Ag Power Web Enhanced Course Materials

Combination Circuit

A combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a combination of the two. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.

INTRODUCTION

A "COMBINATION CIRCUIT" is a circuit that is a blend of series paths and parallel paths. See Figure for a visual explanation. Most circuits are of this variety. Don't be afraid to tackle these circuits as far as the math goes. You merely have to break each part of the circuit down into either a series circuit or parallel circuit. Here's how this is done:

BASICS

You must first figure out the resistance of each individual parallel path in the circuit. Let's take the circuit to the right as an example. There is an 8 Ohm resistor in series (R1) and two 4 Ohm resistors in parallel, R2||R3 (Note: The || means that the two resistors are in parallel). To figure out the total resistance of that section of the circuit we use the following:

Find the resistance of the parallel circuit using the parallel formula.

• 1/R = 1/R2 + 1/R3
• 1/R = 1/4 + 1/4
• 1/R = .25 + .25
• 1/R = .5
• R2||R3 = 1/.5 = 2 Ohms
  

Now that you know the total resistance of the circuit you can figure out the total amperage using Ohm's Law.

• I total = V divide by R total
• It = 12V / 10 Ohms
• I total = 1.2 Amp.
  

From here you can figure out each components voltage drop or current.

The best advice in finding the values for a combination circuit is to first break each part of the circuit down into series and parallel sections and follow those formulas. Once that is complete, combine them for your main calculations.