No problem was indicated by this test, but
let’s run it again, starting with a stone-cold
engine. As soon as I turn on the engine, I add
some electrical loads—all the onboard DC
lighting, the blower fan, and navigation
equipment—to get the alternator working
hard. Now I quickly take some measurements,
before the engine, components, and the com-
partment have a chance to heat up.
This time, I see a rapid increase of 25°F at
the terminal compared to the surrounding
area. Because this large temperature differen-
tial is so isolated, it’s a pretty good indication
that the terminal should be removed and
inspected for damage or corrosion. Remember
that the amount of heat produced varies
directly with the amperage in the circuit and
the resistance in the conductor or termination
point (more amps = more heat potential).
Note that only high-current DC circuits—
those connected to things like bow thrusters,
starter motors, alternators, and anchor
windlasses—have the capability to generate
enough heat for the infrared heat gun to be a
useful diagnostic tool. On the AC side of
things, the gun is useful for tracing from a
shore-power pedestal through to the boat and
at receptacles that have loads plugged in and
operating. The heat will invariably show up at
or near the terminal ends, assuming that the
wire gauge sizes were appropriate to begin with.Other Uses for Temperature Monitoring
Up to now, we have used temperature moni-
toring as a means for identifying electrical
problems. Now let’s shift our focus a bit to
monitoring temperatures to avoid problems.
Admittedly, this falls outside the normal
scope of troubleshooting, so let’s call this
exercise “trouble prediction and avoidance”
instead.64 electrical systems troubleshooting
temperature
sensorThe infrared temperature sensor on the Midtronics
inTELLECT EXP-1000 diagnostic meter.Batteries, Battery Chargers, and
Inverters
Some components on boats need to be kept as
cool as possible to ensure proper or even con-
tinued operation. Examples include isolation
transformers, DC-to-AC inverters, and bat-
tery chargers, all of which generate fairly high
temperatures.
In the case of battery chargers and inverters,
the issue is important enough for the ABYC to
address it in a standard. ABYC Standard A-31
(adopted July 2005) for manufacturers of bat-
tery chargers and inverters states, “Battery
chargers and inverters shall be designed to oper-
ate at 122°F (50°C) continuously and be able
to withstand a maximum of 158°F (70°C).”
Regarding batteries, we saw in Chapter 2
how temperature monitoring was one func-
tion of the Midtronics inTELLECT EXP-- In some marginal situations, the tem-
perature of a battery can affect the test results,
in which case the diagnostic meter will direct
you to measure the battery temperature using
its built-in infrared sensor (measurement