Why Are Only Half of My LED Lights Working?

What Usually Causes Half-Strip Failures?

When only half of your LED strip lights up, it’s likely caused by one of a few common issues. Identifying the root cause early can save you time and effort in troubleshooting. Here are the most frequent reasons:

1. Voltage Drop

One of the most common causes for half of your LED strip not lighting up properly is a voltage drop. When the electrical power doesn’t reach the entire length of the strip, it can result in dimming or failure at the far end of the strip. This is especially common with longer LED strips, where the power gradually weakens as it travels the length of the strip.

Symptoms:

• Dim lights at the end of the strip, often getting worse as you move further from the power source.
• The far end of the strip may not light up at all.

How to Test for Voltage Drop:

1. Use a digital multimeter to measure the voltage at both ends of the LED strip.
2. Set your multimeter to the DC voltage setting (12V or 24V, depending on your strip).
3. Measure the voltage at the input (near the power supply) and the output (the far end of the strip).
4. If the voltage at the far end is significantly lower than the starting voltage, it indicates a voltage drop.

Fixing Voltage Drop:

• Use a stronger power supply to accommodate the voltage requirements for longer strips.
• Divide the strip into shorter sections, each with its own power source.
• Use thicker wires to reduce resistance and allow more power to flow through the strip.
  

2. Reversed Polarity

LED strips are polarity-sensitive, meaning the positive (+) and negative (-) connections must be correctly aligned. If you reverse the polarity when reconnecting or cutting the strip, part of it may stop working. This is commonly seen when strips are cut and reconnected without checking the polarity.

Symptoms:

• Only part of the strip lights up, usually where the polarity was reversed.
• The strip might work intermittently or not at all in certain areas.

How to Fix Reversed Polarity:

• Check the wiring and connections carefully to make sure that the positive and negative ends are connected correctly.
• If the wiring is incorrect, simply switch the connections to their proper polarity.
  

3. Broken Copper Trace or Solder Joint

LED strips are made of small copper traces that connect each LED. If any of these traces are damaged or if there’s a cold solder joint (where the solder didn’t form a proper connection), part of the strip will stop working.

Symptoms:

• One section of the LED strip doesn’t light up, while the rest does.
• The issue is often visible on the strip where the copper trace is damaged or the solder joint is weak.

How to Fix a Broken Trace or Solder Joint:

1. Inspect the strip carefully for visible damage to the copper traces or weak solder joints.
2. Use a soldering iron to repair broken solder joints or reattach the copper trace.
3. If the copper trace is completely damaged, you may need to cut and reconnect the strip at a new point.

4. Over-Driven RGB Channel

If you’re using an RGB LED strip, over-driving one of the channels (red, green, blue) can cause it to stop working or cause uneven lighting. This often happens when too much current is sent through a single color channel, causing the LEDs to burn out.

Symptoms:

• Only one color is visible (for example, only red or green light is present on the strip).
• The strip might flicker or have uneven color output.

How to Fix Over-Driven RGB Channels:

• Check the power supply to make sure it’s not overdriving any of the channels.
• Replace the affected LED module or RGB chip if necessary.

🧾 T1 – Cause-Symptom Table

How to Spot a Voltage-Drop Problem

One of the most common causes of half of your LED strip not lighting up properly is a voltage drop. This happens when the electrical power isn’t able to travel the full length of the LED strip, resulting in dimming or even complete failure at the far end.

Symptoms of Voltage Drop:

• Dimming at the Far End: The further you go from the power supply, the dimmer the strip becomes.
• Dead Sections: The far end of the strip may not light up at all, while the rest of the strip functions normally.

How to Test for Voltage Drop:

To determine if voltage drop is the issue, follow these steps:

1. Use a Digital Multimeter: Set your multimeter to measure DC voltage (usually set to 12V or 24V, depending on your LED strip’s requirement).
2. Measure at the Power Supply: Place the probes at the input end of the LED strip (near the power source) and note the voltage reading.
3. Measure at the Far End: Place the probes at the farthest point of the LED strip and check the voltage.
4. Compare Readings: If the voltage reading at the far end is significantly lower than at the input (more than a 1–2V drop for a 12V system), this confirms that voltage drop is the issue.

