heat sink question

[giggywatts]

ok i have a question on heat sinks.
i was given some old ufo's that are half
working but the drivers are good. i was
going to change the heat sink in them and
put some vero 18's in but the heat sink
turns out to be 16 gauge aluminum plate.
so now i want to get some heat sinks from
heat sink usa and was thinking 3.500 x 22"
with cover on back and a 80mm fan. i was
told by sixstring that i should step up
to 4" wide, but he says he more into
passive then fan cooled. they have a 4.230
wide and i'm now looking at 90mm to 100mm
fans to go on them. the drivers are
model 50w-hv350, output 45-65 vdc,
constant current 630 ma, max output 45w
and can run two 18's each so that would be
four cobs each heat sink. is this enough or
should i go after a bigger heat sink? i'm
slow on this stuff and have finally learned
how to pick my cobs and drivers but still
trying to learn about the heat sinks.
thanks in advance.

 

[Rahz]

A good basic formula for extruded fin heat sinks is: 40sq/cm per heat watt fan cooled or 120sq/cm per heat watt passive. You can calculate the perimeter of the heat sink profile in inches and convert to centimeters per inch of material multiplying by 6.45. Divide that number by 40 or 120 to see how many heat watts an inch of the profile can handle. You can use that info to determine how long the profile will need to be to handle the heat load you are expecting.

 

[giggywatts]

thanks rahz but that is part of what i don't understand. i still can tell how many watts much less heat watts it will have. like i said above i have finally figured how do the voltage thing for cobs to drivers but still trying to learn more.

 

[HotBunz]

Fwiw the 5.4" wide heat sink is only .98 an inch.

 

[Rahz]

Efficiency at 630ma will probably be around 50% or a little more depending on the color temp you selected. At that current Vero18-D will use about 18 watts each so I would plan on 9 watts of heat each.

 

[xX_BHMC_Xx]

The 3.5" profile is a bad value. Here is a link to a calculator I've created to help with chosing a HSUSA profile. It will tell you how much heatsink you need for those cobs and what size/length of the best value. Just enter the electrical characteristics of your setup in the white cells, and it will do the rest. IIRC the 4.85" is your best bang for the buck.

https://drive.google.com/file/d/0B4KikJkcxiy5QXZicmtWMXg4OW8/view?usp=sharing

 

[nfhiggs]

The 3.5" profile is a bad value. Here is a link to a calculator I've created to help with chosing a HSUSA profile. It will tell you how much heatsink you need for those cobs and what size/length of the best value. Just enter the electrical characteristics of your setup in the white cells, and it will do the rest. IIRC the 4.85" is your best bang for the buck.

https://drive.google.com/file/d/0B4KikJkcxiy5QXZicmtWMXg4OW8/view?usp=sharing

Thanks for the link - very nice little spreadsheet!

 

[xX_BHMC_Xx]

Thanks for the link - very nice little spreadsheet!

Happy to help!

 

[giggywatts]

Folks thanks for the info as soon as i get back on a computer i'll try to figure everything out. I hate trying to do stuff on my phone. Yall have a great weekend. Peace

 

[giggywatts]

first i want to thank everybody for the helping hand in this problem, i think i understand it now. i'm a old fart and sometimes i don't catch on to things as fast as i used to.

ok if i did this right i should be able to go with 17w per square cm with the 4.85 profile which is the best price deal. is there a problem running leds too cool?

 

[sixstring2112]

first i want to thank everybody for the helping hand in this problem, i think i understand it now. i'm a old fart and sometimes i don't catch on to things as fast as i used to.

ok if i did this right i should be able to go with 17w per square cm with the 4.85 profile which is the best price deal. is there a problem running leds too cool?

no some guys actually watercool these cobs

 

[giggywatts]

no some guys actually watercool these cobs

cool then i'll start the parts collection.