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Need help with diy LED project Answered

Hello, I am wanting to light my fishtank by using LED's... it is a really big fish tank so this must be a custom job, and i am interested in this field of work. I understand the basics of DC current, and i can solder... but i am still a n00b!

I have 100 LEDs just like these http://cgi.ebay.com/100-5mm-6000mcd-LED-Lamp-Ultra-Bright-Blue-LEDs-DIY_W0QQitemZ350034574270QQihZ022QQcategoryZ66948QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
and i was wanting to use like, 50 or more if you guys think i need it. I understand the need for resistors and my goal, if possible, is to use as few resistors as possible! since they are not readily available to me.

My plan is to use two long separate strands with, say 25 LEDS on each. Is this possible if i can find a 12v+?

is this possible?
Do i need to use series or parallel wiring? ( i want to use fewer resisters)
Can i make two separate strands using one power supply
Which values do i need to use to find resistors?
http://cgi.ebay.com/100-5mm-6000mcd-LED-Lamp-Ultra-Bright-Blue-LEDs-DIY_W0QQitemZ350034574270QQihZ022QQcategoryZ66948QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Thank you guys so much, I have been wanting to work on this project for a long time, but these questions have always kept me.

15 Replies

user
tech-king (author)2008-04-06

i just found this thread, sorry to weigh in late. because this project is for a fishtank, the plug you use MUST BE A GFCI. otherwise, there is a risk of electrical shorts and fires. you can buy gfci outlets at any hardware store.

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westfw (author)tech-king2008-04-06

Interesting; I've had several (smallish) fishtanks over the years, and never seen the "requirement" for GFCI outlets. I mean, it sounds like a good idea, but "Must" ?? (I can see the importance going up as you add homebrew electronics...)

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tech-king (author)westfw2008-04-09

with homebrew electronics, yes. with store bought ones for underwater use, i would add one, but it would not be needed.

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guyfrom7up (author)2008-03-11

well, a dirt cheap option, but not safe is to put all of them in series, put a specified resistor in sereis, a 1,4004 diode in series facing the opposite direction, and plug direclty into a wall. Not safe though cause you can be easily electricuted.

You could ge the 25.2 volt transformer from radioshack.
25.2/3.5=7.2 or 7 diodes in series with 1 resisotr
to have 49 leds you would need 7 resistors.
Lets see how many amps you need. 20mA per led (don't use 30, that's the MAX), so 0.02 times 49 = .98 amps, or pretty much 1 amps. The one at radioshack gives out 2 amps, so it should be fine

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tech-king (author)guyfrom7up2008-04-06

no offense, but that just screams out accident. at least put an isolation transformer.

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guyfrom7up (author)tech-king2008-04-06

I said you could do it, but it'd be very unsafe.

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tech-king (author)guyfrom7up2008-04-06

for future record, you should suggest a gfci outlet for all devices that plug into a wall and are near water. and yeah, you did say it was unsafe.

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guyfrom7up (author)tech-king2008-04-06
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tech-king (author)guyfrom7up2008-04-09

Grond Fault Circuit Interrupter. it detects a ground fault condition and cuts power in milliseconds to prevent the high amperage short from forming. they are used as pluggs in kitchens and bathrooms

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Patrik (author)guyfrom7up2008-03-11

BZZZT! If you have 7 series circuits in parallel, with 7 LEDs in each series circuit, you will only need 140mA current total. You would only need the 1A if you put all 49 LEDs in parallel. ;-)

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chandra_vemulapally (author)2008-04-06

Mr Patrik With 140mA individual channel current lighting of all the 49 LEDs at a time causes .98A load current. Refreshing technique can be used to on all the LEDs with 140mA current while compromising with luminosity to some extent.

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schorhr (author)2008-03-11

Hello,
first of all you need to figure out which config is the best.
Each LED has a forward current of 30mA and requires 3.2 ~ 3.8 Volts.
If you connect them in series that would be 50LEDs*3.5v=175v or 25LEDs*3.5v=87.4v so this is no great option.

If you connect them paralell you'll need 3.2-3.8v and 25*30mA=750mA, or for 50 LEDs 1,5A

Here is a web-based tool that will show you how to wire it (as diagram, text or even wiring image)
http://led.linear1.org/led.wiz
Just enter the LED Data.

The problem with the resistors are that you should not put all the LEDs on a single resistor, since it would probably melt ;-) (of course depending on the resistor).

If you need resistors, many online stores (and ebay) offer dirt cheap resistors, often sold 100s or 1000s.
A single resistor may cost between 1-5 cents.

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punx777 (author)schorhr2008-03-11

Okay, thanks for the help guys!! i have a few more questions.... i found a power supply from an old Rio MP3 player. 5.4V and 2 Amps Can i buy specific batches of resistors on ebay? What is the ideal voltage i should run the LED's on? my goal is to use two seperate long tubes with a single row of LED's.... how many LEDs should i put on a resistor?

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schorhr (author)punx7772008-03-11

If you put all LEDs in series you will have several problems. Also if you are in a country where the power has an alternate current that might damage the LEDs.

The 5,4v 2 Amp powersupply should work, just enter the voltage into the calculator-thingy I linked above.
5.4V Supply
3.5V Diode voltage
30mA current
50 LEDs

It will show you 68 ohms for EACH LED:
You can just get a bag of Resistors close to that value, ebay, radioshack, electronic store, what ever you can get cheapest.

If you have a 12v supply you can connect several in series. Connecting all LEDs paralell behind a single resistor will most likely not work with that many LEDs.

Also check out
http://www.theledlight.com/ledcircuits.html for general instructions
or read a other forums post
http://www.electro-tech-online.com/general-electronics-chat/6378-looking-help-setting-up-large-number-leds.html
with a similar problem.

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schorhr (author)schorhr2008-03-11

Oh, also note that you probably do not want to use the LEDs at maximum voltage and maximum current, so you might want to try 20mA; IF you have a store nearby try with just one LED and different resistors if its still bright enough. If your LEDs dont handle the max. current well, they might have a decreasing brightness after few hours of use or even get damaged.

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