Fixing Voltage Drop:

If voltage drop is confirmed, here are a few solutions to fix the issue:

• Use a Stronger Power Supply: Ensure your power supply has enough capacity to handle the length of the LED strip. You might need a power supply with a higher current rating.
• Use Shorter Strips: Break up your LED strip into smaller sections, each with its own power supply. This will ensure that the power supply is adequate for each section.
• Use Thicker Wires: Increase the wire size to reduce the resistance in the circuit. This will help deliver more power to the LED strip without significant loss.
  

Step-by-Step Fix: Test & Repair a Dead Segment

If you’ve confirmed that one section of your LED strip is not working, here’s a step-by-step guide to test and repair the dead segment.

1. Inspect for Obvious Breaks

First, visually inspect the LED strip for any visible breaks, damaged areas, or burnt-out sections. Look for any discoloration in the LED segments, or any cracks along the copper traces.

2. Test Voltage at Cut Marks

Using a digital multimeter, test the voltage at the cut marks (where the LED strip was previously cut). Check for continuity and ensure the voltage reading at the cut point matches the required value (12V or 24V depending on your LED strip type). If there’s a significant drop in voltage at this point, it’s likely that the break or damage in the circuit is causing the issue.

3. Re-solder Copper Pads or Use Clip Connectors

If you find that the copper pads are broken, you can either re-solder the copper pads or use a clip connector to reconnect the segment. To re-solder:

• Clean the area: Gently sand or scrape the broken copper traces to ensure good solder adhesion.
• Apply solder: Use a soldering iron to re-solder the copper trace and ensure a good connection.

If you prefer an easier method, clip connectors are a good alternative. These allow you to simply attach the two ends of the strip without the need for soldering.

4. Seal with Silicone if IP-rated

If the LED strip is IP-rated for outdoor or waterproof use, make sure to seal the joints and connections with silicone to prevent water or dust from affecting the strip’s functionality.

Voltage-Drop Calculator: Pick the Right Power Supply

To avoid voltage drop, it’s essential to ensure that your power supply matches the total power requirement of your LED strip. Here’s a simple formula to calculate the power needs for your LED setup:

Steps to Calculate the Power Requirement:

1. Measure the Total Length: Measure the total length of your LED strip in meters.
2. Check the Power Consumption: Check the product specifications to find the wattage per meter of your LED strip.
3. Calculate the Total Wattage: Multiply the wattage per meter by the total length of the strip.

Example Calculation:
For a 12V LED strip consuming 12 watts per meter and having a length of 5 meters, the calculation would be:

12W × 5 meters = 60W

This means you need a 60W power supply to run the strip, but to ensure stable performance, it’s recommended to select a power supply rated for 20-30% more than the required wattage.

Why You Need Extra Wattage:

In this case, you should opt for a 72W power supply to provide enough power without overloading. This will help avoid voltage drop and ensure the LEDs perform optimally.

Tip: Always select a power supply with a higher current rating than the total required current. For instance, if the strip needs 5 amps, you should select a 6-amp power supply.

To help you calculate your LED power requirements, check out our Voltage Drop Calculator.

Repair vs Replace: Cost & Time Guide

When dealing with a partially working LED strip, one of the key decisions is whether to repair it or replace the entire strip. This section will help you weigh the pros and cons of each option, based on cost, time, and effectiveness.

Cost Breakdown:

The cost to repair a LED strip depends on several factors:

• Tools Needed: You may need to purchase a soldering iron, multimeter, clip connectors, and silicone sealant. These can cost anywhere from $20 to $100, depending on the quality of the tools.
• Labour Time: If you’re doing the repair yourself, the time spent will depend on your experience. A simple re-solder might take 30 minutes, while a more complex repair (like fixing multiple segments) could take over an hour.
• Replacement Parts: If you need to replace entire segments or a damaged power supply, the cost of parts will add to your overall expense. New LED strips cost approximately $10 to $50 per meter, depending on the type.

When to Replace:

While repairing is often a cost-effective solution, there are situations where replacing the LED strip is the smarter choice:

• Length of Damage: If the damaged segment is over 30 cm in length, it’s often better to replace the whole strip. Repairing a long section can be more time-consuming and may result in a weaker connection.
• Warranties and Guarantees: If your strip is under warranty and the damage is significant, it’s better to replace the strip under the warranty, especially if the failure is due to a manufacturing defect.
• Cost of Repair vs Replacement: If the repair cost is close to the cost of a new strip, replacing the strip is likely the best option.

