led start up - The Planted Tank Forum
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post #1 of 20 (permalink) Old 10-22-2011, 12:40 AM Thread Starter
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led start up

can someone send me a link for dyi led 101
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post #2 of 20 (permalink) Old 10-22-2011, 01:54 AM
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Just as soon as you write it :P

I haven't seen one yet, it's a lot of piecemeal info and guesswork right now.

Of course I may have just missed it....

create random acts of beauty...
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post #3 of 20 (permalink) Old 10-22-2011, 02:22 AM Thread Starter
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guess ill keep digin around
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post #4 of 20 (permalink) Old 10-22-2011, 04:02 AM
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Try this one- tons of useful info http://reefcentral.com/forums/showthread.php?t=1718642
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post #5 of 20 (permalink) Old 10-23-2011, 05:07 PM
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This one is a bit more step-by-step

http://www.nano-reef.com/forums/inde...owtopic=279188

"Hopefully everything doesn't turn out horribly ironic"
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post #6 of 20 (permalink) Old 10-23-2011, 06:32 PM
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correct me if im wrong but no 2 led setups are the same unless u start off copying.

But a real DIY led setup has planning which u decide on what color to go with.

Example.. reef tanks like to use a lot of 10k because of water depth and mix a lot of blues.

But in a fresh water tank, the blues dont need to be strong, and your more after the 6500k cool white ranges as it gets the best results.

Right now im even playing with 660nm LED's and im playing with 3W 10W and 20W LED's.


important thing is to know the voltage your going to be playing with and stick though it.. and not do a mix voltage system... ie.. mixing a 10W and 3W's unless u serial the 3W so its 12V.


Its crazy... its like building a car from ground up and picking what u want to tune.... if fish tank hobby was this fun back when i did it, i dont think i would of quit. :P
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post #7 of 20 (permalink) Old 10-24-2011, 03:15 PM
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Originally Posted by Naekuh View Post
important thing is to know the voltage your going to be playing with and stick though it.. and not do a mix voltage system... ie.. mixing a 10W and 3W's unless u serial the 3W so its 12V.
No. The important thing to know is the current you want to drive the LEDs at. You don't drive LEDs by voltage. The reason being is that small changes in voltage leads to large changes in current, which will ultimately effect light output, and heat generation. Keeping the current supplied to an LED tightly regulated is mandatory to keeping the LEDs alive for a long time.

For example, a common LED like the Cree XR-E runs at about 3.7v at 1000ma, and about 3.4v at 350mA. Thats a 0.3v change in voltage at the LED for about a 300% change in current, and about a 250% change in light output.
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post #8 of 20 (permalink) Old 10-24-2011, 05:28 PM
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No. The important thing to know is the current you want to drive the LEDs at. You don't drive LEDs by voltage. The reason being is that small changes in voltage leads to large changes in current, which will ultimately effect light output, and heat generation. Keeping the current supplied to an LED tightly regulated is mandatory to keeping the LEDs alive for a long time.
this is kinda what i meant... you said it much easier to understand.

and yes i was implying current along with voltage.


And im fairly sure u do drive LED's with voltage as well. Watts / Current = Volts. You cant say LED's are not driven by voltage. :P

DC circuits only use the current they can use... if u have a psu with 100Amps.. and a DC circuit which uses only 1mA, the PSU will put out 1mA in the circuit.
Its like a PC with a 1000W PSU running an ATOM Cpu... its not going to TAX the 1000W psu in any degree.

You can put a potentiometer or a rheobus in the circuit to lower the voltage and hence lower the LED's brightness as you say.


Keeping LED's alive has to do with how cool you can keep them, because heat is an ultimate killer in electronics.
Also how bright you run them will effect life of the LED (Voltage migration... meaning as u run current, you slowly etch away at the circuit's life), on top of how well your PSU is built.
Hence your absolutely correct in what you mean by tightly regulated current.

I do remember using bad PSU's to test LED's was a quick way to burn them out...
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post #9 of 20 (permalink) Old 10-25-2011, 05:42 AM
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Quote:
Originally Posted by Naekuh View Post
this is kinda what i meant... you said it much easier to understand.

and yes i was implying current along with voltage.


