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Old 27th January 2014, 11:01 AM   #1
Kev06 is offline Kev06  England
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Default De-rating heatsink when enclosed?

I notice that a lot (most?) commercial hi-fi amps have their heatsinks inside the case, with grills in the case's top and bottom to permit air flow over them. I'm considering this for various reasons, but it seems likely to me that there would be some reduction in performance of the heatsink if its not stuck completely out in the open, and I've no idea at all about how how to estimate that.

Does anyone know if it actually makes much difference (assuming grills with good open areas), or if there any rules of thumb or rough ways to estimate the effect?

Thanks
kev
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Old 27th January 2014, 11:09 AM   #2
AndrewT is offline AndrewT  Scotland
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add a bit to your Ta.
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Old 27th January 2014, 11:58 AM   #3
Kev06 is offline Kev06  England
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Ah yes; thanks for the suggestion.

I could measure the temperature inside my current amplifier to get a feel for what the temperature in there may be, then allow for ambient increase in summer. If i use larger/more open grills than my current amp, consider the extra power of my new build, and add an additional margin for safety, then it should increase my confidence in the estimate.

Cheers
kev
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Old 27th January 2014, 12:40 PM   #4
Boscoe is offline Boscoe  United Kingdom
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They put them in side the case because it's cheaper to put them inside and have a smaller one because otherwise they get too hot outside and void regulations on how hot the product can get.
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Old 27th January 2014, 01:07 PM   #5
Kev06 is offline Kev06  England
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Thats a good point, I'd not actually thought about it from the perspective of anything but the mosfet's happiness.

I suppose I don't have to meet the regulations and I'm deeply unlikely to go touching the heatsink or take legal action against myself if i do.. but there's always the possibility of pets or children touching it or trying to lick it or something.

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kev
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Old 27th January 2014, 01:36 PM   #6
AndrewT is offline AndrewT  Scotland
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The cat is not going to do it again !

And children should never be left beside your powered up gear without adequate supervision.

I find it very convenient to be able to "finger check" amplifier temperatures. One begins to recognise "normal temps" for each different type.
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Last edited by AndrewT; 27th January 2014 at 02:00 PM.
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Old 27th January 2014, 01:55 PM   #7
CBS240 is offline CBS240  United States
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The cat is not going to do it again !
"Ya know Clark, if that cat had nine lives, she just spent 'em all" --cousin Eddy

Family Christmas Vacation..........

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Old 27th January 2014, 02:03 PM   #8
Kev06 is offline Kev06  England
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True, Andrew. I'm likely to be using large enough heat sinks to keep things reasonably cool in any case; keeping the fets comfortable is more of a priority for me than minimising the size of the sink, as i've got some pretty decent ones waiting to be used for something.

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kev
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Old 27th January 2014, 04:03 PM   #9
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"The cat is not going to do it again!"

An image popped into my head and I almost fell out of my chair laughing

Reminds me of the time my brothers dog chewed on the phone cord and got 50V in his chops.
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