Power supply for LED lighting

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Rye_84

Member
I am currently working on building an LED light for my aquarium, but am having difficulty determining the specifications of the power supply. Is there anyone who can help?

I am trying to run the LEDs from a 12V DC power supply.

LED specifications-
3.4V @ 700mA

The LEDs will be ran in series of 3 with 32 parallels for a total of 96 LEDs.
The resistors in each series will be rated for up to 2W and 2.7 ohms.

Together the total power dissipated by the LEDs and resistors is 270,816mW (271W). The LED's draw 22,400mA from the source (22.4A).

If I have done all of this right a power supply with a 12V output and a maximum wattage of 500W and 28A would work correct? or am I not even in the right ball park with this?

Thanks for the help in advance.
 
Triggerjay

Triggerjay

Well-Known Member
Computer power supply? I have used them for many different things, up to and including a hot wire foam cutter. They also work good for powering 12v dc automotive devices on 120v - cd deck, CB radio, etc..

Jason
 
R

Rye_84

Member
Triggerjay said:
Computer power supply?

Jason
Click to expand...

It is a computer supply, they're inexpensive and put out good power. Do you know if it is too much power or not enough though? The last thing that I want to do is blow 100 LED's or fry the power supply. I always seem to fry simple, little DC transformers.
 
tbittner

tbittner

Well-Known Member
PC power supplies are broken up into rails. It might be a 500w power supply, but each rail only puts out 125w. I don't think you can put out too much power as long as the voltage matches the hardware. But you could quickly fry a power supply with that kind of demand.
 
R

Rye_84

Member
Here are all the ratings of each output from the power supply that I am planning on using-
+3.3V +5V +12V -12V -5V +5VSB
20A 32A 28A 0.8A 0.3A 2A

The 12V at 28A output would max out at 336W and so far I only need 271W. I will need fans which will also need to use the 12V power supply, but they shouldn't need more then a few watts a piece, hopefully. I also plan on adding some 5mm LEDs for night lighting and those I should be able to run off of one of the other outputs.
 
BigAl07

BigAl07

Administrator
RS STAFF
Have you started construction yet? Maybe do a DIY Build Chronicle on this. I would love to see it from start to finish. :)
 
Jason25

Jason25

Active Member
I have built some smaller ones and have plans fon making a bigger one. First off there is no way 96 leds should be pulling 22 amps. That is more than a tablesaw would use. Here is a link you can use that will tell you what size resistors you should use and exactly what amperage you will need. As long as you know the forward voltage you will be good. Just check the specs of the led's you using. If you need more help PM me.

LED calculator for single LEDs
 
Triggerjay

Triggerjay

Well-Known Member
Jason25 said:
I have built some smaller ones and have plans fon making a bigger one. First off there is no way 96 leds should be pulling 22 amps. That is more than a tablesaw would use. Here is a link you can use that will tell you what size resistors you should use and exactly what amperage you will need. As long as you know the forward voltage you will be good. Just check the specs of the led's you using. If you need more help PM me.

LED calculator for single LEDs
Click to expand...


22A 12V DC is very little. Your home PC pulls more. You are thinking 22A on 120V AC, in which case would be a huge amount. But in DC world, thats a very small amount. If you want to figure what it will pull on the 120v AC side, it would be 264 watts / 120v. Or 2.2A on the AC side. The fans will only add about 10 watts each to that #. Total amperage 2.36A with fans, on the 120V side.

Jason
 
R

Rye_84

Member
Just an update on this-
I have found the LEDs that I want to use, along with some circuits for running the LEDs at a constant current for a lot cheaper that buck pucks. My next step is to find ways for controlling the LEDs by dimmers so that they can be set at different levels for night viewing, color temp and whatever else you can think of. I have finals this coming week, so once those are done with and I get the money to buy everything this might actually replace my metal halide and save me some electricity bills....kindof
 
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ReefGuy69

Member
You need to chronicle your supplies and how your doing this. If its enough to replace MH AND lower your electrical bill then i am all in depending on what your final outcome for cost is. and i love DIY stuff. Pictures and a chronicle would be pretty nice.
 
ReefSparky

ReefSparky

Member
Rye_84 said:
Is there anyone who can help?

I am trying to run the LEDs from a 12V DC power supply.

LED specifications-
3.4V @ 700mA

The LEDs will be ran in series of 3 with 32 parallels for a total of 96 LEDs.
The resistors in each series will be rated for up to 2W and 2.7 ohms.

Together the total power dissipated by the LEDs and resistors is 270,816mW (271W). The LED's draw 22,400mA from the source (22.4A).

If I have done all of this right a power supply with a 12V output and a maximum wattage of 500W and 28A would work correct? or am I not even in the right ball park with this?

Thanks for the help in advance.
Click to expand...


I'm not sure I follow. Is that to say that you'll have 32 sets of 3 LEDs in parallel, with each set of 3 in series?
 
R

Rye_84

Member
ReefSparky said:
I'm not sure I follow. Is that to say that you'll have 32 sets of 3 LEDs in parallel, with each set of 3 in series?
Click to expand...

As of right now, yes. Unless someone else knows of a power supply that is reasonably priced that would output more then 12V and a lot of amps. I have found a few, but they are only capable of 150W and those cost about $100 a piece. There are some that would give enough power individually, but those cost anywhere from $3-500 and I'm not looking to spend that much.
 
slakker

slakker

Member
I'm a noob, but since this is a DIY thread, how about building a power supply?

I've build many when I worked in a research lab and they're quit simple to build. Transfomer to down to 12 VAC, then a simple whetstone bridge using 4 diodes. Add a capcitor to smooth out the rectified DC current and it should work. You'll need to size the transformer, capacitor and diodes for the current draw.

Or it would be simpler to use a PC power supply... :)
 
Cassette87

Cassette87

Well-Known Member
was this supposed to be a PM? ???

Edit: Sorry guys, for some reason Only that last post came up when I clicked the thread, and didn't quite follow it at first... now the first page came up :)
 
R

Rye_84

Member
I would prefer to just buy one because I don't want to have to mess with AC current. Thanks for the idea though.
 
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