The Cree XML are designed to run at 3 different levels:
2.9vF @ .700mA (2.03 watts)
3.1vF @ 1500mA (4.6 watts)
3.35vF @ 3000mA (10.05 watts)
---in my opinion, overdriving will possibly shortening the lifespan, as well as generate more heat. In this case, I would just look for an LED that normally runs at a higher voltage/amperage.
SO, lets say for
example, you want to have 15 White XML's, running at the basic 2.9vF @ .700mA. To figure out the driver, you need to do a little math.
Voltage first - You need to take the total number of LED's, and add their voltage together - 15 Cree XML White LED's x 2.9vF = 43.5 volts. Now you know that you need a driver that can supply 43.5v minimum.
The next part is the Current, which will be .700mA (This number does not need to be added like the voltage was, it will stay the same across all the LED's in the circuit).
The last part is Wattage. To figure out wattage you take the individual led numbers, (2.9v x .700mA = 2.03watts) x 15 LED's = 30.45 watts total. Now you know that you will need a driver that can supply atleast 30.45 Watts.
So again, you need a driver that supplies atleast: 43.5v, .700mA constant, and a wattage of atleast 30.45W
If your not confused, keep reading. If your confused, read it again, or just ask any questions
Now lets look at drivers. I'll list a couple here since you did not mention if you wanted to dim them or now.
Non-Dimming: Meanwell LPC-35-700. This driver is rated to supply between 9-48v, a constant .700mA, and up to 35Watts
- The Voltage. The driver is self regulating and will supply a minimum of 9v and up to a maximum of 48v. This will meet your needed voltage of 43.5v, the driver will "sense" the needed voltage and self-adjust to the demand.
- The Amperage, .700mA, remains constant
- The Wattage (35 watts), is more than ample to supply the circuit. Again, this will self adjust depending on demand. The example circuit above needs atleast 30.45watts
Dimming Driver: Meanwell ELN-60-48D or ELN-60-48P. These drivers have dimming capability, AND Voltage and Current can be adjusted manually. They are identical except for the way they are dimmed (more on this below). This is the most widely used driver (IMO) due to it's versatility, and can be used in almost every build.
- The Voltage - The driver is self regulating and will supply a minimum of 24v and up to a maximum of 48v (under normal operation. More on this below)
- The Amperage is adjustable, and can supply up to a maximum of 1300mA (More on this below).
- The Wattage (62.5 watts), is more than enough to supply the circuit, and will self adjust depending on demand. (This is double of what the circuit calls for, but as mentioned, it will self adjust under normal circumstances).
OK, so far so good? Time for "More on this below".
ELN-xx-xxD is dimmed via an external Voltage source, that supplies 0-10vDC on a dedicated circuit to the driver. This voltage usually goes through a potentiometer, or is supplied by a reef controller (Apex). The potentiometer, along with an external 10v power supply (usually a wall charger of some type), will adjust from 0-10v when turning the potentiometer. So lets say you have the potentiometer set at 5v. The LED's will recieve less current, hence the will be dimmer than if it was at 10v.
ELN-xx-xxP is dimmed via a Digital Pulse Width Modulation (PWM). Again, this is 0-10v, but the dimming is done by rapidly turning the LED on and off using a duty cycle (like the Reef Keeper Elite supplies). We don't actually see the LED turning on and off, as it happens faster than the eye can percieve it. There are kits that can supply this type of signal.
Adjustable Current - The ELN series of drivers are current adjustable. What this means is that you can adjust the current by opening the driver, and turning the internal potentiometer to the desired amperage needed. In the example above, you need .700mA, so you would adjust the driver to meet this number. There are a couple videos on youtube demonstrating how to do this:
Adjusting the ELN 60 48D 0001 - YouTube
Hope this helps. It can be really confusing, as I once found out. But, once you understand Voltage/Current/Wattage, it's pretty easy, and will only take minutes to figure out what you need.
Ask questions, and then ask more questions
