Voltage Drop – wiring LED strips to avoid reduced or uneven brightness

What is voltage drop?

‘Voltage drop’ is a reduction in voltage between the initial power supply’s 100% voltage, across all or part of a circuit. Excessive voltage drop can make your lights flicker or burn dimly.

One of the main causes of voltage drop is using the wrong type of connection when adding distance between your LEDs and their power supply.

For example: a transformer outputting 24v DC at source can supply its full 24 volts to an LED strip across 10m of cable – but only if you have used a suitable cable to carry the current. Installing exactly the same circuit with 10m of an incorrect connection (such as an extremely thin cable) will lead to a voltage drop, possibly resulting in a power supply of 22v or even less reaching your LED strip.

What factors affect voltage drop?

Several factors can improve or worsen voltage drop across a circuit. They include the following:

• Cable thickness:

For longer cable runs you will need a thicker cable to avoid voltage drop – while for shorter runs you can use thinner cables and yet still have no voltage drop. Cable thickness is the single most significant factor affecting voltage drop: if you use a cable that is too narrow, this will certainly cause a decrease in voltage towards the end of your long cable run. (Exactly how much voltage you’ll lose will depend on how much thinner your cable is than the correct thickness for the length of the run).

• Cable composition:

As with any circuit, the material a cable is made from will affect how well it conducts a current. Like TV aerials and speakers, a variety of conductors can be used in the manufacture of your cable – substances including aluminium, copper, gold and others. The better the conductor, the further and more effectively it will carry a current from source.

• LED tape length is too long:

Voltage drops cabn happen not only across cables used to power LED tapes, but also across LED tapes themselves. As a general rule, any continuous run of LED tape longer than 6 metres will start to suffer a voltage drop. But it’s no problem to design a LED tape installation longer than 6m that will avoid voltage drop. To learn how to do this, see our how to install large LED tape projects support page.

So how does voltage drop affect my LED strip lights?

If you are looking to mount an LED strip some distance away from its transformer, then voltage drop may affect your lights. If you use the wrong cable (an unsuitable thickness, etc) or fit a continuous length of LED tape longer than 5m, then you may find that you have less volts reaching the beginning of your LED tape – and therefore less brightness!

I want to work out how far I can have my LED strip lights away from my transformer. How can I calculate voltage drop?

There’s a wide choice of voltage-drop calculators and apps online. A search on ‘voltage drop’ via Google or any other search engine will show many websites that offer suitable calculators.

Once you’ve entered the required factors – such as type of cable and length of run – the calculator will recommend the cable thickness you should use for your installation, and let you know how much voltage drop you can expect.

At InStyle, we like the Dr Voltz app for Android devices. You can check it out at the Play Store via the following links…