# 90 LED Infrared Illuminator - Total Draw???

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#### uspilot

##### New Member
Hi Everyone,
I'm not only new to this forum, but new to the electronics field.
I recently built a 90 LED Infrared Illuminator, and had a question about the power supply I was going to use...

Power Supply:
12vDC 500mA

Individual LED Info:
Voltage Drop = 1.5v
Current = 100mA

Project Info:
15 banks of 6 IR LED's, with one 33ohm 1/4watt resistor per bank.
The 6 LED's are wired in series, and the banks themselves are wired in parallel.

----------------------------------------------------------

R = V / I

R = (12v - 6*1.5v) / 0.1A
R = 3V / 0.1A
R = 30 ohm resistor (used 33 ohm resistor)

----------------------------------------------------------

I = V / R

I = (12v - 6*1.5v) / 33 ohms
I = 3v / 33
I = .0909A or 90.9mA

----------------------------------------------------------

So, 90.9mA is close enough to the required 100mA per LED.

Now, here's the question...
With the banks of 6 LED's themselves being wired in parallel in the circuit, will the 500mA power supply cover the total draw?

I don't know enough about the electrical end of it to know what the total draw on a DC parallel circuit would be.

Thank you to anyone that reponds!
Mike

#### Russlk

##### New Member
The total draw is the sum of the parallel circuits, therefore the total is: 15*90.9 = 1.36 amps. So, no the 500 mA supply is not adequate.

#### uspilot

##### New Member
Wow, thanks for the quick response!

Okay, I guess I don't need the power supply I bought then.

I really appreciate the help!
Mike

sorry

#### fat-tony

##### Member
That should be a great IR illuminator though. What are you doing with it?

#### uspilot

##### New Member
Hi fat-tony,
It's being used for my IR CCD security camera.
And by the way...a big thanks to Russlk!

I used a 12vDC 1500mA adapter, and this thing put's out so much light it looks like a 100,000 candle power flashlight to the IR camera! It has about a 6-8 ft. wide beam at about 8 ft. When I tested it, I was in my living room and I shined it into the hallway and bathroom (which was about 15 ft. away) and it was still as bright as can be.

When I turned it towards the camera, it drowned it in what looked like sunlight. It's a great feeling knowing I built this thing from scratch, and the only assistance I had was from Russlk on the power supply.

Mike
p.s. It was running a bit hot, so I had to throw in a cooling fan.

#### e

##### New Member
can i ask where you got all those 100mA IR leds? How mch did they go for?

#### uspilot

##### New Member
Hi,
eBay.
Search for the following seller: bob-ke6f
Bob is a really nice guy, and he says he has plenty more.

#### audioguru

##### Well-Known Member
freeskier89 said:
What is the advantage of putting strings of 6 in parallel over just putting them all in parallel?
LEDs all have a slightly different voltage drop, so having many in parallel will result in the single one with the lowest voltage drop to hog ALL the current and blow up. Then the LED with the second lowest voltage will hog ALL the current and blow up, etc. Each LED or series string of LEDs needs its own current-limiting resistor.
Also as said by Electropierre, 1.5V or 2.0V is not available but 12V is available for a few LEDs to be in series.

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