Download Current Flow in Automotive Circuits

Current Flow in Automotive Circuits
Class Discussion Item 2.9
Presenter: Derek Gilman
Course: EAS 5407
Instructor: Dr. Ham
Question:
How does grounding an electrical component of an
automobile (ie. an alternator or starter motor) to the
frame, result in an electrical current?
Background
• Current is created when free electrons flow
from the negative pole on a voltage source, (a
battery in this case), to the positive pole.
• By convention we consider current to be a
positive flow in the opposite direction of the
electron flow.
• Chassis ground is the name given to the role
performed by the frame of an automobile when
it is connected to the electrical system.
Definition
• Chassis Ground
– A large conducting body used as a common return
for an electric circuit and as an arbitrary zero of
potential. Merriam-Webster Dictionary On-line
Purpose of Grounding
• Grounding is done to prevent a floating voltage
by determining a reference point for the circuit.
• Chassis ground also serves as a connector
between the battery and the electrical
components.
Connection
+
Car
Battery
Alternator
Chassis
Ground
Closing the Circuit
• Current flows from high potential to low
potential in the circuit.
• The battery’s negative pole is grounded to the
chassis.
• Current passes through loads en route to the
chassis.
Why is it done this way?
• Use of chassis ground simplifies circuit
• Replaces wiring
Applied Knowledge
• Car Jump-Start
• Safety Feature in Instruments