# LED/Drive Pairing help

#### Entacmaea

##### Newly Enlightened
(originally posted in LED forum, so re-posting here)

Hi there - I'm building a scuba light, and trying to pair the brightest LED I can find with a suitable driver. I'm wondering if anyone more experienced than myself can confirm or explode my specs below : ) I've built several XML based lights, but only have used single 3.7v 3-mode cheapo drivers - so this set-up is a little different. I'm hoping to run this light with either 4 or 6 18650 2900mA batteries.

I'm pairing this LED:

http://www.ledsupply.com/leds/cree-c...sity-led-array

With this driver in boost mode:

http://www.ledsupply.com/led-drivers...r-with-dimming

Any help confirming this will work, and with approximate run time at 700mA with the 4 18650's would be great - not sure how the voltage boost will effect current draw/run time. . .

Thanks!

Peter

#### hiuintahs

##### Flashlight Enthusiast
To determine if you are in line with your power requirements just know that power out to the LED(s) is equal to the input power minus the power lost to the driver circuit. You can figure the driver circuit at 85% efficient. 90% is too optimistic. The efficiency will vary anyhow depending on conditions.

So here is an example: Say the Vf of the LED is 35v and you are driving it with 500mA. That is 17.5 watts of output power. So input power will be around 21 watts give or take. Four 18650 batteries with a voltage at 3.5v ea is 14v total in series configuration. 21 watts divided by 14v is 1.5 amps. When the cells are freshly charged the current will be less. 1.5 amps is inline with the 18650 capability and would give close to 2 hour run time on 2900mAh batteries.

#### Entacmaea

##### Newly Enlightened
OK - thanks for the info - that clarifies things a little. Another poster on a duplicate thread said that driver was a little "too weak" - but not sure what that means...