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Old 26th March 2012, 05:43 AM   #1
hpp3 is offline hpp3  United States
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Default Can we make heatsinking easy?

Please pardon my audacity or praise my laziness, but I'm getting quite frustrated with this endeavor, and am asking this fine community for help.
I've searched all over the internet, read all the datasheets, tried out all those excel spreadsheet thingies for calculating a heatsink, and have gotten nowhere near translating all that watchamacallitol into the end goal, which is where the rubber meets the road, where the green mile ends, where chickens counted match up with eggs hatched...

Which heat sink should I order from [electronic supplier] for my [chipamp] project?

If I ask politely, can I get a community-compiled list taken from practical experience or jaded wisdom?
Please?
Let's start with the basics, shall we?
I'm talking Mouser/RS/Allied/Maplins part numbers, clear pictures, or detailed specs (like dimensions of a recycled CPU sink, fer example), of heatsinks you've used and worked well.
What heatsink have you used for:

TDA2005
TDA2030
TDA2050
LM3886
LM3875
LM1875

Feel free to add any others, I'd greatly appreciate the info.
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Old 26th March 2012, 05:55 AM   #2
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Are you just looking for a fish,
or would you rather learn something about how to bait and present a hook?
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Old 26th March 2012, 09:41 AM   #3
hpp3 is offline hpp3  United States
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I kinda figured I'd get this response...

I laid it all out in the preamble... I've had about all the learning I can handle, including crawling this forum for way too long, looking for pragmatic heatsink advice.
The present situation is; I'm messing around with chipamps with my son and trying to figure how burly a heatsink we need for a TDA2030 powered at ±18v.
Datasheet says the thermal resistance at the case is 3 C/W, and the power dissipation is 20W when the case is 90C.
The graph and technical notes as far as I can work it out (rather blurry on all the datasheets I can find) say I need a heatsink that can do 2(?)C/W or lower to dissipate the heat from 20 watts (probably not the full power we're going to ask from it, but let's do be conservative).
It's also got a cute little table with values that do not reflect the reality of the datasheet and a picture of an ideal heatsink cross-section, which would be great if I had my own aluminum extrusion plant, but as luck would have it, I don't.

The best I could find at mouser (just for starters) is a TO-220 heatsink rated at 1C/W, but something tells me it's not gonna do the job:
206-1PABH Wakefield Heat Sinks
They have another one rated at 2.9C/W that looks like it'll do the job, but based on the numbers, I'm not sure:
657-20ABP Wakefield Heat Sinks

So... OBVIOUSLY something is over my head or just plain beyond me, I'd like to quit dinking around with calculators and spreadsheets, and just get down to business and order the !@#$%& part I need.
I don't want the next chipamp project to be stalled YET AGAIN while Dad reminds himself of why math was his most hated subject in school.
So, yeah, I guess I'm looking for a fish, BUT if you can offer me some advice that doesn't involve more theory than reality to go with it, I'm all ears; in fact, I'd appreciate that greatly.

...And a part number would be nice as well, so I can link up my eyes with my brain, if it's not too much trouble.
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Old 26th March 2012, 10:25 AM   #4
AndrewT is offline AndrewT  Scotland
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National show a graph/plot/table on their datasheet for the heatsinking requirement for their chipamps.

The only problem I have with that is that the National recommended heatsink size can allow the chip to run more than a bit too warm. I recommend that you double the rating that National give.


Each chipamp application can be different, eg. PSU supply voltage, PSU impedance, PSU smoothing, Speaker impedance, external heatsink, internal heatsink, climate conditions, (from summer to winter from North Pole to equator).
You must select the operational conditions that suit your application and choose the heatsink to suit.

We cannot and National cannot take your responsibility away from you.

This is DIYaudio. Get off your " ! " and start DIYing.

If doing it yourself is not up street, then go out and buy ready assembled.
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Last edited by AndrewT; 26th March 2012 at 10:29 AM.
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Old 26th March 2012, 10:29 AM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by hpp3 View Post
The best I could find at mouser (just for starters) is a TO-220 heatsink rated at 1C/W, but something tells me it's not gonna do the job:
206-1PABH Wakefield Heat Sinks
They have another one rated at 2.9C/W that looks like it'll do the job, but based on the numbers, I'm not sure:
657-20ABP Wakefield Heat Sinks

So... OBVIOUSLY something is over my head or just plain beyond me,
Hi,

Well you've got the basics the wrong way round for a start.
A 1.0C/W heatsink is 2.9 time more effective than a 2.9C/W.

Well it would be it it was 1.0C/W but it
clearly is very much not, that is a misprint.

Click the image to open in full size.

