Conparing heatsinks for TO220

[cupoftea]

Hi ,
We have one of these heatsinks on each of the fets of our 130W two tran forward...(no fans)

581002B02500G

Pardon our interruption...

...However, the PCB is vertically mounted, and so the heatsink is now horizontal.
The fins dont even point upwards.
They point to the side.
We cant turn the fet or anything, as there's no room for that.

How much less degC/W do you think we will suffer?

 

[wwfeldman]

ask the factory

it's a natural convection heatsink
when mounted properly, air naturally flows between the fins and you get the "degC/W"
or thermal resistance, as specified by manufacturer.

since they are not mounted as expected by the manufacturer, they will NOT have the specified "degC/W",
as you know

asking for speculation on what will happen is pointless - ask the factory,
(the ebay listing shows the manufacturer is Aavid - they should be able to make an informed opinion)
or, take a chance, turn it on, and see how hot it gets

 

[crutschow]

Won't surprise me if the sink has double the temperature rise in that position.

 

[cupoftea]

Hi,
We are just comparing the heatsinks

534202B02853G (thin but wide with much area)
&
581002B02500G (thick but narrow with seemingly less surface area)

Heatsink catalog:

https://www.mouser.com/pdfdocs/Aavid-Board-Level-Heatsinks-Catalog.pdf

It is for use with Cooling each TO220 FET of a 130W offline 2 transistor forward converter.
There is no fan.
The enclosure is though, metal, and has vent holes.

From the graphs provided, it appears that when there is forced airflow, then the 581002B02500G is best.
But when there is no forced airflow, the 534202B02853G is better.
Would you agree?

To make things more complicated though, the heatsinks will obviously be mouned vertically, but the
PCB is then mounted vertically.

 

[crutschow]

If you can't get data for that mounting position from the manufacturer, then you will have to do a test with the selected heatsink in the position on the PCB.