20 electrical systems troubleshooting
Charging System Test
The Micro500XL can perform several impor-
tant charging system tests, as shown in the fol-
lowing photo sequence. As you will see, the
unit instructs you at each step. (As with the
starter circuit test, if you are testing an older
diesel engine in cold temperatures, first warm
up the engine for 5 minutes.)
Trend Analysis
One way to use the Micro500XL is to predict
when a battery is going to give up the ghost. You
may remember that in photo 11 on page 19,
the screen display showed the rated CCA and
the measured CCA in real time based on theMINIMUM CRANKING VOLTAGE
AND VOLTAGE SPIKESMinimum cranking voltage is especially important on
today’s modern boats. The computer-driven systems found
aboard virtually all boats, as well as common marine elec-
tronic equipment such as fishfinders and GPS chartplotters,
are all sensitive to the low-voltage conditions that can
occur during engine cranking. In fact, low voltage during
cranking affects any system that shares the same battery(s)
as the starter.
What is the minimum? Most modern engine manufac-
turers recommend nothing less than 10.5 VDC. In most
cases, voltage levels below 10.5 VDC will increase the
possibility of an onboard computer “blinking out” or losing
data, as well as cause a variety of engine symptoms, such
as excessively rich fuel mixtures, rough running, or a com-
plete failure to start. Symptoms will manifest differently from
one engine or system to another, but suffice it to say that
cranking voltage is of more concern now than ever.
High voltage spikes are also a concern, and are some-
times caused by solenoids for battery combiner systems
and the like due to inductance(a property of a conductor
or coil that determines how much voltage will be induced in
it by a change in current) as these devices open and close
circuits. This problem is dealt with most effectively by electri-
cally isolating electronic navigation circuitry from cranking
motor circuits, which is often done by using a completely
separate battery supply for the electronic equipment.The initial screen for the starter circuit test: first, start the
engine. (Note: If you’re testing an older diesel engine in
cold temperatures, warm up the engine for 5 minutes
before beginning this test to prevent inaccurate results.)This next screen shows the results. In this case, the starter
circuit in question brought the system voltage down to
10.89 V, a normal and acceptable condition. (Anything
less than 10.5 V on a computer-controlled engine is con-
sidered unacceptable. On older engines without com-
puter controls, a minimum of 9.6 V is acceptable.)Press the ENTER key on the face of the instrument to begin
the charging system test.11 2