Tall ACA Build Prelim

[JRKO]

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?

 

[Zen Mod]

1. past some length , there is no more optimal position - you're wasting part of heatsink

so , mount them as you like

2.yes , chimney effect is generally beneficial

 

[JRKO]

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?

 

[Bare]

Newbie at this without question
My recent (continuing looks into heatsinking suggests that Vertical orientation requires 4x ! the height change to equal a 1x width change... on a similar design sink/profile.
Something to be aware of is all.

 

[Zen Mod]

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?

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

 

[JRKO]

Thanks zen mod - perfect example of 'give man a fish and you feed him for the day. Teach man to fish and (his wife will never see him again) he can feed his family for life'.


Gets calculator

 

[JRKO]

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

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

Can you overcool your heatsink?

 

[Zen Mod]

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 ...

 

[JRKO]

Ta muchly

Zen mod is legend in his own lunchtime

 

[Zen Mod]

 

[JRKO]