Automotive Batteries; Alternators And Generators; Household Batteries; Dc Milliamp Measurement - Gardner Bender GMT-18A Manual Del Propietário

Common DC Measurements

4.1 Automotive Batteries

Set the function/range switch to 50 DCV. First check the
quality of the battery terminal connector by touching the red
(+) test lead to the connector while touching the black (-) test
lead to any bare metal framework of the vehicle. The tester
should read 12 volts or higher on the 0-50 scale with all of the
vehicle accessories turned off. If the needle indicator moves
sporadically, this indicates a bad terminal connection. Remove
the terminal connectors and clean both terminals and
connectors thoroughly. For improved conductivity and
corrosion resistance, coat the terminals and connectors with
GB #OX-100 anti-oxidant compound (available at your local
hardware store). Replace and tighten the terminal connectors.
Secondly, if the terminals and connectors are making good
contact, touch the test leads to the battery and vehicle
framework as described above (see fig. 2). Note the reading of
the tester. Get an assistant to turn on the headlights while the
test leads are making contact. The needle indicator should
drop a few volts. Should the needle indicator drop 5 volts or
more, the battery should be charged or possibly replaced if the
voltage drop is significant. The circuit may need to be checked
further for problems within the electrical system that may be
draining the battery.
Figure 2

4.2 Alternators and Generators

Set the function/range switch to the 50 DCV range. While the
engine is idling at normal operating speed, touch the black (-)
test lead to the metal framework of the vehicle, then touch the
red (+) test lead to the output terminal connector. The
alternator output cable is always the heaviest gauge cable
attached to the alternator (see fig. 3). The needle indicator
should read 12 volts or more. If the needle indicator moves
sporadically, the cable may need to be tightened. If the engine
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is idling lower than is specified in the vehicle owners manual,
the voltage reading will be lower. If the output voltage
is significantly low, the alternator may require service
or replacement.
Figure 3
WARNING! When making automotive
measurements, observe safety precautions. Stay away from
the fan blades, belts and other moving parts of the engine.
Keep the multimeter and its leads away from moving parts.

4.3 Household Batteries

Household batteries can be tested in either one of two ways.
For a good/bad check, set the function/range switch to the
1.5V or 9V BAT setting depending on which type of battery is
to be tested. Touch the red (+) lead to the (+) terminal of the
battery and the black (-) lead to the (-) terminal of the battery.
Read the BAT scale at the very bottom of the scale plate. The
scale will indicate if the battery is good, questionable or should
be replaced. To more accurately measure the voltage value of
household batteries, set the function/range switch to 2.5VDC
when testing 1.5 volt batteries, and 50VDC when testing 9 volt
rectangular batteries and higher. Touch the leads to the
battery as before. Read the correct scale to determine the
condition of the battery.

5.0 DC Milliamp Measurement

5.
1) Fully seat the test leads in the correct input jacks.
2) Set the function/range switch to the appropriate
DCmA setting.
3) Touch the test leads to the circuit in series (in line with the
circuit) so that the circuit current passes through the
multimeter in order to make the measurement. If the
needle indicator deflects to the left, reverse the test leads.
With a set range of 10mA, read the 0-10 scale. With a set
range of 250mA read the 0-250 scale.
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