# Parallel connection of resistors. Calculations of total resistance, total power.

A resistor is an element of an electrical circuit that has resistance to electrical current. Two types of resistors are classified: fixed and variable (trim). When modeling a particular electrical circuit, as well as when repairing electronic products, there is a need to use a resistor of a certain value. Although there are many different denominations of permanent resistors, at the moment there may not be the required hand, or there is no resistor with this denomination. To get out of this situation, you can use both serial and parallel connection of resistors. How to correctly calculate and select different resistance values will be discussed in this article.

The series connection of resistors is the most elementary circuit for assembling radio components, it is used to increase the overall resistance of the circuit. With a serial connection, the resistance of the resistors used is simply added, but with a parallel connection, it is necessary to calculate by the formulas described below. Parallel connection is necessary to reduce the resulting resistance, as well as to increase power, several parallel-connected resistors have more power than one.

In the photo you can see the parallel connection of resistors.

Below is a schematic diagram of the parallel connection of resistors.

The total nominal resistance must be calculated according to the following scheme:

R (total) = 1 / (1 / R1 + 1 / R2 + 1 / R3 + 1 / R n).

Where:

- R (total) - total resistance;

- R1, R2, R3 and Rn - parallel connected resistors.

When a parallel connection of resistors consists of only two elements, in this case, the total nominal resistance can be calculated by the following formula:

R (total) = R1 * R2 / R1 + R2.

Where:

- R (total) - total resistance;

- R1, R2 - parallel connected resistors.

In radio engineering there is the following rule: if a parallel connection of resistors consists of elements of the same rating, then the resulting resistance can be calculated by dividing the value of the resistor by the number of connected resistors:

R (total) = R1 \ n.

Where:

- R (total) - total resistance;

- R - the value of the parallel connected resistor;

- n is the number of connected elements.

It is important to bear in mind that when connected in parallel, the resulting resistance will always be lower than the resistance of the smallest resistor.

We give a practical example: take three resistors, with the following values of nominal resistance: 100 Ohm, 150 Ohm and 30 Ohm. We will calculate the total resistance, according to the first formula:

R (total) = 1 / (1/100 + 1/150 + 1/30) = 1 / (0.01 + 0.007 + 0.03) = 1 / 0.047 = 21.28 Ohm.

After calculating the formula, we see that a parallel connection of resistors consisting of three elements with the smallest nominal of 30 ohms results in a total resistance in the electrical circuit of 21.28 ohms, which is almost 30 percent lower than the smallest nominal resistance in the circuit.

Parallel connection of resistors is most often used in cases where it is necessary to obtain resistance with greater power. In this case, you must take the resistors of the same power and with the same resistance.The resultant power in this case is calculated by multiplying the power of one resistance element by the total number of parallel-connected resistors in the circuit.

For example: five resistors with a rating of 100 ohms and with a power of 1 watt each, connected in parallel, have a total resistance of 20 ohms and a power of 5 watts.

With a series connection of the same resistors (the power is also added), we obtain the resulting power of 5 W, the total resistance will be 500 Ohms.