Current Calculator

Modern calculation of current from power and voltage

Calculation

Calculate Current

Calculate the current in amperes from power in watts and voltage in volts. Based on Ohm's law: I = P / U

Result
Current:

Information

Current Calculation

The current is calculated from power and voltage. This relationship is based on Ohm's law and the power formula.

Basic Formula
\[I = \frac{P}{U}\]
Current = Power ÷ Voltage
Example

Given: P = 1150W, U = 230V

\[I = \frac{1150}{230} = 5\text{ A}\]
Units

I: Current in Amperes (A)
P: Power in Watts (W)
U: Voltage in Volts (V)

Formulas for Current Calculation

Current can be calculated from various electrical quantities. Here we cover the calculation from power and voltage, which is very commonly used in practice.

Basics of Current Calculation

From Power and Voltage:
\[I = \frac{P}{U}\]

This formula results from combining Ohm's law with the power formula.

Derivation:
\[P = U \times I\]
\[I = \frac{P}{U}\]
Alternative Formulas:
\[I = \frac{U}{R}\]
Ohm's Law
\[I = \sqrt{\frac{P}{R}}\]
From Power and Resistance
\[I = \frac{Q}{t}\]
From Charge and Time

Practical Examples

Example 1: Household Appliance

Vacuum cleaner with 1150W at 230V

\[I = \frac{1150\text{ W}}{230\text{ V}} = 5\text{ A}\]

The vacuum cleaner draws 5 amperes from the outlet.

Example 2: LED Lamp

LED lamp with 10W at 230V

\[I = \frac{10\text{ W}}{230\text{ V}} = 0{,}043\text{ A} = 43\text{ mA}\]

The LED lamp only consumes 43 milliamperes.

Application Areas

Device/Application Power (W) Voltage (V) Current (A) Use
LED Lamp 10 230 0.043 Lighting
Laptop 65 230 0.28 Computer
Microwave 800 230 3.48 Kitchen
Vacuum Cleaner 1150 230 5.0 Household
Hair Dryer 2000 230 8.7 Personal Care

Safety Notes

Fuses and Cables
  • 16A fuse: max. 3680W (230V)
  • 20A fuse: max. 4600W (230V)
  • Consider cable cross-section
  • Continuous load: 80% of rated load
Important Warnings
  • Overloading can lead to fires
  • Power strips have limited capacity
  • Consult an electrician when in doubt
  • Check circuit breakers regularly
Important Notes
  • The calculation applies to resistive loads (DC or AC with cos φ = 1)
  • For inductive loads (motors), the power factor must be considered
  • Starting currents can be significantly higher than rated current
  • Voltage fluctuations affect the actual current
  • For 3-phase systems, the formula must be adapted accordingly
Advanced Calculations
AC Current (with cos φ):
\[I = \frac{P}{U \times \cos(\phi)}\]
For inductive/capacitive loads
Three-Phase (3-phase):
\[I = \frac{P}{\sqrt{3} \times U \times \cos(\phi)}\]
For symmetrical 3-phase systems

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