How do I size a transformer for my lighting installation?

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Answer

Calculate the transformer required by determining the total wattage of all lighting fixtures. This is the minimum required output of the transformer. You typically want to choose a transformer that supplies no more than 30% more.

For example:

  • 10 LED wall lights @ 2 watts each = 20 watts
  • 10 LED deck lights @ 1 watt each = 10 watts
  • 5 LED path lights @ 3 watts = 15 watts
  • Total minimum output required by the transformer = 45 watts

In this example, a 60 watt magnetic or electronic transformer would be ideal.

How do I mount a low voltage transformer?

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Answer
Your power supply should be mounted at least 12 inches above ground level. Many transformers are not completely sealed and should have that clearance according to UL 1838.

Why does my transformer turn on, off, and then back on after a period of time?

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Answer

Most low voltage transformers are equipped with thermal protection. If your power unit is undersized (overloaded) it is probably overheating and causing the thermal protection to shut down the unit. Consider using a larger transformer or splitting the load to an additional unit.

Can I mount my low voltage transformer inside?

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Answer
No. Generally speaking, low voltage transformers are listed and labeled for “Outdoor Use Only.” If your installation requires an indoor transformer, consult your local electrical codes… you may be able to purchase a low voltage power supply locally for that specific use. Remember that if you are using a photocell, you may have to make other provisions for controlling the outdoor lighting.

Why is my transformer making a humming noise?

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Answer

Low voltage transformer cores are built from thin steel laminations that are stuck together. The cycling on and off over time may have loosened the laminations, creating a slight vibration. This is typical of units that have not been encapsulated with epoxy during the manufacturing process. It does not mean that your power supply will fail.

How do I minimize voltage drop?

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Answer
The closer your incandescent fixtures are placed to the transformer, the higher their voltage (and wattage). The farther away you place the fixture, the lower the voltage it will receive. If a cable run is too long, or if too many lights are being powered by a single transformer, noticeable voltage drop may occur.

Voltage drop causes the lights farthest from the transformer to become dimmer than the other lights.

Voltage drop can be minimized in various ways …

  • Upgrade to energy efficient LED fixtures
  • Utilize a heavier gauge cable
  • Install a higher capacity transformer
  • Consider using multiple transformers
  • Shorten your cable length/run
  • Reduce individual fixture wattage
  • Reduce the total number of fixtures on a run

Voltage drop actually works to your advantage if differences in lamp brightness levels add a desired look and feel to your installation. Remember… bulbs with lower voltage will last longer, requiring less replacement.

How do I ensure proper lamp life?

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Answer
Use of a digital voltmeter is the only way to confirm that your voltage is correct. Keep in mind that magnetic transformers reduce primary voltage (house current) as a percentage. Magnetic transformers are not voltage regulators. Every installation is unique due to the variations of our power grid.

For LED installations, consider utilizing our IL200.515 electronic LED transformer. It automatically adjusts for the load and increases the product and system reliability. Visit Electronic LED Transformer for more details.