The temperature rise also depends on the geometry of the heat sink (which would be factored into the temperature rise spec on the heat sink) and the air flow around the heat sink, which is what makes the temperature rise difficult to calculate. Often there is only natural convection, where the only air flow is created by the heat produced by the board. The amount of air flow here, and thus the temperature rise, would be highly dependent on how well the air can circulate around the heat sink. If there are other tall components near the heat sink, these will restrict air flow, so there will be a larger temperature rise. Likewise, if there is an enclosure that limits air flow, there would be a higher temperature rise. If there is forced convective cooling, as would be produced by a cooling fan, the heat will be transferred away more quickly, so the temperature rise will be less. The heat transfer rate is also somewhat dependent on the temperature and humidity of the air, as these affect the thermal and convective properties of the air somewhat. Calculating the heat rise it these cases is difficult. The geometry is likely complex enough that numerical methods (i.e. computer simulation) would be needed to calculate the temperature rise. It is usually easier, faster, and probably more accurate to measure the actual temperature rise on an operating board in its normal environment. Even if numerical methods were used to calculate the temperature rise, the results should be verified by testing an actual board. Heat sink manufacturers that provide specs for thermal characteristics of heat sinks must be making some assumptions about the environment (type of air flow) to provide a spec on heat dissipation. They likely have this information somewhere on their spec sheets. Dave Roach -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair K. Hogg Sent: Monday, March 21, 2005 11:11 AM To: [log in to unmask] Subject: Re: [TN] Temperature conversion Generally a wattage output is referenced into a temperature rise, e.g. x Watts will result in y degrees C rise over ambient. Heat sinks are usually specified in terms of W/deg C as to how well they will cool. The temperature rise in deg C per W will depend upon the material, e.g., 18 gauge wire will have more or a rise than 12 gauge (and of course 12 ga will have lower resistance per foot). But that's about the limit of my knowledge on the subject. Blair Hogg QA Manager, GAI-Tronics Corp. >>> [log in to unmask] 03/21/05 11:05AM >>> That's what I was thinking. I like the hp to speed analogy. Jason Gregory Manufacturing Engineer Innova Electronics (281)653-5593 (281)653-5594 fax (281)212-0844 cell [log in to unmask] -----Original Message----- From: Blomberg, Rainer (FL51) [mailto:[log in to unmask]] Sent: Monday, March 21, 2005 9:58 AM To: TechNet E-Mail Forum; Jason Gregory Subject: RE: [TN] Temperature conversion I don't think so. It would be like converting Horsepower to speed > Rainer G. Blomberg > Honeywell -Space Systems Clearwater > Staff Production Engineer (727) 539-5534 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jason Gregory Sent: Monday, March 21, 2005 10:55 AM To: [log in to unmask] Subject: [TN] Temperature conversion Is there any way to effectively convert a wattage output to a known temperature? 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