<a href=showthread.php?s=&postid=15344566#post15344566 target=_blank>Originally posted</a> by AndyReef
I know everyone says that the Meanwell eln 60-48D can handle 13 of the Cree XREs, and I know this is a rudimentary question, but how does one go about calculating the number of LEDs that can safely be driven by one meanwell?
For ANY driver, you need to know two things to figure out how many LEDs the driver can handle:
1) The forward voltage of the LED(s) you are using. This is published in the datasheets for the various LEDs. It increases as current increases, so when you look it up, you need to know the current you will be running. Assuming you are using Cree XR-E LEDs at 1000mA, the forward voltage is 3.7.
2) The maximum number of volts the driver can produce. This is also usually in the datasheets, but you need to be sure you are interpreting the specs correctly.
Once you have this info, you just multiply the LED forward voltage by the number of LEDs you want, then check to make sure it's under the max for the driver. Or, to find the max number of LEDs for a driver, divide it's max voltage by your LED's forward voltage. For example, the ELN 60-48 is a 60 watt driver that has a max output voltage of 48v. If you are driving XR-E's at 1000mA, that's 3.7V each. If you divide 48v by 3.7, you get 12.97, so running 12 of these LEDs on these drivers really should be the max.
Some other drivers can be powered from DC, over a wide range of supply voltages (for instance, the buckpucks many are using.) Typically, rather than specifying a max output voltage, these types of driver specify a head required by the driver - for the buckpucks, the supply must be 2 volts more than the output voltage.
<a href=showthread.php?s=&postid=15344778#post15344778 target=_blank>Originally posted</a> by JTL
I would really like to build one for my new DT but I don't think I fully understand the amps that it would draw. The tank will be 44x24x24 so I don't even know how many LEDs I would need, but is a lot. As an example let's use 50 as a starting point. I am currently running (4) T5 54 watt on two ballasts that draw 1.15 amps each. I could double that and only use 4.6 amps and have 432 watts. LED's are going to be better watt for watt but how much better and at how many amps? I am concerned about amps because they are a limited resource and I don't have any easy way to add another circuit.
I find it easier to think in terms of watts than amps, but you can roughly convert given a voltage.
Taking your example of 50 LEDs, assuming we're taking Creed XR-E (the standard choice in this thread) driven at 1000mA (the max, and pretty much the default choice), then each LED is seeing 1000mA of current at 3.7 volts. That's 3.7 watts each. For 50 such LEDs, you'll have 185 watts. If we assume the driver(s) being used are 80% efficient (reasonable, but probably on the worst-case end of the spectrum) then the whole rig will be consuming about 230 watts.
On a wall outlet, that's about 2 amps.
Trying to compare LEDs to other types of lighting watt for watt is tricky because there really isn't a track record yet, but it "seems" as if LED are in the range of half the wattage for an equivalent result compared to T5HO or MH. So if you are running your tank on 432 watts of T5, you could probably get similar results from 200 - 300 watts of LED, assuming a really good design.
Besides the high efficiency of LED (in pure terms of output per watt), the output is also in a much more desireable format - in a pretty narrow viewing angle, which means ALL of the light is going more or less "straight down" into our tanks. Especially with optics, which are less lossy than a reflector. Compare that to a T5 or MH lamp, which gives off light in ALL directions. Even with the best reflector design, there's still going to be more losses than with an LED.
<a href=showthread.php?s=&postid=15345623#post15345623 target=_blank>Originally posted</a> by aeternus12
is it ok to use in reef aquarium 6500 k power led or should i use led 10 000 k or even 15 000 ?
The vast majority of folks in this thread are using Cree XR-E or Luxeon Rebels in the "cool white" color, mixed about 50/50% with blue or royal blues. The "cool white" LEDs are rated in the range of 6500k, and the blues and royal blues peak right around what we normally see in actinic reef lighting. So this combo is pretty close to other forms of reef lighting.
I would not try to think of it in terms of kelvin color, since LEDs produce a spectrum that's much different than other types of reef lighting, so trying to compare based on a single (subjective) number might be misleading.