Transformers that reduce, or step-down, higher voltage to voltages less than 30 volts (V) are called low-voltage transformers. They are commonly used to reduce the standard home 120 volt to 12 volts or 24 volts. A wide variety of everyday appliances use these transformers including low voltage external path lighting, under-counter lighting, door bells and thermostats. Both magnetic and electronic low-voltage transformers are in common use, and each has its advantages.
Function of the Magnetic Low-Voltage Transformer
In a magnetic low-voltage transformer, two coils of wire, the primary and secondary coil, are used. The primary coil carries the input or high voltage and creates a magnetic flow, which induces a current in the secondary coil. Since there are more windings in the primary coil than in the secondary, the secondary coil has a lower voltage. The exact output voltage depends on the number of windings in the two coils.
Function of the Electronic Low-Voltage Transformer
The electronic version contains a small transformer and an inverter. The inverter changes the frequency at which the alternating current into the transformer changes directions. In a home low-voltage use, it typically changes the frequency of the 120-volt home power outlet from 50 hertz or 60 hertz (or cycles per second) to around 20,000 hertz. The higher the frequency of the voltage, the smaller the transformer needed to provide the required output voltage.
Benefits of the Magnetic Transformer
There are two types of magnetic transformers: stack laminated and toroidal. The stack laminated are square and the toroidal are shaped like a doughnut. Stack laminated transformers are long-lived, lasting 15 to 20 years. Toroidal transformers last even longer and are very quiet when compared to either the stack laminated magnetic transformer or the electronic transformer. Both types of magnetic transformers are rated at higher operating temperatures than electronic transformers.
Benefits of the Electronic Transformer
Electronic transformers are much smaller and lighter than their magnetic counterparts. They are often small enough to be incorporated in the appliance itself. They are also less expensive than magnetic transformers. Unfortunately they have a much shorter lifespan--5 to 6 years--and they can be noisy. They are also heat-sensitive; warm environments will reduce their lifespan further.
When there is a high-voltage counterpart, such as the case with lighting, low-voltage systems are less expensive. In addition, installation is more likely to be a do-it-yourself project, since the voltage is a harmless 12 volts or 24 volts and wiring can be buried just beneath the surface or laid on the ground. Since both have their advantages and disadvantages, an examination of the requirements of the system in question is necessary to make the best choice.