Slightly OT: voltage drop on low-voltage lighting

[LaurentR]

I have been battling with low-voltage lighting for a week now.

The on-topic part is that I am controlling them using Intermatic's HA04 outdoor switches (which work but don't play as nicely as the rest of Vizia-RF-only dimmers, switches and controllers I use).

Now for the OT stuff:
I have fairly long runs of 200-300ft. That means fairly significant voltage drop over the length. I have been doubling up 12-gauge wires and I am getting there.

I have by now tried various transformers. I have easy access to three brands:
- Malibu (Home Depot)
- Hampton Bay (Home Depot)
- TDC Power (chinese), which came as part of a cheap Lamps Plus bundle.

I have tried the 300 Malibu, the 600W Hampton Bay and the 150W TDC Power.

The totally baffling thing is that I get very different voltage drops from the different brands. I have about 140W of load, evenly distributed. All transformers (with the Hampton Bay on "high") manage to drive around 12.5V at the transformer. At the end of the line, I get about:
- 10V from the TDC
- 9V from the Malibu
- 7V from the Hampton Bay

This is as measured by my BK voltmeter. This is somewhat corroborated by my kill-a-watt where the TDC pulls 145W while the Hampton Bay around 95.
I won't be able to do much more experimentation as I have already returned the Malibu and will the Hampton Bay pretty soon.
I am a bit confused by the results. I can understand different driving voltages under load, but that's not really the case. The only explanation I may have is the power efficiency (I/V phase difference) of the various transformers. Although, as the loads are basically purely resistive, it's a bit confusing.

Another possible (could be the same) reason is that the Malibu and HamptonBay are both higher power, so they may operate in a less efficient range (but what does that mean?). I do remember seeing warning that the transformers should be use at >1/4 or 1/2 load. But I am still missing the why part. Another funny thing is that the HamptonBay docs say that with 12 gauge, you can go to 80ft and 300W while the Malibu says 200ft and 300W... as if HamptonBay was aware that their transformers have a worse IR drop that Malibu's.

The only thing I can think of is to put a scope and look at the I vs. V waveforms. I don't think I want to get to that. Does anyone know what's going on or can point me to some related info? I have searched the www, but all I have found is manufacturers boasting about the drop _at the transformer_, not at the end of the line.

Thanks in advance.

Laurent

 

[Steve]

I don't know about all the math, but I do know that pro transformers have multiple voltage taps precisely for long cable run scenarios. I think mine has a 12V. 13V, 14V and 15V tap (or something like that) where you are supposed to use the higher voltage tap to make up for longer runs or thinner wire.

 

[gatchel]

With the long cable runs you will get varying brightness. The closer lights will also be at the higher voltage and may burn out faster.

Maybe you can relocate and use 2 transformers and split the load. I'm not a LV lighting guy, just thinking out loud.

 

[LightenUP]

It all depends on what's in the glue of the transformers. The Hamptons are electronic and are not as efficiant as the magnetics. The other differences are if the insides are Turtal or Staked which I would bet the Malibu is Tortal.

If you had to use any of them you might want to use 8 guage wire for the first hundred feet or more then hub out to your fixtures.

You could also maybe try a loop method of wiring.

If I were you I would take the suggestion above and paay the $ for a multi-tap. This will save you alot of trouble.

 

[Scrambled]

This is what I did and it worked for me. I ran a piece of the 12 ga. lighting wire from the last light on my long run back to the transformer. This created a loop. Make sure that you keep the Pos. and Neg. on the same terminals.


After I did this, all the lights were outputting the same amount of light.

Hope this helps



Steve

 

[CORT]

This is what I did and it worked for me. I ran a piece of the 12 ga. lighting wire from the last light on my long run back to the transformer. This created a loop. Make sure that you keep the Pos. and Neg. on the same terminals.


After I did this, all the lights were outputting the same amount of light.

Hope this helps



Steve

Interesting idea. At first I thougt "bad idea," but I can see how/why it works. You are helping "balance" the load while improving the conductance to the farthest lights. I would discourage this configuration if we were talking line voltage. You might want to leave a wiring diagram near your transformer, so that a future repairer (if it is not you) can understand your configuration.