DIY moonlight problems

[pjhaddock]

OK, I have 4V 20ma blue LED's. I am hooking them up to a 12V power adapter, so I am using three in a series, hooked end to end. When I plug it in, all is good and bright, but ONE will slowly darken over the course of a minute or two, then another will start darkening until its out. If I unplug it while its going out and replace it, all is good, but another one will start going out.. and so on.... What the heck??? I have not tried doing them in parallel yet, is this a common problem when wiring in series or something???

THanks,
Philip

[Squiddy]

You're probably burning them out! :eek2: What size resistor(s) are you using to drop the voltage down?

EDIT: Reading your post again leads me to think that you're not using resistors at all!

[Squiddy]

If you're connecting them in series, they need to be connected like this with a correctly calculated resistor.

http://www.theledlight.com/img-tech/series101.jpg

However, according to this Calculator (http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng), you don't need a resistor. Are you sure the LEDs have a forward voltage of 4V, not 3.6V? If they are actually 3.6V, you will need a 60ohm resistor in series.

[pjhaddock]

yeah, they say Vf 4.0V which is the forward voltage. 3 LED's X 4V = 12V = power I am supplying them.. I also ran 5 of them without a resister on the same 12V power supply, which means only 2.4V and the same thing happened. :mad:

[orlenz]

if your running them the way the above diagram shows you won't need a resistor, it adds up to 12v. could be a bad power supply.

[Squiddy]

Wouldn't you still want some kind of current limiting in there? I would personally run them parallel.. that's what I'll be doing when I wire my moonlights.

[TimD]

First off, you'd be better off running them in parallel.

Second, get a voltmeter and test the voltage being put out by your transformer. I'd be willing to bet that it's closer to 16V. I've tested a number of old transformers I have lying around while doing a similar project and they all run several volts higher than they're rated at.

[Squiddy]

Transformers like that will have a higher output voltage than specified when there is no load attached so that is probably causing some of the problem.

[bigdaddybo]

Hi this is a DIY moon light i made. I have 3 of them hooked to the same power suppy. I dont remember but i think i used a 470 ohm resistor. 9 leds per moon bar.

http://reefcentral.com/gallery/data/500/77280DSC01823__Small_.JPGly.

Bo

[bigdaddybo]

For some reason the like isn't working. looking in my gallery. sorry. Bo

[Squiddy]

Ooooooh nice :) Where'd you get that casing from?

[bigdaddybo]

I found it at local fish store. it is rigid air tubing. i used 1". for end caps i used rubber caps and resistor that i found at a surplus store. Made my own circut board. Found LEDS on ebay $25.00 for 500. Radio shack for power supply. i did make a total of 15 for my self and other Reefers. Bo