| Grasshopper |
Greetings One and all
I'am a complete newbie to DIY electronic, thus the Grasshopper. I'am taking a stab at building a 25 watt SON and wondering if any one has a cheap source for heatsinks in the eastern Canada area or further afield if need be. I know it will require massive amounts of HS.
Homebrewed designs are most welcome. |
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| Grasshopper |
Thanks for the site. Similar to the idea I had in mind, although, I believe I will need three to four times the amount of sq. inches shown to meet the HS requirements for a 25 watt SON. Now to aquire to raw material.
Cheers, Gustavo
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| cp642 |
| You might want to isolate the MOSFETSs heatsinks with the power resistors's heatsinks as you can run the resistors closer to its limits. |
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| diy student |
Check out the thread titled heatsinks just a short scroll down from your post. I posted a link there for some pretty big sinks you can buy surplus.
Rob |
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| Grasshopper |
I planned to mount the resistors and mosfet on seperate heatsinks.
Cheers, Gustavo |
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| Grasshopper |
I checked out the site with heatsinks. I'll need at least 10 of that type, at $35 US per unit, way too rich for my blood. Scrapyard scrounging for the next few weekends.
Gustavo |
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| jduncan |
at least 10?
What in hell are you building if you don't mind me asking?
And do you realise how BIG 10 of those is? |
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| jduncan |
sorry, just read your first post again....but damn, TEN??
You might want to do those calculations again....I only need 2 of those at $35 a piece for my Aleph 4 and that's with quite a bit of room to spare....so 10 sounds OBSCENE...its not THAT inefficient is it? |
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| cp642 |
jduncan,
you must be missing out the big picture, it's a 25W SOZ....or should i say an amplifier from hell...:) |
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| jduncan |
its TEN 17" lengths of heatsink (thats 170") that have a thermal resistance of roughly 0.8 degrees C/W/3" ...so assuming you're not stupid and spread out the devices evenly thats absolutely ridiculous....
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| GRollins |
It's not an amplifier...it's a space heater that makes music. That's part of why I've got the SOZ w/current sources thread going. Dreadfully inefficient.
Good thing that winter's coming on--at least here in the Northern hemisphere. (Just ask me if I love having a pair of Alephs and a pair of tube amps to help warm up my listening room.)
Grey |
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| cp642 |
| You might want to give it a try....assuming that you're ready for the big surpise....;) |
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| jduncan |
alright i'll accept this...it just shocked me initially...i knew it was inefficient, but wow....my aleph 4's dissipate almost 600W and as i said, 2 of these heatsinks is plenty.....so you're saying for 10, you're dissipating roughly 3000W? 25W out, 3000W dissipated?
i think that defines horribly inefficient....
;) |
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| kasra |
Jduncan:
Are 2 of those really enough for a stereo aleph 4?
What temps do you get on your machine?
//kasra |
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| jduncan |
you have 12 devices per 17" length right?
that means you have roughly 2 devices for each 3 inch length....
that's 48W...the Rjc is 0.83, Rcs is 0.2 and the Rsa for each 3 inch length is 0.8. So 48W * (0.83 + 0.2 + 0.8) = about 88 degrees difference between ambient and junction temperature....thats perfectly ok! It's actually a bit better than this as the 48W per 3" length aren't centered at one particular point and are spread pretty much evenly over the 3 inches....
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| rtirion |
jduncan
How do you get Rcs (R case to sink) at 0.2C/W?
When you need to electrically isolate the FET from the sink reaching 0.2C/W is quite a challenge. Readely available materials such as mica with silicon grease or silicon pads will not come close. BeO, Kapton are very hard to come by.
In practice I can get 0.5 to 0.6C/W with mica and silicon grease. In your example this would mean very hot sinks and probaly a short lifespan for the amplifier, or am I missing something?
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| kasra |
| 2 of those sound very little to me, i have planed to build monoblocks and at least 2 for each channel, if its going to be those. |
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| Grasshopper |
Hello all
I know that 10 of those units appear to be serious overkill on the heatsinking. But discussions with people more knowledgeable than myself, has lead me to believe that having too much HS is never a problem when it comes to a 25 watt SOZ.
HS presently available amounts to approximately 6650sq.inches, I would much rather have more than less.
I understand that 500sq.inches are barely adequate for each power resistor, and the mosfets require about 3000sq.inches. This sounds like a hell of a lot of HS to me, but I have to defer to those with more knowledge and experience.
Comments?
Gustavo
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| jduncan |
0.2 is the figure quoted for SilPad 2000's on the other heatsink thread here in this forum....
GrassHopper: one thing you have to remember is that, unless you can spread the point of heat out (by using many mosfets spread over the area, increasing area has diminishing returns....if you have say only 2 devices on each of these 10 heatsinks....you might as well just use for instance 5 heatsinks and put four devices on each because you're going to get essentially the same performance....heat doesn't SPREAD well through heatsinks.... |
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| Grasshopper |
Brendon
You appear to live in a DIYer's paradise. I have 20 HS that look almost identical to the black ones at the top of the page, but they cost $5 each.
Gustavo |
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| woody |
Usually you see heatsinks used with the fins oriented in
an upright position. With the 17" heatsink discussed earlier
it sure would be easier to use it on it"s side I know this will degrade the thermal preformance but how much?
Thanks |
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| cp642 |
| A beautiful piece of heatsink......grab it up fast...indeed a good buy! |
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| jduncan |
Woody:
too much....cut them in half....and then mount them with fins vertical.... |
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| arnach |
Um..10 is overkill. I have a 50w/ch SOZ, which has about as much heatsink area as 10. They are costly though, make your own, and use Wakefield bond. |
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| cp642 |
| Bonded fins are more suitable for forced cooling as their fins proximity are much closer.Also if you should decide to use these consider placing them in a suitable enclosure. They're fragile! your bonded fins might end up as 'folded fin' :) |
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| arnach |
I used an inner wall of 1/4" aluminium, with 1/8" "dado"s cut every 1/2 of an inch down the 30 inch length. The fins were 3.5 in by 12 in. tall, then there were at the top and bottom of the the fins on the outside wall preforated 1/4" aluminimum pieces of 2" height also 1/8" "dadoed", thus having 4" of the 12" height as preforated, and the remaining 8" out to free air. It is quite strong and much of the chassis is cut from 1/2" alum plate so it is also quite heavy. |
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| Grasshopper |
Brendon
Wow! That is some heatsink.
Gustavo |
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| Super_BQ |
Hello Gustavo,
Glad to hear you like my heatsink collection. I plan to bring most of them back to Canada later next year as I would like to be build another amp there.
How's your SoZ project going? Weather here has been **** which means delays on my speaker project. |
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| cp642 |
There's some heatsinks at ApexJr which might be of interest... black anodized extrusion profile with dimensions
5 1/2" long, 4 5/8" deep and 4 1/2" tall ( info from Steve ) I believe he's got more of these stuff...  |
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