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Electrical Circuit Diagnosis - Course 623. 2-1. A circuit is a complete path for current when voltage is applied. There are three basic types of circuits:.
Typology: Lecture notes
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A circuit is a complete path for current when voltage is applied. There are three basic types of circuits:
All circuits require the same basic components:
Components of a Circuit All circuits have these basic components.
Fig. 2- TL623f
Section 2
Power source − In automotive circuits, the source is typically the battery.
Protection device − Circuits require protection from excessive current. Excessive current generates heat and can damage wires, connectors, and components. Fuses, fusible links, and circuit breakers protect circuits by opening the circuit path when there is too much current.
Load − The load can be any component that uses electricity to do work:
Control device − The simplest control device is a switch. A switch opens or closes the path for current. Close the switch and current is present to operate the load. Open the switch and current stops. The load no longer operates.
A control device can do more than just turn the load on or off. It can also regulate how the load works by varying the amount of current in the circuit. A dimmer is an example of such a control device.
There are other types of control devices:
Ground − The connection to ground provides a shortcut" back to the source. Ground is typically any major metal part of a vehicle. You can think of ground as a zero voltage reference. Ground provides a common connection that all circuits can use so that they do not have to be wired all the way back to the battery.
The circuit type is determined by how the power source, protection devices, conductors, loads, control devices, and grounds are connected.
Section 2
You can use Ohm’s Law to predict the behavior of electricity in a circuit.
For series circuits, apply Ohm’s Law as follows:
− RT = R 1 + R 2
− ER1 = I x R 1 − ER2 = I x R 2
In most modern texts, current is represented as I" and voltage as E." You may also see these represented as A" for amperage, instead of I" for current, and V" instead of E" for voltage. When using that terminology, the Ohm’s Law equation looks like this: A = V/R.
Ohm’s Law in Series Circuits When troubleshooting, use Ohm’s Law to predict the behavior of a series circuit.
Fig. 2- TL623f203c
Electrical Circuits
Use Ohm’s Law to troubleshoot series circuits:
Electrical Circuits
Current in a Series Circuit
When practical, remove the fuse to measure current in a circuit.
Fig. 2- TL623f205c
Current in a series circuit − Current in a series circuit is the same at every point in the circuit.
Section 2
Measuring Resistance in a Series Circuit Remove the fuse before beginning resistance measurements. To test the dimmer, disconnect it from the circuit.
Fig. 2- TL623f206c
Resistance in a series circuit − To make resistance measurements:
In the series circuit above, isolate the dimmer for resistance testing.
EXAMPLE
Section 2
Find an Open Circuit Look for an open circuit by testing for voltage in the circuit. Start with the point closest to the power source (battery) and move toward the circuit ground.
Fig. 2- T623f208c
Testing for available voltage − Find the fault in an open circuit by testing for available voltage.
Electrical Circuits
Split - Half Method
Circuits with easy access to components can use the split-half method to isolate the problem.
Fig. 2- TL623f209c
Split−Half Method − You can use the split−half method on circuits where access to the related components is good. The split−half method works as follows:
− Check for continuity to ground on the ground side.
Electrical Circuits
Short Circuit The short circuit shown in this diagram is before the load. It provides an unwanted path for current to flow to ground. In most cases, a short like this increases current so much that it blows the circuit fuse.
Fig. 2- TL623f211c
Short circuit − A short circuit is a fault in the current path. A short can be:
Excessive current − Short circuits may cause excessive current.
Isolate a short circuit − To isolate a short circuit, disconnect sections or components of the circuit one at a time.
Section 2
Isolating a Short Circuit You can troubleshoot a short circuit with continuity checks, or you can use a sealed beam headlight in the isolation method shown here.
Fig. 2- TL623f212c
Isolating a short circuit − Circuit breakers and short detectors may damage some circuits. The following method works well for locating most short circuits:
Section 2
Parallel Circuit A parallel circuit has a source, protection device, loads with dedicated current path, control device and ground.
Fig. 2- TL623f
A parallel circuit contains all the elements of a series circuit:
However, a parallel circuit has more than one path for current. It typically has two or more loads, and it may have multiple control devices.
The circuit loads are connected in parallel paths called branches." Each branch operates independently of the others. In a parallel circuit, it is possible for one load to be inoperative while other loads continue to operate.
Parallel Circuit Elements
Electrical Circuits
Ohm’s law in Parallel Circuits
You can use Ohm’s law to predict circuit behavior. Total resistance is less than the smallest branch resistance. Voltage drop in each branch equals source voltage.
Fig. 2- TL623f
Applying Ohm’s Law − You can use Ohm’s Law to predict the behavior of electricity in a circuit.
For parallel circuits, apply Ohm’s Law as follows:
RT =
R 1 x R 2 RT = R 1 + R 2
− When you add a branch resistance to a parallel circuit, the equivalent resistance of the circuit decreases.
− When you remove a branch, the equivalent resistance increases.
Electrical Circuits
Current in Parallel Circuits Total current in the circuit equals the sum of current in each branch.
Fig. 2- TL623f216c
Current − Current in a parallel circuit behaves differently than it does in a series circuit.
Current through the lamps is split.
Section 2
Parallel Circuit Tests Diagnose parallel circuits using the DMM to measure voltage, amperage, and resistance.
Fig. 2- TL623f217c
