LESSON
11
SELF-INDUCTION,
CEMF,
MUTUAL INDUCTION, EMI
WHAT IS
SELF-INDUCTION?
Self-induction
- a voltage induced in a coil as it's own magnetic fields expands and
collapses past itself.
The self-induced
voltage is CEMF.
Counter Electromotive Force -
a voltage created in a coil, as its magnetic field expands
and collapses, that
opposes the coil’s applied voltage.
OR
a voltage created in a motor's armature, as it spins,
that opposes the voltage applied to the motor.
The CEMF,
acting as resistance, causes the motor's current draw to decrease as it gains
speed. A motor turning slowly draws
more current than it does when it turns fast.
Mutual
Induction - Two coils next to each other.
As current starts and stops in one coil, its field cuts across the other
coil inducing a voltage in it.
Devices: Ignition
Coils and Transformers.
Two Types
of Transformers:
1. Step-up - Voltage
is increased. More secondary windings.
2. Step-down -
Voltage is decreased. Fewer secondary windings.
Electromagnetic
Interference (EMI) -
voltage spikes generated in conductors from rapidly changing
magnetic fields
Sources - Plug
wires, Alternator, C.B.s, cellular phones
RFI - Radio
Frequency Interference -
EMI occurring at the same frequency as radio waves
HOW CAN
EMI AFFECT A CAR?
plug cross fire,
computer glitches, radio static