CUP-BEARING 9W3756 - Caterpillar

Introduction to Basic Circuit Theory
This information covers basic direct current theory by reviewing the three basic types of electrical circuits and the laws that apply to each type circuit:
Series Circuits
Parallel Circuits
Series-Parallel CircuitsSeries Circuit
Illustration 1 g01070312
A series circuit is the simplest kind of circuit. In a series circuit, each electrical device is connected to other electrical devices. There is only one path for current to flow. In Illustration 1, current flows from the battery (+) through a fuse (protection device) and a switch (control device) to the lamp (load) and then returns to frame ground. All circuit devices and components are connected in series. The following rules apply to all series circuits:
At any given point in the circuit, the current value is the same.
The total circuit resistance is equal to the sum of all the individual resistances. This is called an equivalent resistance.
The voltage drop across all circuit loads is equal to the applied source voltage.The following rules are for a series circuit:
Voltage is the sum of all voltage drops.
Current is the same at any given point in the circuit.
Resistance is the sum of all individual resistances.Applying the Rules
Illustration 2 g01070313
Illustration 2 shows that the circuit is made up of various devices and of various components. This includes a 24 volt power source. Since two of the circuit values are given (voltage and resistance), solving for the unknown value is simple.The first step in solving the above circuit, is to determine the total circuit resistance.The following equation is used for determining total resistance: Rt = R1 + R2 + R3, or Rt = 3Ohms + 3Ohms + 6Ohms, or Rt = 12Ohms.Since the value for the power source was given as 24 volts and the circuit resistance has been calculated as 12Ohms, the only value remaining to calculate is the current flow. Total circuit current is calculated by using the Ohm's Law Circle and by writing the following equation: I = E/R, or I = 24V/12Ohms, or I = 2 amperes.The remaining step is to plug the value for current flow into each of the resistive loads. One of the rules for series circuits stated that current was the same at any given point. The equation E = I × R for each resistor will determine the voltage drop across each load. The following equations are for voltage drops:
E1 = 2A × 3Ohms = 6V
E2 = 2A × 3Ohms = 6V
E3 = 2A × 6Ohms = 12VAll of the circuit values have now been calculated. Verify each answer by using the Ohm's Law Circle.Parallel Circuit
Illustration 3 g01071099
A parallel circuit is more complex than a series circuit because there is more than one path for current to flow. Each current path is called a branch. All branches connect to the same positive terminal and negative terminal. This causes the branches to have the same voltage. Each branch drops the same amount of voltage, regardless of resistance within the branch.The current flow that is in each branch can be different. The difference depends on