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bfessler 
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 Posted: February 23 2011 at 7:28am |
 Davidwillis wrote:
Ok, I have a question. What is so special about these drivers? I mean why can't I just get a power supply (if I am running 4 LED's on it I would get a 12 volt so that each LED would get 3 volts). Then I could just add a Potentiometer to reduce that to dimm it. Obviously I would need to get a power supply that would handle the amps, so I am not sure it would be any cheaper, but I am just curious. |
Powering LED's is a little different than powering other electrical equipment. With most equipment the circuit requires a constant voltage but LED's require a constant current. The LED Drivers are designed to provide the constant current that is required for reliable operation of the LED. Dimming is accomplished by reducing the current through the LED not a voltage drop. This is why you can't just use a common dimmer switch to dim LED's. Dimable LED Drivers use a reference voltage of between 0 and 10 volts to regulate the current through the LED Circuit.
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Burt An equal opportunity reefer, I support all hobbyists and organizations involved in Marine Aquarium Keeping. [email protected]
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Mark Peterson
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Posted: February 23 2011 at 8:21am |
A single Potentiometer adjusts voltage to a single line. If my understanding is correct, a driver is a series of solid state circuits handling a finite number of LED's. LED's can't just be hooked up in a simple parallel circuit where the voltage is adjusted by a potentiometer. The driver adjusts the voltage and amperage for each pair of it's leads to each LED. Asad/seti007 made his own drivers, but then he is also an Electrical Engineer.  Maybe he will see this thread and chime in.
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Davidwillis
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Posted: February 23 2011 at 8:49am |
I guess I just don't understand something, because current is determined by voltage and resistance. So if you have a constant voltage, and constant resistance (the LED string, and the potentiometer) then the current will remain the constant. To dimm, if you increase the resistance (by turning the potentiometer) you will reduce the current, and voltage drop across each LED. I must really be missing something.
My thinking is that you could just use one constant voltage power source, the run as many lines in parallel. The lines would be in series within the line, and each line would need a potentiometer to control the resistance of the line. Where the line resistance would equal the sum of the LED's resistances plus the potentiometer resistance.
All my thinking is just based off ohms law... I=V/R
I hope someone can explain why this does not apply...????
Edited by Davidwillis - February 23 2011 at 8:49am
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bfessler
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Posted: February 23 2011 at 9:00am |
Actually the LED doesn't work like a resistor with a constant resistance. As it warms up resistance drops allowing more current through increasing the current which increases the light and heat which will cause the LED to burn up. That's why you need a special circuit to control the current. There is a lot of information on Nano-reef.com in the LED section regarding the construction of these circuits.
Check out this thread. It's a great place to start understanding how to build LED fixtures.
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Burt An equal opportunity reefer, I support all hobbyists and organizations involved in Marine Aquarium Keeping. [email protected]
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thefu
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Posted: February 23 2011 at 9:06am |
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You CAN build simple circuits to do the driving of the LED if you want to go through the hassle. The only issue is it is a PITA and you cannot easily do the dimming. For the average fixture size, and if you want to easily mix (dim) the colors, spending $30 per each 12 LED is not that bad. Remember, one mistake making your own driver and you create a $72 flash bulb!
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Davidwillis
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Posted: February 23 2011 at 9:09am |
Thanks Burt, that would explain it...LOL
One more quick question before I read up on that thread you linked.... Could you plan on final resistance (or is there no final resistance)? Basically just set the voltage at a level where at your maximum level it is safe after warmup. With this you will not be able to get full 100% until the LED's are warm, but you will not burn up...?
Ok, I am going to read up on that thread now.
Thanks
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bfessler
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Posted: February 23 2011 at 9:15am |
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Like Terence posted you can make the driver circuits if you want and there are examples of these circuits in the thread. You just need to think about regulating current rather than voltage. Ohms law does still apply the application is just a little different.
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Burt An equal opportunity reefer, I support all hobbyists and organizations involved in Marine Aquarium Keeping. [email protected]
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BnK
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Posted: February 23 2011 at 11:39am |
WOOOOO WHAT THE  ?????? I though it was just a simple question now I feel like im reading a physics college exam or something lol. j/k well ummm thanx for the help guys lol. At least I learned something today
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jcoulter17
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Posted: February 23 2011 at 12:23pm |
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Look into Current Usa TrueLumen Pro LED Strip Lights
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thefu
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Posted: February 23 2011 at 2:07pm |
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Those TruLumens look very interesting, but there are two open questions...price and cooling. Let me know if you find the price because ReefBuilders still does not have an official one from them. Also, though, the TruLumens unlike the AI and DIY set ups are not dimmable.
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