Low voltage transformers can be found in a wide range of sizes.
There are 3 basic types:
1. Timer models must be manually set. The cheaper models have integrated timers that can't be replaced. More expensive versions have replaceable timers that are not expensive.
2. Photocell models automatically turn lights on at dusk and off at daybreak.
3. Photocell with Timer models are the most versatile transformers. They allow you to automatically time your system and save on your power bill. These transformers must be located outside.
Complete installation and use instructions are included with each transformer.
These units are meant for use with low voltage, outdoor landscape lighting only; not for use with submersible lighting or pool/spa equipment.

It's better to have more transformer power than you need when initially installing a system. If you don't get extra wattage at the start, you can't upgrade or add to your system later without buying another transformer. Smart planning saves money! When selecting a transformer, allocate 20% of the stated wattage output for future additions, i.e., if the total wattage of all your lights adds up to 500, get a 600 watt transformer, not a 500 watt model.
Always replace burned out bulbs quickly. If not replaced, they place a load on other bulbs that can result in bulb failure throughout the entire run. Save money and headaches later by using heavier gauge low-voltage cable now! We recommend a minimum of 12-gauge wire for all but the shortest, or light wattage runs. You can expand your system or up size wattages without having to replace the cable. If voltage drops below 10.5v at any fixture, heavier gauge wire or a multi-volt transformer should be used.

Powers systems up to 121 watts. Integrated timer has two on and off pins. Single terminal post can accept 16 or12 gauge cable.
Intermatic model ML121RT
121 Watts
Timer with 2 sets of trippers
Accommodates 16 or 12 gauge wire sizes
Keyhole Mountings
Complete wiring instructions included