LE Calculations 1

1. Limited Energy Calculations
A Review of
Ohm’s Law
Kirchoff’s Law
& Voltage Drop
Calculations

2. WARNING!!!
BEFORE STARTING THIS COURSE
YOU WILL NEED TO HAVE THE
FOLLOWING AT HAND:
1. The NEC
2. A copy of the LERC PDF on
Calculations (downloaded at this site).
3. A battery operated calculator that has
a M+, M- and MRC keys.

3. Ohm’s Law Formula Wheel

4. Ohm’s Law Rules
• 1. Always solve parallel portions of the
circuit first then use those answers to solve
the series portion of the problem
• 2. In a series circuit voltages are added, in
a parallel circuit voltage is constant.
• 3. In a series circuit current is constant, in
a parallel circuit currents are added.

5. Ohm’s Law and Resistance's
• In a series circuit resistance is added.
R1 + R2 + R3 = RT
• A circuit with 2 resistors in parallel we use
R1 x R2 / R1 + R2 = RT
• in parallel circuits having more than 2
parallel resistance's it really gets confusing
but we have a new way of solving any
amount of resistors in parallel with a simple
calculator

6. Calculator Solution to Parallel
Resistors
• Lets take a circuit
with three parallel
resistors
• R1 = 3 Ω
• R2 = 6 Ω
• R3 = 9 Ω

7. Kirchoff’s Voltage Law
• The sum of the voltage drop is always
equal to the source voltage.
• Remember: whenever you are using
Ohm’s law you can also invoke
Kirchoff’s law and vice-versa.

8. Calculation of Parallel Resistors
• First turn on and clear your calculators
memory (MRC, C, C) the memory should
be clear now.
• Now enter the resistors as follows:
1 / 3 M+ 1 / 6 M+ 1 /9 M+
• Now to get the answer do the following:
1 / MRC = this should display 1.6363639Ω

9. Lets try a few problems
Next we have a few problems for you to work
on. Use both sets of laws to work them.
First you will see the problem only. Try to
find the total resistance of the circuit.
After you have work the problem yourself
THEN right click to solve the problem step
by step using both sets of laws.

10. Ohm’s Law - #1
R1 = 3Ω R2 = 5Ω
R3 = 2Ω
R4 = 4 Ω
R5 = 5 Ω

11. Ohm’s Law - #1
• Solve for RT (Total Resistance)
RA = 1.05 Ω
• First solve for the parallel circuit
this gives us a subtotal for RA of
• Now add the two remaining resistors
to get RT
R1 = 3Ω R2 = 5Ω
R3 = 2Ω
R4 = 4 Ω
R5 = 5 Ω
RT = 9.05 Ω

12. Ohm’s Law - #2
• 1st Solve for the parallel of R3 and R4
• 2nd Solve the series circuit of R2, RA
and R5
• 3rd Solve the parallel of R1 and RB
• Solve for RT (Total Resistance)
R1=4Ω R2 = 2Ω R3 = 3Ω R4 = 5Ω
R5 = 6Ω
RA = 1.875 Ω
RB = 9.875 Ω
RT = 2.84 Ω

13. Ohm’s Law - #3
• 2nd Solve for the parallel of RA and R4
• 1st Solve for the series of R2 and R3
• 3rd Solve for the series of R1 and RB
• Solve for RT (Total Resistance)
R1 = 2Ω R3 = 6 Ω
R4 = 8Ω
R2 = 4Ω
RA = 10 Ω
RB = 4.44 Ω
RT = 6.44 Ω

14. Ohm’s Law - #4
• 3rd Solve the parallel of R2, R3 & RB
• 2nd Solve the series of R4, RA, & R7
• 4th Solve the series of R1, RC, & R8
• 1st Solve for the parallel of R5 and R6
R1=2Ω R2= 4Ω R3=6Ω R4= 8Ω R6=12Ω
R8 =16Ω R7=14Ω R5 = 10Ω
RA = 5.45 Ω
RB = 27.45 Ω
RC = 2.2 Ω
RT = 20.2 Ω

15. Completing the Circuit
Calculations
• Up to this point our problems have dealt
primarily with resistance issues.
• Remember, in order for a circuit to have
resistance it must have volts and amps also.
NOW > Go over all your formula and get use
to how they interact to find ALL the
measurements of a circuit, through each of
the items in the circuit.

16. Quiz 1