Adding fan on 120mm/133mm PIN heatsink

Most 120 and 133 heatsinks out there are compatible with 50mm fans.
These 50mm fans are not as cheep so you have to decide if smaller heatsinks with fan is better or just a bigger heatsink without fan
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR11.TRC1.A0.H0.X50mm+sunon.TRS0&_nkw=50mm+sunon&_sacat=0

I have highlighted the position where fan goes. These are not tapped holes so you will need self tapping screws or you can tap these
Left- 133mm Diameter Pin heatsink
Right 120mm Diameter Pin heatsink




Sharing a test data from a test i did back in Jan and forgot to share

Tambient = 20C
COB = CLU048 1818 4000K 90 CRI
Note that adding a Fan on top blocks passive cooling and raises temps by 1C-2C if fan is not running.

55Watt Test
Fan Off 50C, Fan On 33.3C

75Watt Test
Fan Off 58.5C, Fan On 38C

110Watt Test
Fan Off 77C, Fan On 50C

No air movement, temps measured on the back of heatsink behind the COB.

50mm fan option on back of 120mm heatsink. $5 Sunon Fans.
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR11.TRC1.A0.H0.X50mm+sunon.TRS0&_nkw=50mm+sunon&_sacat=0



Feel free to post anything in this thread

I like the idea of a little fan to make them run cooler which translates into longer cob life and better efficiency and if the fan or fan driver fails the cob will still survive until you can replace it.

Edit: then again if you can get the same or close temps with the use of a bigger heat sink then I would just go all passive for the ease of it.

do those fans really pull 500 mA each?

if they do thats 6W


so lets look at an 1818 in citi calc:

no fan:
case temp 77C, 2103 mA, 110.0W, Tj 95 >15345 lm/110W = 139.5 lm/W

w/fan, 110 cob W
case temp 50C, 2071mA, 110.0W, Tj 68 >16067 lm/116W = 138.5 lm/W

w/fan, 110 total W
case temp 50C, 2071mA, 110.0W, Tj 67>15364 lm/110W = 139.7 lm/W


so it seems like depending on how you run it, with the fan using 5-6W its about a wash, and as you mentioned, if running only occasionally they have a thermal penalty when they are off

i think the real advantage would be being able to run 120W cob on a pin fin

Not to mention, in a real world application there would be ambient airflow hitting the heatsinks. Perhaps those numbers would fall somewhere between the fan/no fan results.

I think you could use a much larger fan that uses less energy, cools better and could be attached with zip ties or whatever you have around. It's not like it would start taking off in flight.

CobKits said:

do those fans really pull 500 mA each?

if they do thats 6W

Click to expand...

0.8 W 12V

sorry i read 0.5W as 0.5A in your first link

so yeah, 4-5% efficiency bump for $7-8 with fan driver seems legit.

think about 150W 1825 or 3618 on a 133mm