Voltage Drop Calculator

Voltage drop calculator is a simple tool that helps you determine what part of voltage is lost when the electric current moves through a wire, as well as calculate the voltage output at the end of the cable. Alternatively, you can use it as a wire size calculator to decide which wire diameter will ensure that your voltage drop doesn’t exceed acceptable levels.

What is the voltage drop?

By definition, the voltage drop is the reduction in the voltage, occurring when the electric current moves through passive elements of the circuit.

Let’s consider a wire that connects a house to the local electricity supplier. At ideal conditions, electrical current flows unobstructed along the wire until it reaches the house. There, it is used to power up multiple devices. In reality, though, the current is obstructed by some kind of opposing pressure. It means that some part of the voltage is lost when the current has to overcome this resistance. This loss is called voltage drop.

If you have troubles with understanding it, you can imagine a person running along a straight path. If the path is clear, without any obstacles, and with appropriate pavement, the person will move fast and steady. On the other hand, if the road is difficult to run along, and there are stones blocking the way, it is more likely that the person will lose a lot of her energy just trying to overcome all obstacles.

What influences the magnitude of voltage drop?

In general, the voltage drop occurs when the current has to travel along a wire. In such a system, both components – the current and the wire – influence the voltage drop. In particular, it is possible to distinguish the following factors:

  • Wire material. The application of better conductors will result in a lower voltage drop. For example, copper is a much better conductor than carbon steel; if you will analyze the same current flowing through two identical wires, one made of copper and one made of steel, you will discover that the voltage drop is higher in the steel one.
  • Wire size. The cross-sectional area of the wire has a large influence on the voltage drop. The thinner the wire, the higher the voltage drop will be.
  • Wire length. Intuitively, a longer wire means a longer way for the current to travel, and hence higher voltage losses. You should always try to minimize the length of a wire.
  • Load current. The higher the current, the higher the voltage drop. You should also double-check whether your wires or components such as LEDs can withstand a large current.
LED Resistor Calculator

This LED resistor calculator is a tool for determining what resistor you should use when creating different electronic circuits with LEDs. Thanks to these calculations, you can be sure that you won’t damage the diodes with excessive current.

You can use this LED calculator to find both the required resistance and the power dissipation in a single LED, all LEDs, or in the resistor.

LED calculator: an overview

LEDs, or light-emitting diodes, are small electronic components. When current is applied to LEDs, they emit light in various colors, such as red, green, or blue. If the current passing through the diode is too high, though, it will damage the LED.

LED resistorTo limit the current passing through the diode, it’s common practice to add a resistor to the circuit, as shown in this image. This resistor is usually added in series. Even though this method is uncomplicated and solves the problem in basic circuits, it shouldn’t be applied for high-current LEDs.

What do you need to know?

In order to calculate the resistance and power dissipation, you need to input a few parameters into this LED resistor calculator:

  • Circuit type. Are your LEDs connected in series or in parallel?
  • n – number of connected LEDs.
  • V – supply voltage of your circuit. Typical values are 5, 7 and 12 volts for molex connectors and 1.5 or 9 volts for batteries.
  • Vₒ – voltage drop across one LED. This value depends on the LED color and ranges from 1.7 volts (infrared) to 3.6 (white or blue diodes).
  • Iₒ – current across one LED. Regular LEDs require 20 or 30 mA.
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