Improving Heatsinks for an Amplifier?

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I've been having trouble sourcing decent heatsinks for my projects. I have a few thoughts though, but I'm unsure how this might impact anything. First, if anyone knows of good US sources for heatsinks large enough for DIY amplifiers, at decent enough prices, and without minimum orders, that would be great. I would prefer a heatsink large enough for a 2u and also for a 3U case size, I.E. 4 and 5.5 inches, or so.

Now, I understand that copper is a considerably better conductor of heat than Aluminum, but is heavy and expensive. My question is, would using Copper between my current undersized heatsink and the chipes themselves improve my thermal dissipation much. I know it wouldn't have much exposed surface area, just the thickness of the metal really, but I can buy strips of stock pretty cheap.

Another issue is that I need spacers between the amp and the heatsink, so that they can fit in the case right, they only need to be about 1/16 or 1/8" thick, but I used 1/4" aluminum instead. Now would replacing these with copper improve anything, I can do that with copper scraps off ebay for less than 10 dollars.

What other ways, besides really long fins, can a heatsink be improved, or rather, cooling be improved in a rather small case, such as a 2U case. I know forced air is a great option, but noise is an issue. I've thought about using a silent fan, like they make for PC's and carefully mounting it, but I would like to avoid that. What about a heat pipe running through a copper plate to even out the heat distribution?

Ok final thought on this, My enclosure is from DIY Enclosures, and thus uses 4 heatsinks for 3 amplifier modules. I didn't have a way to connect the heatsinks together, other than via the 14 guage, or whatever it is, side panel. Would using a copper plate as mentioned earlier improve things by giving the amps one larger heatsink, plus a much thicker base made of copper. My assumption is that, other than maybe during an action movie, its unlikely the amps will be loaded heavily all at the same time, and so sharing the heatsinks will improve performance.

Now before I get yelled at for using under sized heatsinks, These are adequate for the amplifier's running with a lowish Bias current, I just want to try increasing the bias, and I'm afraid it will be too hot for the current heatsink. I'm also building a larger amplifier, and again, I'm limited in my heatsink sources, so anything I can do to improve things would be great.
 
Thats exactly what I was looking at for the quiet fan idea. They are as low as 16db's, and as much as I wish I had a noise floor below that, I don't, so I'm pretty sure it will be masked by other noises in my house. I mean my next door neighbor is at least 18 decibels, so I'm sure she will mask it.

Still wouldn't mind a good source for heatsinks if anyone has them, and info on the copper. I know Conrad is a good source, but shipping from Australia is a bit high.
 
Hmmm.. So there' s a Conrad in Australia- who'd a thunk it?

IMO, what's important is junction temperature. I'd far rather have an excellent path to a small heatsink, than a bad path to a huge heat sink. If the heat sink base is thin, a copper heat spreader will improve the situation, moving heat out to the perimeter of the heatsink. I'm not up on the latest pads, but find the best interface, be it mica and grease, Sil-Pads, or some other solution. Best is grease alone, if you have electrically isolated devices. Be sure the mounting surface of the heatsink is perfectly flat, preferably machined flat. Remember that when you really want to know what's happening, you drill a tiny hole through the heat sink, to the bottom of the active device, and attach a thermocouple there, rather than worry only about heatsink temperature.

******
A salesman came into my office and said, "Heatsinks". I threw him out because any fool knows that heat rises.
 
Thermaflo is expensive, and they were unresponsive to my emails about purchasing products. I almost feel like I would have been better off asking for some samples rather than trying to purchase any from them. I think they are not a company prepared to cater to the Diyer, but if anyone has been successful, let me know your experience.

Conrad, as for your comments, I completely understand that. First let me say that I think the 1/4" pieces of aluminum I used to spaces the amps away from the heatsinks increased the thickness of the base drastically. The base is pretty think anyway though, that isn't a major concern of mine. The base of the actual heat sink is 3/8" and the fins are about 1" long. The heatsink is about 3" tall and 6" long, and I have 4 of them. One of those is really not enough for the amp modules if they are working hard, say into a 4 ohm load, or if they are biased more heavily. The copper "heatspreader" was meant to combine the two heatsinks into one larger 12" heatsink, which seems like a better option. Especially given that right now, one heatsink is doing nothing but cooling the case, which doesn't get hot.

As for Conrad in Australia, I honestly thought you were teasing me, and that Conrad was not in Australia, but maybe New Zealand, or even the US, and I was mistaken in saying that. I had to go recheck before I realized you were basing that on your name, not a mistake I made in Location. To make that long rant short, apparently I'm a bit slow this morning.

