Some ideas around A5 needed

[Stabist]

Hi!

The situation is: now I have more or less everything I need for my Aleph5:
- all electronic parts;
- PCB design (made by kirc)
- trannie (4x25V and 900VA)
- power capacitors (4 x Sprague Powerlytic 36D: 69.000uF/50V each)
- 4 x heatsink: 300mm x 145mm x 40mm (Fisher one - same stuff as used in my Zen v4; just 5 cm longer)

So - the idea for chassis was to use one heatsink/side - so it would look very similar to original Aleph design - with internal measures 300 x 300 x 145 (and outside 380 x 380 x 155)
BUT! - capacitors are so big - that there is no way to combine them and transformer inside that place - well - it's possible - but then capacitors are almost touching heatsinks (that means they are around 1cm away from them - and that exactely almost beside MosFet - and that's the hotest place I guess) - and I guess that's not OK for them! What do you think??

So - posible solutions:
1) use of some extra corner Al plates (around 6 cm width) - so the chassis would change from "4 corner" to "8 corner" one ...

2) to add extra cca 12cm height to the chassis - simple - with using so thick Al plate as the "meat" of the heatsink is and just add it (but then upper floor would be wider because of the fins) - to put transformer in it and obove it capacitors - and above that PCB ...

3) separate chassis for PSU ...

Hmm - my thoughts about each of them:
1) The first one seems OK to me - and I think also the design could be quite interesting. But suddenly costs can rise a lot - because base and cover plate are suddenly 400 x 400 .. And also with internal WxD 460mm x 460mm that's quite big amp ...

2) The second - hmm - I guess it could look a bit odd - because the top would be 3cm wider on each side. And also the height would be at least 250mm - maybe even 300mm ...
- of course: It would be great looking if made in Aleph0 manner - but I'm not sure - in that way the air circulation could be a bit problematic ...

3) Separate PSU seems OK - it's not possible to get hum because of induction in loops; the temperature of chassis is normal - so it would also be better environment for capacitors; I guess it easier to have 2 smaller boxes than one that is huge from W x D or H point of view ...
OK, it would be a bit more expensive to build as 2nd solution; and somewhere equal to 1st.


Now I wonder - what are PROs and CONs for separated PSU?!?!
Are there any bad points??
And - how "bad" is to have capacitors in warm environment?? If the chassis itself is on cca 55°C - I guess the interior can get pretty warm too - at least 40°C ... And if they are located very near MosFets ...


Thanks for help!

OK

Stabist

[Stabist]

I feel a bit disapointed ... If such discussion was allready done - can atleast someone send me a link - I've done some "search" - but nothing came up that I could "use" ...

Can you please tell me at least what to consider when building up separate PSU?? I guess that we'll be my final solution - so I need some "tips & tricks" - is there something I must extra include or left out because of separate PSU??

Thanks again allready in advance!

[Tim F]

I was shortly going to place the same questions for an Aleph 2 so I hope someone gives you a reply. It would be useful to know what temperature caps you are using. I need to know what items to keep apart to avoid stray inteference & I expect you may need to know same. Perhaps if you don't get an answer it's because only Mr.Pass knows.

[Stabist]

Spragues are rated at max +85°C

[wuffwaff]

Stabist,

since your heatsinks will be around 50 to 60°C I would put the caps at 1 cm distance and leave it that way. This is about 20° under there max. working temperature for the specified lifespan so I wouldn´t bother.
In my opinion this will give you the nicest design.

william

[Mad_K]

Originally posted by wuffwaff

In my opinion this will give you the nicest design.

william

I second that.

[Kermit]

How about something like this? The black area is the heatsink and the red is a thick aluminum bar with angled corners. I doubt that you will find something exactly like the ones I tried to draw, but something similar would do to. Perhaps a square tube? Or you could make something yourselves. I once thought about doing this myself, but never got around to it.

[Stabist]

Kermit - something like that was one of my ideas ... Except - that corners would be a bit thinner ... But - now when I see your drawing - hmm - it's worth of invest some extra money - cause it could look stunning
Thanks


So - you guys think there is no problem about temp - that's very good
The only thing is - yes - the heatsinks will here around 55-60°C - but trazsistor case will be at least at around 75-80°C - and capacitor will be very very close to it - that's the reason I'm concerned a bit ...

[Tim F]

Stabist
Can you post dimensions of tranny, caps & pcb's to give us an idea of the scale of the problem

[Stabist]

Sure - tranny has fi=155mm and height 70mm
Each capacitor has fi=78mm and 132mm height (and there are four of them
The central pcb has 160x160
And then there will be aditional 4 pcbs: for each heatsink one - with 3 transistors each. But they are not made yet ...
And then - there are four heatsinks - 300 x 40 x 145

Any ideas very welcomed ...

If I'll find some extra time today - I'll go to friend and scan some drawings with some ideas I've allready made ...