Heatsinks

[I like Cheese]

OK- let me see if I get this. Cheese wants build a couple of arrays using 4- 36v cob's and needs to find out how much thermal dissipation he needs to be safe. The driver he spec'd will run each cob @1400mA when wired in series and that driver will be able to provide enough forward voltage(it does) for 4 led's in series. Each cob will run at approx. 50W at the driver rating-gives you a total of 200W/array. Most info I've seen for passive cooling suggests using 50% efficiency of the cob so 100W/array needs to get dissipated. You should be able to calculate the total area a sink design based on W/in2 the manufacturer provides. I do agree with Dan about using a 10k resistor to give the driver a base setting.

Hi gbauto

I am building 3 bars with 3 2 3 cobs. The bars are 8000cm2. The 2 bars with 3 cobs on I am going with active cooling. The 1 bar with 2 cobs on I am going with passive. Please speak slowly, apparently I do not understand English .

 

[gbauto]

It seems like you MAY be able to understand what I'm saying to you.....
As long as you have figured out how you want to power and wire you bars safely then it comes back to the simple fact-you need to get rid of 25w/cob of heat. Figure out the # of cob's/light array and you have total/light of heat to get rid of. Heatsink manufactures give specs on dissipation/area so a simple calc will give you the area needed to provide adequate cooling.....proceed

 

[Maximo]

I've built a few lights using various heat sinks.

Basically just weigh the heat sink. For every 100 grams of aluminium it will dissipate 10watts passively. So a 500 gram heat sink will be okay for a 50 watt COB without a fan. With a fan or 'active cooling' you can double the wattage figure, so 100 watts with a fan.

 

[I like Cheese]

I've built a few lights using various heat sinks.

Basically just weigh the heat sink. For every 100 grams of aluminium it will dissipate 10watts passively. So a 500 gram heat sink will be okay for a 50 watt COB without a fan. With a fan or 'active cooling' you can double the wattage figure, so 100 watts with a fan.

That actually sounds about right for the heatsinks I have. Very cool.