I'm building Anthonys sym-amp but after reading a thread about different method of mechanical design(dont remember wich..) I want to change....
Is there any problem to mount all IRFP240 on one copper plate and all IRFP9240 on another, so that they are electricly connected on each plate, and then isolate the two plates and mount them to the heatsink? Im hopin this will better the thermal resistance. I really dont see any problems with this, or is there (oscillating??)? What do you think?
Thanx!
Richard
Is there any problem to mount all IRFP240 on one copper plate and all IRFP9240 on another, so that they are electricly connected on each plate, and then isolate the two plates and mount them to the heatsink? Im hopin this will better the thermal resistance. I really dont see any problems with this, or is there (oscillating??)? What do you think?
Thanx!
Richard
That should be ok but I wouldnt count on getting lower Rth because you've then got an extra thermal joint.
Richard, I guess your cooling is not a big problem. Adding copper won't add much besides the coolness factor. It's nothing wrong with mounting transistors on isolated heatsinks but the basic rule is to keep it compact. I would recommend to have grounded heatsinks and isolated MOSFET's.
As Audiofreak says, try to have as few thermal junctions as possible. The best thing is actually to mount the transistors directly on the heatsink (if it's possible).
As Audiofreak says, try to have as few thermal junctions as possible. The best thing is actually to mount the transistors directly on the heatsink (if it's possible).
richeros said:
Gonna do the same thing as you describe for the Holton
Av800 I want to prototype. Gonna use 3/16" thick copper
plate and mount each mosfet to the copper with no
insulation, just white goo. Then isolate the copper plate
(mica?) to the aluminum heatsink. If you search the archives,
there is a good thread about this. 1/2 the people seemed
to like the idea, the other 1/2 didn't. heheh
In my case, my copper plate is 3/16" thick x 1.5" width
and the length is about 10".. The heatsink plate is 1/4" thick
aluminum.
Doesn't hurt to experiment.
Also, I wonder if the copper plate will be a good +V and -V
for the transistors since the tab = drain if I'm not mistaken?
I might try this stuff instead of generic white thermal compound..
http://www.arcticsilver.com/as3.htm
Anyone use this before ?
i've used it on my CPUs HSF. if you want info on it you may wanna go to any computer hardware forum, overclockers are always trying to get the extra degree of cooling.
as i recall, hardocp.com did a review:
http://www.hardocp.com/article.html?art=MTQ0
however it only goes up to AS2, not AS3.
as i recall, hardocp.com did a review:
http://www.hardocp.com/article.html?art=MTQ0
however it only goes up to AS2, not AS3.
Flat chat. or, On the level.
I have done this twice and my experience is - too get good results the copper and heatsink surfaces really have to be FLAT. The extruded aluminium heatsink I used had a bit of a bow in it; no big deal for small contact areas but when you span a much greater width with your copper plate there is a far greater chance of only marginal contact.
There are much better heat conducting materials than mica available nowadays from the likes of Bergquist, Chomerics and the like. The tradeoff in different grades of materials offered is voltage rating vs thermal resistance. You don't need much of a voltage rating so this should work out well.
I have done this twice and my experience is - too get good results the copper and heatsink surfaces really have to be FLAT. The extruded aluminium heatsink I used had a bit of a bow in it; no big deal for small contact areas but when you span a much greater width with your copper plate there is a far greater chance of only marginal contact.
There are much better heat conducting materials than mica available nowadays from the likes of Bergquist, Chomerics and the like. The tradeoff in different grades of materials offered is voltage rating vs thermal resistance. You don't need much of a voltage rating so this should work out well.
tip
just a tip i tryed arcticsilver on eletronics if your heat zinc is grounded it will short......
conducts electricity..... allso shorts out athlon's
just a tip i tryed arcticsilver on eletronics if your heat zinc is grounded it will short......
conducts electricity..... allso shorts out athlon's
hmm, that's odd. my athlon is very much fine with the AS3. i need to put the kt266/333 cooling mod back on. i had cpu temps 2 degrees BELOW ambient at idle! full load was the same. i've used AS3 for a TBird and a Palimino and had no ill effects.
athlon
ya works good on athlon's if thin my customers put it on thick
doo
a fet hmm u take your chances
ya works good on athlon's if thin my customers put it on thick
doo
a fet hmm u take your chances
What I ment was like thylantyr wrote.... Mount the fets without isolation (with goo) to the copper and then mount the copper plate to a grounded heatsink with isolation. (Think I gonna use some silicone based isolation.. 30mmx200mm sheet) I will then get a bigger surface between the copper plate (witch spreads the heat very good over the plate) and the heatsink, and therefor a lower thermal resistanse....!?
Let me know how it goes thylantyr!
Richard
Let me know how it goes thylantyr!
Richard
There are much better heat conducting materials than mica available nowadays from the likes of Bergquist, Chomerics and the like.
Thanks for the tip. I will be checking this stuff out.....
Thanks for the tip. I will be checking this stuff out.....
Yea, Arctic Silver is no good for amps. I applied some on my p3a yesterday - bad idea, becomes conductive as you tighten the screw. Fortunally i tested the thing with a multimeter first - pheew. AS is also a pain in the *** to get rid of, i wasted a bottle of acetone (150ml) to clean it.
Hi richeros,
Good to see you've started your sym amp. Mine's, uh, mostly working.
I simply used some silicone-fiberglass insulator pads, like the one Peter Daniel was selling, to isolate the Mosfets electrically. See http://users.erols.com/jdprice1/module.jpg... shorting the cases together might be unsafe.
Arctic Silver is a good thermal compound but it is not recommended that you use it for electrical isolation, because it has some capacitance and is not really a perfect dielectric.
Heat dissipation isn't too big of a problem with this amplifier, it's not Class A or anything and dissipates 50-60 watts per channel at standard bias. My big heatsinks get only slightly warm and the Mosfets themselves are moderately hot (45C?). Don't worry about using fancy techniques to lower the thermal resistance... but copper plates sure would look cool.
BTW, you can use the Arctic Silver epoxy (not regular Arctic Silver) to mount Q10 solidly on a Mosfet. That's the way I'd do if I had to do this again.
Good to see you've started your sym amp. Mine's, uh, mostly working.
I simply used some silicone-fiberglass insulator pads, like the one Peter Daniel was selling, to isolate the Mosfets electrically. See http://users.erols.com/jdprice1/module.jpg... shorting the cases together might be unsafe.
Arctic Silver is a good thermal compound but it is not recommended that you use it for electrical isolation, because it has some capacitance and is not really a perfect dielectric.
Heat dissipation isn't too big of a problem with this amplifier, it's not Class A or anything and dissipates 50-60 watts per channel at standard bias. My big heatsinks get only slightly warm and the Mosfets themselves are moderately hot (45C?). Don't worry about using fancy techniques to lower the thermal resistance... but copper plates sure would look cool.
BTW, you can use the Arctic Silver epoxy (not regular Arctic Silver) to mount Q10 solidly on a Mosfet. That's the way I'd do if I had to do this again.
I simply used some silicone-fiberglass insulator pads, like the one Peter Daniel was selling, to isolate the Mosfets electrically. See http://users.erols.com/jdprice1/module.jpg... shorting the cases together might be unsafe.
Why would it be unsafe to shorten the cases together( IRFP9240 seperated from the IRFP240...)?...
Why would it be unsafe to shorten the cases together( IRFP9240 seperated from the IRFP240...)?...
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