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Old 03/30/2009, 05:36 PM   #576
kcress
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Quote:
Originally posted by ReefEnabler
Stu thanks for posting that reminder.

Most of my LEDs are 1000ma rated and I'm using 700ma pucks.

But I was planning to mix a Cyan LED in one of the arrays, its rated at 700ma max.

Could I just position it at the end of a series and put a resister before it to step it down?
Negative, negative, negative!!

The same current runs thru all of the elements in a series chain.


But! You can achieve what you want by shunting the LED of your choice with a resistor so some of the current runs around your LED. Since properly sized and mounted resistors don't fail this is a safe 'paralleling'.

Tell me the expected VF for the LED you want toned down and the current you will be running and I can tell you what resistor you'll want. (Better would be the actual VF, of the actual LED, at the actual current.)


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Old 03/30/2009, 07:08 PM   #577
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Hi ReefEnabler,

If you want to reduce the current thru a particular LED in a chain you put an appropriate resistor in parallel with the LED of interest.

To do this you need to figure out what the resistance needs to be and the resistor's required power rating.

If we take a cyan triple chip as an example:
Looking at the data sheet we see the forward voltage is 6.84V at 700mA.

Now if you only want to run 550mA thru this puppy you need to shunt 150mA around it somehow, (700-550 = 150). Hence the shunt resistor.

Using the voltage: 6.84V / 150mA = 45.6 ohms.

So if there is a 45.6ohm resistor in parallel with the LED it will be robbing 150mA of the 700mA that is being provided. This means there is 150mA less to run thru the LED and it will get only 550mA thru it.

There is a caveat here which is why I said the actual measured values would be better - but we will persevere. If the LED's forward voltage is 6.84V at 700mA it will be less than this at 550mA. How much less? It could be a lot less.. Especially if, out of the box, your LED is already a low VF value out of the batch it was made in.

What does this really mean? Well it means that after the math above the the actual shunt current will end up being something a little less than what's calculated. This means you will reduce the current thru your LED a little less than expected. But since this is all a bit seat-of-the-pants, less than 700mA, is already going to help the LED's life dramatically.

Ok, now on to the power calculation.

It's easy:
Power(watts) = V x V / Resistance.

P = 6.84V x 6.84V / 45.6 ohms
P = 1 watt

Prudent design requires you use a resistor that is at least two times this and better would be 3 times. Two times would probably still lift your finger prints off instantly. I would probably go 3X

So you want a 3 watt or larger resistor. Now that we know what size we are hunting we can find one. No one makes a 45.6 ohm resistor so you pick a lesser value due the 'caveat'.

43 ohms is a standard value.

I would use one of these two they are both 5W which is much more common and will run cooler yet:

http://search.digikey.com/scripts/Dk...&name=43W-5-ND
http://search.digikey.com/scripts/Dk...me=805F40RE-ND

Hook it up in parallel with the aforementioned LED.


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Old 03/31/2009, 11:47 AM   #578
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Does anyone know how difficult it is to wire a Potentiometer to a buck puck?

Can you wire one Pot to multiple buckpucks to do the dimming?
For example, buy a buckpuck with Pot and wire them together with the ones that don't come with the Pot.

I ask because it costs $4 more for a buckpuck with Potentiometer, and depending on how many buckpuck I buy, I can save some money here. ( I lose the ability to dim each buckpuck, but I'm okay with that as long as there are some cost savings)

Thanks.


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Old 03/31/2009, 03:16 PM   #579
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Read the whole thread and I just want to say excellent work. Simplicity with positive results at its finest. Kudos!


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Old 03/31/2009, 11:23 PM   #580
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Great build up


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Old 04/01/2009, 07:51 AM   #581
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you guys might find this article on plasma light bulbs interesting.

"Luxim Plasma Light Bulb Kicks Some Serious LED Butt
by Michael Graham Richard, Gatineau, Canada on 04. 7.08
Design & Architecture (lighting) "

http://www.treehugger.com/files/2008...lb-led-cfl.php


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Old 04/01/2009, 09:58 AM   #582
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It is interesting but will probably be a while before we see those in use by hobbyists.


I finally last night finished wiring up one of my LED arrays with ~28v on a buckpuck (5 royalblue Luxeon3s, 1 green endor triemitter).

Looked pretty darn bright and the color was what I was hoping for. (a nice 15k with tons of actinic and some green). Now I have to finish putting my buckpucks and associated wiring into the hobby box, and start wiring the other 3 arrays.