And im fairly sure u do drive LED's with voltage as well. Watts / Current = Volts. You cant say LED's are not driven by voltage. :P

DC circuits only use the current they can use... if u have a psu with 100Amps.. and a DC circuit which uses only 1mA, the PSU will put out 1mA in the circuit.
Its like a PC with a 1000W PSU running an ATOM Cpu... its not going to TAX the 1000W psu in any degree.

You can put a potentiometer or a rheobus in the circuit to lower the voltage and hence lower the LED's brightness as you say.


Keeping LED's alive has to do with how cool you can keep them, because heat is an ultimate killer in electronics.
Also how bright you run them will effect life of the LED (Voltage migration... meaning as u run current, you slowly etch away at the circuit's life), on top of how well your PSU is built.
Hence your absolutely correct in what you mean by tightly regulated current.

I do remember using bad PSU's to test LED's was a quick way to burn them out...
It won't work like that. LEDs don't work like other DC circuits. You need to supply enough voltage for the forward voltage drop on the LEDs, which is fairly constant over a wide range of currents. Then you need to externally control the current to a constant value. You can limit the current with a series resistor, properly sized, but not control it to a constant value. For that you need a constant current driver, which can be done with a simple DIY circuit, or for best results and the ability to dim the LED by reducing the current, a commercial LED driver, like the Meanwell drivers. If you put LEDs in series, the forward voltage drops all add up and the total must be supplied by the power supply or LED driver. If one LED fails they all go out, assuming the LED fails open circuit. But, if it fails by shorting out, you can have problems because you have too much applied voltage, unless you are using a good LED driver which can reduce the applied voltage to just what is needed. If you put LEDs in parallel, they take less total voltage, but if one LED fails open circuit, the current through the other LEDs goes up, possibly high enough to cause all of them to fail. None of this is simple Ohms Law stuff.

Hoppy
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post #10 of 20 (permalink) Old 10-25-2011, 04:12 PM
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Quote:
Originally Posted by Naekuh View Post
this is kinda what i meant... you said it much easier to understand.

and yes i was implying current along with voltage.


And im fairly sure u do drive LED's with voltage as well. Watts / Current = Volts. You cant say LED's are not driven by voltage. :P

DC circuits only use the current they can use... if u have a psu with 100Amps.. and a DC circuit which uses only 1mA, the PSU will put out 1mA in the circuit.
Its like a PC with a 1000W PSU running an ATOM Cpu... its not going to TAX the 1000W psu in any degree.

You can put a potentiometer or a rheobus in the circuit to lower the voltage and hence lower the LED's brightness as you say.
Like Hoppy said, it's not that simple. What you are not factoring in is voltage drift due to die heating, voltage differences due to binning, etc... It's not nearly as simple as just saying that an LED runs at X voltage at Y current, so if I apply X voltage, I should see Y current. It's never that simple. LEDs are not simple resistive devices like a light bulb. In fact, they have an inverse dynamic resistance which complicates things considerably, and makes generalizations like yours inacurate.

Another issue here is when you start to run many LEDs in series. Each LED will differ slightly in the voltage drop it has at a given current. If you drive by current, the forward voltage becomes irrelevant, provided the driver used is capable of supplying the necessary voltage. This way, each LED produces the same light output. In a voltage driven setup, the voltage drop across each LED is identicle, but the current seen at each LED will not be, and as a result, you get differences in light output, and heat generated. You may think this can't happen due to ohms law, but remember that the resistance internal to the LED is dynamic, and complicates things.

I'm not trying to bash on you. Just trying to educate.


Quote:
Keeping LED's alive has to do with how cool you can keep them, because heat is an ultimate killer in electronics.
Also how bright you run them will effect life of the LED (Voltage migration... meaning as u run current, you slowly etch away at the circuit's life), on top of how well your PSU is built.
Hence your absolutely correct in what you mean by tightly regulated current.

I do remember using bad PSU's to test LED's was a quick way to burn them out...
I think what you are refering to is current creep, which is a phenomenon associated with over volting CPUs. LEDs do not suffer from this, as current creep is due to the fact that the traces and gates in the CPU die are so close together, you can induce a voltage on one trace/gate by turning on an adjacent one. This can damage the isolation in the CPU.

