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Heat Sinking and Cooling
I have found a lot of blank heat sink material at the scrap yards. Another good place to find them used and already machined for pass transistors, is at your favorite local electronics surplus store.
The cost of buying them new is not cost effective to the people that are trying to build a power supply on a budget. But if just the fun of building and tinkering is your objective, then it might be worth considering.
It is always good practice to try and mount the heat sink to the cabinet so that the ambient air flow helps in the cooling process. Sometimes it is not practical. If you don't have good luck finding a nice heat sink, then you can make due with what you have found.
One can mount a fan, if need be for additional cooling, on the heat sink. You can take the power from the power supply to run it. Old computer power supplies usually have a 12 volt fan that sill works, in them. Doing the cooling this way forces a load on the power supply all the time, so it might be a good idea to watch the current or amp rating on the fans that you get. Try to keep it to the minimum current draw.
There are several things to keep in mind, when looking for a good heat sink. Of course the ideal heat sinks are the ones that you can salvage out of a parts bin power supply. Try to find them with the base material being fairly thick. The fins need to be thin and tall or long.
Another good place to look, might be at you local electronics repair stores. I have been to a few that have junk power supplies in the back room. These are like gold mines to the author. Sometimes, I guess, that it was not cost effective for the shop to repair these broken jewels and the customer tells them to keep the junk.
A lot of times those that may be doing the repair service at the shop may not be in the know about how easy that it is to repair power supplies. There just is not that much to a power supply to go wrong. I have seen a few that were not salvageable because of a lightning hit. Once in a great while you will find one that the transformer has melted down. These are usually due to someone installing a large fuse in the place where a small value was required.
These heat sinks are made out of extruded aluminum, they are worth a bit in scrap value, so as I said before, it is a good place to look for them. The bigger they are the better the cooling. And the more that they are worth in scrap value.
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