Calculators

Ohms Law
In a D.C. circuit the current is directly proportional to the applied voltage and inversely proportional to the resistance.
Current (A) = I
Voltage (V) = V
Resistance = R

Ohms Law

Kirchoff's Laws

1st. Law
At any electrical junction the current flowing into the junction is equal to the sum of currents flowing out of the junction.
Therefore I1 = I2 + I3 + I4

Kirchoffs First Law


2nd Law
The sum of the voltage drop across any complete path of components connected across the voltage supply equals the voltage provided by the power supply.
Therefore V4 = V1 + V2 +V3


Kirchoffs Second Law

Component Layout

Series
If two components are connected in series and they each have the same resistance the voltage flowing through component is the same (half of the supply voltage)
Therefore V1 = V2 + V3
and the current flowing through each lamp is the same.

Series Component Layout


Parallel
When two components are connected in parallel the voltage appears across both components
Therefore V1 = V2 = V3
The current flowing across the two components are equal but half of the current from the power supply so I1 + I2 = IT
Therefore I1 = I2 +I3


Parallel Component Layout

Impedance
In A.C. circuits the current is limited by the impedance (Z). Impedance is measured in ohms, and voltage = current (amperes) X impedance (ohms)
U = I x Z

Impedance in AC Circuits

Inductive Reactance
In alternating current circuits which set up significant magnetic fields, there is opposition to the current in addition to that caused by the resistance of the wires. This in additional opposition is called inductive reactance.

Impedance in AC Circuits

Capacitive Reactants
In alternating current circuits which set up significant magnetic fields, there is opposition to the current in addition to that caused by the resistance of the wires. This in additional opposition is called inductive reactance.

Capacitive Reactance in AC Circuits

Impedance in Series Circuit
Impedance is the name given to the combined effect of resistance (R) and reactance (XL or XC). It is measured in ohms.
For series circuit, impedance (Z) is given by:

Where
X = XL for a resistive inductive circuit
X = XC for a resistive capacitive circuit
And
X = XC - XL or XL - XC (the larger minus the smaller for a circuit with resistance, capacitance and inductance)

Impedance in AC Circuits

Star Connections
Figure 1 shows three loads connected in the star formation to a three phase four wire supply system. Figure 2 shows the phasor diagram, the red to neutral voltage URN is taken as reference and the phase sequence is red, yellow, blue so that the other line to neutral voltages or phase voltages lie as shown. If URN = UYN = UBN and they are equally spaced the system of voltage is balanced.
Let UL be the voltage between any pair of lines (the line voltage) and UP = URN = UYN = UBN (the phase voltage)

Then UL = √ 3UP
and IL = IP

where IL is the current in any line and IP is the current in any load or phase. The power per phase is P = UPIPcos θ and the total power is the sum of the amount of power in each phase
If the currents are equal and the phase angles are the same as in figure 3 the load on the system is balanced, the current in the neutral is zero and the total power is

P = √ 3UL IL cos θ

Star Connections - Figure 1 Figure 1

Star Connections - Figure 2 Figure 2

Star Connections - Figure 3 Figure 3

Star Connections
Figure 1 shows three loads connected in the delta or mesh formation to a three phase supply system. Figure 2 shows the phasor diagram of the line voltages with the red to yellow voltage taken as reference.
The voltage applied to any load is the line voltage UL and the line current is the phasor difference between the currents in the two loads connected to that line. If the load currents are all equal and make equal phase angles with their respective voltages the system is balanced and

IL = √ 3IP

The total power under these conditions is

P = √ 3UL IL cos θ

Delta Connections - Figure 1 Figure 1

Delta Connections - Figure 2 Figure 2

Ohms Law

Fill in two of the three fields to calculate the third

Horse Power to Kilowatts

Enter the voltage and horse power to calculate the kilowatts and amps

KW:
A: approx

Kilowatts to Amps

Enter the voltage, kilowatts and power factor to calculate the amps

Amps: