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Why Do Lighting Transformers Fail?

When something goes wrong with one of your lights in your landscape lighting setup, then it’ll usually just knock that one light out.

Sometimes you’ll have a problem with part of the circuit that’ll maybe affect a few of the lights, especially if you’ve done the smart thing and wired in parallel rather than series.

But when your transformer fails, that’s your entire lighting system compromised, so you’ll need to identify what the problem is and fix it to get your lights working again.

Sometimes you can either remove the cause of the issue, or fix the problem. Other times you may need to replace the transformer.

The most common reasons a transformer will fail are due to high voltage stress or degradation over time. You can remove bulbs or use lower wattage lights to reduce voltage stress, but it may have already accelerated the end of your transformer’s life.

In this article, I’ll take you through some common transformer issues in more detail, and explain how you can test your transformer to make sure it’s working correctly.

Common Low Voltage Transformer Problems

240V to 24V step down transformer

These are the four most common reasons that a transformer might start having issues.

High Voltage Stress

One of the most obvious issues with transformers, and yet one that is probably the most common, is when it is overloaded.

Transformers aren’t limitless – they are designed to be able to handle a maximum power draw.

Some of the most common transformer sizes for landscape lighting are 120W, 200W and 300W but there are other ones too, including some mini transformers and some much larger ones for epic installations.

However, that advertised power rating is the maximum they can handle at peak, not what they can manage on a consistent basis.

You need to make sure that you don’t exceed 80% of the transformer’s capacity.

If you’ve got too many bulbs on the circuit with your transformer, you’re going to damage it due to high voltage stress.

Expect bulbs to flicker or potentially blow, and in cheaper transformers there’s also the potential for overheating to cause a fire.

The first thing to check is the type of lights you’re using. If they have halogen bulbs and you can swap them to LED, without swapping the whole fixture, then this is the best solution.

But if the fixtures are sealed, or you’re already using LEDs and the power draw is still too high, then you’ve two options – remove some lights, or replace the transformer with one suited to a higher power draw.

The second option is more expensive, since you’re buying a new transformer, but it’s the best option because:

  • You don’t have to sacrifice your lighting
  • You might have already shortened the life of your transformer due to the stress placed on it

Thermal Degradation

heated electronic circuit

Heat is often created by electrical circuits, but it’s also the enemy of electrical components because, over time, it will cause them to wear out.

Your transformer won’t last forever, and it’s often wear and tear caused by heat that will stop it from working properly.

Especially if it’s a cheaper model, or if you’ve overloaded it for any periods of time.

If your lights aren’t working, check your transformer.

A little bit of warmth is normal, but you should be able to touch it – so put on some safety gloves and test it by touching the outside of the box.

If it’s hot, then that’s a sign it’s degraded. The only fix here is to replace it.

Excessive Buzzing

Transformer with cables on the wall

Transformers will always emit a buzzing sound. It’s caused by the magnetostriction of the core laminations while the transformer is powered and stepping the current down.

A lot of transformers will have some form of dampening to help mitigate the noise, but it can’t be completely eliminated.

However, if the buzzing is louder than normal, then there’s a chance it’s a sign that something is wrong.

It could be caused by a short, either within the transformer or in the power supply feeding the transformer.

You’ll need to test the transformer to see if there are fluctuations in power, and if the issue is with the supply then you’ll likely need to seek professional help.

If it’s an issue with the transformer itself then you can replace it, since a short is likely caused by corrosion or wear and tear.

Faulty Timer

electric box with timers

Sometimes the fault is as simple as a timer misbehaving.

Whether your transformer has a digital or a mechanical timer, it may be that it’s fallen out of sync or it’s just not behaving.

You can try resetting the timer. If it’s digital there is likely to be a reset button or switch, and if it’s mechanical you just need to move all of the pegs into the off position and leave them there, then power the transformer off and on again before resetting the pegs into the right position.

If that works, then it shows that the timer was the issue.

If not, and you’re still having problems with your lights working, it’s usually an indicator that one of the more serious issues above is affecting it.

How To Test Low Voltage Transformer?

Digital electric tester current probe pair of safety gloves

If you want to test your transformer, you’re going to need a multimeter (Amazon).

They’re not terribly expensive, and they’re a useful tool to own if you want to check the electrical circuits in and around your home.

Start by testing the input voltage on your transformer by placing the leads on the input terminals.

If you’re not getting a 120V reading (or whatever the standard power rating in your country) then you know the issue is with the power supply.

Next, place the leads on the output terminal. If it’s a 12V transformer you should get a reading of 12V – if it’s too high or too low then the transformer isn’t working properly and needs to be replaced.

If the power is reading correctly, the next step is to disconnect the power to your transformer, and switch your multimeter to the resistance/ohms function.

Your manual will explain what to look for in your multimeter display, but you’ll be testing both the input and output terminals to make sure the circuit is correct.

If it’s showing an error, it means there’s a short and again you need to replace the transformer.

Final Words

Replacing a transformer isn’t a massive job, but it’s an unwanted expense, so it’s important you troubleshoot any issues before you instantly make a decision to buy a new one.

However, unless you’re overloading the circuit and able to replace or reduce the lights, or the timer’s faulty, the most common issues do still mean that a new transformer will be needed.

But if you buy one that’s rated for the wattage of your system, and from a reliable manufacturer, a new one should last you between 20 and 25 years if properly maintained.

Have you had any problems with your landscape lighting transformer not covered here? How did you fix it?