Why has my MEAN WELL LED driver failed

Why has my MEAN WELL LED driver failed?

12 December 2017

It is very rare that a MEAN WELL LED driver fails because of a manufacturing fault. In most cases the failure is caused by a problem with the installation, or there are some environmental factors at play.

We were recently contacted by a customer, who has been using MEAN WELL LED drivers for years without experiencing any problems, but had two fail instantly on a new installation of festoon LED lights.

LED Festoon Lights

The fact that there had been two immediate failures on one installation would indicate that there is a reason external from the power supply, which is causing the failure.

If you find yourself in this situation, the first thing to do is look for a short on the output.

There might be a connection somewhere in the string of lights that has shorted out, causing the power supply to shut down.

As a quick test, disconnect the power supply from the string of lights and measure the voltage coming out of the supply. If it is OK, you know the problem is in your string of lights.

Test voltage output of LED driver

You should also make sure that there are not too many lights on the output of the LED driver.

If you have done some previous testing with only some lights installed, you may have been misled into thinking that the LED driver can run the whole string.

There are issues with some sorts of LED strings. Some of them have inbuilt electronics that compensate for voltage drop and this can cause problems when starting up from a cold start.

The light's inbuilt electronics will start working at about 9V. This means that when you turn on the power and the output voltage of the LED driver reaches 9V the string of lights will start drawing current.

Because the electronics compensate for the voltage, the string tries to draw more current to keep the lights operating at full power. For example, the current drawn by a 40W string of lights at 24V is 1.67A (40/24 = 1.67). However, at 9V, the current drawn is 4.44A (40/9 = 4.44). This is too much current for a your 40W LED driver, so it won't start the lights.


The answer is to use a higher power, 12V LED driver, one that has enough current to provide the startup load of the lights. The MEAN WELL data sheet will tell you how much current the LED driver can handle.

If you have a question about installing MEAN WELL LED drivers, please do not hesitate to contact Power Supplies Australia. A member of our expert team will gladly answer any questions that you may have.