Hi all
I'm in the process of build an Elliot P68 Subwoofer amp with 4 pairs of MJ15003/4 outputs. I have a number of options with regards to heatsinks. Have a look at 3 ideas i've had so far and tell me which you think is best. I will use fan cooling at both ends, and the sink is about 30cm long, 9.5cm wide (12inchx4inch) The light grey bits are aluminum profiles about 6mm thick (1/4 inch). Using Mr Elliots Excel spreadsheet, I get about 0,4C/W for both sinks together with a heatsink temp of 100C which is about right.
I calculated dissipation as follows:
Rails: +-56V
Max dissipation: 56V/2 = 28V. Current is 28/4ohms = 7A
therefor P= 28*6 = 196Watts
For 4 pairs or TR's, each TR dissipates 196/4 = 49W
Tjunction = 0,7C/W Tcase-heatsink = 0.5C/W Total= 1.2C/W
1.2C/W * 49W = 59C.
So max heatsink temp is 200-59 = 141C for junction temp of 200C
Let's assume ambient T is 35C.
Then heatsink can dissipate (141-35/0.4) = 265W before it reaches 141C.
At a dissipation of 196W max, heatsink is at temp of (0,4*196) = 113C if ambient temp is 35C. This seems to work out fine.
Since i will be using fan cooling, does anyone have any formulae for working out the new thermal rating of the sink because of the forced air cooling?
I'm in the process of build an Elliot P68 Subwoofer amp with 4 pairs of MJ15003/4 outputs. I have a number of options with regards to heatsinks. Have a look at 3 ideas i've had so far and tell me which you think is best. I will use fan cooling at both ends, and the sink is about 30cm long, 9.5cm wide (12inchx4inch) The light grey bits are aluminum profiles about 6mm thick (1/4 inch). Using Mr Elliots Excel spreadsheet, I get about 0,4C/W for both sinks together with a heatsink temp of 100C which is about right.
I calculated dissipation as follows:
Rails: +-56V
Max dissipation: 56V/2 = 28V. Current is 28/4ohms = 7A
therefor P= 28*6 = 196Watts
For 4 pairs or TR's, each TR dissipates 196/4 = 49W
Tjunction = 0,7C/W Tcase-heatsink = 0.5C/W Total= 1.2C/W
1.2C/W * 49W = 59C.
So max heatsink temp is 200-59 = 141C for junction temp of 200C
Let's assume ambient T is 35C.
Then heatsink can dissipate (141-35/0.4) = 265W before it reaches 141C.
At a dissipation of 196W max, heatsink is at temp of (0,4*196) = 113C if ambient temp is 35C. This seems to work out fine.
Since i will be using fan cooling, does anyone have any formulae for working out the new thermal rating of the sink because of the forced air cooling?