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Old 19th December 2007, 01:42 AM   #1
pjpoes is offline pjpoes  United States
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Question Improving Heatsinks for an Amplifier?

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.
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Old 19th December 2007, 02:16 AM   #2
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You might want to check out 120mm computer case fans. If you get the low speed/silent type, they won't be audible.

http://www.xoxide.com/xoxide-120mm-silent-fan.html

just for an example.


Dave
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Old 19th December 2007, 02:28 AM   #3
pjpoes is offline pjpoes  United States
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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.
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Old 19th December 2007, 03:37 AM   #4
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With those 120mm fans, you can reduce the speed of them if you find the noise too much...
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Old 19th December 2007, 04:13 AM   #5
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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.
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Old 19th December 2007, 04:47 AM   #6
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Default Heat

Try these guys...they make hundreds of different sizes & styles from pea size to telephone book size & bigger. www.thermaflo.com
_________________________________________Rick..... .......
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Old 19th December 2007, 03:45 PM   #7
pjpoes is offline pjpoes  United States
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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.
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Old 19th December 2007, 03:53 PM   #8
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try Russ Boss on E:bay -- seller ID barredboss.

I've bought heatsinks from him -- they are top notch.

JJ
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Old 19th December 2007, 03:56 PM   #9
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http://cgi.ebay.com/HEATSINK-ALUMINU...QQcmdZViewItem


oops, 3 R's in his user name Barrredboss.

JJ
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Old 19th December 2007, 05:57 PM   #10
Minion is offline Minion  Canada
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I also had problems sourceing Large heatsinks for a Good price but recently I have been Finding old Car amps which are usually housed in Large Finned aluminum enclosures and have been cutting the enclosures down into Reasonable sized heatsinks...

just a thought
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