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Old 02-17-2006, 02:36 PM   #31
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If you don't have the led's yet, try Ebay, you get a much better price (11$ for a hundred, or 6$ or so for 50) and they come with resistors rated for 12VDC... most eletronics shops try to gouge you for 2$/led and 1$/resistor.

The value of resistor depends on the DC adapter voltage. the coles notes breakdown for the average value can be calculated by.

(InputVoltage-.7)/.03 = Resistor value.

So, assume 12 volts in.

12 -.7 = 11.3 / .03 = 376Ohms , or the nearest common resistor which is greater (probably 380Ohm)

Most 12v adapters put out 13.8v, so putting it through the works it is 470Ohms ~

The resistors colour codes are
0 - black
1 - brown
2 - red
3 - orange
4 - yellow
5 - green
6 - blue
7 - violet
8 - grey
9 - white

The breakdown of the bands are
moving towards the gold/silver band (tolerance, gold = 5%, silver = 10%)
first band = first digit
second band = second digit
third band = multiplier (unless a 4th band is present, in which case, this is the 3rd digit, the next is the multiplier. But typically you won't see this)

So for example, the resistors that came with my LED's rated for 13.8v are

yellow violet brown gold
4 - 7 - 1 - 5%
using what was said above.
47 * 10^1 = 470Ohms at 5% tolerance (+/- 5%)

The ones in this example are
red red brown gold
2-2-10^1 5%
or 220 Ohms.

And the adapter he was probably using is a 6v DC adapter.

Hope it's not too winded, I just think it's better for people to know how to calculate the right resistor rather then assuming the same resistance is used for every transformer.

For those that care beyond that where I got those numbers..

.7 is the voltage that the LED uses
.03 is the maximum current that can travel to the LED (.03a or 30mA)
the formula is basic ohms law. *Voltage divided by current = resistance*, resistance * current = Voltage and Voltage / Resistance = Current

You subtract the .7 volts from the source voltage because this is the voltage drop across the LED. The remainder must be dropped across the resistor that must have 30ma travelling through it. Knowing this, you can divide the remaining voltage you need to drop by the 30mA you need to flow through to get the resistance. This formula is fundemental to electronics.

120 Gal SW, 150lbs Prem. Fiji, 23Gal Sump, 2x250w 15K MH, 4x65w Actinic
3 x Halichoeres Chrysus (1 surfed), 3 x Nemateleotris magnifica, 1 x Centropyge bicolor, 11 x Scarlet Hermits, 6 x Zebra Hermits, 40 x Astrea Snails, 6 x Nassarius Snails, 3 x Cerith Snails
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Old 02-17-2006, 02:45 PM   #32
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Thank you Wizard for that lengthly but very instructive answer. I had taken some many years ago some electronic classes and remembered a bit about the resistance table, but not all of it, so really and trully thank you, and I'll be checking Ebay for the leds as well.

Ill try to post some pics after my NEW project is complete.
I have a new 29 gall tank that is dieying for some attention. ( don't worry, it has not been set up yet, no fish are in danger... just my lower back! )

**** it! Give me Full Power,
Lets have some fun boys, time to test our metal!
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Old 04-25-2006, 11:19 PM   #33
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Nice post RLG2182.well done.

I'm going to do this in some fashion and will probably buy the supplies online tonight.It looks to good and is to cheap not too imo.

A question or thought though....

What would be the down side of mounting the leds inside the bulb housing itself....like the standard strip that comes with start up kits.I realize that the leds would also light up the inside of the strip housing,but wouldn't most of the light make it to the tank without the "beam" effect?

Any one try this or know why I shouldn't?

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29g fw planted at 1.2 wpg
10g fw planted at 3 wpg cf
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Old 08-11-2006, 06:22 PM   #34
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led lights

that looks so cool one day ill do that hopefully
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Old 01-22-2007, 06:44 PM   #35
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Can anyone comment on another site that has a kit like this? I am completely stupid when it comes to DIY but I really would like to give this a shot! Thanks!
Main (20g) - A throng of guppy and platy, Pressurized CO2, Ferts, All Live Plants (Very old pic, new one forthcoming)
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Old 04-04-2011, 01:40 AM   #36
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what resistors did you use and what is the output of the ac adaptor?

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diy, light, lights

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