Low Voltage Transformers

Low Voltage Transformers

Low Voltage Transformer FAQ

Q) What is a low voltage transformer?

A) A low voltage transformer is an electrical device that transforms line voltage (usually 120 volts but sometimes 277 volts) into 12 volts or 24 volts (low voltage). It is sometimes made by winding two wires around an iron core with one wire connected to the primary side (line voltage side) and the second wire connected to the secondary side (low voltage side). In the case of low voltage halogen or low voltage xenon lighting the low voltage transformer has an input or primary voltage of 120 volts (sometimes 277 volts) and an output or secondary voltage of 12 volts or 24 volts.

Q) What is a DC low voltage transformer?

A) A DC low voltage transformer is a conventional electronic low voltage transformer in which the output is converted to direct current (DC) by using an electronic device called a rectifier. The DC output reduces radio frequency interference (RFI) and virtually eliminates any possible voltage drop (the drop in voltage over a long circuit). A DC low voltage transformer, although smaller and lighter than a corresponding magnetic low voltage transformer, is usually slightly larger than an AC electronic low voltage transformer providing similar power.

Q) How is a low voltage transformer wired into the lighting circuit?

A) Please make certain that the input wires (primary side) of the low voltage transformer are connected to the power line (120 volts) using wire nuts and that the output wires (secondary side) of the low voltage transformer are connected to the low-voltage light source using wire “terminal blocks” of appropriate size (for solid contact). Low voltage halogen or low voltage xenon lighting systems carry relatively large currents so all of the low voltage connections must be very tight to prevent arcing (a possible fire hazard) within those connections. That’s why we recommend that you use terminal blocks for these low voltage connections. If a low voltage transformer is equipped with wires, then you will usually find that the thicker wires (larger gauge) are on the low voltage side and the thinner wires (smaller gauge) are on the line voltage side.

Q) How does the use of an electronic low voltage transformer differ from the use of a magnetic low voltage transformer?

A) The output of an electronic low voltage transformer, unless it is a DC low voltage transformer, is high frequency (20,000-50,000 Hertz). This means that there can be a substantial voltage drop if the wires carrying the high-frequency current are long, thin, or far apart. Always follow these rules to avoid a large voltage drop. Use thick wires on the secondary/output side. The thicker the wire, the less the voltage drop you will experience. The shorter the distance between transformer and lamp(s), the less the voltage drop you will experience. Try to use a pair of secondary wires that are twisted together. The closer the two output wires are to each other, the lower the voltage drop you will experience. When a low voltage transformer powers more than one fixture or circuit, split the output of the low voltage transformer immediately into several separate circuits rather than carrying all the power in one pair of wires. The less power per circuit, the less the voltage drop you will experience. That is, a circuit with a total of 300 watts of load will have a greater voltage drop than a circuit with only 50 watts of load. A DC low voltage transformer offers the only electronic solution that overcomes this type of voltage drop issue.

Q) How can a circuit that doesn't seem to be working be checked for problems?

A) (1) Please make certain that the input wires (primary side) of the low voltage transformer are connected to the power line (120 volts or 277 volts) and that the output wires (secondary side) of the low voltage transformer are connected to the low voltage light source (12 volts or 24 volts). Most failures occur as a result of reverse or improper wiring.
(2) Check the filament of the lamp to see if is burned out. (Remember the glass envelope of a halogen lamp should NOT be touched by bare hands because the natural oil from your hands will cause the lamp to burn out prematurely.)
(3) Check the connections of the lamp with the socket by moving the lamp inside the lamp holder.
(4) Since most voltmeters give misleading readings when applied to high frequency currents the voltage on an electronic low voltage transformer can be measured only by using a "true RMS" voltmeter with a sufficient range.

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