Aavid Thermalloy Possible Group Buy

[Coulomb]

Originally posted by argofanatic



Buy a 10" and cut it in two.

ok be nice...

Khundude there is not enough interest in a 5" non machined profle to make it worthwhile to offfer one.

Even the 5" machined is slow to show any interest, even after a few members asked for it. I have considered moving it up to a 6" as I have been working on a configuration that would work for an F5 stereo.

Anthony

[Coulomb]

Originally posted by argofanatic



Buy a 10" and cut it in two.

ok be nice...

Khundude there is not enough interest in a 5" non machined profle to make it worthwhile to offfer one.

Even the 5" machined is slow to show any interest, even after a few members asked for it. I have considered moving it up to a 6" as I have been working on a configuration that would work for an F5 stereo.

Anthony

[Coulomb]

OK some good news for F5 Builders.

As you all know there has been quite some discussion about using these Heat Sinks for an F5 build. The issue is not so much the Tsink-avg but the Tjunction. I spent some time optimizing the parameters by trying different components and this is what I have come up with.

Increase from 5" to 6" in length, hopefully at no additional charge.

Switch from Sil Pad 400 to Sill Pad 2000, much higher W/M-K

Use IRFP250N which has a RèJC of 0.7, an IRFP240PbF has an RèJC of 0.83, I was using 1.1 from an old data sheet from an IRFP140N.

The new IRFP250N has an Input Capacitance of 2190Pf a little higher than the 1400Pf of an IRFP240 device, but as it is not in parallel with other HEXFETs it should be fine.

IRFP250

Sil Pad 2000

I have attached a report that indicates the vital thermal parameters for a 6" Profile with these changes.

The result is a very usable profile for an F5, (1 per transistor). 4 sections to make a Stereo chassis using the small Chassis kit if you are so inclined.

I hope this helps members still on the fence to sign up for our little GB. The option still remains to use the 10" with these changes as well.

Regards

Anthony

[Coulomb]

Here is the report for the 10" length with the new parameters.

Anthony

[samoloko]

how much for a stereo F5 - only heatsink
and heatsink with chassis

[AndrewT]

Hi Coulomb,
your reports show Ts=Tc. This can't be right for 32W passing across the interface.

[Coulomb]

Originally posted by AndrewT
Hi Coulomb,
your reports show Ts=Tc. This can't be right for 32W passing across the interface.

Yes curious that isn't it. I assume you are talking about Tsink-max & Tcase, I have asked the Engineering department at R-Theta and I have as yet to get a reply. I have tried hundreds of simulations changing all known variables and although they do react to the changes the react exactly the same.

I had assumed that the report was trying to indicate that the hottest measurable spot on the heatsink was the case of the device.

To segway to a somewhat related topic, when looking at the Thermal Imedance and Resistivity of an insulator be aware that they use 50lbf/in squared clamping pressure to express thier typical values. Sometimes wrongly expressed in Psi, which is a measure of pressure, this amount of force is fine on a tabbed device like a TO-220. 50lbf/in squared clamping pressure is considered to be the average for most devices and offers lower more attractive values, most specs for these insulators offer a chart of relative clamping force applied to the device and the resultant values that can be expected from the insulator performance wise.

This is very important as the maximum clamping pressure allowable on a TO-247 device is only 10lbf/in squared, thus all ratings on insulators must be derated.

Anthony

[Coulomb]

Originally posted by samoloko
how much for a stereo F5 - only heatsink
and heatsink with chassis

Pricing is on the wiki. You can buy Heatsinks only or Heatsinks and a Chassis kit with or without the options.

GB wiki

Regards

Anthony

[Coulomb]

Originally posted by AndrewT
Hi Coulomb,
your reports show Ts=Tc. This can't be right for 32W passing across the interface.

I just got this email from R-Theta.

Hello Anthony,

There is a display bug that doesn’t show the proper calculation for T-case. It is on our to-do list to fix. The Tjunction temperature is properly calculated and does include the proper Tcase temperature.

R-Theta Thermal Solutions

[AndrewT]

Originally posted by Coulomb
looking at the Thermal Imedance and Resistivity of an insulator be aware that they use 50lbf/in squared clamping pressure to express thier typical values. Sometimes wrongly expressed in Psi, which is a measure of pressure, this amount of force is fine on a tabbed device like a TO-220. 50lbf/in squared clamping pressure is considered to be the average for most devices and offers lower more attractive values, most specs for these insulators offer a chart of relative clamping force applied to the device and the resultant values that can be expected from the insulator performance wise.

This is very important as the maximum clamping pressure allowable on a TO-247 device is only 10lbf/in squared, thus all ratings on insulators must be derated.

there is nothing wrong with using clamping pressure for the interface loading, similarly PSI is a valid method of quoting that clamping pressure.

Don't confuse Force with Pressure. They are different.