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In summary:
Unless you are confident that you have a purpose designed LED lamp for use with your particular model of electronic transformer, it is not a good idea to install a standard LED lamp on a halogen transformer. Light output and lamp life will likely be reduced. Apart from warranty issues, and having to fix problems it can be considered unfair on the end user, as the installation may not perform as expected in the long run.
Firstly: Drivers vs transformers
AC power supplies are referred to as transformers whereas DC power supplies are referred to as drivers.
Transformers step down the 240V input to 12V AC output, and although they have circuit protection, they do not regulate the output from voltage spikes.
Drivers convert 240V AC input to regulated DC output (typically 12V or 24V) to provide the best operating conditions for the LED to last its full life. Drivers are power supplies for LED loads. They are available in constant current and constant voltage types, and they isolate the LED’s from the voltage spikes. In NZ voltage spikes are a factor.
Current issue
LED’s require DC power. If AC is used without properly converting it to DC the LED’s will have an “AC flicker”. In addition to DC power, LED’s also require a constant current or regulated voltage to maintain their long life. Fluctuations in output that are inherent in AC power will shorten the expected life as well as cause AC flicker.
Voltage issue:
Existing transformers typically used with halogen spotlights can usually be used however there is one problem – since the transformer expects one or more 20-50W halogen bulbs to be connected to it, the voltage output when a few 1 Watt LED spotlights are connected can exceed the transformer’s 12V rating. LED spotlights are sensitive to voltage, with 13 to 13.5V being the typical absolute maximum useable before permanent damage to the bulbs occurs. This will decrease light output and average lamp life.
Loading issue:
LED bulbs draw so little power that they won’t reach the minimum wattage, and therefore the electronic transformer can’t be depended on to operate within its specification. Generally single transformers load range is about 20–60W. The result is usually flickering, or not starting up at all.
Solutions:
1) Find a compatible LED lamp.There are lamps available that are designed to operate on electronic transformers. The better brands actually publish a compatibility table, listing local compatible transformers. The down side is they are relatively expensive compared to the cheaper Chinese sourced lamps.
2) Or remove the electronic transformer and fit an LED driver. Prices are coming down all the time so cost is becoming less of a factor. A proper LED driver will always be the first choice for reliability.
Magnetic transformers:
Fixtures that use magnetic transformers can generally be used with LED lamps without modification. Made from primary and secondary wire windings around a magnetic core, this produces an unregulated 12 volts AC, which is fine for driving halogen bulbs and will produce good results with most LED bulbs. It’s recommended to have an electrician measure the output voltage because if it is above 12.5 volts the life of the LED units will be greatly reduced.