Time Consideration:

• Repairing a LED strip might take 30 minutes to a couple of hours, depending on the complexity of the issue and your skill level.
• Replacing the strip is faster in most cases—especially if you’re buying a pre-cut replacement strip.

Conclusion:

When deciding between repairing and replacing your LED strip, consider both the cost and time involved. If the damage is minor and the tools are available, repairing the strip can be a great solution. However, if the damage is extensive or the cost of repair approaches the cost of a new strip, replacing the strip may be the more practical and reliable choice.

Let’s continue with the next section:

Prevention: Keep Your Entire Strip Working

Once you’ve repaired your LED strip, the next step is to ensure it continues to work properly in the future. Proper maintenance and preventive measures can extend the lifespan of your LED strip and reduce the chances of partial failures.

1. Ensure Proper Power Supply

A stable power supply is crucial for preventing voltage drop and other issues. Always choose a power supply that provides 20-30% more capacity than the total wattage required by the LED strip. This ensures that your power supply is not overloaded and will provide consistent voltage throughout the strip.

2. Use an Aluminium Profile Heat-Sink

LED strips can get hot, especially if you’re running long lengths at high brightness. To prevent overheating, consider installing the LED strip in an aluminium profile. These profiles act as heat sinks, helping to dissipate the heat and keep the LEDs cool, which will improve their performance and longevity.

3. Avoid Tight Bends

LED strips are flexible, but tight bends can cause internal damage to the copper traces and the LEDs themselves. When installing your LED strips, make sure to avoid sharp angles and bends. Try to keep a larger bend radius (the minimum allowed by the manufacturer) to ensure the strip lasts longer.

4. Keep It Clean

Dust and debris can accumulate on the strip, especially in areas with poor ventilation. Regularly clean the strip with a dry, soft cloth to remove dust and dirt. Be careful not to get moisture or cleaning chemicals on the strip, as this can damage the circuit.

Conclusion:

By ensuring you use a proper power supply, protecting your LED strips from heat, and avoiding tight bends, you can prolong the life of your LED strip and prevent the common causes of partial failures. Preventive maintenance is key to keeping your strips running smoothly for years to come.

FAQs

Here are some of the most frequently asked questions about LED strips and their common issues:

1. Half of my RGB strip shows only green—why?

Answer: This issue often occurs when one of the channels (red, green, or blue) stops functioning. The most likely causes include a damaged chip on the LED or an issue with the controller. Try testing the voltage at the controller, and if necessary, replace the faulty LED module or controller.

2. Do these fixes work for Christmas string lights?

Answer: Yes, many of the same troubleshooting steps apply to Christmas string lights that use LED technology. Voltage drop, reversed polarity, and broken traces are common issues in both LED strips and string lights. Just ensure that the string lights have a compatible power supply for your repair.

3. Will cutting out the dark segment damage the rest?

Answer: Cutting out the dark segment of an LED strip will not damage the remaining part of the strip as long as the cut is made along the proper cut line (usually marked on the strip). However, make sure to reattach the power connections properly after cutting.

4. How long will a repaired strip last?

Answer: A properly repaired LED strip can last for several more years, especially if the issue was minor (e.g., broken trace or solder joint). However, if the strip had significant damage, the repaired segment may not be as durable as the original. Always monitor repaired sections for any signs of further failure.

5. Is polarity reversal dangerous to the controller?

Answer: Polarity reversal can damage the LED controller if the connections are made incorrectly. Always double-check the wiring before powering up your LED strip to ensure the correct polarity. Some controllers have built-in protection against polarity reversal, but it’s better to be cautious.

6. What tools do I need for a quick repair?

Answer: For a basic LED strip repair, you’ll need:

• A soldering iron for fixing copper traces or joints.
• A multimeter to test voltage and continuity.
• Clip connectors if you prefer not to solder.
• Silicone sealant for waterproof strips.
  

Conclusion & CTA

In this guide, we’ve covered the most common causes of partial LED strip failure, from voltage drop and reversed polarity to broken traces and over-driven RGB channels. We’ve also provided step-by-step instructions on how to test and repair these issues, ensuring your LED strips stay bright and functional.

If you’re still facing issues after trying the repairs, it might be time to replace your LED strip or upgrade to a more powerful power supply to prevent voltage drop.

Still unsure about your setup? Check out our Voltage Drop Guide for more information on how to calculate the right power supply.