Another thing I should mention is that I recently purchased another set of amp modules from Mr. Holton at Aussieamps capable of over 500 watts rms, and I wanted to have a setup ready for them to test in. I will be running them at a rail voltage that probably will only produce 200 watts rms into an 8ohm load, but that still is enough that it might be too much for my amp modules.
 
Though about it, but I'm kinda getting sick of the amps looking like I built them. If I had better tools at my disposal I could probably use those just fine, but without the ability do all this, it ends up coming out kinda shotty.

I hate the costs involved, but I've been very close to just buying a complete enclosure from someone like Hi-Fi 2000 or ATI and being done with it. Problem to me is shipping, the shipping prices are so high I end up spending too much on the projects. Especially on the big enclosures I want. I really like the enclosure at the bottom of this link, and it would be more than enough for my project, but will end up costing me in excess of 400 dollars, plus the company hasn't been responding to my emails.
HiFi 2000 large enclosure
 
I just reread an old article on heatsinks and I'm starting to Think Conrads advice was more prolific for me than I originally thought. I mean, maybe I should make sure that I have minimized thermal resistance as much as possible. I bet a different mounting scheme, a replacement of those spacers with copper, some fine polishing work, etc. might go a long way toward fixing some issues.
 
MikeHunt79 said:
With those 120mm fans, you can reduce the speed of them if you find the noise too much...


If you use a mains rated fan you can use a series capacitor to slow the fan down and make it completely noiseless whilst still maintaining a reasonable amount of airflow. It takes a bit of trial and error to get the right value capacitor but the results are worth it. With a fan you also get the benefit of cooling all the components inside the case and not just the heatsinks.

Note you need to use a mains rated capacitor with a bleed resistor across it (100k 1W)

Cheers
Q
 
quasi said:



If you use a mains rated fan you can use a series capacitor to slow the fan down and make it completely noiseless whilst still maintaining a reasonable amount of airflow. It takes a bit of trial and error to get the right value capacitor but the results are worth it. With a fan you also get the benefit of cooling all the components inside the case and not just the heatsinks.

Note you need to use a mains rated capacitor with a bleed resistor across it (100k 1W)

Cheers
Q

I've never tried mains powered fans, but use those cheapy 120mm fans for cooling all sorts of things. They are a little easier to control as you can just use a resistor in series... I find they are inaudible below 800rpm or so. :)
 
Thanks that one from Allied might actually work. I would prefer other options, but if I can't find something else, that might work. The biggest problem with those is that they aren't anodized, so thats an extra expense, and the one from Ebay is a little cheaper, with a similar rating, and a thicker base. Thanks again for the feedback guys.

Anyone else have thoughts on the copper idea, is it a silly waste of money. I mean, a chunk of similar aluminum is a whole lot cheaper, but if the copper is that much better, we still aren't talking a lot of money here.
 
Being the diy forum, I'll toss out a diy idea. It's pretty easy to get aluminum extrusions at the local home/hardware outlet. It's also pretty easy to get aluminum or copper plate from various metal vendors. IMO, there's a good advantage with copper if you can afford it. You'll also need a jar of fine alumina powder from a lab supply company. It's inert, so there shouldn't be any problem buying or shipping it. Now, mix up a batch of your favorite epoxy, and load it up with alumina powder. Glue some pieces of u-channel aluminum extrusion to the plate, clamping to keep the glue joint thin. Voila! Homemade diy heatsinks. This method gives you a lot of freedom on fin placement and size.

FYI, there's a local company that manufactures heatsinks in an unusual manner. They have an aluminum plate with narrow slots. They just cut aluminum fins and press fit them in the slots. This allows them to get a much higher fin count than can be extruded. No, they won't sell small quantities, but if you had a small milling machine and a saw blade. Hmmm... wonder if the technique could be done with a carbide blade on a table saw. I've never cut aluminum on the table saw, but many say it can be done.

Finally, here's a truly crazy diy idea, and you can use it for air or water cooling. Get a copper plate and clean it. For water cooling, set up a pattern of small diameter copper refrigeration tubing, and just solder it to the surface. For air cooling, use a set of parallel copper tubes of say 1/2" diameter, and maybe use a couple few layers. Solder the whole mess together, one layer at a time. You'll need a big torch head, but propane will likely still be sufficient. I think the small tube idea can also be used for a heat pipe system. They use a wick of some sort to transfer the liquid to the hot side, where it vaporizes and heads back to the cool side. I believe methanol is used. Google fancy microprocessor coolers.

IMO, any project worth it's name has to involve oxy-acetylene, burns, sheet metal cuts, and the use of a large hammer:smash:
 
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