Series and Parallel Circuits

• Series circuits

• Parallel circuits

• Series-parallel circuits

Series circuits

• A circuit that has more than one load and all current flows through all the loads in the circuit

• Series circuits used in an automobile:– Blower circuit where variable fan speeds are

required– Seat heaters using a variable resistor to

control temperature

Example of a series circuit for a blower motor

Series circuits

• Total of all voltage drops will equal the source voltage

• Voltage drop is proportional to resistance

• The higher the resistance, the greater the voltage drop

• As resistance increases, current flow decreases

Parallel circuits

• A complete circuit with more than one path for current to flow

• Current flowing into each branch or leg varies according to the amount of resistance in that branch of the circuit

• The current flowing into any junction of an electrical circuit is equal to the current flowing out of that junction

Parallel circuits

• The total resistance of a parallel circuit is always less than that of the smallest resistance of any branch of the entire circuit

• The voltage is the same for each branch of the parallel circuit

• The sum of the individual currents in each leg will equal the total current

Parallel circuits

• Most of the current flow in a parallel circuit will occur in the branch with the least resistance

• As long as other branches of the circuit are complete, current will flow through them in accordance with Ohm’s law

• The only place where electricity can take the path of least resistance is in a series circuit

• Most lighting circuits on automobiles are parallel circuits

Series-parallel circuits

• Includes both parallel loads and loads that are electrically connected in series

• Added resistance in series portion of circuit, will decrease current flow through parallel branches evenly

• Example of series-parallel circuit used in automotive applications: dash board illumination with a dimmer switch

• As resistance increases with variable resistor in dimmer switch: current flow is decreased through dash lights