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Basic Electrical Equations

Watts, Volts & Amps

The most commonly used equation in electrics is the relationship between Watts, Volts and Amps. This can be displayed in a simple triangular reference diagram:




240V x 10A = 2400W

2400W/240V = 10A

2400W/10A = 240V


Ohms, Volts & Amps

Resistance is an electrical quantity that measures how the device or material reduces the electric current flow through it. The resistance is measured in units of ohms (Ω).


1Ω = 1V





R = V



The resistance of a conductor is resistivity of the conductor's material times the conductor's length divided by the conductor's cross sectional area.


R = p x l


R is the resistance in ohms (Ω).

ρ is the resistivity in ohms-meter (Ω×m)

l is the length of the conductor in meter (m)

A is the cross sectional area of the conductor in square meters (m2)


Amp Hours

Commonly used to demonstrate the amount of power available in a battery. It literally states the amount of amps that you can draw from the source for 1 hour or 1 amp for a number of hours.

 1Ah = 1A x 1hour


200Ah = 200A x 1 hour

                or 1A x 200 hours


NB: This is not necessarily a linear equation and more accurate power delivery data should be looked up in the datasheet for the battery.


Kilowatt Hours


Commonly used to measure the amount of electrical energy used by the consumers over a period of time. This is the unit that is used on domestic and industrial electricity meters.


1kWh = 1kW x 1h


1kWh = 1000W x 1h



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