I'll get some pics soon when I have time.


quick question though: I'm having a hard time getting excess solder off of my soldering iron tip after I tin it for cleaning. I wype it on the moist sponge thats part of my helping-hands, but the solder likes to cling to whatever part of the tip touched the sponge last..... I've been having to hold the sponge in my hand and fold it over the tip to get the solder off.

I know that's not the safest way, so what am I doing wrong that's making it so hard to clean off excess solder? Using a cheap 30w iron and rosin-core solder from radio shack...


Soldering the regular luxeonstars is pretty easy. The Endor rebel tri-emitters are a bit more difficult because the contacts are about 1/2 sized. I think smaller wire like 20 or 22gauge would be alot easier there.


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Old 04/01/2009, 10:21 AM   #583
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Congratulations, this thread has been nominated as "Aprils Thread of the Month".

Thanks to all that voted.


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Old 04/01/2009, 12:03 PM   #584
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Quote:
Originally posted by ReefEnabler
quick question though: I'm having a hard time getting excess solder off of my soldering iron tip after I tin it for cleaning. I wype it on the moist sponge thats part of my helping-hands, but the solder likes to cling to whatever part of the tip touched the sponge last..... I've been having to hold the sponge in my hand and fold it over the tip to get the solder off.

I know that's not the safest way, so what am I doing wrong that's making it so hard to clean off excess solder? Using a cheap 30w iron and rosin-core solder from radio shack....
the soldering iron i have has the sponge but they had put slits in the sponge, so that when you pulled the tip thru the slits, it would take the solder of all sides of the iron's tip.


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Old 04/01/2009, 12:38 PM   #585
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Grats on thread of the month Soundwave


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Old 04/01/2009, 01:36 PM   #586
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Quote:
Originally posted by ReefEnabler
quick question though: I'm having a hard time getting excess solder off of my soldering iron tip after I tin it for cleaning.
The sponge cannot be "wet" it should only be damp.
You need to move very quickly across the sponge using a twirl motion, about 1/3 of a turn. If the sponge is too wet or you move too slowly the tip freezes nearly instantly and the solder congeals onto it. By the time you get it to your face it has melted again. So it looks likes the cleaning isn't working. (and it's not)





Quote:
I think smaller wire like 20 or 22gauge would be alot easier there.
See! I told you so!


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Old 04/01/2009, 01:59 PM   #587
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thanks... hopefully my technique will be much better by the time I'm done with all of this

I actually tried to get some smaller gauge wire, but my local radio shack was strangely sold out of everything stranded in the smaller gauges ... they had 'speaker wire' in 18 gauge but this turned out to be not so good.... the insulation seems to have a much lower melting point and would constantly get smashed by the helping hands as soon as I tinned the wire...and bleeding onto the wires.... yuck.


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Old 04/01/2009, 02:22 PM   #588
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Since we are on Wreath Central now, I'm thinking that LED technology could be converted over to holiday decorations. Could you do a write-up on that for us please?

Imagine long strands of LEDs, carefully wrapped in and out of wreaths, round and round on fir trees, and possibly even used outdoors on the facia board of our homes? If you can explain how to make them turn on and off, that would be even better. That phenomenon needs a name, too. Please give this some thought.


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Old 04/01/2009, 02:36 PM   #589
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That's making me wreath..


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Old 04/01/2009, 11:58 PM   #590
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soundwave-Can you take a picture of your tank just with the white LEDs on?


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Old 04/02/2009, 12:28 AM   #591
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Here is a less powerful LED panel than one based one HPLEDs. This is one I just finished for a turf scrubber. It uses "super flux" LEDs which need 100mA rather than the 350 to 1000mA Soundwave used in his nice setup.

These could work for a shallower tank. I wouldn't try to use this style LED for a tank deeper than about a foot. One of the benefits is no cooling issues the LEDs have radiators built in. You can just use resistors for current limiting. No current drivers! But of course they are not as bright.

Since this is for growing algae it's just red and blue LEDs I used no white units.

Here I'm routing the copper clad board to create the required circuit traces. (I'm amazed the camera stopped the router chuck since it's turning 23,000rpm!)



Here's the stuffed panel. A lot of soldering. 100 SFlux reds and 48 blues. Whew!



Here it is lit up.




