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Old 03-28-2006, 11:51 AM   #1
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Yet another LED Post ;)

A couple of questions... First, made my own led system, consisting of 2 2600mcd/3.7V(4.5max)/20mA LED's. wired them in series to create 7.4V... with a variable Voltage AC adapter set at 6V. I have no resistors in my setup and it runs fine...Ok, do i need resistors if my system is running fine without them? and can i run my set up at 7.5V without hurting the fish psychologically? Wondering if it was too bright...I also sanded down the tip of the LED's to create more of a glow instead of a burst of light. Thanks in advance.

John
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Old 03-28-2006, 12:07 PM   #2
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HmmMm thats a hard question. I have a 1 watt moon light and that give i serious burst of light buy my fish just hide under some decorations at night.... And as far as the resistors... cant help ya there...
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Old 03-28-2006, 02:06 PM   #3
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LEDs running on AC without resistors will not last long. Mark my words.

Good practice would be to mount them in parallel with each their own resistor for current limiting purposes and voltage reduction. A regulated DC power supply is highly recommended. For the LED specifications you provided above, a series resistor of 115 ohms is suggested, or a little higher value.

Good luck,

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Old 03-29-2006, 11:05 AM   #4
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LOL, i was really worried, when i read the post thinking crap, i have just ruined my led's, but after about an hour of trying to figure out which resistors to use, utilizing multiples of variables in coordination of ohm's law....i figured out that my AC--->DC adapter is regulated, and thats why it costed me an arm and a leg....Its funny how i can do mathmatics like this but to overlook something sooooo simple...man i feel stupid

Now, since i have a regulated dc, and since my led's are at 7.4 in series, would running 7.5 on my adapter kill my led's? thnx in advance...


also, my adapter is rated at 300mA.
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Old 03-29-2006, 01:22 PM   #5
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If the power supply is regulated DC then it is fine. The two LEDs can, at most, consume 40 mA (0.04 amp) of current, unless they go ballistic. They are well below the limit of your PS. As I mentioned earlier, I would suggest setting them up in parallel, as shown in the attach pictures. Also, I never supply the maximum voltage indicated, that pushes the devices to the limit and can be calling for early failure of devices. Adding the two resistors will probably cost you an extra 20-30 cents. I would also suggest, for safety purposes, using a 0.5 Amp fuse in your circuit. Always play it safe with electricity. HTH

Cheers!

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Old 03-29-2006, 02:28 PM   #6
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Serge, thank you for all the advice and nice schematic!!!... the reason why i ask, is because i have already made the system and installed in my tank... granted, by not utilizing resistors and not having the "safety" precautions, I maybe in a "world of hurt". But, the LED's have a MAX of 4.5 (1 LED) and im only running 7.5 which is 2 volts less than max for the pair run in a series. The thing that might happen is that i lose the LED's due to over lighting. But i feel these can probably last for at least 5/6 years if i leave them on for 24hr/day. I will be upgrading to a maybe a 200 Gallon when i buy a house anyhow, and my led's will be upgraded at that time...I just may use that schematic...
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Old 03-29-2006, 07:35 PM   #7
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Hey, no sweat! I was only letting you know my thoughts and views on the design. Glad you like the schematic. Hehehe

Cheers!

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Old 03-30-2006, 12:25 PM   #8
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lets say i wanted to use 6 led's with a 12 v power source...the voltage calculator says to use 47 ohm resistors, ran in 2X3led series in parallel...how can i achieve a "current limiting resistor?" and where do i put it in the circuit? thnx

John
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Old 03-31-2006, 10:52 AM   #9
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ok, i figured it out lol, current is common in a series...!!! **** i knew it from all my marine tech training but figured it out after my master sergeant talked with me...i figured it out.
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