What is LED strip voltage drop?

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When working with high power LED strip projects, you may have observed firsthand or heard warnings about voltage drop affecting your LED strips. What is LED strip voltage drop? In this article, we explain the cause of it and how you can avoid it from happening.

Why LED strip voltage drop happens

Although it may appear otherwise, an LED strip (we'll assume 12V for this discussion) is essentially many groups of 3 LEDs that are connected in parallel.

Therefore, even though each group of 3 LEDs is designed around the full 12V, in many cases, LED groups farther away from the power source will actually be fed less than 12V, resulting in noticeably dimmer light output. Why does this happen?

The first reason is that the LEDs that are farther away from the power supply end have to have power carried across a longer distance of copper trace to reach it.

The internal resistance of the copper traces increases as the length of distance increases, and this in turn reduces the amount of voltage that can reach the LEDs that are located farther from the power supply.

The second reason is that the copper traces nearer to the power supply have to handle a lot more current as it needs to carry all of the current that is used by the LEDs further downstream.

For example, for an LED strip that is rated at 5 Amps per reel (5 meters), almost all of those 5 Amps will be fed through the very first section of the LED strip. About 1 meter in, 4 Amps will still be travelling through this point. At 3 meters in, only 2 Amp will be travelling through.

Why does this matter? As current density in copper increases, its resistance increases. So the 5 Amps at the very start of the LED strip could be too much for the copper traces to handle, adding a significant amount of electrical resistance right off the bat, thereby further reducing the actual voltage applied to all of the downstream LEDs.

Be aware that this also applies to the connectors and all wiring between the power supply and the LED strip as well. The wire gauge of the connecting wires needs to be sufficient, otherwise, you may already have lost some voltage before the signal even reaches the LED strip!

As we see in our voltage analysis of LED strips, even a small decrease in voltage can result in significantly less brightness.

Factors that can worsen the effect of LED strip voltage drop

The primary factors that determine the extent to which voltage drop can occur are current draw and copper thickness.

Current draw of the LED strip is the most important factor, and can be affected by the LED strip's initial design (e.g. watts per meter) or by the length of the LED strip that is being used. Even for a high power LED strip, if only a 1 meter segment is used, your amperage will be limited to 2 Amps or so.

Copper thickness is usually rated in ounces. (Defined as the amount of copper needed to flood a 1 sq ft surface area). The thicker the copper, the more current can flow through the circuit. We recommend 2.0 oz, and ideally 3.0 oz for higher power LED strips.

Read more about the copper used in LED strip substrates.

Is LED strip voltage drop harmful?

LED strip voltage drop is typically not detrimental to the performance of the LEDs themselves, as it is a case where less voltage is being supplied to the LEDs than was originally desired.

However, voltage drop typically signifies that you are losing power to electrical resistance, and this generates lots of heat. If your LED strips are installed in or near heat-sensitive materials, this may lead to an issue. The 3M adhesive backing as well as the LEDs are also heat-sensitive to some extent, so excessive voltage drop can be an issue.

How can I avoid LED strip voltage drop?

The best way to avoid LED strip voltage drop is to understand its root cause - too much current flowing through too little copper. You can reduce current by:

  • Reducing the length of LED strip used per power supply, or connecting multiple power supplies to the same LED strip at different points

  • Selecting 24V instead of 12V (typically same light output but half the current)

  • Selecting a lower power rating

  • Increasing the wire gauge for connecting wires

It's hard to increase copper without purchasing new LED strip lights, but be sure to find out the copper weight used if you think voltage drop might be an issue.

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