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Old 12th April 2012, 03:33 AM   #1
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Default How Hot Is My F5?

Apparently not that hot. In previous listening sessions when my F5 got up to peak temperature I had trouble holding my hand on the heatsink for the so called 5 second rule. This caused me some concern so I borrowed a friends infrared temperature gun similar to the one picture here. Amazon.com: HDE Temperature Gun Infrared Thermometer w/ Laser Sight: Home Improvement. At peak operating temperature my heatsinks only measured 46C. I have the top cover off so I tried to measure the mosfets and I got 50C. While I'm happy with these temps I'm wondering if that makes me a bit of a wimp?

To add some technical data to this post my heatsinks seen in the picture below are 13" x 6" x 3" high. The base flange is 1/2" thick

Regards,
Dan

Click the image to open in full size.

Last edited by dantwomey; 12th April 2012 at 11:15 AM.
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Old 12th April 2012, 06:20 AM   #2
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If your thermometer came with a thermocouple, try measuring the temp again using the thermocouple.

Problem with the laser units is reflection. They should be calibrated for the material being measured. Most often they are not set to measure (reflective) metals. Contact testing will give the best results.
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Old 12th April 2012, 11:14 AM   #3
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It's not that critical. I'm building SIT monoblocks incase the F5 goes POOF!!!!!!!!

Regards,
Dan
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Old 12th April 2012, 11:28 AM   #4
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The heatsinks are very inefficient when mounted horizontally.

I would cut them in half and mount them vertically.
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Old 12th April 2012, 11:40 AM   #5
Skorpio is offline Skorpio  Denmark
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Quote:
Originally Posted by KatieandDad View Post
The heatsinks are very inefficient when mounted horizontally.

I would cut them in half and mount them vertically.
Do you know how much?

I have not notice a big temperature decrease when mounting fins horisontally, but on the other hand, I was not pushing to the limits.

How much space is needed below then for airflow to work?

Looking at Pass Firstwatt chassis, they are in fact not positioned correctly?
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Old 12th April 2012, 11:50 AM   #6
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It depends on the heatsink, but as a general rule horizontal performance will be less than 50% of its vertical performance.

You must have at least 20-25mm of space below the vertical fins to allow air to flow freely.

As a test, run it stood on its end.
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Old 12th April 2012, 12:09 PM   #7
Skorpio is offline Skorpio  Denmark
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Quote:
Originally Posted by KatieandDad View Post
It depends on the heatsink, but as a general rule horizontal performance will be less than 50% of its vertical performance.

You must have at least 20-25mm of space below the vertical fins to allow air to flow freely.

As a test, run it stood on its end.
If that holds, the temperature on the sink on the amp in picture could drop to 33 degrees if it is placed on the front plate with som 20mm spacers?

Could be a nice and quick test
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Old 12th April 2012, 12:13 PM   #8
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It will certainly run cooler but maybe not quite that cool.

As I said try running it face down sitting on a couple of blocks.

The heatsink needs air to flow across it to work efficiently. That doesn't happen with it mounted horizontally.

Horizontally it is relying more on radiated heat transfer.

In the same vein a small fan can improve the heatsink efficiency by almost 100%.

Last edited by KatieandDad; 12th April 2012 at 12:17 PM.
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Old 12th April 2012, 01:09 PM   #9
AndrewT is offline AndrewT  Scotland
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Dan,
you are either a wimp or your temperature measurement is wrong.

If you feel it burning in under 5seconds, then I suspect you are over 50C

Tc is likely to be about 10 to 15C degrees above the sink interface temperature, the hottest part that you cannot get into.
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Old 12th April 2012, 01:11 PM   #10
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Another reason I'm not that concerned is that other posts seem to indicate that that 50C is an acceptable operating temperature with 60 to 70C being the danger zone.

Regards,
Dan
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