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Old 1st November 2010, 11:19 AM   #401
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Kühlkörper is heatsink.

(kühlung is the word for cooling)
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Old 1st November 2010, 06:51 PM   #402
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Hi jacco,
Talking of Kuhlkorpers, some have arrived. Do you have the dimensions of the power boards? I'll see if they fit. Yeah, I know I should have done that bit the other way round.
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Chris
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Old 3rd November 2010, 06:17 PM   #403
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Some progress has been made on the heatsink attachment problems. If you go to this address: Extrusion Profiles with Clip Attachments - Max Clips
you will see that clips can be retro-fitted using screws instead of using machine made countersunk attachment points. This method will allow a degree of Mosfet movement under the clip whilst fully aligning the attached pcb which I feel should be a major bonus.
The MAX07G is 12mm wide and applies 11.2lbs whilst the MAX08G is 18mm wide and applies 16.9lbs.
I'm going for it.
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Chris
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Old 4th November 2010, 10:40 AM   #404
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the screw on clips you have linked to are an almost perfect DIY solution for mounting power devices.
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Old 4th November 2010, 01:36 PM   #405
AR2 is offline AR2  United States
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Quote:
Originally Posted by Backbones View Post
Incidentally, does one need to electrically insulate the Mosfets from the metal heatsink?
Regards,
Chris
Yes you do. Mosfets's back plate is Drain (as well as middle leg). You need to provide electrical insulation and at the same time the best possible thermal conductivity. That is achieved by placing mica insulators between MOSFET and heat sink and applying thermal compound-paste on the both sides of the mica insulator. There are also Kapton pads that do not require thermal paste. You could also buy kit all together with mica, washers, bolt and nut.
Check at the bottom of the page.
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File Type: pdf 2006.pdf (69.3 KB, 90 views)
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Old 4th November 2010, 01:42 PM   #406
AndrewT is offline AndrewT  Scotland
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Kapton pads are a thin sheet of flat plastic.
They too need thermal paste on both sides.
Similarly all hard surfaced thermal conductors need thermal paste at the interfaces.
Thermal pads, that conform to the device and heatsink, do not need thermal paste. There is some literature that suggests that adding thermal paste hinders heat flow.
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Old 4th November 2010, 03:20 PM   #407
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Quote:
Originally Posted by Backbones View Post
This method will allow a degree of Mosfet movement under the clip whilst fully aligning the attached pcb which I feel should be a major bonus.
I hope those clips are very strong and keeps a firm tight pressure on the devices
remember we are approaching the limits of cooling, temperature stability, etc

or else it might be possible to adjust pressure with copper plate
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Old 4th November 2010, 04:18 PM   #408
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The manufacturer makes the point that a screw-in method directly through the hole in the semiconductor case (as this hole is up one end of the device) can cause part of the casing to ride up, away from the heatsink. The other advantage to the clip is that it rests against the plastic and shouldn't need electrically insulating, whereas a conventional screw would need an insulating collar.
I see on Mouser Electronics they have an insulator called Thermasil. Is this Kapton or Mica does anyone know. I see also the insulator kit AR2 is referring to but I can't see whether it is the same material.
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Chris
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Old 4th November 2010, 04:27 PM   #409
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Incidentally, I couldn't find anyone selling the Keystone CL-60 Thermistor in the UK but I have bought, what I think is an identical part, under the GE Sensing/Thermometrics brand called the CL-60, which is rated at 5A and 10ohms. Its part number from Farnell is 1653469.
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Chris
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Old 4th November 2010, 05:01 PM   #410
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Another bonus feature of the clips is that they allow the use of a #6 screw which is much easier for those of us who are metal working challenged to tap.

Thermalsil is a silicone rubber isolator. Good: no need for goop Other: higher thermal resistance than mica, .9C/W vs. ~.7 with appropriate grease. If you are pushing it go for mica.

I think the issue with grease causing higher thermal resistance comes if you use too much. You want just enough to fill the surface irregularities, not so much that it squeezes out all over the place when you tighten the mounting screw(s).

The GE CL-60 is what you want.
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