Question: Mounting heatsinks

[StuartAmbient]

This is sort of a half cocked question as I've yet to determine my thermal needs.
However I've read and searched through a good number of posts at diyaudio and still am unclear, if I"m building my own chassis how heatsinks are mounted.
First my chassis is going to be relatively deep and high. (5" H, 14"D)
I've looked at some flat sided heatsinks and I gather those are the ones that would work best. Do they replace the side panels of the chassis ? What type of mounting should I be looking at?
Also I've seen some posts here showing the very small heatsinks, some I think were selling for a few dollars on ebay. Would I just build a whole panel of those ?

Thanks for any ideas and answers
StuartAmbient

[Nuuk]

Some people have found that the case (usually aluminium extrusion) is enough to keep a GC temperature in check.

Some like PC heatsinks and some prefer a solid mass, either bar or angle.

As regards how much heatsink you need, you can either go to the data sheet for the chip that you are using and calculate the correct size, or you can play safe and use as big a one as you can squeeze in your layout.

Have a look around at what others have used, that is a good guide to what works.

[sam9]

I have successfully used "L" brackets to mount heatsinks inside a case. (2x 50W amps) Just be sure the case has adequate ventilation.

Some people use rectangular 4 pieces of sheet metal plus 2 heatsinks to make a 6 sided box. Usually angle bars are involved. This puts the fins on the exterior where cooling is more efficient.

You can also use a chasis (4 sides + a bottom, make cutouts in two of the sides for the device to be heatsinked, then bolt the heatsinks over the sides with the cutouts.

Two decision factors A- the termal requirements, B- you metal working skill.

Unless you finf some surplus heatsinks on ebay (or whereever) that are suitable, the best deal I know of is www.conradheatsinks.com. Even when shipped all the way from Australia to the US, they are cheaper than the minimum order you can get from Aavid or MM Metals. The quality and appearance are very good.

[ultrachrome]

The heatsink requirements seem to be so low for this amp. I have two channels on a 2" x 2" x 6" heatsink and it barely feels warm.

I have another two channels bolted to a 1/16" x 6" x 10" plate and it gets warm but not hot.

If you want to use a heatsink for a side or front panel, chances are it's going to be well more than enough for your cooling needs. Given the dimensions you state, you will have way more heat sink than you need for two channels. If you like the way it looks, go for it.

Mounting the heatsink depends on it's size and shape. It's probably easier to mount the heatsink inside the chassis or if the chassis is aluminum, try mounting the chips directly to the chassis and see if it provides adequate cooling.

[joensd]

You can also get some heatsinks like these (post3) where you can directly put screw heads in and mount to front and back plate. (perfect for a lazy chassis builder like me;-))

You should also have a look at the calculation tool from National Semiconductor here to find out more about your thermal needs.

A lot of people here actually right things like the amplifier gets barely warm and so but this is running at probably moderate levels (or lower rail voltages).
Most chip amps like LMXXXX are "normal" class AB/B amplifiers that certainly dissipate a lot whilst running from +-40V for example driving an inefficient 4Ohm speaker at high volume levels. Watch your plastic case melt...
I already burnt my fingers on a chip doing some hardcore tests so don´t be fooled too easy. It all depends....