# How to Wire LED Lights in Series

Written by david robinson
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Light Emitting Diode lights (LEDs) are an increasingly popular alternative to traditional incandescent lights. Their low power consumption, long life, low operating temperature and physical strength all exceed the best expectations of a traditional light. Unlike incandescent light bulbs, LEDs are polarised and illuminate only when correctly wired. Connecting LED lights in series requires a basic understanding of electricity and the ability to use a calculator.

Skill level:
Moderate

### Things you need

• Calculator
• Wiring suitable for the voltage used
• Battery clips
• Soldering iron
• Solder

## Instructions

1. 1

Determine the voltage of the power supply. LEDs linked in series each consume some of the available volts, leaving fewer volts for the remaining LEDs in the series. The available voltage therefore determines the number of LEDs you can link in a series circuit.

2. 2

Calculate the maximum number of LEDs by dividing the battery voltage by the forward voltage (Vf) of the individual LEDs. The technical data sheet for the type of LED will state the forward voltage. For example, if the LED forward voltage is 3.4 volts, and the battery is 24 volts, use seven LEDs in series because 24/3.4 = 7.05. Never exceed the available voltage. When the combined voltage of the LEDs is less than the battery voltage, find the difference by subtracting the combined LED voltage from the battery voltage. Record this value.

3. 3

Solder or otherwise attach a battery clip to one end of a wire. This wire will connect to the positive side of the power supply. Solder the longer leg of the first LED to the other end of the wire. The longer leg is always the positive side of an LED. Solder the remaining LED's together in a line, adding wire between them if desired, and always wiring the positive leg to the negative leg of the preceding LED.

4. 4

Solder a wire to the negative leg of the final LED. If the combined LED voltage exactly equals the voltage of the power supply, attach a battery clip to the other end of the wire and then connect both battery clips to the battery to complete the circuit.

5. 5

Add a resistor to the circuit if the LED voltage does not exactly match the battery voltage. Resistors burn off the excess voltage as heat. Find the current drawn by the LED by reading the technical data sheet. Divide the differences in the voltages, established in Step 2, by the LED current in amps. The answer is the value of the resistor to add to the circuit. For example, a voltage difference of 3 volts and an LED current of 0.02 amps would require a 150-ohm resistor. Attach the resistor anywhere between the last LED leg and the negative battery terminal.

#### Tips and warnings

• When possible, add additional LEDs to use up excess voltage rather than using a large resistor to burn it off.
• If an LED fails to light, check that the wiring has the correct polarity.
• Normal LED lights use DC electricity and cannot work with AC current.
• Soldering irons and guns may have a tip temperature in excess of 200 degrees Celsius (200C).

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