Low-Voltage Lighting Primer
Jun 1, 2008 12:00 PM
The use of low-voltage lighting systems has become increasingly popular over the past several years. In fact, low-voltage halogen and xenon lighting systems can be found in almost any setting — from restaurants, hotels, and bars to retail stores, museums, art galleries, offices, and homes. Working in the industry for more than 20 years, Dr. Tom Farin, founder and president of Pegasus Associates Lighting, Beaver Falls, Pa., offers the following technical tips for transformers used in low-voltage lighting systems.
Transformer
A transformer is generally used with low-voltage lighting systems to “transform” the standard voltage that is normally available (usually 120V or 277V) to either 12V or 24V.
Type of transformer
The transformer used in a low-voltage lighting system may be either electronic or magnetic.
Maximum transformer wattage
The wattage rating of the transformer should always be equal to or greater than the total wattage of the lighting system. If an electronic or a toroidal magnetic transformer is used, then the maximum wattage of the lighting system may be equal to but not greater than the wattage rating of the transformer. If, however, a conventional EI magnetic transformer is used, then the maximum wattage of the lighting system may be equal to but not greater than 80% of the wattage rating of the conventional transformer.
Minimum transformer wattage
Transformers usually have a minimum wattage that they must power before they work. For example, it is not uncommon for 60W electronic transformer to require that there be at least 10W of lighting load. If there is only 5W of lighting load connected to this 60W electronic transformer, the lighting system will not work.
Electronic transformers
An electronic transformer is generally lighter in weight, smaller in size, cooler to operate, and quieter than a magnetic transformer. However, electronic transformers cannot provide more than 300W of power whereas some magnetic transformers can provide as much as 1,200W of power.
AC electronic transformer
An alternating current (AC) electronic transformer should not be placed any farther than 10 feet from the lighting system. This is done to prevent problems associated with voltage drop. In addition, the longer the distance from the AC electronic transformer and the lighting system, the greater the chance that it might create radio frequency interference (RFI) with other electronic components in the area.
DC electronic transformer
A direct current (DC) electronic transformer may be placed as far as 50 feet from the lighting system. The DC output significantly reduces RFI and virtually eliminates the possibility of any voltage drop (the drop in voltage over a long circuit).
Toroidal magnetic transformer
If a magnetic transformer is used to power a low-voltage lighting system, a toroidal magnetic transformer should be considered. This type of magnetic transformer is more efficient, lighter in weight, smaller in size, cooler to operate, and quieter than a conventional EI magnetic transformer.
Here's one final tip: Because an electronic transformer provides its power at very high frequencies (usually greater than 20,000 Hertz), a standard voltmeter cannot be used to accurately measure the output voltage. Instead, a “true rms” voltmeter must be used to measure the secondary voltage of an electronic transformer.
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