Leadbelly
It honestly depends on the bias you'll be running but with extrusions that long I think you should be able to get away with 2 devices per sink if you keep the dissipation per device reasonable like 20W and under for each device. I'd suggest you get yourself a decent power resistor and mount it on the heatsink (use thermal compound) and run a test to see what the temperature rise over ambient will be for a given dissipation. With a 20v supply and a 50w 1 ohm resistor it will dissipate 20w, bolt that to the sink and see how much the temperature will rise over ambient, that will give you a decent idea. Try to keep your design at no more than 50-55 degrees C when running to help reliability and also saftey if you have children or pets.
Kevin
It honestly depends on the bias you'll be running but with extrusions that long I think you should be able to get away with 2 devices per sink if you keep the dissipation per device reasonable like 20W and under for each device. I'd suggest you get yourself a decent power resistor and mount it on the heatsink (use thermal compound) and run a test to see what the temperature rise over ambient will be for a given dissipation. With a 20v supply and a 50w 1 ohm resistor it will dissipate 20w, bolt that to the sink and see how much the temperature will rise over ambient, that will give you a decent idea. Try to keep your design at no more than 50-55 degrees C when running to help reliability and also saftey if you have children or pets.
Kevin
PrimeCase said:
PrimeCase said:
That's just it, they're not extrusions, the fins are epoxied on to the base. I don't know whether to expect them to have a similar coefficient to an extruded sink.
I was planning to make a stereo amp, common PS supplying 20A total, each channel using 5 of the heatsinks.
Yep.....forgot about the epoxied fins LOL 
I think you'll be better served being slightly less ambitious, remember that if you are using groups of 5 fets that is 20 fets per channel running 10A total bias?
So 4 devices per heatsink at around 72W per sink, this will give you a temperature rise of 50 degrees over ambient if you run with 10A bias assuming the heatsinks are as good as this particular extrusion Thermaflo example
have a look and maybe you'll revise your plans
Kevin
I think you'll be better served being slightly less ambitious, remember that if you are using groups of 5 fets that is 20 fets per channel running 10A total bias?
So 4 devices per heatsink at around 72W per sink, this will give you a temperature rise of 50 degrees over ambient if you run with 10A bias assuming the heatsinks are as good as this particular extrusion Thermaflo example
have a look and maybe you'll revise your plans
Kevin
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