Hi...I have a 12v. computer power supply which I want to use as a power source for a DC controller. Can anybody out there come up with the "rating" for the potentiometer I need to use to get good current response over a wide range of the pot "travel"..? I have one, but I get response only over 1/2 of its travel.
Any suggestions will be most welcome.
It is almost impossible to size a pot properly due to the wide variety of motors and currents drawn in present and past locomotives. For example (I'll use HO locomotives for illustration purposes), an Athearn with open frame motor might draw 0.6 amps, while a new locomotive with a good can motor might draw 0.2 amps.
If you use a 60 ohm pot set at half its range (30 ohms), the Athearn with open frame motor will not receive enough voltage/current to start moving - 0.6 x 30 = 18 volt drop at the pot. At the same pot setting, the can motor will be running at 6 volts - 0.2 x 30 = 6 volts drop at the pot.
Unless your motors draw pretty much the same current in situations encountered on your layout, a simple pot is a poor controller. As Kevin said, you need a voltage controller. This is usually done with a few transistors. Google DC throttles or similar terms for circuits.
"Pulse power" is often used to overcome motor cogging and assist in smoother slow speed running. Some circuits will use the AC ripple or 1/2 wave input from the rectifier to generate the pulses. Your computer power supply carefully eliminates all the ripple so that if you want pulse power, you will have to use a circuit with its own pulse generator/oscillator.
hope this helps