DigiCore Technology Ctrack iS100 Series II Installation Manual page 23

and solenoids, all with coils of their own, now consider all the switches across those contacts
that an arc could be created.
Voltage is increased even more when the magnetic field collapses around a metal core, as in an
ignition coil. High voltage is useful from the ignition coil, but unwanted when it comes from
something else, In order to prevent a voltage spike from going somewhere it does not belong,
the circuit usually has some sort of protection, most commonly clamping diodes, capacitors and
resistors.
A diode acts like an electrical check-valve and only lets current flow in one direction. A capacitor
acts like an electrical cushion and a resistor acts like an electrical sponge. All three act to
prevent stray voltage spikes from harming circuits.
Most relay solenoids have diodes across the coil to prevent back EMF when the voltage
collapses. If this diode is blown, the protection is lost. The back EMF from the coil can be
several times higher than the supply voltage; the high back EMF can cause damage in time to
the circuit that drives it, often some type of onboard computer system.
Ground
The ground circuit is one of the most neglected and possibly the most misunderstood and
misdiagnosed circuits in a vehicle. Basic electrical theory says that a circuit must be a complete
loop, rather than run a return wire for every circuit. Automotive engineers use the vehicles metal
body to carry the current back to the battery.
The most common problem with the ground side is a missing or weak ground. Missing grounds
are often the result of a forgetful panel beater who did not replace the ground strap between the
engine block and the firewall or fender. Sometimes DIYers will replace a battery and forget the
ground pigtail. Sometimes the ground strap just breaks as a result of corrosion. If there is poor
contact due to a loose screw or due to corrosion ate the ground connection, resistance is
created in the circuit. The ground is still there but it is resistant to the flow of electricity, which
looks for the path of least resistance home to the battery. Sometimes this path can be through
some other circuit like the Ctrack unit.
Voltage Drop
How important is voltage drop? Support Engineers make their living measuring voltage drops.
Arm yourself with an accurate DMM, accurate to within 10mV on AC or DC measurement.
Properly used, it will save you a lot of time and money unnecessarily changing electronic
modules or vehicle wiring. Resistance in a circuit causes the voltage drop. This is normal if the
resistance is a light bulb or "blower" resistor. However voltage drops caused by bad circuits can
create some strange symptoms including rough running engines, starting problems, chattering
relays, radio interference, false problem codes from service computers and problems with
OBC's.
Revision: 02 05 December 2012
DigiCore Technology (Pty) Ltd
P.O. Box 68270, Highveld Park 0169, South Africa
Ctrack iS100 Series II Installation Manual
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Manual
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