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Old 1st April 2003, 06:49 PM   #1
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Default Heatsink effieciency

what is the effieciency of a heatsink measured in? is it the degrees C that the temperature rises per watt of power?

how do i work out the effieciency of a heatsink? i will post a pic of some heatsinks i found in a skip.
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Old 1st April 2003, 07:30 PM   #2
Mad_K is offline Mad_K  Norway
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1. Yes C/W

2. You can apply a known amount of Watts on it and measure the temp rise Then you get the C/W number
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Old 1st April 2003, 07:50 PM   #3
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how could i do that? with a big resistor? like a 20 watt one, and put volts through it?
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Old 2nd April 2003, 02:43 AM   #4
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Default Thermal resistance

You will preferably need a metal encased resistor that can be efficiently clamped to the heat sink. Then you will need a voltage souce or just stepped down ac from the mains. You should pick some convenient current , say 1 Amp. Then with a 12 volt step down transformer , the resistor would be 12/1 = 12 ohms. You can pick anything close to that. This would give you (in this case)12x1=12watts. Measure the temperature rise after say 30 minutes and then divide by the wattage. Note that you must measure voltage and current in your setup.
Note that the heat sink must be oriented the way you intend to use it.
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Old 2nd April 2003, 03:20 AM   #5
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Here's a pic of my test setup. I used 4 50W 150ohm resistors in parallel. Measure the resistance and voltage and compute wattage. I bought a thermometer and packed it in between fins with a paper towel tohold in contact with aluminum. Also use heat sink grease to insure the heat is transmitted to the sink and try to test in the same temp/watt range you hope to use the sink in.
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