The heatsinks in the 4U-300 dissipante are close to identical to a Fischer SK56.
A SK56 in 150mm does 0.34C/W, see e.g. : FISCHER ELEKTRONIK|SK 56/ 150 SA|HEAT SINK, EXTRUDED | Farnell United Kingdom
The 3U-400 looks like a Fischer SK479, 120mm has a close to identical C/W value, see e.g. : http://www.hifituning24.de/downloads/sk93.pdf
For the same type heatsink profile there's indeed a close to linear relationship between C/W and L*W*D (aka volume) within a comparable heatsink length range.
(beats me where HiFi2000 get's their numbers)
A SK56 in 150mm does 0.34C/W, see e.g. : FISCHER ELEKTRONIK|SK 56/ 150 SA|HEAT SINK, EXTRUDED | Farnell United Kingdom
The 3U-400 looks like a Fischer SK479, 120mm has a close to identical C/W value, see e.g. : http://www.hifituning24.de/downloads/sk93.pdf
For the same type heatsink profile there's indeed a close to linear relationship between C/W and L*W*D (aka volume) within a comparable heatsink length range.
(beats me where HiFi2000 get's their numbers)
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That c/W you must multiply with correction factor, witch you can find in
http://www.aavidthermalloy.com/technical/correct.shtml
because i think these Fischer Rth is for temperature rise of 75
http://www.aavidthermalloy.com/technical/correct.shtml
because i think these Fischer Rth is for temperature rise of 75
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I do have one F5 with such heatsinks. I lower bias to 1A during summer when outside temperature may reach 38°C.
I don't think so, but you can enlighten me.
Btw, for those interested in the effect of a change of rib size, added/reduced mass, at different heatsink lengths, a "cool" one : www.farnell.com/datasheets/22486.pdf
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Post 2482858 in this thread.
Edit: Found a web reference. Check the section 'Thermal Performance and Temperature Rise Above Ambient'.
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I'm familiar with Conrad heatsinks, for quite a while, longer than this forum exists.
The question was about Fischer heatsinks and their reference temperature rise above ambient (hint 1 : read Fischer literature)
The question was about Fischer heatsinks and their reference temperature rise above ambient (hint 1 : read Fischer literature)
I am building an F5 cviller standard F5 board( 2 o/p trannies irf's), I am planning to use my F1 p/s as long as VA is good all is good n'est pa???
Regards,El
I promise I'll try not to be to intrusive to other peoples threads...
Regards,El
I promise I'll try not to be to intrusive to other peoples threads...
I hope you have two, one for each channel
if it gets too hot you can always back off the bias, just a bit
and it might help with a base or something, lifting it from the floor
I build two alephs with Fischer heat sinks, and if you don’t take this correction factors in account, they run hot. Method for temperature is touch for 5 sec, Indeed they are not painted but far as I know that can reduce temperature about max 10%
for 20years or more I have heard that claim
but I have never seen any proof
though it ought to be easy
I do not doubt that black cools better, under certain circumstances
but I would like to see the proof that it works on a heatsink
Yes I have two, and its working the temp is 40-45 deg c .59 volts across R11 and R12.
Couldn't find any hard numbers from Fischer, which is why I used the values for Conrad, and tried to do a cross reference as far as possible. Please link any info you may have.
I did some rough calculations, where I compared heatsink from the Conrad and Fischer catalogs. I used the big, German catalog from Fischer, and had to compensate a bit for different volumes and number of fins. Used a standard height of 100mm (4") throughout:
MF10-100: 0.83 K/W (80 deg C)
SK92-100: 0.75 K/W (Compensation 40/30 for lower fin height)
MF20-100: 0.47 K/W (80 deg C)
SK47-100: 0.52 K/W (Compensation 40/30 for lower fin height)
MF30-100: 0.32 K/W (80 deg C)
SK568-100: 0.36 (Compensation (40/50) * (30/23), fewer fins, but higher)
MF35-100: 0.28 K/W (80 deg C)
SK523-100: 0.5 K/W (? deg C)
So the first three examples match pretty well for a temperature rise of 80 degrees Centigrade. None of the Fisher heatsinks are anywhere near having a thermal resistance 50% higher than their Conrad counterpart. Yet on the last example the thermal resistance shoots up on the Fischer sink, suggesting the data is now for a different rise in temperature.
With data like this and no word to the contrary I take the safe route, and assume both sets of data is for a temperature increase of 80 C. Would love to learn differently, the Fischer data seems odd...
- Frank.
IMHO, even precise calculations won'nt tell you completely how the heatsink will behave as it depends also where you place it.
The air flow can be way different following environnement/placement conditions.
The air flow can be way different following environnement/placement conditions.
I couldn't agree more, but we have to start *somewhere*. 🙂
The original datasheet values would hopefully give us an absolute minimum size, if a builder feel this point is very important. More is always better here, of course. 😉
Compare Fischer SK435 and Aavid thermalloy http://www.aavidthermalloy.com/cgi-bin/euro_exdisp.pl?Pnum=0S215&LengthUnits=mm&ExLength=150.00&TReff=0.331