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Old 04/02/2009, 01:48 AM   #592
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Wow this thread is awesome, I really wish I had the smarts to do this do bad some body doesn't make a kit...
This thread has me sold on LEDs and I really do think they are worth the high price, but when you think about it its not high at all


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Old 04/02/2009, 07:44 AM   #593
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Kcress, the pics are not showing.


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Old 04/02/2009, 10:29 AM   #594
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My build attempt

Hi All -

After much reading, I have deceided to tackle this project for my 225g tank (72 x 30 x 24h) - I would greatly appreciate any comments. Here is my plan:

Parts (major parts only) -

Heatsink - 2'
18 - Cree White LEDs mounted on star boards
18 - Royal Blue LEDs mounted on star boards
2 - Xitanium 25W 1050mA Off-line Dimming Driver (http://www.ledsupply.com/xi-led120a0024v10d.php )
2 - 120mm Fans
Wall Dimmer
Optics

Concept -

My desire is to create a lighting system with enough light to support a decent SPS colony. I am going to create 3 of these 2' panels which will run front to back on the tank. The 2' heat sink will have 2 groups of 18 LEDs (each group with 9 white / 9 blue) and each group will be spaced evenly on the heatsink.

I came up with the number 36 because each drive can handle 18 LEDs. I choose this driver because I can do without a power supply and it can be dimmed easily. Comparing the cost of this driver to 6 buck pucks and a power supply, this is a cheaper and more compact route.

Problems / questions:

* Is this going to be enough light? It doesn't feel like it, but at more than $600 per panel, adding another few panels gets cost prohibitive (or at least I might as well get the Aqua Illuminations with all of the toys)...
* Which type of optics should I be looking at?
* What can I do to power the fans without getting another power supply?

Thanks in advance...


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Old 04/02/2009, 11:14 AM   #595
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I am confused.... why can you get by with 2 of the Xitaniums but would require 6 buckpucks?? To me looks like they have the same output. You posted a 24v 1.05a driver...

There are 32v 1a buckpucks, which is even more output. Did I miss something? How did you figure that 25w could power 18 LEDs? What is the Vf of the LED's you are using? They'd have to be pretty low wattage to fit 18 on 25w.


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Old 04/02/2009, 11:20 AM   #596
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I am just going by the datashet (http://www.ledsupply.com/docs/xitanium-120v-drivers.pdf ) - It says that it can handle up to18 - 1 watt LED's.

I am no electrician, but I am guessing that it has something to do with the way it gets wired up. Their diagram shows 6 LEDS wired in series, and then 3 sets of those all wired together in parallel and attached to one driver. The driver puts 350mA across each of the parallel lines...

Shawn


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Old 04/02/2009, 11:25 AM   #597
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Driving in parallel has been discussed many times in this thread... the more experienced guys are recommending against it since if one LED in one of the series goes, it will end up redirecting current into the other series which will overdrive them and burn them up. It's possible to use more electronics and carefully design a system to safeguard against this, but the general consensus is that its easier/safer/cheaper to simply wire things in series and get LEDs that are matched to the drivers.

I'm sure some of these experienced people will chime in. I learned most of this from this very thread so perhaps I'm not the best one to be telling you, but maybe at least I can convince you to hold off for a bit and get more information first.

I think its a shame they dont make the Xitanium drivers in lower current, higher voltage configurations (like a 32v 700ma for example, instead its 12w 700ma).


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Old 04/02/2009, 11:27 AM   #598
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Yea - I am definitely holding off until I get more input, but I assume that since the driver is designed to work in parallel that it would be ok...


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Old 04/02/2009, 01:54 PM   #599
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fernandokng; Still not showing? They show for me.


adova; ReefEnabler has it - Parallel is evil.

That is just a specsmanship game the driver people play. "You can drive a zillion LEDs with our driver." -If you run them in parallel-

This is the same as saying "This car will travel 200 miles on a gallon of gas". -Only if it's all down hill-

Quote:
Originally posted by adova
I am definitely holding off until I get more input, but I assume that since the driver is designed to work in parallel that it would be ok...
The current driver doesn't care about the LEDs It just puts out a given current. Go back up-thread and look at the the discussion on parallel.





As for fans.. You either need line voltage fans or or a wall wart.


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Old 04/02/2009, 02:03 PM   #600
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Ok - back to the buck pucks then, I guess - and I will just use the power supply for them to run the fans.

Any suggestion as to the # of LEDs / "panels" I am going to need for my application? And optic suggestions?


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