Aleph 5

Stabist

Member
2002-09-22 10:56 am
Slovenia
Toni hi!

DO you have original marks for those Fisher heatsinks? So we could see K/W factor ...

Btw - one thing that is VERY important in your way of heatsinking - be sure that the base Al plate isn't bent a bit - and also check that heatsinks are really flat ... Otherwise you will get a very bad "contact" between surfaces - and so the plate will get much much hotter rhan heatsinks themselfes ...
 
Dear Primoz,
I think that heat sinks have 1.9/W. It is very difficult to find them as a part number on Fisherelectronik.de. Any way I’m planning to use alu plate at least of 7mm thickens. Between surfaces I’m planning to use thermal paste so I think that will be a good thermal contact. As I said before, heat sinks have dimensions 85mm x 100mm with 40mm fins.
One more question about power supply. I’m planning to use, per monoblock, 2 x 33000mF-RIFA, 2 x 10000mf-KENDEIL and 2 x 3300mF-NIPON nichicon with dual rectifier and 2 x 28V 400VA transformer. Do you think that this would be enough???
Thank you for you reply,
Regards,
Toni
 

Stabist

Member
2002-09-22 10:56 am
Slovenia
tonistefanovski said:
Dear Primoz,
I think that heat sinks have 1.9/W. It is very difficult to find them as a part number on Fisherelectronik.de. Any way I’m planning to use alu plate at least of 7mm thickens. Between surfaces I’m planning to use thermal paste so I think that will be a good thermal contact. As I said before, heat sinks have dimensions 85mm x 100mm with 40mm fins.
One more question about power supply. I’m planning to use, per monoblock, 2 x 33000mF-RIFA, 2 x 10000mf-KENDEIL and 2 x 3300mF-NIPON nichicon with dual rectifier and 2 x 28V 400VA transformer. Do you think that this would be enough???
Thank you for you reply,
Regards,
Toni

Hi Toni,

so - if you mount them e.g. 4 per side - you will get K/W around 0,5K/W//side - that would be enough for around 80W dissipation (or 160W on all 8 heatsinks) - and that's quite allright for A5.
Than again - by mounting them in height - you will not get so good K/W factor - because by increasing height the K/W curve flatens very quickly ...

It's not the thickness af Al plate that is problematic - and also not the thermal grease - which is, btw - a little bit tricky to use than noticable at first moment - the problem is - that you will rarely get really flat Al plate and really flat heatsink surface - ussualy both are bent a bit - so on the contact you get a big air gap - OK - it will be filled by grease - BUT - the trick with the grease is - there shouldn't be too many of it - and in the case of such gaps - it surely be too thick - and heat transfer will be far from good!!!

You have 2 solutions:
- to find someone with router that will flatten you heatsinks and/or Al plate
- to mount transistors on heatsinks dirrectly - and only use Al profiles (or smaller plates) to connect heatsinks together

About your PSU - I think it will be more than enough! Maybe just add some MKP or similar bypass capacitors!