Heatsink math gurus look here.

[Frazzled]

Hello everyone...

Has anyone ever used one of these:



I purchased 4 last year and modified one so that I could mount an AV800 (Anthony Holton) on each side.



These heatsinks are made by Wakefield Eng. Inc and are MOD. FCA-800, they measure 12 inches (30.5cm) long and all 4 sections are electrically isolated from each other. My aluminum inserts basically split the heatsink into 2 halves electrically.

I was wondering if anyone knew any more information on these, specifically their thermal resistance with a 80cfm fan attached. Any info would be more than I have, here is the actual extrusion from wakefield, but I just don't know how to figure out if what i have done will meet the requirements of the AV800, Anthony specifies .2degrees/watt or .5 degrees/watt with fan cooling. Thanks!

[jleaman]

I have some of that stuff but my stuff is in storage. : O) Good stuff too.

[Magura]

The easy solution would be to load it and measure the temperature rise VS. power dissipation.

Magura

[roddyama]

You can find the A-40 article by Nelson Pass at his DIY site. He uses the same heatsinks for his A-40 in the article. He also talks a little about class A heat and heatsinks.

[Jocko Homo]

I found an equation for forced convection thermal resistance:

272.16/(A*h)

Where A is the surface area of the extrusion in sq in (get that from the data sheet.....)

And h is the heat transfer coefficient.

Since you have a 12" long extrusion, and probably not a hurricane blowing across it..........figure h is around 1. That will get you close. The value of h rises to 2 at a flow velocity of 400 ft/min.

Jocko

[Frazzled]

Thanks JOCKO!!!


OK I did the math and it looks like I am at about .4 per side with just the heat sinks without taking into account the surface area of my aluminum inserts so I think I should be OK.

Thanks

[boholm]

http://www.fischerelektronik.de/down...ownload_fr.htm is more - i think - what you are searching for, especially the the D Gruppe.zip under "D".

Using one myself albeit only with a length of 2 units (71 mm.). My fan is spinning only enough to make it start - and then a tad for safety. Two 2N5884/2N5886 on each arm and each running at 0.5 A. /10 V. Works perfectly and without noise from the fan.

[Frazzled]

SWEET!

Thanks!

Originally posted by boholm
http://www.fischerelektronik.de/down...ownload_fr.htm is more - i think - what you are searching for, especially the the D Gruppe.zip under "D".

Using one myself albeit only with a length of 2 units (71 mm.). My fan is spinning only enough to make it start - and then a tad for safety. Two 2N5884/2N5886 on each arm and each running at 0.5 A. /10 V. Works perfectly and without noise from the fan.

[Frazzled]

Has anyone ever mounted a fan at either end of a tunnel and have the second fan come on at a preset temperature.

Does having the first fan running while the second is unpowered reduce the efficiency of the first by a lot?

I was just considering having the first fan on all the time or say come on at 50°C and the second at 65°C and shutdown at 80°C.

Any thoughts?
Thanks again!

[Magura]

Ive seen it done, the second fan will spin freely, following the airflow with little resistance when the first fan is running.

Magura