Author Topic: How hot can a 10W LED get?  (Read 13832 times)

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Offline BigBrother

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How hot can a 10W LED get?
« on: March 19, 2013, 08:59:08 am »
Recently I've been using a 10W Hong Kong  LED on an aftermarket northbridge cooler (with fan) for a motherboard. I wanted to test the temperature of it and used a 5.25" bay fan controller with some temp sensors on it. Long story short, just 1cm in front of the LED will make the temp sensor smoke (the polyimide covering it) and the display will show 'max' (>250F/~121C).

is this even remotely normal?
 

Offline Rerouter

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Re: How hot can a 10W LED get?
« Reply #1 on: March 19, 2013, 09:15:29 am »
very much so, you don't mount your sensor in the light path of the led, as it will be cooked with a constant 10W of power, rather secure it very close to where the led die meets the heat sink,

as for how hot your led is getting, your led will have the relevant thermal resistance in oC per W, which for 10W is pretty easy, you then measure the heatsink at that point while running and add that temperature to what you expect for the led, e.g. a junction temp of 5 degrees per watt would be 50C rise, plus heat sink temp, or to better calculate also measure the ambient, this will give you a rough outline of the heat-sinks thermal resistance, so it might be 50C + 18C for the heat sink, + 22C for ambient, 
 

Offline M. András

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Re: How hot can a 10W LED get?
« Reply #2 on: March 19, 2013, 09:16:50 am »
with that heatsink its gonna be hot, with a large 150*69x mm god knows how tall is it approx 4-5cm heatsink without fan keeps a 10 watt led around4-60celsius depending on the orientation, with fan blowing on the fins it drops to around 30 celsius
 

Offline BigBrother

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Re: How hot can a 10W LED get?
« Reply #3 on: March 19, 2013, 10:56:05 am »
very much so, you don't mount your sensor in the light path of the led, as it will be cooked with a constant 10W of power, rather secure it very close to where the led die meets the heat sink,

as for how hot your led is getting, your led will have the relevant thermal resistance in oC per W, which for 10W is pretty easy, you then measure the heatsink at that point while running and add that temperature to what you expect for the led, e.g. a junction temp of 5 degrees per watt would be 50C rise, plus heat sink temp, or to better calculate also measure the ambient, this will give you a rough outline of the heat-sinks thermal resistance, so it might be 50C + 18C for the heat sink, + 22C for ambient,
Then approximately, it's still 100C. I'll stick one on a pure copper heatsink (for an intel prescott P4).

with that heatsink its gonna be hot, with a large 150*69x mm god knows how tall is it approx 4-5cm heatsink without fan keeps a 10 watt led around4-60celsius depending on the orientation, with fan blowing on the fins it drops to around 30 celsius
I don't have anything that large nor a place to put something that large. If it means anything, I have a fan on the heatsink that moves close to 10CFM.
 

Offline ptricks

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Re: How hot can a 10W LED get?
« Reply #4 on: March 19, 2013, 01:55:25 pm »
You might want to look through the data sheets of companies like Cree to see how they suggest mounting the higher watt LED.
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLampThermalManagement.pdf
 

Offline G7PSK

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Re: How hot can a 10W LED get?
« Reply #5 on: March 19, 2013, 04:16:54 pm »
I was just going to ask a similar question as I have just got a 12 watt (3x4W) MR16 led lamp to replace a 20 watt halogen lamp in a display cabinet. The thing is it appears to get just as hot as the halogen that it replaces the temperature on top of the housing is 72 deg C.The lap that I got is this one from ebay it says that it is a cree but who knows.

http://www.ebay.co.uk/itm/390553728998?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I would not want to fit a fan as the cabinet is in the drawing room (sitting room for those in the antipodes and US)
 

Offline SeanB

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Re: How hot can a 10W LED get?
« Reply #6 on: March 19, 2013, 06:44:17 pm »
Add ventilation to the cabinet to allow air to flow past the lamp to cool it. that will help a lot. I run a 4W unit on a desk lamp and it gets barely warm, running on an old Celeron cooler without a fan. It does have air flow though, the top is warmer than the bottom ( quick feel with calibrated finger method, no crispy noted even on the led die) and it works well, replacing the 1W one I had in there. Need to get a lot more lead blocks for the base though, must go to scrapyard and look for some lead and cast it. The other 4W units on their original heatsinks run hotter though, even though they are in open air.
 

