For starters : 0.45 C/in2/W makes >1 C/W for the body size of a TO-247
1 C/W is in the order of what you get for a TO-220 mica.
(for high fin density, you might enjoy this one : http://frigprim.x10.mx/articels2/parallel_plchim.html )
1 C/W is in the order of what you get for a TO-220 mica.
(for high fin density, you might enjoy this one : http://frigprim.x10.mx/articels2/parallel_plchim.html )
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jerfer - that sounds about right, bro. it's tough. I suggest you head to the market section of these forums and track down the Keratherm pads. They're super high-tech german blah blah blah but the bottom line is that once your transistor is torqued down they have a thermal resistance of 0.07 C/W (per square cm maybe? it's still exceptionally low.)
SilPad isn't That bad.
Suppose the software assumes 0.45 C/in2/W for the SilPad, it can calculate the thermal resistance of the insulator by taking the total contact cross sectional area of the power device, or just the metal surface of the mounting side.
125C junction -51C heatsink = 74C between junction and heatsink.
74C divided by 30W makes 2.47 C/W thermal resistance from junction to heatsink.
2.47 minus 0.89 is 1.58 C/W for the SilPad.
0.45 C/in2/W divided by 1.58 C/W makes ~0.3 square inches.
Pretty much corresponds to the area of the metal surface.
Suppose the software assumes 0.45 C/in2/W for the SilPad, it can calculate the thermal resistance of the insulator by taking the total contact cross sectional area of the power device, or just the metal surface of the mounting side.
125C junction -51C heatsink = 74C between junction and heatsink.
74C divided by 30W makes 2.47 C/W thermal resistance from junction to heatsink.
2.47 minus 0.89 is 1.58 C/W for the SilPad.
0.45 C/in2/W divided by 1.58 C/W makes ~0.3 square inches.
Pretty much corresponds to the area of the metal surface.
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Do you mean the heatsink's mounting plate? I'm interested in some sinks that are more efficient than the Rtheta profile I simulated. They have thicker base-plates (1/2" instead of 0.230") and higher fins (3.5" instead of 1.7"). I wanted to see how they would perform knowing that the simulation would be more conservative using the Rtheta profile.
So, do you think that with the thicker base-plate I'll get lower junction temps? If so, cool (yeah, that was a pun alright).
I thought about and simulated with the FETs placed all in a row and ended up with worse performance: junction temps were ~4 degrees higher and heatsink temp under devices was 4.5 higher. To be honest I didn't expect that since I've only ever read that the ideal placement is in a row and not stacked.
So, do you think the SilPad can do better than what R-Tools assumes?
That what I was talking about with my initial question! I had posited that the sink be mounted laying flat but it was the stack or chimney effect I was trying to describe. The nice thing about this is that you can get away with less heatsink. Although you still end up with the total height because of the chimney.
Will do. Thanks for the pointer.
--edit
I just modeled it using the Keratherm's Rth and WOW! Junction temps are down to 80 C or below. So, how can anyone build a J or anything with this much bias per FET and mount it using anything but this?
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I modeled it using only the metal surface area of the mounting side. I was trying to be as conservative as possible while remaining reasonable. Ignore my last question to you. You just answered it.
heat sinks used
Hi,
Sorry I have not been looking here for a few weeks. The heatsinks I am useing are two for each mono Aleph J-X, each of the two with a value of 0.33 degC/W, these also have one 5in. fan each attached to the each heatsink, the two heatsink fans are fed by two additional 5inch fans cooling the power supply components by having the two fans mounted inside the enclosures first & second barrier and the air is sucked by the first chaimber power supply components, these fans then blow the air through the three next air tight compartments and finally becomeing the source air for the power transistor heatsinks quietly keeping the output transistors with a tempiture of below 60degree Celcius while using a high bias.
here is the heatsink I am useing:
http://canada.newark.com/aavid-thermalloy/d180-20/heat-sink-t-slots/dp/10WX1020
Thank You For Your Interest
Ian
... again ... and again...
& for fun!
Hi,
Sorry I have not been looking here for a few weeks. The heatsinks I am useing are two for each mono Aleph J-X, each of the two with a value of 0.33 degC/W, these also have one 5in. fan each attached to the each heatsink, the two heatsink fans are fed by two additional 5inch fans cooling the power supply components by having the two fans mounted inside the enclosures first & second barrier and the air is sucked by the first chaimber power supply components, these fans then blow the air through the three next air tight compartments and finally becomeing the source air for the power transistor heatsinks quietly keeping the output transistors with a tempiture of below 60degree Celcius while using a high bias.
here is the heatsink I am useing:
http://canada.newark.com/aavid-thermalloy/d180-20/heat-sink-t-slots/dp/10WX1020
Thank You For Your Interest
Ian
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Hello,
I am kinda new here. (Going to build an AJX 100 or 80)
Maybe an heatsink shop in europe tip:
Any one tried ordering the heatsinks only in the spare part section of the shop that sells hifi-2000 cases in italy ?
modushop.biz
In a few months i am going to try to order the spare parts only.
30 Euro's looks like a great price for an 300 X 40 H 210 mm HS.
But i am afraid they won't let you buy it seperatly.
I have also a question concerning PSU designer :
Where do you guys get the Transformer source resistance value ?
I looked at datasheets of toroids but dont find it.
- Is the impedance of the secondary wire ?
- You can just calculated it via the law of Ohm ?
I.E R = 18volts/22ampere (800va 2x18v toroid)
Best regards,
Jannick
I am kinda new here. (Going to build an AJX 100 or 80)
Maybe an heatsink shop in europe tip:
Any one tried ordering the heatsinks only in the spare part section of the shop that sells hifi-2000 cases in italy ?
modushop.biz
In a few months i am going to try to order the spare parts only.
30 Euro's looks like a great price for an 300 X 40 H 210 mm HS.
But i am afraid they won't let you buy it seperatly.
I have also a question concerning PSU designer :
Where do you guys get the Transformer source resistance value ?
I looked at datasheets of toroids but dont find it.
- Is the impedance of the secondary wire ?
- You can just calculated it via the law of Ohm ?
I.E R = 18volts/22ampere (800va 2x18v toroid)
Best regards,
Jannick
speaker Xover with ballanced amplifier
Hi Everyone,
I was just thinking that since the output of a ballanced amplifier is just the same signal for positive & negative 180degrees out of phase then the xover must have the same filter components on its positive and negative speaker cables ? I was thinking of this because I am now assembleing my Aleph J-X input Line Level Crossover of 12db per octive at 100Hz, and here I must treat the positive and negitive Line Level Inputs with the same filter components, inother words two seporate xovers, one for positive Line and one for the negative Line.
Thanks For Any Help With This Issue So I Dont Blow My Speakers
Ian
Hi Everyone,
I was just thinking that since the output of a ballanced amplifier is just the same signal for positive & negative 180degrees out of phase then the xover must have the same filter components on its positive and negative speaker cables ? I was thinking of this because I am now assembleing my Aleph J-X input Line Level Crossover of 12db per octive at 100Hz, and here I must treat the positive and negitive Line Level Inputs with the same filter components, inother words two seporate xovers, one for positive Line and one for the negative Line.
Thanks For Any Help With This Issue So I Dont Blow My Speakers
Ian
You bastard.
This is doing my head in.
If the positive phase of the signal is split through the passive crossover network, but the negative phase is not, resulting in the full frequency response of the negative phase across all woofers, then ...............
I am sure it must be a non-issue, but this is giving me a headache