Open Circuit Voltage / Repair “Smog” License Certification
Free ASE PREP – Open Circuit Voltage
Open circuit voltage readings are when there is no voltage drop across a load or no voltage being applied to a load in a circuit, in other words there is source voltage on both sides of the circuit, “open ground” or voltage being applied to a load that has a open before the load.
Remember, for voltage too drop, current has to be flowing, if there is system voltage on the ground side of the circuit, there is no voltage drop across the load .
Open-Circuit-Voltage is basically when there is a break in that circuit and current stops flowing basically there is no current flowing in that circuit.
An open circuit can be on the feed or power side of a circuit where you have no voltage to a component, perhaps the circuit has a blown fuse or open wire.
The load device it self has a break or open within the load, you can even have a circuit with no ground.
Yes, a circuit that has no ground is still considered an open circuit, usually the clue of a non grounded circuit is, there will be source voltage on the ground side of the circuit.
Source voltage on the ground side of the circuit indicates no ground, no current flow and the load is not dropping any of the applied voltage.
Remember when there is an open circuit there will be no voltage drop across the load in that circuit.
A complete circuit is when source voltage has a path back to ground, when that circuit is interrupted or broken it’s called an open circuit.
Current will not flow through a circuit if it has an open.
When the current has pass though the last load in a circuit, all of the voltage should have been used up. If you have a voltage reading over a .1 of a volt on the ground side, there is resistance on the ground side of the circuit.
Anytime you find system voltage on the ground side of the circuit you have no ground for that circuit.
Quick review on Ohm’s law:
Voltage divide by Resistance will give you Amps
Voltage divide by Amps will give you Resistance
Amperage multiply by Resistance will give you Voltage
A.) A vehicle you are working on has a injector amperage specification of 3 amps on a 12 volt circuit. When you ohm out that injector it reads 1 ohm, what condition if any would this cause?
B.) If a vehicle has a short in the circuit what would happen to the current flow?
C.) Switches and contacts should have a voltage drop of no more than _______ millivolts?
D.) A 12volt series circuit has a voltage drop of a .3v across a connector before the load device, how would this effect the circuit?
E.) You have a reading of near zero volts after the last load in the circuit, this indicates what?
A.) The current will increase causing the injector to stop functioning and the vehicle will have a misfire.
B.) The current will increase.
D.) The load will function normally
E.) The circuit has a complete path to ground