Most heatsink data for thermal resistance is valid for a temperature increase of 80 degrees C. A heatsink becomes less effective as the temperature differential between air and sink decreases, so you need to compensate for this if you want your estimate to be accurate.
For a 20 deg C increase, the factor is rather exactly (and conveniently) 1.5. So for this example, the increase will be 60 * 0.31 * 1.5 = 27.9. In reality it will run slightly cooler than this, as the difference here is not exactly 20 deg C. But you get the idea.
Indeed. As soon as you hit 15cm/6" in height and without forced air cooling, then you are better off making the heatsinks wider instead of taller still. Doubling the height from, say, 6 to 12" only reduces the thermal resistance by about 30%, and not 100% as one might have hoped for.
we had a long debate about heatsinks, way back here, long time ago
on charts you will notice that each individual heatsink design has its own optimal size
they are not all the same
with some it stops at 100mm, and others at 150mm, or even 250mm
each heatsink design is different
but many other factors influence its efficiency
on charts you will notice that each individual heatsink design has its own optimal size
they are not all the same
with some it stops at 100mm, and others at 150mm, or even 250mm
each heatsink design is different
but many other factors influence its efficiency
Elna Silmec Caps on the Boards
I read Nelson's post about his fondness for the Elna silk caps. I assumed he was talking about using those in the power section, but I didn't find them on Digikey in sizes above 10k. Anyway, I'm thinking about springing for the Jensen 4-pole caps in my power section (four 33,000, 40v) to replace some generic, all-purpose caps.
I have 2 questions if anyone cares to venture an answer. Does it make much sense to replace the smaller caps on the mosfet boards with the Silmec?
Has anyone heard of issues with the Jensens, regarding current? I saw a few vague posts about this, but I've also read that some of the more experienced builders are using Jensens, so I'm under the impression that there's nothing to worry about.
Thanks
I read Nelson's post about his fondness for the Elna silk caps. I assumed he was talking about using those in the power section, but I didn't find them on Digikey in sizes above 10k. Anyway, I'm thinking about springing for the Jensen 4-pole caps in my power section (four 33,000, 40v) to replace some generic, all-purpose caps.
I have 2 questions if anyone cares to venture an answer. Does it make much sense to replace the smaller caps on the mosfet boards with the Silmec?
Has anyone heard of issues with the Jensens, regarding current? I saw a few vague posts about this, but I've also read that some of the more experienced builders are using Jensens, so I'm under the impression that there's nothing to worry about.
Thanks
would be nice if there was more info from actual users with actual bias settings and "real" temp measurements for all the different heatsinks that are being used here instead of relying on manufacturers specs and guess work .
My bad, after reviewing the schematic, I just remembered that there are no electrolytics on the mosfet boards.
nice suggestion, but not realistic
each amp may be built differently
the free flow of air makes a difference
and several other factors
figure a 250-500watt highend monster
thats about the size you need
it really aint that complicated
just dont under estimate the heat
touch it, and you will know
well, I started having two pices of 400mm x 300mm
I learned here that cutting them in half would give maybe 50% better cooling
if all of it was still being used for the same design, ofcourse
now I have 4 heatsinks, instead of 2
two heatsinks per mono block
nice suggestion, but not realistic
each amp may be built differently
the free flow of air makes a difference
and several other factors
figure a 250-500watt highend monster
thats about the size you need
it really aint that complicated
just dont under estimate the heat
touch it, and you will know
well, I started having two pices of 400mm x 300mm
I learned here that cutting them in half would give maybe 50% better cooling
if all of it was still being used for the same design, ofcourse
now I have 4 heatsinks, instead of 2
two heatsinks per mono block
and they are brand model number and your temp readings ?
bought 10years ago, cant remember that long
but I would go for 2" finning, or more
I know, most are maybe 1.5", which would work too
but no less than that
finning size, very important
and equally important with smooth plane surface to mount on, very important
hey, as said, its not that complicated, not rocket science
its just as important to ensure fresh air flow
inside and outside
think air flow
the more free fresh flowing freely to the bottom, the faster the hot air leaves the heatsink
use the hot air leaving top of heatsink to draw the hot air from inside amp
its like a self reinforcing cyclone
its about directing air to where you want it to go
and the cross your fingers and hope it works
OK I have really done it now I have purchased DIY Audio F5V2.0 boards and I am looking at the boards and I see the corner where LED1 goes there is a diode symbol and pads to mount diode the BOM does not list a diode other than the LED(choose a color that your wife likes)between R35 and LED1. What the heck is it ??? I would guess a 1n4148 or similar. I just love a good mystery.
A cry for help in the dark...
Regards, El
A cry for help in the dark...
Regards, El
Heatsink performance aid
The best heatsink performance aid I have found is: Natural convection heat sink. They also have a design aid for forced air: Forced convection heat sink.
The best heatsink performance aid I have found is: Natural convection heat sink. They also have a design aid for forced air: Forced convection heat sink.
Many people like to have a convenient way of mounting a LED, so I put the footprints there for a normal LED and the resistor (R35) you need also.
But you can use any led you like and the resistor can be anything in the 10k to 50k range depending on how much light you want. You can find an LED calculator online somewhere, or use U=R*I to find the right value.
The easiest solution is obviously to no mount a LED, but don't use a 1n4148 because it is just a diode - no light.
BTW, there are two footprints for the LED depending on whether you like to use wires or mount it directly on the board.
Fin spacing is also important, as there are two distinct types of heatsinks being made. For forced air cooling, and for natural convection. Heatsinks with very closely spaced fins are sometimes found at low cost, but they are intended for forced air applications. For a given size/volume they will be much less effective than a heatsink intended for natural convection, if that is what you use.
So oddly you don't want as many fins as possible. Stay with spacings above 6mm, 1/4", or even a bit higher than that.
Edit: The spacing I am talking about is surface-to-surface, not center-to-center. Big difference in practice.
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Damn you're right.
4U 300mm -> 16 x 30 = 480cm2
3U 400mm -> 12 x 40 = 480cm2
So, I guess they have the same thermal resistance.
Good, I can keep it and finally start building the amp. Thx a lot everyone!