heatsinks

[Raj1]

Hi,
can any one please tell me if using multiple heatsinks on a chassis is effective when;

1) I have a 2 mono amps, each has two mosfets on it which obviously need heatsinks.


2) the outside of my chassis has approx enough room for 3 heatsinks per pcb.

3) as there are only 2 mosfets per pcb, this means that 2 of the heatsinks will each have a mosfet, whilst the third heatsink is partially 'redundant'..

4) all 3 of the heatsinks per pcbs will be on the same plate of aluminium,

how effeftive will the third 'redundant' heatsink, with no mosfet attached directly to it be?

arrrrgh! someone please reply!!!!!!!
Thanks
Raj

[joensd]

arrrrgh! someone please reply!!!!!!!

I think you´d have to provide a little bit more information to get an answer to this.
What class is your amplifier for example?(A/AB/B...)
What´s the maximum output power?
Which mosfet packages are you using?
How thick is the aluminium plate and thermal rating of heatsinks?
Will you use insulators?
And still it´s not easy to calculate the final thermal resistance of this big heatsink.

It´s nice to know all of this and especially the maximum power dissipation of the amp but some even experienced people would still say:

We don´t calculate heatsinks. We just make them big.

So....

Jens

[Mark A. Gulbrandsen]

"We don´t calculate heatsinks. We just make them big."

I love this line and I followed it to the hilt when I planned out my Aleph 2's. Here is a photo of my fairly cool running Alsph 2's...probably almost double what everyone else here is doing for heatinking....The pcb is 4"X6" for a size refrence. Each amp weighs in at almost 70 lbs!!
Mark

[Raj1]

Hi,
the amp is a mosfet 250watt amp. At the moment I using a single 0.42k heatsink per pcb. The amp is being run at 250ma quiescient current, according to the designer the mosfets are dissapating around 35watts of heat at this setting. This only gives about 1 watt of class A op.

The new heatsinks I've seen are available from dick smith electronics in australia part no H3408 the thermal resistance is reputed to be 0.37oC/w

I was planning of placing three of these per side with only two of them connected to the heat sinks. However the mounting of the mosfets won't be central. Also I was thinking of using part of my old heatsinks over the front of the heatsinks. The gap between the two mosfets is around 40-60mm (can't quite remember) The space I have available is 300mm length by 200mm height. Is using a single large heatsink on the outside of the chassis preferable to using three like the ones mentioned Any ideas or other sugestions for heatsinks which are suitable?

Thanks
Raj

[joensd]

The space I have available is 300mm length by 200mm height

For my next project (ZenV4) I want to use heatsinks with exactly that size.
It´s the SK157 in 200mm height.
It´s produced by Fischer Elektronik.
At this size you get 0,22K/W.(and that´s only for the black anodized version which must be vertically orientated as well)
I only got an old catalog but at that time the heatsink was 65€ and 76€ for the black anodized one.

Jens

[Cobra2]

Have anybody checked out these?

http://www.meci.com/default.asp?mode...ms&category=39

Seems like a bargain?

Arne K

[Mark A. Gulbrandsen]

Ahhhh, So Dick Smith has finally landed his Hellichopper??? They used to have several stores here in the western states too but I think they packed up and flew back down under......don't know why though.
Mark

[Raj1]

Hi Arne K,

What's the thermal rating for those babies?

Thanks
Raj

[Cobra2]

If I knew, I would probably have emptied their stock...?

Arne K

[Raj1]

Well it's gotta be less than 0.2oC, what do ya reckon?