Cob Heat

How do you accurately measure the heat of a cob?

Ive been pointing my temp gun directly at the cob about 2 inchs away and it shows around 95-97c?

Im using 0.700ma to run them & they are glued to heatsinks with arctic alumina thermal adhesive

What are you trying to measure? (Tj, Tc, etc)

I don't think measuring the LES will give you an accurate reading. To measure closest to the thermal junction there is a small test point on the cob for use with a thermocouple. There's no other way to get an accurate reading of the temp the diodes are running at AFAIK.

if left to get to steady state backside of heatsink is pretty linear with Tc, though may be 2-10+C down depending on heatsink geometry and airflow

Is a thermocouple the name of the device i need to buy to test it? if so i shal get one -

I wouldnt know the heatsinks geometry but i do know its almost cold to touch & there is a fan 1 1/2 inchs above the heatsink pulling air away

CobKits said:

if left to get to steady state backside of heatsink is pretty linear with Tc, though may be 2-10+C down depending on heatsink geometry and airflow

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If thats the case my heatsinks , at the backside, read 26-28c, so if i were to give them 10c that would be 38c? give or take a phew..

that seems low.

26C is room temperature and chips throw off some heat

Well you shouldn't be trying to measure it that way. If using an IR temp meter then take a reading from an indirect angle at a few feet away. At 2" you are picking up the light energy being converted to heat on the meter itself.

Happy Tc is generally anything below 85c as most CoBs are rated to run at 125c. Vero 29 g7 'C' are extremely efficient at transferring heat with a resistance of only 0.04c/W, whihc works out to about 2c for 50w.

CobKits said:

that seems low.

26C is room temperature and chips throw off some heat

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Yeah another reason why i would like to check to see if they are indeed using 0.700ma .. i have a feeling their using less due to the fact i only have 66v out of the 107v required for the driver

Chech said:

Yeah another reason why i would like to check to see if they are indeed using 0.700ma .. i have a feeling their using less due to the fact i only have 66v out of the 107v required for the driver

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Well, the easiest way to find that out is to put a multimeter in series and do a dc current measurement.

Chech said:

Yeah another reason why i would like to check to see if they are indeed using 0.700ma .. i have a feeling their using less due to the fact i only have 66v out of the 107v required for the driver

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which type of cob...rather which brand....
crees use a j type because of the ceramic base i would guess and veros use a k type and probably anything else with a metal slug base...
a simple digital lcd thermocouple and reader are on ebay for $4 or so...get the fine tip and attach with kapton tape for temporary measurements or high temp silicone for a permanent attachment....

Cree cob, cxbw530 ceramic base

Thanks both of you

Abiqua said:

which type of cob...rather which brand....
crees use a j type because of the ceramic base i would guess and veros use a k type and probably anything else with a metal slug base...
a simple digital lcd thermocouple and reader are on ebay for $4 or so...get the fine tip and attach with kapton tape for temporary measurements or high temp silicone for a permanent attachment....

Click to expand...

That's what Bridgelux recommends in the datasheets. They also had some suggestions in one of the AN documents that were good as well, so take a look on their website.