Still need a heatsink for flashing XP-G??- Mtbr.com

# Thread: Still need a heatsink for flashing XP-G??

1. ## Still need a heatsink for flashing XP-G??

I'm looking to strobe a XP-G @ 700mA. About 2-3 flashes per second. It's going to be mounted in an amber dome on top of a car. What type of heatsink, if any, do I need for this??

Thanks,
Bryan

2. I'm no expert on this, but the general rule of thumb used in this forum is 2 sq in of surface per watt of heat. Your XPG at 700mA will consume roughly 2.2-2.5w running continuously, say half that when flashing. So, theoretically you need about 2-2.5 sq in of surface exposed to ambient air to dissipate the heat IMO.

3. Originally Posted by Bryank930
It's going to be mounted in an amber dome on top of a car.
If the dome has a metal base, then there is no need of heatsinks.

4. Originally Posted by zemike
If the dome has a metal base, then there is no need of heatsinks.
+1 especially if aluminum. I also concur with a 2-2.5" area for that metal base if it is to run with nothing but breezes for cooling (standing still). You'd have that to spare with a 2" diameter or more dome light.

5. You have not said what the duty cycel is. I run my xpg daylight flasher on the bike at 2hz but only a 10% duty cycle. Even running full power at 1500ma I still have an all day runtime avalibe. I have it mounted on a small piece of L shaped aluminium no problem with the heat even when stationary. I would get overheating if running it non strobed and stationary probobly OK when moving though.

6. Calculate the total power dissipation of the LED. That depends on the duty cycle (percentage of on time) multiplied by Vf times the current. It's pretty common for the duty cycle of a flashing light to be less than 50%. As an example, let's assume a duty cycle of 40%.

Total power: 0.40 * 3.1 * 0.7 = 0.87 watts

So unless your duty cycle is a lot higher, you don't need much of a heat sink. Power in that range could be handled if the LED is mounted on an mcpcb and that is attached to anything that's somewhat thermally conductive.

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