Re: which way does the fan blow?


Steve Sawicki
 

Good Evening Deacon Dave,
Excellent write up on the subject of heat and silicone design parameters'.
Spent some time in similar pursuits but in SeaSystems.
If I was assured as Adam suggest that Icom did their thermal budgets using Mil Spec parameters, which where developed using real field data and not the typical "lab" environment then I have no problems operating my mobile 7K in my sometimes 120 deg Explorer (its Hot in South Florida now) but since Icom only list minimal information I have installed a small 12V fan on the back heat sinks using plastic anchor sleeves, its not Mil Spec bur Helps tremendously.
Ran a 706MKII before and it was cooler then the 7K in the same space.
A bit of prevention is worth way more then a multi week trip to the west coast. Hi hi
Best Regards.
Steve
AB2ET/4

--- In ic7000@yahoogroups.com, "Deacon Dave" <w1mce@...> wrote:

I learned it in a Military Design Handbook, DH-1 I think, and the various Military Reliability Specifications. I don't know of any open literature on the subject. I've been away from design for too many years ...


----- Original Message -----
From: Renaissance Man
To: ic7000@yahoogroups.com
Sent: Monday, July 20, 2009 7:42 PM
Subject: [IC-7000] Re:which way does the fan blow?


Dave,

Thanks for your response.

It's not that I don't trust the designers. I was just curious. I'm pretty sure that Icom has this all figured out. I do have a college degree in electrical engineering, but my knowledge of heat transfer and thermodynamics is weak, since this isn't my specialty. Am trying to learn more about heat dissipation since this is becoming a major issue as electronics gets more complicated.

Any books you can recommend on the topic?

Thanks and 73,
Mike

--- In ic7000@yahoogroups.com, "Deacon Dave" <w1mce@> wrote:
>
> Do I gather that you do NOT trust the designers?
>
> Physically small radios that dissipate 35 to 50 watts into a closed space make a locally warm environment. That's normal. Put an operating 50 watt lightbulb inside a shoe box, close the cover and come back in an hour ... the cover is quite warm.
>
> Solid state devices all have thermal derating factors, many based on dissipation deratings at 200C [that's 392F] junction temperature.
>
> The designers worry about temperature rise profiles based upon the thermal resistances of the components: Junction to Case, Case to Heat sink, Heat Sink to Ambient, all added together for a thermal heat rise profile.
>
> There is little effective difference in junction temperature for a case at 120F and 75F when compared to a junction temperature of 392F maximum.
>
> Trust the designers! They have been doing just fine for years.
>
> Keep the airways and vents clear of obstruction and remove accumulated dust occasionally. Make sure the internal cooling subsystem operates properly [AKA does the fan come on?].
>
> Dave, W1MCE
> Manager Strategic [as in missiles] Product Design, Electronic, Textron Defense System, retired.
> Program Chief Engineer, LGM-118A/RS-RV [MX Missile RS/RV] retired
>
>
>
> [Non-text portions of this message have been removed]
>






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