900 high bright led array serie-paralel

Milhox

Joined Apr 8, 2016
4
Hello!

I'm trying to make calculations for a 900 led matrix (the 5mm white transparent & bright ones) that I want to use it for videography ligths, as a DIY proyect.

I'm a beginner on electronics, but after read the basics I can make simple circuits with leds (I'm already make a few ones but only 7 led max.).

Data:
Power suply: 12v
Led: 3,7v, 20ma

My first thought was make a simple paralel conection: 30 treads of 30 leds each one. but, after calculations I had this results:

-A resistor of 15ohm for each thread, with 5w consumption
- 2,2w of consumption for each thread for leds

so... 5w+2,2w=7,2w x 30 threads, 216w. To move all this circuit need a 18amp power supply (20ma X 900led= 18amp).

Then I think: Must be a more efficient way to connect all leds, in fact, commercial lamps made it of leds can work whit batteries (that is a VERY desirable feature that I would like make in this project)!

I array them in series-paralel in that way: 10 treads of 30 subseries of 3 leds each one, the resistor is for each thread.

Make calculations:

-A resistor of 45ohm for each thread , but only dispate 0,54w.
-A led consumption of 6,6w for thread

So.. 0,54w+6,6w=71,1w. But this array only needs 20ma X 300 (groups of 3 led in series)= 6amp power suply

Any error on my calculations?

TheButtonThief

Joined Feb 26, 2011
237
With that many LED's, you may want to consider using a higher voltage power supply so that your circuit drawl less current and produces less heat. Also, I wouldn't use one resistor to limit the current to as many as 30 LED's, not even 10. Ideally, you need to use one resistor for every LED but that's not always practical, maybe try to place a tighter limit on this.

John P

Joined Oct 14, 2008
1,859
People keep asking about LEDs in series with a resistor to limit current, yet they'll say efficiency is important. No, forget the resistor. Buy or build an electronic constant-current switching (not linear) circuit for each string of LEDs. They seem to have typical limits of 36V, which works OK with 8 LEDs in series.

But really I suggest that this is a crazy design. 900 LEDs is an outrageous number of components to fiddle with; you could and should be using many fewer LEDs with each emitting more light. In terms of electrical input, you seem to expect 66 Watts, so if you used 1W LEDs, you'd need 66 of them, or if they were 3W, just 22.

TheButtonThief

Joined Feb 26, 2011
237
you could and should be using many fewer LEDs with each emitting more light. In terms of electrical input, you seem to expect 66 Watts, so if you used 1W LEDs, you'd need 66 of them, or if they were 3W, just 22.
Videography lights generally need to output a large amount of light from a big surface that has an even spread. This gives for a defused effect even though the light source is very bright. The best way to do this is to use a lot of little lights on a bed rather that one very bright light.

Dodgydave

Joined Jun 22, 2012
9,852
12v supply,with two leds in series and a 220R 1/8W resistor on each strip, thats 450 lots of parallel led strips, each taking 21ma approx, thats 9.4amps.

Milhox

Joined Apr 8, 2016
4
People keep asking about LEDs in series with a resistor to limit current, yet they'll say efficiency is important. No, forget the resistor. Buy or build an electronic constant-current switching (not linear) circuit for each string of LEDs. They seem to have typical limits of 36V, which works OK with 8 LEDs in series.

But really I suggest that this is a crazy design. 900 LEDs is an outrageous number of components to fiddle with; you could and should be using many fewer LEDs with each emitting more light. In terms of electrical input, you seem to expect 66 Watts, so if you used 1W LEDs, you'd need 66 of them, or if they were 3W, just 22.
Can you ilustrate me better? maybe link me examples that you mean?

Thanks!

Milhox

Joined Apr 8, 2016
4
12v supply,with two leds in series and a 220R 1/8W resistor on each strip, thats 450 lots of parallel led strips, each taking 21ma approx, thats 9.4amps.
Can you please, explain me once again? maybe with a draw. Im not english speaker, so many times I can get lost easy