I'm the person who gets the 9:47 p.m. call when a commercial lighting system dies. In my line of work—emergency repair coordination for lighting systems across the Southwest—no sentence costs more than 'just replace the power supply first.'

Six years and 200-plus rush calls in, I can tell you the Mean Well unit inside that metal box is usually not the problem. Before you order another LRS-50-5 because a forum thread said to, run through this checklist. It might save you a service trip and the part you never needed.

In March 2024, I drove to a Tucson spotlight project with 36 hours to go before final inspection. The contractor had read the Mean Well LRS-50-5 switching power supply reviews, decided the 5 V supplies were dying because the motion sensor lights kept cycling, and replaced eleven units in two days. None of the eleven were faulty. A loose neutral in one junction box was taking down three lighting circuits. The fix took 40 minutes.

So consider this the resumen spotlight: the short version of every mean well power supply troubleshooting checklist I wish someone had handed me years ago. Seven checks. No theory. Start with the boring possibilities.

Mean Well Power Supply Troubleshooting: Seven Field Checks

  1. Verify input voltage at the supply's terminals—not at the breaker. Mean Well's LRS family accepts 85–264 VAC, so an apparently low reading like 108 VAC is usually not the real issue. What matters is whether the voltage sags when loads cycle. If the supply browns out every time a contactor pulls in, hunt for loose connections. We once traced a two-month 'intermittent driver failure' to a burned neutral lug (which, honestly, nobody checked because the breaker measured fine).
  2. Read output voltage with no load, but don't celebrate yet. On an LRS-50-5, you should see about 5.1–5.2 VDC with nothing connected. That only means the control circuit is running. A switching supply can hold perfect no-load voltage and still collapse the moment you connect a real load.
  3. Load-test the supply. If the unit powers a motion sensor controller that draws, say, half an amp, test at one amp or more. Watch the output under load. If the voltage sags badly or the supply enters hiccup protection, then suspect the supply. If it holds steady, you're chasing a wiring or sensor issue, not a power supply issue.
  4. Measure DC voltage at the load, not at the supply. This is the step most people skip. Five volts over a 50-foot run of thin control wire can arrive as 4.1 V, making sensor logic reset every time it switches. The LRS-50-5 is doing its job; the cable is not.
  5. Inspect every control and dimming wire. Many lighting systems pair motion sensors with Mean Well LED drivers using 3-in-1 dimming (resistor, PWM, or 1–10 V). If the DIM+ and DIM− wires are swapped, crossed, or left floating, you'll get flicker and false triggers. If your sensor outputs a dim signal, connect it to a dimmable driver—not to a plain AC-DC power supply.
  6. Check the temperature inside the enclosure. The LRS-50-5 operating range extends to roughly 70°C, but output derating depends on the model and mounting conditions. A sealed metal box exposed to Tucson summer heat is not the same as a ventilated panel. Over-temperature protection shuts the supply down; when it cools, it restarts—so a light can blink for weeks without tripping a breaker.
  7. Bypass the motion sensor to test the load directly. Here's the fastest 'how to fix motion sensor light' trick I know: disconnect the sensor's output, jumper the load side to force the light on, and observe. If the light runs steady, the supply and fixture are fine. The problem is the sensor, its settings, or its placement.

How to Fix a Motion Sensor Light: After the Supply Checks Out

When the power supply passes all seven checks, the sensor itself is usually the culprit. A few fixes that handle most of the calls I take:

  • Look for test mode. Many motion sensors ship in test mode. That makes the light turn off after five seconds even when you're standing right there, which is exactly what 'broken' looks like.
  • Confirm the sensor has a neutral. Some sensors need a neutral wire and will misbehave if it's missing. Check the manufacturer's diagram.
  • Check what the sensor is looking at. HVAC vents, moving branches, and headlights from the street can all cause false triggers at night. Reposition before replacing parts.
  • Match the sensor to LED loads. Sensors designed for incandescent bulbs sometimes don't work with LED fixtures or LED drivers. The sensor may fail to detect, turn off early, or leave the light on. Look for a motion sensor rated for LED or use a sensor with a 0–10 V dimming output.

What Most Mean Well LRS-50-5 Switching Power Supply Reviews Leave Out

For the record: I don't work for Mean Well. I'm the person who opens their boxes at 11 p.m. So here's the honest field view of the LRS-50-5: it's a 50 W, 5 V, 10 A enclosed switching supply with short-circuit, overload, over-voltage, and over-temperature protection. For control panels, sensor logic, or small constant-voltage loads, it's a solid workhorse—just not a glamorous one.

But the typical online review skips four details:

  1. At 5 V, voltage drop is a huge deal. Losing 0.5 V along a cable run is a 10% loss. Keep wires short and properly sized.
  2. It's not an LED driver. It's constant voltage. LED fixtures still need their own current regulation. Connecting it to bare LED strips without a controller is asking for problems.
  3. Beware of deals that look too good. Unofficial listings are common. Transparent pricing is one thing; a new-in-box supply at half the distributor price is usually a counterfeit, refurb, or worse.
  4. The green DC OK light is not a passing grade. It confirms the supply is on, not that it can deliver current. That's why the load test in the checklist above matters.

If you want to verify specs or derating curves, the LRS-50 series datasheet on mean-well.com is the right reference. Use it before you mount the supply in a tight enclosure, not after.

One last thing: when a client tells me they need a 'Mean Well power supply troubleshooting' visit, I ask what the load test showed. Don't hold me to the exact percentage, but two-thirds of the emergency calls in my own job log end with the original supply still in the panel, working fine. The skill isn't knowing how to swap parts—it's knowing which part to leave alone.