With two TDA3020 devices your ideally looking at 2 to 3 C/W
per device or 1 to 1.5 C/W for two devices. I'd guesstimate
the heatsink used in the illustration above is about 2.0C/W.

rgds, sreten.

In my little Bass practice amp the TDA2030 is simply mounted
onto the aluminium front panel. Hasn't died in the 15 years
I've had it, but I bought it non-working with a fried chip.
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Last edited by sreten; 26th March 2012 at 10:34 AM.
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Old 26th March 2012, 11:13 AM   #6
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Hehehe... I understand your situation. There was insufficient info in your first post, so it was hard to give any other response. It looks like you need a ~2C/W or better heatsink. That first Mouser link sure looks like a typo.
OK, so some others have responded while I was poking around Mouser's heatsink pages. Something like this may work for you, but I was looking for something more along the lines of the one in sreten's photo, with a flat side. That way, if the single heatsink proves insufficient, there's nothing stopping a person from fitting another heatsink to the front of the chipamps' tabs.

addendum: You might want to look over this short primer on choosing a heatsink. It's not terribly theoretical. "Easy heatsinking" is often just using the biggest you can find and afford.
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Last edited by sofaspud; 26th March 2012 at 11:21 AM.
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Old 26th March 2012, 12:07 PM   #7
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Quote:
Originally Posted by hpp3 View Post
Feel free to add...info.
Easy, take a reading class.

I haven't looked at a TDA sheet in 25 years, but still recall that all you have to do is eyeball the thermometer on your livingroom wall.
Then the datasheet tells you which C/W number you'll need, same same for the LM chippers.
The corresponding term is Foolproof, provided the fool can read !

Then again, i speaks abo*t a dozen lingos, of which Englandish is by far the easiest to handle.
(though yanks mess it up again by skipping letters as U)

I'm so terribly sorry, having a Mr Hyde day again.
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Old 26th March 2012, 05:01 PM   #8
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2" of this profile is about the smallest I would use (one per chip):

7.280" - HeatsinkUSA, LLC Store

You will not find much cheaper than that either.

Feel free to use one of the bigger profiles, but make sure the fin-spacing is not denser than 0.4".
Denser fin spacing requires forced ventilation (a fan).

Contrary to many of the builds seen here, the fins of the sink must be exposed to ambient air and orientated vertically.
So lots of holes below and above the sink, or better yet, the sink protruding outside of the enclosure.
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Old 26th March 2012, 05:25 PM   #9
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I've always found the http://www.rs-online.com website a good source for looking at heatsinks. They have recently become expensive but for one-offs they are convenient and reliable.

2 Deg C/W heatsinks are pretty commonplace so you can choose the size to suit your application.

Hopefully you understand that 1 Deg C/W will run cooler than 2 Deg C/W so anything less that your required heatsink will work fine.

Most Heatsinks are rated, mounted so that the fins run vertically as in post #5. As has been muted, they need a good 2.5cm above and below them to allow the air to pass across them.

If you must use a heatsink in a confined area, ie inside a case, buy a bigger heatsink and drill large holes above and beneath it to allow the air to flow.

Even the smallest amount of forced air (ie a fan) will improve the efficiency of a heatsink markedly. Fans can be noisy but a good quality fan run at 1/2 or 1/3 of its rated voltage will be pretty quiet.

Buy Heat Sinks Heatsink SK 508 100mm Fischer SK508-100SA online from RS for next day delivery.

Last edited by KatieandDad; 26th March 2012 at 05:30 PM.
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Old 26th March 2012, 06:16 PM   #10
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Quote:
Originally Posted by hpp3 View Post
a community-compiled list taken from practical experience or jaded wisdom?
Such a list will leave you just as wise as you were before. The trouble with heatsinking is that we can only calculate the worst case heat dissipation with sufficient presicion, but that is only one of many steps to determine the right heatsink. Everything else is pretty imprecise and indeed rather a question of experience than calculations.

The recommendations of other users will be as manyfold as their music taste, their amp designs, the speakers they use and the climatic conditions in which the amps operate.

You will have to mix math and your personal assessment to find the right heatsink for your amp.

One of the biggest hurdles is that heatsink sellers often do not give you all the information you need. You will find heatsinks with e.g. 1 K/W of thermal resistance, but it takes some effort to find out at what temperature and at what heat dissipation that value was determined. E.g. the Wakefield 657-20 from post #3 is offered as 2,9 K/W. The datasheet shows that it has that thermal resistance at a heat dissipation of 19 W leading to a temperature rise of 60 K versus the ambient temperature. Another seller might offer that same heatsink with 1 K/W, and the datasheet says that he can, but he might prefer not to tell you that it is only good for that at a heat dissipation of 3 W and a temperature rise of 20 K.
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