KBB,
Would a 1.5 inch piece of this be enough
heatsink for a single DO-5 case power diode at 50 watts max or so?
This is without a fan.
The alternator is only a 65 amp type.

The diode has an operating temp range of -65 to +190 C

Aluminum Rectangle Tube 6063 T52
Height 0.75"
Width 1.5"
Wall 0.125"

W/o calculating anything, I think your heat sink looks too small for safety. The fan will help a lot, but probably not enough.

On the other hand, it only sees very intermittant use and you may be able to get away with it even if you exceed the manf. specs.

Personally, I'd go with more heat sink and keep the fan. Increase the thickness will allow more heat to flow better (don't forget the heat sink grease!) and fins will increase the are. Shear bulk will for a limited time too.

Delete the fan and move to Canada, where it's freezing cold.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Sharp-lookin' work! (Or should I say it looks...cool?)

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks. It's a passive heatsink from an early socket 7 pentium that clipped on. The blank strip for the clip wasn't wide enough, so I removed one row of fins with a mini-hacksaw.
All of the ring terminals are thick copper 8 guage.
I trimmed the ring off one and drilled a small hole in the shank, creating a mini-ring terminal with an 8 ga barrel than connects to the small diode terminal.

The diode's leads are 8 ga SOLID copper. One function is to position the heatsink. The shorter one is bare (reminds tech that the heatsink is electrically hot) and sits in a groove cut for it in the heatsink. This prevents heatsink rotation.
The lower solid copper lead loops along the floor of the pastic box. It presses lightly against the floor, and so acts as a dampener.

The leads from the alt , battery and bulkhead connector all stack on the brass terminals that the diode and fusible links are connected to.

There are some open terminals where a wire can be added later to power headlight relays.

This is meant to be installed in a ventilated plastic box on the convenient ledge near the voltage regulator.

There's room for a sideways fan, but I am hoping to keep the design simple by avoiding a fan...

There was no fan mounted on this CPU heatsink, but there was a nearby case fan or power supply fan moving the air.

There's a lot more surface area than my original heatsink of rectangular aluminum tubing, but is that enough to allow it to keep the diode from overheating without a fan?

Lookin' good! Let us know if it works out for you.

Here is the same shunt, ready for testing
http://slantsix.org/forum/viewtopic.php ... highlight=

"Experimental Active Shunt using one Si diode"