Just starting my research on building a low voltage LED landscape lighting system. So far, the only guidance I've seen on choosing the correct transformer wattage is related to the total wattage expected in the system, i.e., add all fixture/bulb wattage and add at least 20% to choose wattage of transformer. How does run length and number of fixtures/bulbs factor in to selection of wattage for the transformer?
Total wattage is the most determining factor (while considering the recommended 80% usage of the transformer's max rating you mentioned), but the number of runs and sometimes length could play a part as well. For a larger size property where you're expecting to have multiple runs, this is where larger transformers would typically be most ideal. The VOLT® 100 Watt Slim Line LED Transformer for example is an extra compact, easy to install transformer designed for smaller to average sized jobs having (3) 15V output taps with the clamp connect style connectors - these style connectors are ideal for one wire run typically, so essentially (3) runs max. Whereas the VOLT® 300 Watt (12v-15v) Multi-Tap Low Voltage Transformer has multiple power output taps (12V, 13V, 14V, 15V) and has classic screw-style connectors on the terminals - with these style of terminals you can usually braid stripped wire ends together and insert multiple runs into a single output tap (obviously there is still limits to this as well). But, you'll essentially have the capacity for noticeably more wire runs. Also, having a 15V tap can be handy for longer runs where you may need more voltage so that the fixtures towards the end of the longer run can receive the desired input voltage range. How large is the project you're planning - fixtures & wattage? And, how long do you expect your longest wire run to be?
I estimate 40 to 50 fixtures, with total wattage of roughly 100 watts. The longest run will be about 300 feet, with at least two other runs of 150 to 200 feet each, plus 2 or 3 runs of 100 feet or less. I anticipate using 2 transformers, one near the front of the house, one near the rear.
For a system of that size & length, I'd likely use the VOLT® 300 Watt (12v-15v) Multi-Tap Low Voltage Transformer myself if using a single transformer. If using (2) transformers, the safest bet would be (2)150Ws which would also likely allow for plenty of room for expansion in the future if you ultimately wanted to add more fixtures to either zone. Using 100Ws could be cutting it close - say you had ~25 fixtures in one zone with a minimum average wattage of 3W; you'd be cutting it close to the recommended 80W of consumption for a 100W unit (and that's if the average was 3W, which you could very well have a few 4W+ fixtures.) Or you could use (1) 150W & (1) 100w, using the more powerful unit in the zone you expect to have more lights in. In this case, I'd recommend double-checking the wattage of the zone the 100W would be installed in just to make sure it was at or below 80W.
thanks, that's helpful. On a separate note, what wattage is most common for a single spotlight to uplight a small to medium tree or house feature such as a column? I was assuming 2W to be sufficient, but what do most people use?
For our LED MR16s, 3W & 5W would be most common. Depending on the tree & canopy size, multiple spotlights may be needed - also depending on what lighting effect you're looking for.
When it comes to wiring methods, I have a few questions: Can I use more than one hub on a single run? If so, I assume it's best to use "T" method, with one hub on each branch of the "T"? Can I put a hub at the end of a daisy chain? For example, two or three individual lights connected to the wire run via daisy chain and then a hub with several lights at the end of the run? Can I put a hub in the middle of a daisy chain? Does polarity matter when I'm making connections? Thanks.
Sorry for delayed response - 1.) We typically recommend 8-10 fixtures -or about 80W per run- (whichever threshold comes first). LED input voltage ranges are quite flexible - you can in theory use (2) hubs on a single run, but there is a potential risk of voltage loss at some fixtures (which a voltmeter is always handy to detect & troubleshoot). We would never recommend wiring one hub directly to another hub though - this can usually lead to issues with input voltages. 2.)This is something you can do - a voltmeter would be handy for double-checking that all of the fixtures wired into the hub at the end of the run are all receiving the recommended input voltage range. 3.) In theory, you can place a hub anywhere on a run as long as it's not overloading the individual run (8-10 fixtures or 80W), or placed at an extreme distance (longer than typical low-voltage runs; ≈300ft) where it can potentially cause voltage issues. 4.) Great question - there is no polarity to consider when installing low-voltage. The important thing to note is that the lead wires with VOLT fixtures will come pre-spliced & split at the ends and you will always insert one side into the COM tap, and the other side into a voltage tap (12V+). For pro junction hubs or direct burial hubs, you will also split the wires in this manner; for pro hubs, the terminal block is split in 2 on the lid of the unit, and for direct burial hubs you will receive (2) connectors in a pack to split the wires in this manner. If using traditional silicone filled wire nuts, you'd use (2) nuts at every connection point.
