12 v led volt drop?

I'm having one of those moments where I cant work out anything.

12 volt led driver feeding garden lighting,  run of 40 metres is proposed. 80 watts total load, led driver is rated at 150 watts. Is it the 12 volt ampage for the calculation, or the mains? I am presuming the 12 volts for the calculation, which gives 7 amps current draw, which , on 1.5mm cable, gives a near 60% volt drop.

Does that look about right?

If so, it is going to need either mains voltage outside lights, or local transformers.


Parents Reply
  • There are 9 different lights attached, all at around 5-10 watts each, all branching off along the route, the total length is 40 metres. Even with the first few being compliant, I don't think it will any good for the last few, as the voltage will be down to 6V or less.

  • I have had a bit of a think about this one and I think that the answer is not easy. As you go along the cable, the load decreases, so the VD is not uniform. Moreover, what assumptions can be made about each lamp? If the voltage drops, do they draw less current (rather like a filament lamp) or does the circuitry try to keep the power constant?

    Then if you think about an LED headlamp or torch, they do seem to work with a significantly reduced voltage, albeit dimly.

    I suspect that Alan's original conclusion is correct: mains voltage cable and local transformers, which is rather like the way that DNOs distribute their power.