Heatsinks for DIY LED lamps

on average for passive cooling how much hotter is the chips vs the sink
i remember reading on the reef forums a few years bacj it was like 40c

so recently i cooked 2 cxa2540s the sink was 67c wondering how hot the chips was and if it was the thermal interface that caused them to cook......

dionysus4 said:

on average for passive cooling how much hotter is the chips vs the sink
i remember reading on the reef forums a few years bacj it was like 40c

so recently i cooked 2 cxa2540s the sink was 67c wondering how hot the chips was and if it was the thermal interface that caused them to cook......

Click to expand...

Should be able to handle 67c... Not recommended of course.

Haven't had problems using pk3 type tim hand spread thinly and evenly. With a clamp providing pressure..

A temp meter with thermocouple is a good way to see the actual Tc temp of led. Check Amazon for good prices. Attach it to Tc point on led..

I was going to epoxy a thermocouple to a CXB3590 but there is no way with the Ideal holder, I don't think.

I bought a common K-type only temperature meter and extra thermocouples. Then I read the Cree manual in more detail and they recommend T-type for the CX series but K-type for the XL--I wonder why.

...maybe help a bit... ...from wikipedia...

Type K (chromel – alumel) is the most common general purpose thermocouple with a sensitivity of approximately 41 µV/°C (chromel positive relative to alumel when the junction temperature is higher than the reference temperature).[9]
It is inexpensive, and a wide variety of probes are available in its −200°C to +1350°C / -330°F to +2460°F range.
Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples.
One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point; this occurs for type K thermocouples at around 185°C.

Type K thermocouples may be used up to 1260°C in non-oxidizing or inert atmospheres without rapid aging.
In marginally oxidizing atmospheres (such as carbon dioxide) between 800°C – 1050°C, the chromel wire rapidly corrodes and becomes magnetic in a phenomenon known as "green rot"; this induces a large and permanent degradation of the thermocouple, causing the thermocouple to read too low if the corroded area is exposed to thermal gradient.[10]
Another source of drift in type K thermocouples is that near 400°C, a slow reordering in the chromel wire occurs; this is reversible and leads to hysteresis between heating and cooling

...

Type T (copper – constantan) thermocouples are suited for measurements in the −200 to 350 °C range.
Often used as a differential measurement since only copper wire touches the probes.
Since both conductors are non-magnetic, there is no Curie point and thus no abrupt change in characteristics. Type T thermocouples have a sensitivity of about 43 µV/°C.
Note that copper has a much higher thermal conductivity than the alloys generally used in thermocouple constructions, and so it is necessary to exercise extra care with thermally anchoring type T thermocouples.

pd... i saw SDS using a k thermocouple on ideal holding adaptation...look on her threads...

pd1... i saw info about k and t types ...and some info about amplifier for t-type on this pdf...(but we know amplifiers for k type on arduino way too)...

http://www.ti.com/lit/ml/slyp161/slyp161.pdf

pd2...upsss thanks Wilson... on the max31855 datasheet....

Versions Available for Most Common Thermocouple Types:
K-, J-, N-, T-, S-, R-, and E-Type ....

...max31855K for K types ....max31855T for T types..

...other upgrade way for the reflow oven shield... interchangable system for change the max chip...



... and ready for t types or others too... not?...

autoanswer... not... the reflow oven used a smd chip model...need other adaptador connector... maybe similar to ...



saludos

sanjuan said:

I was going to epoxy a thermocouple to a CXB3590 but there is no way with the Ideal holder, I don't think.

I bought a common K-type only temperature meter and extra thermocouples. Then I read the Cree manual in more detail and they recommend T-type for the CX series but K-type for the XL--I wonder why.

Click to expand...

It's easy to modify the ideal holder with a dremel and cutting wheel. Simply cut a notch. Could probably do it with a file... Not much material needs to come off

I just use kapton tape to hold it in place... Works great.. Doesn't really need to be permanent when you have a holder. Just get initial measurements is enough for me now

sanjuan said:

I was going to epoxy a thermocouple to a CXB3590 but there is no way with the Ideal holder, I don't think.

I bought a common K-type only temperature meter and extra thermocouples. Then I read the Cree manual in more detail and they recommend T-type for the CX series but K-type for the XL--I wonder why.

Click to expand...

Heres a shot of a k type mounted with kapton. first boxed light i made, still reads temps and works great. Not really necessary but it was great for learning a little more about cobs.

You can kinda see where i cut away a little metal by the Tc spot..



Vegging in a 2 x 4 with 2 3590s at .210a......

Positivity said:

Should be able to handle 67c... Not recommended of course.

Haven't had problems using pk3 type tim hand spread thinly and evenly. With a clamp providing pressure..

A temp meter with thermocouple is a good way to see the actual Tc temp of led. Check Amazon for good prices. Attach it to Tc point on led..

Click to expand...

yup i have one- but the chip holder i used covered the point to check tj so i have to go off the heatsinsk temp
just wodering if anyone has experience or can check for me

ive got replacement chips and am adding a fan to the 400g alu heatsinsks but agian cannot test on the chip bcause of the holder

Hello U.S weederz!
To cool a 3590 @ 1400mA on a 10x6, 6x1,4 inch (250x165x35mm) ) heatsink. What size and cfm/rpm should I use for a fan? 140mm X1 or maybe 2 120mm(is using 2 120mm fans allow me to lower the V (3V?) Or maybe one who pulse and the other suck the air?
Thanks

just dropping 2 cents :

- Pulse works better than pulling, more pressure == more dissipation.
- 3V on fan => Depends, some don't even start at such a low voltage, aim for 5-7V in my opinion.

