How big of a transformer do I need for outdoor low voltage lights...?

Question

Roughly how many low voltage outdoor lights can I run off of a 150W 120v to 12v transformer, 300W 120v to 12v, and 600W 120v to 12v.

Do I need a transformer for every couple of lights to make sure they are all equally the same brightness/dimness?

Anyone have any good websites about this type of information?

THANKS!

These lights will be used on my deck off the back of the house for evenings...

Answer 1

You can roughly add up the wattage of the individual bulbs and choose a transformer that meets or exceeds that power rating (assuming that the power ratings you note are referring to the secondary (output) power capacity.

In general, matching the load is a good idea - if you put in a 600 W transformer on a lighting system that only requires 100 watts, the output voltage (most of them are completely unregulated) may be high enough above 12 v that your bulb life may be shortened (but they'll burn nice and bright while they last!).    IOW, using a 150 W transformer in that 100 W scenario would result in a loaded output voltage closer to 12 volts, whereas the much more lightly loaded 600 W transformer might still be outputting 15 volts or more.  

So add up the wattages, include some room for expansion if you intend any, and choose a transformer that doesn't significantly exceed that power rating.

Answer 2

I run eight 12 volt lights garden lights off of one transformer at the front of the house and 6 12 volt lights at the back from another transformer, with no problems. Have a great day!

Answer 3

Plan which lights you want to use first, then buy a transformer accordingly.  Many lights depending on their usage (accent vs. spotlight) range from ~10 to 50 watts, respectively.  Add the wattages of each bulb/fixture, then add about 10% to allow for the possibility of expansion in the future.  The transformer output in watts should be equal to or above your number.

Many home improvement stores have displays which demonstrate the brightness of each model.  

You typically only need one transformer (provided the output is large enough, and all lights are in a continuous run).  Use a large-gauge wire to eliminate resistance, which causes lights far from the transformer to dim.

Answer 4

The aswer to that depends on the wattage of the bulbs you use in the fixtures. By adding up the wattage you can choose the correct tranformer. Select your fixtures, add the wattage and buy the correct transformer. Most fixtures are 8,10,15,20,or 50 watt bulbs so you could put (15) 10watt lights on a 150 watt tranformer, but I try to keep the load 10% under the transformer rating  like 135 watt load on a 150  trans. also buy the 8-10 gauge wire because the voltage drop is extreme with the 16 gauge stuff that comes with the kits. hope this helped you......

Answer 5

To determine the size, add up wattage of all lamps and add 10% more for safety factor.

(TRANSFORMER SIZE = TOTAL FIXTURES WATTAGE X 1.1)

Example:

Selecting Fixtures: For the project 8 fixtures were selected

(6) 16 Watt Fixtures and (2) 35 Watt Fixtures

Selecting a Transformer: To select a transformer the total wattage of the fixtures is needed

16 + 16 + 16 + 16 + 16 + 16 + 35 + 35 = 166

Transformer size = 166 x 1.1 = 182 Watts

A 200 Watt transformer would be a good choice for this project. If additional lights might be added in the future it would be a good investment to purchase a slightly higher wattage transformer.

Answer 6

Most low-voltage lighting I've installed comes as a kit; you must use the transformer from that kit in order to keep the product's "listing". If you start to "mix-and-match" parts from different manufacturers, you could end up with a real mess on your hands.

Without a product listing, there is no way to prove that the installation is safe. If that doesn't bother you, it WILL bother your insurance company, and it should bother your local Inspector.

"Low-Voltage" does not mean "safe", the amperage is still enough to kill you.

Purchase a listed set, and install it exactly as the Installation Instructions tell you to.