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hot heatsinks

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brianpublic2(at)starband.
Guest

Posted: Thu Oct 26, 2006 5:59 am Post subject: hot heatsinks

I have a couple schottky diodes with heatsinks.  Due to the diode package design, the base is the cathode.  This in turn means that the heatsink is electrically “hot”.  For all my other exposed +12v connections, I have covered them either with a rubber boot or multiple layers of liquid insulation.  I am concerned about these heatsinks, and the +12v passing through them, being exposed.  It would defeat the purpose of the heatsink if I cover them with liquid insulation.   I was thinking perhaps I could build a perforated Plexiglas or fiberglass box to put over them.  What do you electrical gurus think about this situation with exposed heatsinks that are +12v?  

brian  

http://brian76.mystarband.net/RV-7Ahome.htm  

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nuckollsr(at)cox.net
Guest

Posted: Thu Oct 26, 2006 7:27 am Post subject: hot heatsinks

At 09:56 AM 10/26/2006 -0400, you wrote:



 	  Quote: 	
		  I have a couple schottky diodes with heatsinks.  Due to the diode package 

design, the base is the cathode.  This in turn means that the heatsink is 

electrically "hot".  For all my other exposed +12v connections, I have 

covered them either with a rubber boot or multiple layers of liquid 

insulation.  I am concerned about these heatsinks, and the +12v passing 

through them, being exposed.  It would defeat the purpose of the heatsink 

if I cover them with liquid insulation.   I was thinking perhaps I could 

build a perforated Plexiglas or fiberglass box to put over them.  What do 

you electrical gurus think about this situation with exposed heatsinks 

that are +12v?



brian


	




  The electronics industry has been insulating electrically "hot"

  cases of components from their mounting surfaces for decades. See:



http://dkc3.digikey.com/PDF/T063/0873.pdf



   . . . where you will find a variety of semiconductor insulator

   products used to electrically isolate but thermally heat sink

   devices to their mounting surfaces.



   Radio Shack has a few such products too that you may

   find useful and/or adaptable to your needs.



   See also:



http://www.kpsec.freeuk.com/components/heatsink.htm



http://sound.westhost.com/heatsinks.htm#8

http://sound.westhost.com/heatsinks.htm#9



http://www.bcae1.com/heatsink.htm





   Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

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craig(at)craigandjean.com
Guest

Posted: Thu Oct 26, 2006 10:53 am Post subject: hot heatsinks

Better to electrically (but not thermally) isolate the  diodes from the heat sink. This is common practice. Search the archives for  "mica". Here is a quote from a message I sent back in  January:

  

 "Electrical isolation is done with thin plates placed  between the chip and the heat sink. In the old days the plate was mica. Heat  sink "grease" is used to ensure a good thermal bond between all the layers.  There are newer insulators that don't require the grease. If you are using metal  nuts and screws to bolt the chip down then you need special non-conducting  shoulder washers to keep the nuts and screws from forming electrical contact  between the chip's case and the heat sink."

  

 -- Craig

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hooverra(at)verizon.net
Guest

Posted: Thu Oct 26, 2006 3:42 pm Post subject: hot heatsinks

Brian,

    One solution is to electrically isolate the diode from the heatsink. 

Aavid Thermolloy, Bergquist and others all make insulation for this 

purpose. Try DigiKey.

http://dkc3.digikey.com/PDF/T063/0872.pdf



Brian Meyette wrote:

 	  Quote: 	
		  

 I have a couple schottky diodes with heatsinks.  Due to the diode 

 package design, the base is the cathode.  This in turn means that the 

 heatsink is electrically “hot”.  For all my other exposed +12v 

 connections, I have covered them either with a rubber boot or multiple 

 layers of liquid insulation.  I am concerned about these heatsinks, 

 and the +12v passing through them, being exposed.  It would defeat the 

 purpose of the heatsink if I cover them with liquid insulation.   I 

 was thinking perhaps I could build a perforated Plexiglas or 

 fiberglass box to put over them.  What do you electrical gurus think 

 about this situation with exposed heatsinks that are +12v?



 brian



 http://brian76.mystarband.net/RV-7Ahome.htm



  



 *

 *

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tshank(at)core.com
Guest

Posted: Sat Oct 28, 2006 6:29 am Post subject: hot heatsinks

Brian,

 I had the same concern, attached is a picture of my solution. I would be concerned if you are covering the heat sink with a rubber boot or insulation because that would greatly reduce its effectiveness.  The picture is of a plastic cover that protects both the heat sink and the connections from accidental contact with other conductors.

 

 Tim Shankland

 

 Brian Meyette wrote:  	  Quote: 	
		                          <![endif]-->     0   DocumentEmail      <![endif]-->             

I have a couple schottky diodes with heatsinks.  Due to the diode package design, the base is the cathode.  This in turn means that the heatsink is electrically “hot”.  For all my other exposed +12v connections, I have covered them either with a rubber boot or multiple layers of liquid insulation.  I am concerned about these heatsinks, and the +12v passing through them, being exposed.    It would defeat the purpose of the heatsink if I cover them with liquid insulation.   I was thinking perhaps I could build a perforated Plexiglas or fiberglass box to put over them.  What do you electrical gurus think about this situation with exposed heatsinks that are +12v?   

brian   

http://brian76.mystarband.net/RV-7Ahome.htm   

    

    	  Quote: 	
		  



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brianpublic2(at)starband.
Guest

Posted: Mon Oct 30, 2006 11:50 am Post subject: hot heatsinks

Thanks, Tim.  In my case, I decided to do whatever was needed to electrically insulate the heatsink from the case, so the heatsink is not hot.  

brian  

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