help with led moonlighting wiring - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 08-17-2005, 05:32 PM Thread Starter
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help with led moonlighting wiring

im getting these leds off of ebay. I plan to use them with a 12v power supply. I sent them an email asking about their resistors they include. I told them what I would be using this for and how I wanted to set it up and they told me that if I ran 4 leds with a 12v power supply then I would not need to run them with resistors. They said if I ran 4 of them then each would receive 3 volts. Is this correct? I have done some reading but still do not have a full understanding of how to wire leds. If this does not sound correct, then around what range of resistors would I need to get 3.2-3.6 volts to 4 leds from a 12 volt (or lower) power supply.

Help is appreciated.
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post #2 of 13 (permalink) Old 08-17-2005, 06:19 PM
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Quote:
Originally Posted by accord86
im getting these leds off of ebay. I plan to use them with a 12v power supply. I sent them an email asking about their resistors they include. I told them what I would be using this for and how I wanted to set it up and they told me that if I ran 4 leds with a 12v power supply then I would not need to run them with resistors. They said if I ran 4 of them then each would receive 3 volts. Is this correct? I have done some reading but still do not have a full understanding of how to wire leds. If this does not sound correct, then around what range of resistors would I need to get 3.2-3.6 volts to 4 leds from a 12 volt (or lower) power supply.

Help is appreciated.
I don't know about the resisters, but from playing with LEDs in the past, you can connect them "in series" to drop the voltage. To do this, connect the four of them together with one negative lead to the next LED's positive lead. Then connect the wires with the positive wire to the positive lead of the first LED, and the negative wire to the negative lead of the fourth LED. This will give you three volts on each of the four LEDs.

If you haven't already, a piece of PC board from Radio shack makes it easier, since it has holes for the LED Leads.

I'll try to get a diagram I can post, since it is harder for me to explain than draw.


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post #3 of 13 (permalink) Old 08-17-2005, 06:35 PM
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I hope this works. It's quick and dirty, but let me know if you can see it and have any questions:

Edit: What you can't read is the long Leads are the positive ones. Also for some reason the middle right LED lost its positive lead, and the middle left lost its negative lead.
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Last edited by Safado; 08-17-2005 at 06:37 PM. Reason: Couldn't read text.
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post #4 of 13 (permalink) Old 08-17-2005, 09:00 PM
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There are some issues however with running them in series.
1) Running them series means each only gets 3 volts, they are much brighter at 3.2-3.4 volts.
2) Wiring in series mean they are all acting like current sinks, meaning they may run hotter. If one burns out then rest will quicklly follow due to overvoltage.
Wiring them in parallel with a resistor on each is a safer more reliable method.

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post #5 of 13 (permalink) Old 08-17-2005, 11:09 PM
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Quote:
Originally Posted by BOTIA
There are some issues however with running them in series.
1) Running them series means each only gets 3 volts, they are much brighter at 3.2-3.4 volts.
2) Wiring in series mean they are all acting like current sinks, meaning they may run hotter. If one burns out then rest will quicklly follow due to overvoltage.
Wiring them in parallel with a resistor on each is a safer more reliable method.
Botia, Thanks for the clarification. A few more questions:

about #2 when one burns out ( a very long time if I'm not mistaken), wouldn't it break the series, and like a fuse, make all 4 go out? Can this be avoided by setting up a series of 4 groups of a couple bulbs in parallel? if one goes out, the current would be transferred to another rout, still maintaining the series.

About the resister. How does a resister work (quick version )? does the resister heat up? Do they ever burn out?

Finally does anyone know what kind of temperature these LEDs run at? Can Silicone be used over the soldering, or is this more of a fire hazard than leaving them bare? Are either of these is a big deal at 12?


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post #6 of 13 (permalink) Old 08-18-2005, 04:49 PM Thread Starter
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I've read about wiring them in parallel, but getting into series would probably just confuse me more. So if I were to wire them in parallel, then I would need to wire in resistors correct? And also in order to get around say 3.3 volts to each LED, then what resistors would I need, and what voltage power supply would I need. Is there a very simple method of figuring this out?
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post #7 of 13 (permalink) Old 08-25-2005, 03:49 AM
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i set one up with about 10 lights in parallel, 9 volt 300 ma power ac adapter. If i remember correctly i used 220 ohm resisters 1/4 volt (i think) before each led. After i soldered i painted on liquid electrical tape. Put the whole thing in to a clear tubing and sealed the ends with silicone. It does not produce much heat at all, stays really cool.
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post #8 of 13 (permalink) Old 08-25-2005, 01:18 PM
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If you want some more info on LED's:

http://www.twoengineers.com/Richard/leds.html
http://www.iguanalabs.com/1stled.htm

And general info on circuits:
http://www.ibiblio.org/obp/electricC...s/DC/DC_6.html

FWIW, I use a radio shack variable voltage transformer block (Bottom line, without getting into it, the variable voltage allows you to change the brightness of the LED's).
http://www.radioshack.com/product.as...%5Fid=273-1662

It powers 4 white LED's in my hood, and I wound up leaving it at 9V.
The LED's are from an "accent" light kit I found a car parts store for $4.


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post #9 of 13 (permalink) Old 08-29-2005, 03:26 AM
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I also found a great link for DIY moonlights:
http://www.kaotica.com/frag/diy/moonlight/

HTH

Steve

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post #10 of 13 (permalink) Old 01-14-2006, 05:18 PM
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how do you which whire on the led is Postive and which one is negative..

Thanks
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post #11 of 13 (permalink) Old 01-14-2006, 05:27 PM
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Here's a great little article about LED moon lighting for your tank. Most of the info you need is there.http://www.csd.net/~cgadd/aqua/art_nightlight.htm
I just bought a led kit for moonlighting on eBay too. I haven't recieved it yet, but I can't wait to get it all soldered and installed.
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post #12 of 13 (permalink) Old 01-14-2006, 08:34 PM
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Quote:
Originally Posted by kamla
how do you which whire on the led is Postive and which one is negative..

Thanks
Three ways:

1) Positive side has a longer lead.
2) For round LEDs, negative side has a flattened area on the plastic rim.
3) Hook one up and test. I have seen cheap LEDs in the surplus market where the lead indicators were reversed, explaining why they were cheap and in the surplus market. As long as your voltage/current is correct, hooking one up backwards doesn't hurt it.
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post #13 of 13 (permalink) Old 10-19-2006, 01:37 AM
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If you haven't already figured it out, (this thread is a couple of months old), it isn't the voltage so much to be concerned about...it's the current. If the supplier said that they will work fine with 12 volts then that may be the calculated voltage for the supplied resistor. Resistors limit the current to the LED so that too much electricity does not flow through it. Definately run the LED's in parallel and definately use the resistors (on the positive side). The resistors supplied with your LEDs are obviously meant to light the LED with a 12v source. However, if you ever decided to use a different voltage, lets say 6 volts the calculation is fairly easy. It's just Ohm's law R = E x I. Where R = resistance, E = Voltage, and I equals current in Amps. So....if the LED was rated at 50ma or 0.05 amps, the voltage rating was 3.3 volts, and the supply voltage was 6 volts, the equation for figuring the resistance is (6v - 3.3v)/0.05 amps = 54 ohms. A resistor with a value of 54 ohms would safely light the LED. The reason for doing this little calculation is not only to safely limit the current through the LED, but a resistor which is too large will dim the light too much and not be good either.
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