Voltage Drop Test For The Negative And Positive Terminals Of The Battery; The Ac Ripple Test - DigiCore Technology Ctrack iS100 Series II Installation Manual

Here are some voltage maximums you can use as a general rule. These are absolute voltage
listings, which may still be too high for certain sensitive OBC's
Across a connector = 0.000V
Across Ground
Across a wire or cable (depending on the length of the wire or cable) = 0.200V (200mV)
Across a switch = 0.300V (300mV)
How do you measure voltage drop?
voltmeter positive probe is always attached to the most positive side of the circuit being tested,
the negative probe to the less positive location.
Important: The circuit must be live during the measurement.
9.2. VOLTAGE DROP TEST FOR THE NEGATIVE AND POSITIVE
TERMINALS OF THE BATTERY
Checking the GND Terminal: Set your DMM to the low voltage scale or the mV scale. The most
positive point in any automotive circuit is the battery positive post, not the battery cable terminal.
In fact, check this connection first for any voltage drop. Connect your DMM positive lead to the
battery post and the negative lead to the terminal. Turn on the headlights so that the system is
drawing a lot of power. If there is any drop whatsoever remove the terminal and clean it along
with the battery post and check again. To check the drop from the block to the battery, connect
the positive lead to the block, the negative lead to the negative battery terminal, crank the
engine and note the reading, it should also be below0.100 volts.
Ground connection voltage drop is acceptable if it's below 0.100 volts, but many technicians
claim that anything in excess of 0.050 volts (50mV) in the grounds for electronic computer
controls is too much. Computer controls usually operate on five volts and carry extremely low
currents that are incapable of punching through even the slightest corrosion. The lower the
ground-side voltage drop, the better.
Follow the same procedure above for the positive terminal of the battery.
9.3.

THE AC RIPPLE TEST

The electrical system in all vehicles operates from a DC power source. By using an accurate DMM
we can measure the AC ripple from a DC power source. An ideal measurement would be zero
volts. Unfortunately this is not possible due to the noisy accessories, starters, alternators etc
operating off the vehicles power source. The test measurement must be carried out with the engine
running.
Revision: 02 05 December 2012
DigiCore Technology (Pty) Ltd
P.O. Box 68270, Highveld Park 0169, South Africa
Ctrack iS100 Series II Installation Manual
= 0.100V (100mV)
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