a shore-power cord plugged into a shoreside receptacle (2) by the optional generator running
onboard (3) by inverting DC power from a battery into AC power. The AC components aboard
your boat include the cooktop, microwave, flat-screen TV, the air-conditioning, AC water heater,
inverter, and receptacles (for use with your own AC equipment).
Both AC and DC electrical power sources are potentially dangerous. Do
not attempt to work on any part of your boat’s electrical system if you are not a qualified
marine electrician.
6.2 DC
SYSTEM
There are two battery banks on your boat. The house bank consists of (2) 200Ah, absorbed-glass
mat (AGM) batteries. The engine bank consists of a single 105Ah AGM battery, and it is used to
start the engine and also to run the windlass and bow-thruster. Whenever a charging source is
present (either from the battery charger or an engine-driven alternator) both banks are
automatically charged. AGM batteries are essentially no-maintenance. Do not attempt to open the
batteries. Other than keeping them properly charged, stored, and clean (especially between the
terminals), there is virtually nothing you need to do to them. The battery charger is factory set
specifically for AGMs.
If the engine is not running, the batteries can be charged via the battery charger, which is
powered by AC electricity either from your generator or shore-power. It is important to read and
understand the inverter/charger manual to be sure that the unit is functioning as you expect.
Never allow your DC system’s voltage to fall below 11.2 volts. Sensitive electronics may fail to
function. For this reason, it is advisable when leaving the boat to turn off all loads, turn off their
respective circuit breakers, and turn off the main DC battery switches. The only load that remains
on when the battery switches are in the OFF position is the bilge pump circuit. (The CD/DVD also
uses a tiny amount of DC power to maintain memory settings.
To use DC components, the house battery bank switch must be ON, the main DC disconnect
breaker on the panel must be ON, and the component’s respective breaker must be ON. The
engine start battery switch must be ON to start the engine, or to use the windlass or bow-thruster.
The generator (if fitted)
uses the engine start
battery, but it has a
dedicated battery
switch. The engine
battery switch needs to
remain ON while the
engine is running.
Likewise for the
generator battery
switch when it is running.
BATTERY SELECTOR SWITCHES
A 4 th Switch will be added if a Generator is Installed