Arduino Forum

Using Arduino => General Electronics => Topic started by: arduinopi on Aug 05, 2015, 11:57 pm

Title: over powerinh high powerd leds
Post by: arduinopi on Aug 05, 2015, 11:57 pm
hello everyone,

few questions here. I have a 10 watt led. is suppose to run on 12 volts around 800 mA. Obviously if I run it on say 2 amps and it is using over 10 extra watts of energy it will heat up. Now is it the heat that destroys the led in this circumstance? If I was able to keep the LED cool with peltier units would the led still not last as long?

thank you !
Title: Re: over powerinh high powerd leds
Post by: DVDdoug on Aug 06, 2015, 12:10 am
You'll need a heatsink or cooling device even at 10W.   Under normal conditions high-power LEDs are operated near their limits.   You might  get away with pulsing it at higher power if the average  power is 10W or less.   

But, check the datasheet and proceed at your own risk!   It's sort-of like over-clocking...   You might get away with it or you might not...   But you shouldn't go "into production" or build anything that needs to be reliable with at design that goes beyond the manufacturer's specs and recommendations.
Title: Re: over powerinh high powerd leds
Post by: raschemmel on Aug 06, 2015, 07:09 am
Quote
You might  get away with pulsing it at higher power if the average  power is 10W or less.     
I think the general rule for overcurrent pulsing is that it is ok as long as the duty cycle <= 10%.
The smart way to do it is get a thermocouple or temp sensor and gradually ramp up the duty cycle in small increments while monitoring the temp on an LCD. Adafruit has a really cool thermocouple.
Title: Re: over powerinh high powerd leds
Post by: Grumpy_Mike on Aug 06, 2015, 08:15 am
The problem with over running an LED is that the light output from the LED will drop quite rapidly over time. You need equipment to measure this.

If however you run it at twice the rating you will just burn it out. Not only will the heat kill it but also the current density in the doped semiconductor will deplete the free charge carriers.
Title: Re: over powerinh high powerd leds
Post by: raschemmel on Aug 06, 2015, 08:26 am
I hate when that happens...
Title: Re: over powerinh high powerd leds
Post by: arduinopi on Aug 07, 2015, 06:05 am
If however you run it at twice the rating you will just burn it out. Not only will the heat kill it but also the current density in the doped semiconductor will deplete the free charge carriers.
Thank you, that's exactly what I was looking for! I was thinking of water cooling it since it will be in a boat but I will just run it at its normal current
Title: Re: over powerinh high powerd leds
Post by: Grumpy_Mike on Aug 07, 2015, 07:52 am
Good choice.

Also no amount of cooling can actually keep the chip temprature down below a certain point because of the thermal resistance between the chip and case. There is the concept of the " infinite heat sink" which assumes the case is at the ambient temprature and the chip at its maximum. That governs the so called head line dissipation you see in data sheets. In practice this is not attainable. See:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html (http://www.thebox.myzen.co.uk/Tutorial/Power.html)
Title: Re: over powerinh high powerd leds
Post by: MarkT on Aug 07, 2015, 01:45 pm
Efficiency of high power LEDs is already falling at 70% output, taking them to 200% is foolish.
The manufacturer's are already pushing things to the limit.  I believe white LEDs should not be overdriven
as you risk overheating the phosphor blob and degrading it.  If you are pulsing above nominal that's
much more reasonable as the temperature won't be changing that much with short pulses.  IR
LEDs are regularly abused like this in IR remote controls - its the temperature that does the damage
in most things.
Title: Re: over powerinh high powerd leds
Post by: Boardburner2 on Aug 07, 2015, 03:28 pm
The manufacturer's are already pushing things to the limit. 
And possibly lying.

Replacing halogen lights with efficient leds can be costly.

They fail regularly.
Halogen fittings are generaly unable to meet the temperature dissipation requirments of leds.