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This motor controller controls the speed and direction of an attached motor with a 5,000 ohm linear potentiometer. The potentiometer is connected to the PH (pot high), PW (pot wiper) and PL (pot low) terminals on the circuit board. To limit the top speed of the motor, an optional 25K speed limiting pot may be placed in series with the center lead of the control pot which normally goes to the PW terminal on the PCB (see schematic elsewhere on this site). The board is energized by applying +24 volts to the "SW" terminal on the PCB. The high current B+ and B- leads can be permanently left connected without an on-off switch. The PCB draws no current until the required 24 volts is applied to the SW terminal.
Across the PH and PL terminals is a regulated reference voltage of 12 volts supplied by the PCB. This voltage is applied across the potentiometer. The potentiometer applies a divided down voltage to the PW terminal that is determined by it's position. The motor controller is designed to interpret 6.0 volts as "neutral". So, with the pot at dead center position, no motor movement occurs. When the potentiometer is moved off dead center and towards the 12 volt end of the pot, the motor moves in the forward direction. It's speed is dependent on how much toward the 12 volt source the wiper is moved. The more the voltage the faster the motor goes (to a point). Conversely, and in the same manner, if the potentiometer is moved off dead center and toward the 0 volt end of the pot, the motor will go increasingly faster in the reverse direction (to a point). The current through the potentiometer is minimal (2 ma.) so the physical size or shape of the pot is not a serious consideration and is determined by the requirements of your application.
In the previous paragraph, I said "(to a point)" twice. That is because it is important to note that this motor control does not utilize the full range of the 5K potentiometer, i.e. while 6.0 volts IS neutral, 12 volts at the PW terminal is not full forward and 0V is not full reverse. This card was designed as a electric scooter motor control where the full range of operation had to be realized within +/- 15 degrees of center. This means that full forward is from 6.5 to about 9 volts (adjustable by a gain control on the board) and full reverse is about 3 volts (adjustable by a "rev spd" pot on the board. Any voltage applied outside this range will cause the motor controller input amplifiers to overdrive and to discontinue output and the motor will stop abruptly. If your application would work better with a full range pot (center is neutral, full CW is full forward, and full CCW is full reverse) than I suggest a series network of a 2200 ohm resistor, 1000 ohm linear pot (not logarithmic or audio taper), and another 2200 ohm resistor. The free end of one 2200 ohm resistor now goes to the PH terminal, the free end of the other 2200 ohm resistor now goes to the PL terminal and the center terminal of the potentiometer still goes to the PW terminal.
If you get tired of diddling with a pot, or if your application requires it, this motor control board can also be controlled by a micro controller. To do this, you must put a 5.1k resistor across the PH and PL terminals to fake out the controller and make it "think" it has a pot connected. Internal safeguards prevent the controller from working without it. A control voltage from a filtered PWM output of a micro controller such as the Basic Stamp, or PIC16F84 or any other of your choice can be utilized. It must be within the voltage constraints discussed previously and is applied to the PW terminal directly. See other pages of this site for examples of how to do this as well as downloadable sample programs. It is important to be sure that the ground from the microprocessor circuitry and the ground from the motor control circuit are tied together.
The BK+ and BK- terminals on the PCB are for an external electromagnetic brake which is utilized by most scooters so they don't go for unanticipated joy rides. If not used, they may be left unconnected or you can amuse yourself by connecting a 24 volt light bulb which draws no more than 1/2 amp across the terminals and watch the light go on & off when you operate the throttle :>) DO NOT SHORT THESE TERMINALS. Smoke & burnt things will happen. For some strange reason, this is not covered under warranty.
The motor used with this controller can be anything from a toy motor up to a motor rated at about 1/2 HP and drawing 35 amps. The controller will allow brief excursions to 50 amps or so but only for a short while. If you try to do this for a sustained time, the controller will "fold back" the current to 35 amps or less until it cools off. You can use a voltage source of up to 28 volts MAXIMUM with this card. Anything in excess of that WILL destroy components on the card. This is easily identifiable and will also void the warranty.
This card cannot be modified to work at higher than 28 volts.
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