Thermal copper pours for radial electrolytic capacitors?

[treez]

Hello,
Is it correct to state that at least 50% of the heat that escapes from a radial electrolytic capacitor escapes by conducting down the metal legs and going into the PCB copper pour around the place where the legs are soldered into the board?

Or does most of the heat that escapes from a radial electrolytic capacitor escape from the case surface and into the surrounding air that way?

 

[chuckey]

Unless the leads are exceptionally thick, I reckon that most of the heat is dissipated by the case to the air. I have seen that you are troubled with the capacitor temperature, how about cutting a large hole in the PCB to get through air flow on the capacitor. If you cut its sleeve off and sprayed it matt black you would be able to dissipate heat more effectively. Have you considered putting a current limiting resistor in series with the cap, it will increase the ripple but its for a pump not a hifi amp.
Years ago I used this technique on a tropicalised transmitter power supply. When the RF was keyed the voltage across the capacitor dropped by 150 V with a current peak of 10s of amps. A 10 ohm resistor in series with capacitor reduced this to 5 amps and did not seem to affect the ripple.
Frank
Frank

 

[treez]

but surely its well known that axial and radial components are significantly cooled by heat conducting down their leads and into the PCB copper?
Are you saying its not worth putting thermal copper pours around the lead holes at all?

What about snap-in capacitors, such as the B43547 series from Epcos...surely you agree that most heat escapes out of these capacitors by conducting through the snap-in terminals and on into the PCB thermal copper pour?

B43547 snap-in capacitor datsheet:
**broken link removed**

Certainly cornell dubilier electrolytic capacitors are said to conduct heat out more effectively via the bottom rather than the sides, as the following says....

http://maelabs.ucsd.edu/mae_es/partsnlinks/PopDataShts/capacitorguide.rtf

Cornell Dubilier computergrade capacitors conduct heat
from the core to the bottom much more effectively than out
the sides. You can take advantage of this heat path by
mounting the capacitors directly to metal chassis. In many
case sizes this can double the permitted ripple current for
the same temperature rise.