Cheapest and easiest way to slow down a motor

[sciguy125]

Originally Posted by sanddrag

In Al's drawing of the simple pot and transistor setup, how do I know which way to oreint the transistor so the pns go to the right places. I know where the middle one goes, but how do I know which way the others go, or does it not matter? Does that trapezoidal shape represent the shape of the actual transistor? Does the arrow signify something?

I've attached a labeled transistor symbol.

If you've got the 2N3055 that Al suggested, then hold it such that the pins are facing you, then rotate it so that the pins are closer to the left side (see P.4 of the linked datasheet). The lower pin is the base, the upper pin is the emitter, the case is the collector.

If you have the TIP3055 that I mentioned to you, hold it such that you can read the writing on its face and have the pins pointing down. From left to right: base, collector, emitter. The tab is also connected to the collector.

There's also an issue that someone, maybe Al, can resolve. I noticed that the gain with Ic = 4A is only 20-70. That would require a base current of 200-57mA to get up to the 4A. With 12V, your pot would have up to 2.4W going through it. That much power seems a little disconcerning to me. The readily available transistors with higher gains can't handle enough current. Any ideas?