I have a single landscape spot in the front of my house. When I installed it 6 years ago the fixture I used had a bulb, and it worked great, although it was a pain to change the bulb out every 18 months. Both the fixture and the transformer finally failed, and I have now replaced them.
Using the replacement transformer and brand new LED fixture I couldn’t get it to work at all. I read the specs on the fixture and realized that it was 12 VDC, as opposed to the 12 VAC like my old fixture. I went out and got a 12 volt AC to DC converter and everything worked fine again.
I installed the new fixture outside along with the voltage converter and the light works, but it considerably dimmer than it was when I tested it in my house using a short length of landscape wiring. The run from the transformer to the fixture is only about 40 feet, which I wouldn’t think is long enough to have significant loss. I then tightened the connection from the fixture to wire but it didn’t help.
Is a 40 feet run long enough to cause significant loss?
The wire is not terminated at the end but it just cut off. Do I need to connect the end so that it completes a circuit?
Any advice anyone can provide would be appreciated!
How thick is the wire? 40 feet of thin wire can have pretty significant line loss.
Not sure what you mean by the end of the wire is just cut off. You should have a positive and negative terminal on the LED fixture, and the positive wire should be screwed onto the positive terminal and the negative wire onto the negative terminal. Most wire types have some way of differentiating the wires (a stripe or ridges on the insulation or something) so you can make sure that you get the positive on the right terminal on both the fixture and the power supply.
For landscape lighting, the way it typically works is that you have a long line of wire, it looks like speaker wire but is outdoor rated, and each fixture has a connector that clamps onto to the wire somewhere along the length, piercing the wire with two prongs. In some instances you may have a dozen fixtures attached to the wire along a fairly long length. There is nothing at the end of the wire, it’s just cut off cleanly. This is how I have always done it for 12 volt AC deployments, but I have never used 12 volt DC before, hence my question about the termination.
Since polarity matters I will switch the clamp around and see if that makes any difference.
I suspect that engineer_comp_geek has it right. DC needs bigger wiring than AC does, for long distances runs. Could you move the AC to DC converter closer to the light? It may help.
To answer your questions;
#1. Yes, 40’ is a long distance for a 12 Volt DC circuit, heck it is long for a 24 volt DC circuit.
#2. No, you do not need to do anything at the end as long as it is in a dry place.
The piercing connetion are marginal for DC circuits as well. Try to hard wire it.
There are few things to think about. Incandescent lights are vastly less efficient than LEDs, so the actual current draw for you LED light is most likely much less than before, and thus the voltage drop actually much less.
However the brightness drop off with reduced voltage for a LED lamp is quite brutal, with a drop to 20% brightness possible with only a half a volt drop. Incandescent lamps are quite sensitive to voltage, but nothing like as bad. If you can, measure the voltage across the LED lamp when it is running. It would be useful to have some idea of the nature of the AC to DC converter you are using to power the LED. There are a great many possibilities for solving the problem depending upon how nasty this device is.
The reason AC is used is because it permits the use of transformers which allow the easy conversion of low-voltage/high current to high-voltage/low current, thereby reducing I^2R losses.
For a given current, AC is no more efficient than DC.
In a yard lighting system, there are no transformers in the circuit (after the 120v has been reduced to 12v), so 12VDC is just as efficient as 12VAC.
Energy loss = I[sup]2[/sup]R So, for the same energy down a line, the best answer is to get the voltage up, and the current down. Thus the use of high voltage distribution lines.
Problem. You can’t power a household item with a hundreds of thousands of volts. So you need to reduce the voltage to sensible levels with minimal loss. For that you need a transformer. Transformers only work with AC. (Modern DC distribution systems exist, but need to use very fancy DC to AC converters at the receiving end to get AC back, before it can be transformed down to lower voltages.
Sorry, I came back to amend that statement, my mistake. There are situations where AC is more efficient than DC, though. Cite. The I2R losses are I2R losses, and there are solution that would allow direct HVDC-LVDC conversion but they are expensive.
As to the OP, connecting the ends of the wire will short it, not good. Most LEDs won’t light at all if you reverse the polarity so I suspect that it’s OK. How old is the wiring on the 40’run? It may be oxidized or the insulation may be compromised. Hook up a small 12V battery and see if it lights up OK. If so, then your problem is the converter.