4000w LED Chip Array Driven Directly by Mains

[Justin18]

Hi folks. I'm currently designing a 4000w LED chip array in which I plan on using 3x 1500w 12v switch mode power supply's. A DC-DC converter will convert the 12v to 35v powering two chips. This totals to 20 step up converters and 3 switch mode power supplies to drive the proposed 40 100w chips. However the cost is staggering. Driving the chips will cost much more than the chips themselves. The questions I have is would it be feasible running the LED's directly from the mains. I live in Australia so our mains voltage is 240v RMS. In essence I would have to run the chips on 340v peak. Since each chip requires a max voltage drop of 35v, I have contemplated wiring 10 chips in series with the mains so each receives it's required 34-35 v. Then four of these sets in parallel. Of course I would use a full bridge rectifier, MCB and RCD. But is this possible. Would each chip in series receive a different voltage drop?

 

[Alec Dacyczyn]

Holy mackerel. 4000 watts directly off the mains?

No, you shouldn't drive them directly off the mains. I remind you that LEDs are constant-voltage-drop devices (roughly speaking). And that voltage drop decreases with rising temperature, due to heating during operation. This is why LEDs are always connected to a constant-current source (even if it's just a crude dropper resistor, and relying on fixed voltage drop and Ohm's law).

If you didn't care about efficiency or efficacy then, sure, you could stick a dumb dropper-resistor in there and throw it all across the mains. Hobbyists do that for chuckles all the time with arrays of little indicator LEDs. But this is not recommended for four thousand watts worth.

What you want is a real, professionally designed LED power supply with a voltage output suitable for a string of the LEDs that you are going to be using, at appropriate regulated current. Yes, you can put several in series to take advantage of a single regulator (this is the typical layout in real-world systems for economic reasons); it will simply require more voltage.

Don't worry about slight differences in voltage drop between the elements due to manufacturing variations. That would only matter if you tried connecting multiples in parallel without balance resistors. I imagine that whatever supply you find will likely be driving only a single string per unit, not multiple parallel strings, you probably won't need to worry about balance resistors.

In short, you want a higher voltage constant-current supply.

 

[Alec Dacyczyn]

And manufactures often produce technical design guides which to explain practical details to people designing systems using their products (these are where I learned half of what I know about practical EE ).

I googled around a bit and stumbled upon this:
OPTOTRONIC Power Supplies Technical Guide
It looks promising.

EDIT: Or it may just be easier to buy forty separate 100W supplies. You can find them on eBay for cheap.