Positivity said:

Heres a shot of a k type mounted with kapton. first boxed light i made, still reads temps and works great. Not really necessary but it was great for learning a little more about cobs.

You can kinda see where i cut away a little metal by the Tc spot..

View attachment 3439175 View attachment 3439176

Vegging in a 2 x 4 with 2 3590s at .210a......

Click to expand...

36v or 72v? How's the growth in your veg chamber?

bicit said:

36v or 72v? How's the growth in your veg chamber?

Click to expand...

72v...its actually vegging at .310a or something. I dimmed it a bit for the picture.

Just happy all around with the growth from 5k. Nicely branched, green and healthy, even the remote corners off to the side are nice.

I was wondering if anyone had any leads on some radial heat sinks large enough to fit a CXB3590 and a holder?

bicit said:

I was wondering if anyone had any leads on some radial heat sinks large enough to fit a CXB3590 and a holder?

Click to expand...

Nuventix or mechatronics?

Something like that..

http://www.mechatronix-asia.com

Need a recommendation on heatsink for single Vero 29 , 2.9Amps or more, active cooling
looking for Heatsink with long fins
I have USA heatsink 4.900" X 12" . USA heatsink 10.080"X8" Wide Extruded might be better suited due to larger fins but might be too big

Ive just been running some calculations with a heatsink company and wanted to double check their recommendations.
Ill be running 3 light bars; each with 4 cxb3590s running at 48.8w and 50% efficient. Ive rounded it up to a 100w of heat dissipation per light bar.
At the moment i use 600w hps in a 1.2m parabolic reflector over 12 plants. Ive assigned a cob per plant.
The company has recommended me a 1200mm length x 165.5mm width x 40.6mm height (base plate 5mm fins 35.6mm) On their calculations they have said i could achieve a 0.194C increase in heat per watt of energy via convection only.

Am i right in thinking that 100w of heat * 0.194c per watt = 19.4C increase to the heatsink temperature?
If my ambient was 20C, would i add 20 to the 19.4 to get my stabilised heat sink temperature roughly at 39.4C.

The calculations used to get 0.194c per watt are based upon the heat spreading evenly across the heat sink which is not the case in our circumstances. For this reason we should expect an increased thermal resistance of 33% to the 0.194C figure which takes us to 0.258C per watt of heat.
Adding the ambient temperature with the expected heatsink temperature should = 45.8C passively cooled.

Thanks

bruce786 said:

Ive just been running some calculations with a heatsink company and wanted to double check their recommendations.
Ill be running 3 light bars; each with 4 cxb3590s running at 48.8w and 50% efficient. Ive rounded it up to a 100w of heat dissipation per light bar.
At the moment i use 600w hps in a 1.2m parabolic reflector over 12 plants. Ive assigned a cob per plant.
The company has recommended me a 1200mm length x 165.5mm width x 40.6mm height (base plate 5mm fins 35.6mm) On their calculations they have said i could achieve a 0.194C increase in heat per watt of energy via convection only.

Am i right in thinking that 100w of heat * 0.194c per watt = 19.4C increase to the heatsink temperature?
If my ambient was 20C, would i add 20 to the 19.4 to get my stabilised heat sink temperature roughly at 39.4C.

The calculations used to get 0.194c per watt are based upon the heat spreading evenly across the heat sink which is not the case in our circumstances. For this reason we should expect an increased thermal resistance of 33% to the 0.194C figure which takes us to 0.258C per watt of heat.
Adding the ambient temperature with the expected heatsink temperature should = 45.8C passively cooled.

Thanks

Click to expand...

If the thermal resistance of the heat sink they provided is correct then yes, temp rise would be around these numbers. I expect that you've got some ventilation and most probably even a circulation fan. Slightly moving air improves these figures drastically and even 45-50°C on the heat sink isn't that much.

Most heatsink thermal figures are based on vertical orientation of the fins and a 70C difference between the heatsink and the ambient temp so it is tricky to use their figures. How many fins does it have? The 5mm base is thinner than what we are normally use and since each COB will be dissipating 50W a thicker base might benefit your junction temp. Are you in EU or North America?

what would ones recommendations be to cool 800w in a 4x4area? Anyone know the cost? I'm a die hard water cooler guy but a buddy of mine wants me to retro fit an air cooled hps hood w a fan set up in trying to get a reasonable quote for materials. He likes the simplicity of it and water makes him nervous around DC power LOL ill be running 12 100w Chinese cobs off 2 400w power supplies. Also how far apart are u guys spreading the leds? I had mine stacked in tight in pairs. Worked good but I'm a newbie.

Thanks for the replies, i will definitely have ventilation and circulation fans blowing all over the place.
There are 15 fins across the width of the heat sink Supra, and i think if my calculations are correct each cob will dissipate about 24watts of heat. Im not sure if your talking 50 watts of heat per cob. Im in the United Kingdom and the heat sink place is literally a 5minute drive from me. Very convenient and no shipping costs!
Ive messaged realstyles about his heat sink and he is running a way higher wattage on similar sized sinks and seems to be doing pretty damn good.
I may buy one this week and post up exactly what kind of dissipation im seeing once my cobs arrive; ill be building a 600w 3590cxb 3000k light (12 cobs running at 50w each) so id love to share my experience once i get going.

Gotcha so it is similar to the 5.88" profile we are familiar with, good fin spacing for passive cooling but slightly taller fins. So a 1200mm piece like you described is 16,800 cm². Should be good for 130W of heat with passive cooling and as you said it will benefit from some air circulation.