Transcript Ch 2 PPt 2 Basic Theories

CHAPTER TWO CONTINUED
VOLTAGE
• Electrical pressure or potential
• The Electromotive force that causes the
movement of electons
• Electrical pressure is measured in volts
• Automotive electrical systems run on 12
volts
CURRENT
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Is the rate of electron flow
Measure in amperes or amps
As voltage goes up, current goes up
As voltage goes down, current goes
down
RESISTANCE
• Opposition to current flow – measured in
ohms
• Size, type, length, temperature and physical
condition of conductor affect its resistance
• An increase in resistance causes a decrease
in current flow.
• Voltage drops as current flows through
resistance
VOLTAGE DROP
• Is the amount of electrical pressure lost or
consumed as it pushes current through a
resistance
• The Sum (total) of all voltage drops in an
electrical circuit will always equal source
voltage – all the voltage is used up.
OHMS LAW
E = Voltage
I = Current flow
R = Resistance
E/I=R
E/R=I
IxR=E
TRY THESE…
E=12V R=12W
E=?
I=?
R=120W I=0.1A
E=12V R=24W
I=?
E=12V R=?
I=24A
CAPACITANCE
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Stores electrical charges
Does not consume any voltage
Absorbs voltage changes – Spikes
Discharges back into circuit
Rated in farads and microfarads
ELECTRICAL CIRCUITS
• A simple automotive circuit has three parts:
– Battery (power source)
– Wires (conductor)
– Load (lights motors)
• A circuit must have continuity, protective
devices (fuses), and controls (switches)
SERIES CIRCUIT
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Only one path for current to flow
Total resistance is the sum of all resistances
Current flow through each resistor is the same
Current flow is the same throughout the circuit
Voltage drop across each resistor will vary if the
reistor values are different
• The sum of all voltage drops will equal source
voltage
PARALLEL CIRCUIT
• Two or more paths for current to flow
• Voltage applied to each leg is the same
• Voltage dropped across each leg will be the same
– If more that one resistor in a leg, voltage drop will depend on
the resistance of each resistor in that leg
• Total resistance will always be less than the resistance of
any of its legs
• Current flow through the legs will differ if resistance is
different
• The sum of the current in each leg equals the total
current in the parallel circuit
SERIES-PARALLEL CIRCUITS
• Is a combination of series and parallel
circuits
DIGITAL VOLT OHM METER –
DVOM
• Values are displayed digitally
• Can Measure Volts, Ohms, Current,
Frequency, Duty Cycle, Rpm
• Have a high impedance, safe on
sensitive components and circuits
• Wide variety of adapters available
• Internally fused against overload
DVOM – Continued
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Common Prefixes used on meters:
Mega (M) 1,000,000
Kilo (K) 1,000
Milli (m) .001
DVOM - RULES
• Measuring voltage must be done on a live
circuit
• Measuring resistance (ohms) must be dome
on a dead circuit
• Measuring current flow (amps) must be
done in series within the circuit