Welcome to a technical discussion of slot car controllers. Most of the following tips are specifically for Professor Motor electronic slot racing controllers, but many would also generally apply to a conventional resistor type controller or any other technology.
Professor Motor "Plus" & "Silver" Series controllers use electronic semiconductors in place of resistive elements that are used in the more conventional controllers that have been produced since the 1960's. These electronic semiconductor devices have some really amazing properties that make them ideal for application in a device to control power to model racing cars. The most valuable of these properties is that these semiconductors have an almost constant voltage drop of around 600 millivolts (6/10 of a volt) independent of the amount of current going through the device. This results in a very wide range of control possible for a large number of different classes of cars and performance levels of motors for a single Professor Motor controller. On the other hand, conventional resistor controllers are highly sensitive to variation in motor performance whereas cars with very high performance motors generally need greatly reduced resistance in the controller and cars with very mild motors requiring much more resistance in the controller. This is evident in the tremendous range of available resistor values ranging from 0.4 Ohms to 90 Ohms. In effect, resistor controllers simply divide the available voltage between the voltage drop in the controller and the voltage drop across the motor. As a result, it is generally necessary to change resistors when changing classes of motors.
The semiconductor type design we use in effect subtracts from the available voltage the number of devices in the circuit times the 600 millivolts. For example, if the the controller is only slightly open, 10 of the available semiconductors might be in the circuit (of the 16 total that the controller carries), in this case 10x0.6 or 6 volts would be used in the semiconductors, with the remaining 8 volts (assuming a 14 volt supply) would be supplied to the car.
The semiconductors also are polarity sensitive. They conduct electricity in one direction, but block it in the other. This feature has some advantages and also some disadvantages. The advantage can come from a natural resistance to miswiring since the semiconductors will block the flow of electricity if proper polarity is not applied. The disadvantage of this polarity sensitivity that the controller can not immediately be used with negative polarity track wiring can be easily overcome by the addition of a polarity switch, now available for all Professor Motor controllers.
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