cheap LED

M

maaltan

AC Members
Sep 11, 2004
259
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16
If anybody is looking to build a DIY moonlight. I found a place on ebay that is selling massive lots of LEDs much cheaper than anywhere else I've seen them.

They have just about every color and are sold in lots of 100 to 50000. They come straight from the factory in hong kong so the english isn't that great and you can't get paypal protection. The webpage advertised appears to be defunct. But my order went through. YMMV

I got 100 blue leds for $16 (USD). Whites are around $20, Reds are like $6 i think.

They seem to be of good quality. Just installed them, look great. I just used 10 of them. Assuming they don't burn out in the next little bit. I will probably be ordering another color. I might eventually rig a sunrise system, start with blues and violets which shifts to reds and then to the yellows and whites. then kick on the main florescents. Reverse at night. hmmm big project :)

oh yeah i guess you want a link

http://stores.ebay.com/besthongkong-Dot-com



PS beware. 100 blue ultrabrights all shining at once is dangerously bright at short range. I saw spots for 15 minutes.
 
OK , got my system built. Sort of. Not going to win any UL awards(more likely they will confiscate my soldering iron if they see that monstrosity). But it comes on when the lights go out and vice versa.

I will warn you though. Not all of the 100 leds worked. I screened them and found that after about 5 min at full illumination about 4-5 of them dimmed to practicaly nothing. Still not worth complaining about really, Thats pretty standard when ordering from a factory. 3-5% failure rate is expected for most things. i think.

what im getting at is test them at full illumination (3.5v at 20ma, I will try to help with the ohm-ing if needed ;) ) before getting them all wired up in the system just to have thm go out.
 
I'd love to see pictures or details of how you got it all together, and how you wired it to come on when the main lights go out.

I'm looking to put 2 or 3 of my blue LEDs in the tank I just built into the wall but I'm not sure what kind of enclosure to build it in or if I should just drill a few holes in my light hood and cram them in there.
 
No camera handy, sorry. I'm not really happy with it anyway all the lights are kinda pointing toward the center. I need to find a better way to aim them. Plus my water lillies are blocking several as well as my dense undergrowth (java moss and a particuarly dense hybrid apongeton). I still cant see my khulis :(

2-3? i put twenty. overkill probably. I have a logarytmic potentiometer (variable resistor) for a dimmer. a wall dimmer switch (a variac?) will not work and possibly damage your circuit.

The way i connected them together basicly boils down to pulling a long twisted pair out of a cat 5 cable (any paired wire would work, something with tougher insulation proably preferred. I'm a networker and have loads of scrap cat 5 laying around). carefully seperate the pair where you want the led. Solder the long led to the white/colored wire and the short one to the solid colored one. tape it up very well paying close attention to dividing the leads of the led and covering your soldering. Do this down the length of the wire wherever you want them. this will wire the led's in parellel (sp) This will allow you to use a 3-4v power supply to power them all. unfortunately batteries don't last long at this load. A pair of D's lasted about 16-20 hours.

I then taped this to the makeshift stand that i have my regular lights mounted on. If you have a full hood this should be easier for you.

As for the dark switch I used a relativley simple circuit that turned complicated during implementaiton.

Hint. Wall adaptors (brick, transformers, those black things that take up like 3 plug ins) do not output what is on the label. Under maximum load they probably drop down to close but this circuit will in no way load it to the maximum. I have huge arrays of little resistors burning away the extra voltage my 5v (actually 11.2v) adaptor i bought. I reccomend buying either a power resistor (5-$10) to handle the massive power drop or spending a little time wiring up a simple regulated 5v power supply (http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html) YOu will still need to drop about 1.5 volts with resistors but it will be much easier to do so (and easier on the components).

here is a kit for the dark switch itself. you will still need a power source.
http://www.quasarelectronics.com/3079a.htm

I had a schematic I used for mine but the page seems to have evaporated. Google keeps shuffleing results.

I know this is erratic and confusing. Let me know what points you get confused about and I will try to clarify when i have time.
 
Lots of good information in that post, thank you! I've been experimenting and after I get something more made up I'll probably have more questions.

I wired up 2 of these blue LEDs late on Saturday night and am powering them from 3 C-cell batteries to see how long it will last. I guess I can estimate that from your experiment with 20 hooked up to 2 batteries.

Anyway, thanks for the reply and links. I'm sure I'll be back to this topic again. :)
 
ooh watch it .. 3 batterys in series (+ to - in a row)is 4.5 volts (more or less) .. you need to check out the maximum rating of your led's(probably 3.5v). YOu can burn them out quickly.or at least shorten their lives considerably.


When you wire the leds in series (long lead (Positive or anode) to short lead(negative or cathode) you add the voltage rating. so if you have 4 - 3v max LEDS you can hit it with 12v without worry.

When wiring in paralell (i really need to learn to spell that word :) ) or wired positve to positive etc and negative to negative etc you add the current ratings. my leds were rated at 3.5v or 20 miliamps so 20 wired in parrellelelell (to many l's) so I could hit it with 400MA at 3.5v.

now the funny thing is amps and volts are irrevocably linked. 3v at 20ma is the same (as far as the as the led is concerned) as 30v 2ma. voltage pushes the current though. so running your leds at a higher voltage requires a current limiting resistor (notated my ohms). This wastes your power as heat. droping alot of power requires bigger resistors to prevent meltdown. In my situation i was dropping 10v down to 5v at 400ma which required about 20 ohms. this required about 3-4 watts of resistor. the regular ones you see at radio shack are 1/4 to 1/2 watts. my little test 20 ohm 1/4 watt resistor gave up as the magic blue smoke that makes all electronics work was released.

all this is regulated and measured by a series of mathmatical formulae called ohm's law.

http://www.the12volt.com/ohm/ohmslaw.asp

is a good primer overall look at ohm's law. a google search will give you much more info.

if your led's are warm you are sending too much current into them and burning them out (slowly or possibly fast)
 
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Well I don't know entirely what I'm doing, but I did use the resistor calculator on BestHongKong.com's web site and I added in either 33 or 47 ohms, I don't remember which. So far it's been running for 6 days and the resistor hasn't burned up. It's just a test anyway, I'll be wiring it up to a power supply when I make my "real one". :)
 
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