Page 62 - Electromechanical Devices and Components Illustrated Sourcebook

24 Electromechanical Devices & Components Illustrated Sourcebook

a typical voltage measurement. Measuring the voltage will
only give a general assessment of the condition of the battery.
This is because the battery will produce its full voltage even
Automatic Battery Charger
when its charge is substantially spent. The voltage only starts
to diminish at the end of the life of the battery.
Charge Cables
The charge on a lead/acid cell may be checked by measur-
ing the specific gravity of the electrolyte. The measurement is
Negative
Terminal accomplished by using a hydrometer as shown in Figure 3-22.
These devices are very similar in appearance to a turkey
baster. They consist of a transparent tube with a pickup tube
on one end and a squeeze bulb is attached to the other end.
Interconnect
Buss Bar Inside the transparent tube is a calibrated float. When elec-
trolyte is drawn up into the transparent tube, the float adopts
a level that corresponds to the specific gravity.

Stand

Squeeze Bulb
6-Volt Lead/Acid Batteries
Positive
Terminal
Figure 3-20 6-Volt Industrial Battery Bank with Automatic
Charger

Transparent Tube
Testing Batteries
Being able to assess the charge and condition is important to
the effective use of batteries. Most of us gauge the charge and
condition of our batteries by noticing that the appliance that Calibrated Float
they power isn’t working anymore. Time to change the batter-
ies! This really isn’t a bad method for small personal appli-
ances such as flashlights, calculators, cameras, and cell
Electrolyte
phones. Unfortunately, most of us use this same method for
our more important batteries. Discovering that your car battery
has failed is a great way to top off an evening at the symphony.
For standard dry cells, the general condition can be
assessed by simply measuring the voltage. Figure 3-21 shows
Pickup Tube
Figure 3-22 Hydrometer
Voltmeter

The float itself, Figure 3-23, is a glass ampoule with a
weight at the bottom. The neck of the ampoule is marked with
+ −
a specific gravity scale. By reading the point on the scale that
corresponds to the electrolyte level, the specific gravity of the
+ −
electrolyte can be determined and the charge state of the bat-
tery can be gauged.
Measuring the voltage and charge state of a battery will not
tell you the whole story, however. The internals of the battery
may be in poor physical condition and although the charge
state and voltage may be OK, the capacity of the battery may
be greatly diminished. To gauge the capacity of a battery, a
current load test must be conducted. Current load testing is
Battery only practical on rechargeable batteries because the test
Figure 3-21 Testing Voltage requires a substantial amount of current flow. This creates an