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I'm working on some LED fixtures and I can see several ways to skin this cat, but are there things I should be aware of for safety or for any other reason?

I need to supply around 1300W worth of LEDs with power. The largest chip uses 3A @ 18V. Should I use:

1. 18v 72A Supplies
2. 72v 18A Supplies

Why should I chose one over the other? If 5ma can cause fibrillation and I am already working with 3A chips (assume 3A regulated current) do I care what the voltage potential is? I have to move the same amount of power.

As you have already indicated P = IV.

You need to consider the I^2R loss of your wiring.

Big V => small I.

That's why mains is high voltage and the National Grid is very, very high voltage.

Go for the highest voltage but if you keep below 48V then I think you stay within the limits of the Low Voltage Directive:

http://en.wikipedia.org/wiki/Low_Voltage_Directive

and avoid all sorts of high voltage safety requirements.

I'm in the US so I don't think that is applicable. It also says over 75v DC anyway. The Wiki on high voltage http://en.wikipedia.org/wiki/High_voltage says anything under 1500v DC is considered low voltage.

I am planning to use the higher voltage to power things for the wiring reason you pointed out. It makes all the parts in my circuit get significantly more expensive to use more current.

Is it correct then that the answer is power is power and if you have that many watts being delivered that it doesn't matter which voltage or amperage is being used? The hazard is the same since in the end the amount of power being delivered is still the same? Since they are the same the better answer would be to use more voltage so that the load on the components in the circuit will be less?

The chip you mention. Is that an led lamp that works from DC 18V and takes 3 Amp. If it is you need to look at the spec to see the tolerance on the 18V. When you mention 1300W is that the equivalent light output from incandescent lamps, or do you need 1300W of energy into the leds you mention? Leds will vary in effeciency and spectral output.

How far apart will the leds be from the power source. Will this be in a dry indoor area or a wet outdoor one?

Seen this?

http://www.onsemi.com/PowerSolutions/content.do?id=15102

Search Diodes Inc:

http://www.diodes.com

for:

zxld137

In particular:

http://www.diodes.com/datasheets/ZXLD1370.pdf

http://www.diodes.com/_files/calculators/ZXLD1370%20calculator%20v1.3.xls

http://www.diodes.com/datasheets/ZXLD1371.pdf

http://www.diodes.com/_files/calculators/ZXLD1371%20calculator%20v1.0.xls

http://www.diodes.com/destools/appnote_dnote.html

http://www.diodes.com/_files/design_note_pdfs/zetex/dn95.pdf

:)

Thanks for all the info, guys. I will check out the links. I understand that LEDs are current driven and that I will need to buck or boost the circuit to not waste power to get what I need. I am trying to understand if there was anything I was missing in my basic understanding of electricity. It will be 1300W of power to the LEDs. This is for aquarium and hydroponic use so there is the potential that something will accidently get wet at some point in time - thus the questions.

Typically, most people in my circles are getting a few dozen meanwell drivers, but spending $50-$100/ea for a bunch of preconfigured drivers doesn't make sense when I could have something that was designed with the capabilities I need in mind. I have been using PWM with some mosfet chips to control my test circuits. The final design will be a buck on a 72V 18A capable power supply. I just want one power supply instead of a whole pile of units designed for smaller applications.

72vdc and water oh please say its salt water ! I'm kidding but you watch out that any hazards are clearly marked