Offline croberts

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Re: How hot can a 10W LED get?
« Reply #7 on: March 19, 2013, 07:37:16 pm »
In my LED light design, I mount a 12W Bridgelux LED to a 6.125"L x 4.5"D x 1.75"D x 0.125"T aluminum extrusion. Conductivity (determined by material and thickness) and surface area are the two main criteria with heat sinks. The extrusion I use is a rectangular tube so as long as the ends are not blocked both the outside and inside surface count as surface area. I monitor LED temperature with a thermistor mounted behind the LED and a circuit on the driver board turns off the LED if it's temp goes above 70C (LED operating temperature determines LED life. This is being compromised in commercial designs and it will result in shorter life in those units.). To date with the lights operating at room temperature ambient and in free air no LEDs have been turned off due to over temperature. I've attached some photos. All the best!
 

Offline mzzj

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Re: How hot can a 10W LED get?
« Reply #8 on: March 19, 2013, 07:59:06 pm »
I was just going to ask a similar question as I have just got a 12 watt (3x4W) MR16 led lamp to replace a 20 watt halogen lamp in a display cabinet. The thing is it appears to get just as hot as the halogen that it replaces the temperature on top of the housing is 72 deg C.The lap that I got is this one from ebay it says that it is a cree but who knows.

http://www.ebay.co.uk/itm/390553728998?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I would not want to fit a fan as the cabinet is in the drawing room (sitting room for those in the antipodes and US)
Halogen incadescents are easy as they radiate most of the heat out. LED's cool down hardly at all by radiation so you need big heatsinks and/or forced cooling.

Most of the electrical energy put in the led is still lost as a heat so it's good to assume that 12W led produces roughly 12 watts of heat that needs to be taken care of.
 

Offline G7PSK

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Re: How hot can a 10W LED get?
« Reply #9 on: March 20, 2013, 01:23:39 pm »
The problem is the led's are already mounted on a pcb and the cooling is provided by this and the metal case for the lamp by the manufacturer as it is made as a direct replacement for an MR16 halogen lamp and mounts into ceiling type holder.
 

Offline BigBrother

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Re: How hot can a 10W LED get?
« Reply #10 on: March 20, 2013, 10:31:58 pm »
I was just going to ask a similar question as I have just got a 12 watt (3x4W) MR16 led lamp to replace a 20 watt halogen lamp in a display cabinet. The thing is it appears to get just as hot as the halogen that it replaces the temperature on top of the housing is 72 deg C.The lap that I got is this one from ebay it says that it is a cree but who knows.

http://www.ebay.co.uk/itm/390553728998?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I would not want to fit a fan as the cabinet is in the drawing room (sitting room for those in the antipodes and US)
Halogen incadescents are easy as they radiate most of the heat out. LED's cool down hardly at all by radiation so you need big heatsinks and/or forced cooling.

Most of the electrical energy put in the led is still lost as a heat so it's good to assume that 12W led produces roughly 12 watts of heat that needs to be taken care of.
I thought LEDs were approximately 75/25(%) in heat/light.
 

Offline mzzj

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Re: How hot can a 10W LED get?
« Reply #11 on: March 21, 2013, 08:09:27 am »


Most of the electrical energy put in the led is still lost as a heat so it's good to assume that 12W led produces roughly 12 watts of heat that needs to be taken care of.
I thought LEDs were approximately 75/25(%) in heat/light.

Something like that.  Latest Cree blue color leds are already over 50% efficient and white leds something like 40%.
Assuming that nearly 100% is lost as a heat gives some safety factor for cooling requirements.
 

Offline SeanB

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Re: How hot can a 10W LED get?
« Reply #12 on: March 21, 2013, 08:45:54 am »
Halogens also have the advantage of not failing if they run at 150C case temperature.

Just checked the open 4W ones I have, the one on a Intel heatsink is running at 40C at the bottom, the top is 42C, the others in the standard housings are at 47C. Not bad with an ambient of 25C. I got the standard ones to drop by 5C by removing the one piece lens assembly, so they do have a larger spread now.
 

Offline BigBrother

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Re: How hot can a 10W LED get?
« Reply #13 on: March 21, 2013, 03:14:40 pm »
quick update:

(click for higher resolution)
« Last Edit: March 21, 2013, 03:28:29 pm by BigBrother »
 


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