3
\$\begingroup\$

Looking around here for a heat-sink for a TO-18 (2n2222) form I don't quite see one around that will serve. The thought in my mind is whether I may cut the top off the Coke Can, and use it as a sink; punch a hole the size of the TO-18, cut tabs along the perimeter of the cap, and stick the transistor in it.

Will the aluminum from a coke/beer can serve as a heat sink?

| improve this question | |
\$\endgroup\$
  • 2
    \$\begingroup\$ Not much heat capacity in the thin metal of a can. However, several layers of it, tightly bolted at the heat sink tab, could help you get by for trying it out. Also, the thin metal could then be shaped with a pair of pliers, for a good set of heat radiating fins! \$\endgroup\$ – Anindo Ghosh Jun 27 '13 at 18:45
  • 2
    \$\begingroup\$ Sure it will work to a degree. But there is a real concern with how thin it is - heat conductivity is a function of cross section. Also the coatings - some sort of plastic on the inside, and paint on the outside. The coatings could also limit the effectiveness of stacking multiple layers. That said, the top of a can is likely a bit thicker than the sides, and isn't usually painted so it does seem like the best part to use. Using the outside to contact the part would seem best, so the inside coating will be on the larger dissipating area rather than on the smaller junction area. \$\endgroup\$ – Chris Stratton Jun 27 '13 at 19:01
  • 1
    \$\begingroup\$ How about a copper (pre-1982) penny? Drill a hole in a couple pennies that allows a tight fit with the TO-18 case, and slide them on with a bit of heatsink paste, leaving an air-gap between them? \$\endgroup\$ – Johnny Jun 27 '13 at 19:13
  • \$\begingroup\$ @Johnny: Very good call! Only it won't work in my geography; no copper coins here in atleast the last 40 years. But it makes me wonder about a copper gasket, or even the brass jet into a carburetter - if one can be found \$\endgroup\$ – Everyone Jun 27 '13 at 19:20
  • \$\begingroup\$ @Johnny a couple of pennies fanned out might work, but you are trading physical space for the effort. Tangent did a comparison between a paper clip, a penny (in different formations), and actual heatsink, and four pennies tangentsoft.net/elec/diy-hs.html \$\endgroup\$ – Passerby Jun 27 '13 at 20:39
1
\$\begingroup\$

As long as you can get good thermal and mechanical contact I don't see why it can't work. I think this version used a bit of heat shrink to hold it nice and tight.

enter image description here

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ Erm. Just corrected the form from TO-92 to TO-18 \$\endgroup\$ – Everyone Jun 27 '13 at 18:50
  • \$\begingroup\$ same answer applies - good thermal and mechanical contact and of course a good radiating area \$\endgroup\$ – JIm Dearden Jun 27 '13 at 18:53
1
\$\begingroup\$

Any metal will be better than nothing at all, and depending on size and shape will be more/less effective. There is no reason a coke can lid correctly shaped won't serve as a heatsink. Make sure you connect the surfaces (heatsink/transistor) together well, you can use a dab of thermal compound if you have some.

Forced air cooling is also worth considering if you have a few components you need to keep cool.

For reference/info, TO-18 heatsinks do exist (although they are not so common):

Example - see this page for dimensions and thermal details.

enter image description here

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ They are available; just a wee bit prohibitively expensive for an amateur being priced at ~INR 94.00/each. in.element14.com/jsp/search/… \$\endgroup\$ – Everyone Jun 27 '13 at 19:06
  • 3
    \$\begingroup\$ It is cheaper to buy a transistor in TO-220 package and not use a heatsink than to use one of these heatsinks. Rth j-c of 2N2222 in TO-18 is 146K/W! \$\endgroup\$ – Szymon Bęczkowski Jun 27 '13 at 20:58
  • \$\begingroup\$ Yes, good point, I agree - the link was just for info purposes and a reference design. If at all possible I would avoid the TO-18 package and use TO-220 as you mention, or another more common package - the thermal properties are better and heatsinks are readily available cheaply if needed. \$\endgroup\$ – Oli Glaser Jun 27 '13 at 22:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.