Download Series – Parallel Dc Circuits

Jimmie Fouts
Houston County Career Academy
OBJECTIVES
 Review individual series and parallel DC circuit calculations and
operation
 Determine the equivalent circuit resistance for a given
combination circuit
 Determine the voltage drops in a circuit
 Determine the current values in a circuit
 Apply combination circuit theory to troubleshoot a combination
circuit
REVIEW : DC SERIES CIRCUIT CALCULATION
R1
10Ω
R2
30Ω
Es = 20 volts
Rt = R1 + R2 = 10 Ω + 30 Ω = 40 Ω
It = Es / Rt = 20 volts / 40 Ω = 0.5 amps
I1 = I2 = It
E1 = R1 X I1 = 10 ohm X 0.5 amp = 5 volts
E2 = R2 X I2 = 30 ohm X 0.5 amp = 15 volts
REVIEW: DC PARALLEL CIRCUIT CALCULATION
Es = 15 volts
R1
10 Ω
R2
30Ω
DC COMBINATION CIRCUITS
• Often called complex circuits
• Not complicated when considered as
individual series and parallel circuits
• E, I, & R solved using Ohm’s Law!
BAT T ERY
BASIC PROCEDURE FOR DC CALCULATIONS
Reduce the Complex Circuit to a Simple Equivalent

Reduce the circuit to Individual Series and Parallel Circuits

Perform Calculations on the Individual Circuits

Combine Calculations as Appropriate
COMBINATION CIRCUIT EXAMPLE
10
Reduce to individual series
and parallel circuit
A 10 ohm resistor is
In series with two 20 ohm
resistors
20
20
..
..
DETERMINE SIMPLE SERIES PARALLEL PARTS
In the parallel portion of the circuit,
the equivalent of two 20 ohm resistors
is 10 ohms
Parallel Circuit Equivalent
Is 10 Ohms
R1
R2
R3
COMBINE CALCULATIONS AS APPROPRIATE
The equivalent circuit is a
R1
10
10 ohm resistor in series
with the equivalent circuit
resistor of 10 ohms
Rt = R1 + Re = 10 + 10
Rt = 20 ohms
Rt
Re
10
USE OHMS LAW FOR CIRCUIT VALUES
Lets now apply a source voltage of
20 volts. The voltage drop across R1
will be 10 volts.
E = 20 volts
CALCULATIONS CONTINUED
CALCULATION OF PARALLEL CIRCUIT VALUES
Is calculated in the same manner
R2
R3
THE RESULTING CIRCUIT VALUES
A summary of the circuit values would therefore be:
ohms
1 amp
10 volts
= 20 volts
ohms
10 volts
0.5 amp
ohms
10 volts
0.5 amps
TROUBLESHOOTING COMBINATION CIRCUITS
 Look for obvious damaged components
 Take voltage readings of individual
components (observe safety requirements)
 Look for an open or a short circuit condition
 Check against expected values
IMPORTANT SAFETY NOTE!
Before making any resistance measurements in
a circuit, ensure there NO power is being
supplied to the circuit! Failure to follow this
caution will likely result in equipment damage.
CALCULATE EXPECTED VALUES!
•
It is important to first calculate the expected values before making
measurements using the meter!
•
Using the calculated values, prior to selecting the scale to use, will help prevent
meter damage.
•
Some things to consider:
• An open across a resistance in a series circuit will result in a measurement of the
source voltage across the defective resistor.
• An open across a resistance in a parallel circuit will be difficult to identify, without
calculating the expected value. Remember, the voltage across a parallel circuit is
the same on all legs of the circuit. An open on a parallel circuit leg will result in
the circuit exhibiting a greater resistance and larger voltage drop across the
parallel circuit.