I am looking for some solutions to improving my backyard lighting setup. I have a 400 watt transformer powering about 12 lights. Unfortunately, the 12 lights are spread out over about 250, so obviously my problem is that the lights at the end of the run are running dim. The lightbulbs are 25 watts each, so I'm using 300 of the 400 watts.
I'd like to be able to add more lights and have the ones on the end be brighter as well. I can't add another transformer because I connect it to my pool timer (so that I can turn them on from the controls inside our house) and I only have one input available. For that same reason, I can't add another transformer at the end of the 250 foot run.
Is my only option to increase the size of the transformer?
You issue is a voltage drop problem to the far end. Use larger wire (#10) will help Or run separate #12 to the last three lights from the transformer. Be sure all your connections are tight and sealed with silicone to afford heat loss (increasing power loss). You should be able to swap your 400 watt transformer to a 600 watt transformer. Test your lights to see if you can get by with lower wattage bulbs.
Sounds like you are in need of a new transformer. Since you want to add more lights anyway,a larger trans with multiple output voltages may help your dimming problem and allow you to add lights as needed.