Since LED bulbs use so much less electricity than traditional halogen bulbs, the overall electrical draw of typical outdoor lighting systems has gone down a lot. That makes very small cheap transformers tempting to use. After all, why install a 300W transformer if you need less than 50W total for your lights?
Well, here’s why:
There’s a lot more to a low voltage transformer than just it’s total power rating. And cheap, low-wattage transformers are cheap for reasons beyond just lower quality materials. They also skimp on important features.
Let’s compare 3 popular styles of low voltage transformer, and see if I can talk you out of considering 2 of them.
One style of low cost transformer is the “egg timer” style such as the one pictured above. These typically are black painted metal, which means they eventually fade, peel, and rust is a concern. I can’t even estimate how many rusted, broken versions of this kind of transformer we have removed and replaced from properties (none of them were originally installed by us).
A more immediate concern is their integrated manual timer. These plastic rotating timers have a lot of downsides: they don’t change for daylight saving time, they aren’t smart enough to know when dusk/dawn are, and they get out of synch whenever there is a power outage however brief. Also, if you rotate them the wrong way the plastic “gears” inside will break, effectively ruining your transformer.
They often put out “noisy” current, bouncing over and under 12V, and usually have just a single tap (connector for your wires) which is not just awkward for installing but also means you can’t “amp out” or balance the electrical load among your various lights and zones.
Basically, that style of transformer is a perfect example of paying very little and getting what you pay for.
Another common style of low voltage transformer is the “digital integrated” style, like the one shown above. These are also typically made of black painted metal to keep costs down (with all the downsides as above).
This style avoids the plastic egg timer problem by including a basic digital timer, but again it’s an integrated timer which can be a point of failure that ruins your complete transformer. This kind of timer is also highly limited, with only “stay on for X hours” settings rather than specific time control, which is inconvenient especially in Canada where our dusk times vary hugely from Summer to Winter. Most people want their lights to come on at dusk and go off at a fixed time, for instance midnight, but if that’s what you want these transformers can’t provide it.
Speaking of dusk, these transformers usually include an “electronic eye” to turn on when it gets dark, but that means the transformer has to be placed somewhere in sunlight and cannot be hidden away inside sheds, garages, or under decks where they’d be out of sight. Also, these electronic eyes can be fooled by leaves falling on them, or car lights shining on them. They are prone to fail, and even when they work they are inconveniently unpredictable.
In short, this is a low cost style of transformer were you get (barely) what you pay for, with lots of inconveniences.
Both of the above styles share another big downside: they only have 12V connectors, and usually just one of them. You might think that’s okay, since outdoor lights are typically 12V. However, the longer the wire the more resistance, which drops the voltage. It’s important to be able to start the voltage higher at the transformer so that by the time it reaches the actual fixture it’s at 12V. That means you often need multiple lines starting at different voltages, so that across your landscape each fixture receives the correct final voltage.
A third style improves on the above in all ways. These are stainless steel, so no worries about paint fading or rust. They have multiple taps from 12V up to 15V or more, so each fixture gets the right final voltage. Plus they have have low voltage circuit breakers for safety and to protect the transformer from electrical shorts.
And instead of an integrated timer they have a place to plug in a range of smart timers. That means you can select the right kind for you, including low cost digital timers that understand dusk, dawn, times, self-change for daylight saving, include a 7+ day battery backup, and more. Plus because they use an internal, removable timer, then if the timer fails you haven’t lost your whole transformer. Also, such smart timers know when dusk and dawn are without the need for an electronic eye, so you can have “on at dusk” settings but still tuck your transformer into a shed, garage, or under a deck. You can also seamlessly add these transformers to a complete home automation system. And you can upgrade the timer as your needs change.
This style of stainless steel professional transformers cost a little more than the cheap black ones from big box stores, but their long-life, safety, expandability, and convenience are more than worth it.
Those are some of the many reasons why you should not settle for a low quality black painted transformer. And remember, even if a transformer is rated at 300W or more, it’ll only draw the actual electrical needs of your lighting system. So it is not wasteful to have a transformer with a higher capacity than you currently need — and a lot less wasteful than disposing of or recycling a whole transformer because of a broken plastic egg timer!
It certainly pays to be picky when picking your transformer.