Tall ACA Build Prelim


2003-12-26 11:20 pm
I'm looking to build some more ACAs in a vertical orientation. I fancy using this style of heatsink running vertically up the back of the amp http://www.farnell.com/datasheets/1286778.pdf

I have a couple of questions.

1. In my original kit the board was mounted near the top of the heatsink as per papa's design. Where is the optimum mounting position on a vertical and narrow heatsink like this?

2. These heatsinks have T slots for mounting against each of the exposed sides. Could I extend the side panels and add a rear panel to enclose the heatsink (In my head it seems it might even make for better directional flow of heat) without detrimental effect on cooling?
Cheers Zen Mod!

So in that case would this P3/180B - SEMIKRON - Heat Sink, For Isolated Power Modules, IGBT Power Module, 0.39 °C/W, 135 mm, 125 mm, 180 mm | Farnell element14 heatsink, which is rated at 0.39C/W be sufficient for a pair of ACA running at 24v with R15 mod? :redhot: :scared: :flame:

let respond to that question with some logic :

- what's Iq with R15 mod ?

multiply that with 24Vdc and you have dissipation per channel

multiply that with 2 (channels)

multiply that with 0.39C/W

add 15%

add temp. of ambient

now you have appr. temperature of mosfets

if you still aren't in 55C -60C bracket , you're good to go


2003-12-26 11:20 pm
I've erred on the side of caution using a higher max ambient temp of 30C for us here in the balmy UK. You know, in case the sun comes out for more than 2 days in a row and I set fire to the sofa :hot:

1.6A x 24v x 2 x 0.39 x 115% + 30 = 64.44C

Which is too hot

If I add a fan the C/W drops to around 0.14. So

1.6A x 24v x 2 x 0.14 x 115% + 30 = 42.36C which is nice and cool.

I should be able to reduce fan speed by about 50% to reduce noise and still be chilly cool :D

Can you overcool your heatsink?
well ....... many lines were written about significance of mosfet temperature

things are simple - if mosfet is on higher temperature , then minute changes in temperature due to current/voltage signal play (ΔT) are smaller (in percentage) vs. idle temp. thus giving lesser minute change in xconductance and few other important physical thingies

that's at least how my non-engineer peanut brain is grasping that

so - if you kkeep heatsink in 45-50C bracket , mosfets are happy and your ears are happy

I hope , at least for ears part


that just means that you always can regulate speed of fan on Babysitter base ...


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