Electrical Systems; The Dc Electrical System - Tayana 37 Operation & Maintenance Manual

G. Electrical Systems
You will operate two different electrical systems on your TAYANA 37--a direct current
(DC) system which is the primary electrical system and an alternating current system
(AC) which is used primarily at a dock. Neither of the systems is difficult to use but
certain important rules must be followed.

1. The DC Electrical System

The primary source of electrical DC power is the storage battery(s). It is
important to remember that storage batteries are not the unlimited source
of power to which one is accustomed in the home. While a battery is
rechargeable, one can only take out of it what one has put into it. Thus, it
is important to keep track of how much charging is done and how much
current is drawn by the various DC accessories. When the engine is
running, accessories are not likely to draw enough to run down a battery--
the engine charge will maintain battery charge level. Under sail, however,
lights, instruments, autopilots, and other such wonderful devices can bring
a battery to its knees in relatively quick time.
a. The Energy Audit System
The best system which we know to help you use your power wisely is the
DC energy audit. Make a list of every DC electrical device, which you
have on board. Determine from markings on the equipment or from
equipment handbooks how many amperes each device draws in normal
operation. Add al1 of the amperes together and you wi11 see how much
TOTAL current would be drawn if al1 devices were operated at one time.
The Table on the following page will help you make such an audit for
your yacht. See Table IV.-1.
Your battery(s) are rated by ampere-hours. For example, a standard
battery, which comes with the TAYANA 37, is rated at 120 ampere-hours.
Theoretically, this means that the battery will provide one ampere 120
hours or 120 amperes for one hour. As with most things the theoretical
capacity and the actual usable capacity are quite different. In the case of a
wet cel1 battery one should plan on a maximum capacity of 50 percent of
the rated capacity. Thus, your standard battery wi11 provide you with
about 60 ampere-hours
On your electrical control board you wi11 find a DC ammeter which
shows the number of amperes which are being drawn from the battery at
any particular time. It is easy to see that if your ammeter shows 10
IV-9