Damage done to an LED by heat is just from that, not current alone. In theory, as long as the die can be kept cool enough, and the bond wires in the LED can handle the current (and not act as a fuse), then you can pump as much current into the LED as you like. Flashlight guys have been doing this for years.

Heat damage to an LED can be at any current. Take a Cree XR-E for example. What do you think is worse; 160C die temperature at 100mA, or 80C die temperatures at 1200mA? 1200mA is out of spec for an XR-E, but with a much lower die temp (really good heatsinking) and will probably make 30K-50K hours. 100mA is well within the LED spec, but the temperature is way out of spec, and will dramatically shorten the life of the LED as a result.

So, after al of this, yes, you can drive an LED by voltage, but you shouldn't. Beyond the fact that the LEDs are far more stable when driven by current, trying to adjust the forward voltage using basic devices like potentiometers in a usable range for the LED is difficult. Not so hard when you are driving large series strings of LEDs, where the total voltage change from minimum to maximum current is larger, but when you are trying to adjust less than a volt for even 3 LEDs, it can be a major pain.
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post #11 of 20 (permalink) Old 10-25-2011, 04:22 PM
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Originally Posted by Hoppy View Post
It won't work like that. LEDs don't work like other DC circuits. You need to supply enough voltage for the forward voltage drop on the LEDs, which is fairly constant over a wide range of currents. Then you need to externally control the current to a constant value. You can limit the current with a series resistor, properly sized, but not control it to a constant value. For that you need a constant current driver, which can be done with a simple DIY circuit, or for best results and the ability to dim the LED by reducing the current, a commercial LED driver, like the Meanwell drivers. If you put LEDs in series, the forward voltage drops all add up and the total must be supplied by the power supply or LED driver. If one LED fails they all go out, assuming the LED fails open circuit. But, if it fails by shorting out, you can have problems because you have too much applied voltage, unless you are using a good LED driver which can reduce the applied voltage to just what is needed. If you put LEDs in parallel, they take less total voltage, but if one LED fails open circuit, the current through the other LEDs goes up, possibly high enough to cause all of them to fail. None of this is simple Ohms Law stuff.
Amen Hoppy! Leds are definitely not "simple Ohms Law stuff". I think a lot of people have a hard time understanding that. Controlling current is the name of the game with Leds.
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post #12 of 20 (permalink) Old 10-25-2011, 06:07 PM Thread Starter
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Now im wondering what im gettin my self into this is way different than making t5 ho
Ill keep studying because if you guys canr agree on the best way to build a fixture how can i design one.
Still truley appreciated
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post #13 of 20 (permalink) Old 10-25-2011, 07:55 PM
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WOW thanks guys.. im learning a lot about LED's here in how they apply to fish tanks...

I am still a noob, so i will admit when i need to learn.

Quote:
Originally Posted by Hoppy View Post
It won't work like that. LEDs don't work like other DC circuits. You need to supply enough voltage for the forward voltage drop on the LEDs, which is fairly constant over a wide range of currents.
OK so is that why the chinese LEd's are rated at 1A, yet they are 12V?
So im asusming the difference in mA, is the forwarding current?

so when i take a 12V LED, and i downvolt it to 5V, and yes ive been doing it on a fan controller, the current draw is still kept constant?

Can u guys explain this... this is the LED at 12V from multi meter readings:


This is the LED dim'd to 5V.


Anything below 3V and the LED's turn off. Ive been simulating moon light with the led's at 5V, and it does a nice job.


Dammit.. i should get an amperage reading...
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post #14 of 20 (permalink) Old 10-25-2011, 08:28 PM
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You may be controlling the intensity by changing the voltage, but I suspect there is a lot more to it than that. The 12 volt LEDs are LED arrays, with several junctions involved, not a single junction LED like a Cree XP-G. I haven't played with the multiple junction LEDs at all, so there is a lot I don't know about them.

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post #15 of 20 (permalink) Old 10-25-2011, 08:33 PM
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I haven't played with the multiple junction LEDs at all, so there is a lot I don't know about them.
lol great... i am treading untreaded waters blindly!

Excellent!


There seems to be 9 tiny LED's inside the array... im guessing they are 1W's smashed together... and the LED is really a 10V led and not a 12V led?

I really should take an amp meter reading.
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