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Old 23rd October 2010, 09:39 PM   #241
Melon Head is offline Melon Head  Australia
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Originally Posted by EUVL View Post
I did some simulation and extrapolation from previous builds and come to a heat sink temperature rise of 45~55C above ambient for dissipation of 145W, which is indeed a bit high. So the concern was well justified.

The MOSFET itself has a thermal resistance of 0.83C/W, or 27C rise at 32W. Give another 5C for Kerafoil insulation. For ambient temperature of 25C, the junction temperature would be 112C. So too high for my own taste.

Need experimental verification. Not easy to solve without increasing cost (larger heatsinks and case) or reducing wife acceptance factor (fans on the outside).

Back to the drawing board.




Patrick
Worst case scenario is, we have to buy 2 cases and build monoblocks.
It might cost a bit more but in the end, the result will be worth it.
It also allows margin for increased power in the future.
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Old 23rd October 2010, 09:44 PM   #242
Melon Head is offline Melon Head  Australia
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Originally Posted by EUVL View Post
OK, possibly a simple solution.

Add 2 more smaller heatsinks on the inside surfaces of the front and rear plate, something like 250 x 150 x 25mm.
E.g. Fischer SK49-150. Costs 40 Euros extra, but gets the temperature down to 35C above ambient.
Small price to pay than to go to 400mm sinks (and hence larger housing in all dimensions)

Test on Conrad still useful.


Patrick

PS
Any of the previous mentioned commercial housings from Schuro & Hifi200 has essentially the same heatsink as Conrad MF35-151.
So none of them will do in any case.
That sounds like a good idea regarding the extra heatsink internally.

I will try and test the heatsinks some time next week.
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Old 23rd October 2010, 10:04 PM   #243
EUVL is offline EUVL  Europe
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> Worst case scenario is, we have to buy 2 cases and build monoblocks.

You have a high bandwidth power amp.
You don't want long wires between mosfets mounted on opposite heatsinks in a monoblock running over your transformer.

So only solution is ..... Mini Tower. (The original PCB layout was also designed for this.)
Expensive solution.

And my task was (is) to design a (sort of universal) case that will suit other DIYA Class A projects and not just the F5X.

I'll stick to inner sinks for now, and wait for your measurements.


Patrick

Last edited by EUVL; 23rd October 2010 at 10:25 PM.
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Old 23rd October 2010, 10:57 PM   #244
bobodioulasso is offline bobodioulasso  Europe
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As far as i could experiment with my aleph j biased at 2 x 1.3A dissipating 125w per channel, two heatsinks measuring 400mm x 140mm x 80mm do the job perfectly, even at 35C ambient..

A stereo case costs anyway less than monobloks. And moderately high heatsinks are more efficient than tall ones.

The only drawback is the weigh.

I will cannibalise my alephJ case to give it a try.

Last edited by bobodioulasso; 23rd October 2010 at 11:05 PM.
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Old 23rd October 2010, 11:25 PM   #245
massimo is offline massimo  Italy
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hifi2000 can make special cases on order for a reasonable quantity (lets say 50 units)
A custom "all alu" Pesante Dissipante 4U or 5U/300mm with a nice 10 mm engraved front panel and some bigger heatsinks such as Fischer SK568 or similar (300 * 60 mm height 165-210 mm) can do the job.
Its only matter to resize rear panel and covers, not a difficult task indeed.
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Old 24th October 2010, 05:25 AM   #246
EUVL is offline EUVL  Europe
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I checked out the Fischer online catalog.

I am afraid that SK568 is too small and will not do. It is listed with Rth 0.3C/W at 150mm, but this corresponds to a temperature rise of 80C. If you apply the correction factor for 35C rise, you end up something like 0.4~0.45. Realistically you have about 150W dissipation per F5X, which means dT close to 60C.

So you need to search for a catalog Rth value of about 0.2C/W per heatsink, which was why I chose the Conrad in the first place.

Realistically if you do not want to use the inner sinks (i.e.sinks on all 4 sides), you should be looking at a sink of about 400x200x50mm or 350x150x60mm. The first you can buy (2x SK90 or 4x SK88 side by side), cost a bit more, but need larger plates all round, and higher shipment cost. The second will fit the design without significant changes, but I cannot find one as standard catalog item. Probably 3x SK88 with 15mm between sinks is the closest we can get. No idea about costs. Fischer is not cheap, and no special machining unless you order > 500 pieces. Which means shipping to somewhere else to machine and anodise. I doubt we will sell 50 cases.

No easy option I am afraid.

If Hifi2000 can provide a solution for less than 500 Euros including world wide shipment and a good donation to DIYA, you are welcome to take over from me.


Patrick

Last edited by EUVL; 24th October 2010 at 05:28 AM.
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Old 24th October 2010, 05:56 AM   #247
Luke is offline Luke  New Zealand
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Quote:
Originally Posted by EUVL View Post
If Hifi2000 can provide a solution for less than 500 Euros including world wide shipment and a good donation to DIYA, you are welcome to take over from me.
Patrick
I would love a couple of your towers in my lounge, but hifi2000 is hard to beat for value. Pics at bottom of the page are quite nice for 250 euro. I dont think I could make and anodise a case for this.

modushop.biz
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Old 24th October 2010, 06:20 AM   #248
EUVL is offline EUVL  Europe
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You are right.

I cannot beat them for value, because I don't have local source of cheap heatsink extrusion.
Feel free to bulk order from them. The 4pcs 250x210x40mm heatsinks looks big enough for 2x F5X.
The handles in the picture are not included in the price.
And I wonder what they charge for shipment (I would guess 80 Euros).

Do watch vibrations on the bottom plate when you put heavy Trafos on.
Make a good drum especially if you are unlucky that the resonance frequency of Tx + Btm Plate combo get close to low order harmonics of 50/60Hz.
But you can always special order a thicker bottom plate of say 6mm.

As I said all along, aluminium has its price. You can always save cost by using thin plates.
And he has basically no machining costs.
Front plate can be sawed; the rest is sheet metal (plunge or laser cut).


Patrick

Last edited by EUVL; 24th October 2010 at 06:29 AM.
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Old 24th October 2010, 06:34 AM   #249
EUVL is offline EUVL  Europe
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You can even download their drawing :

Hi-Fi 2000 contenitori per l'elettronica, case modding HTPC, Galaxy, rack, DIYaudio, computer cases, front panel express, knobs,milled Handles, milled fronts, hi-end,


Patrick
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Old 24th October 2010, 09:17 AM   #250
bobodioulasso is offline bobodioulasso  Europe
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Just an idea.
Shouldn't it be possible that Conrad accept to produce a batch of 100 pieces custom cut of their 350 mm x 50mm extruded profile?
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