RESISTANCE COMPENSATION IN A MOTOR USING A THERMALLY VARIABLE RESISTIVE NETWORK

A motor is disclosed comprising a housing and a plurality of parallel stator laminations mounted on the interior wall of the housing surrounding the rotor. The stator comprises a plurality of coils wound around the stator poles. Each coil or group of coils connected in series with each other are further connected in series with a thermistor network. Preferably, the thermistor is supported on a printed circuit board mounted adjacent to the coils, with the thermistor being inserted in a space directly adjacent to or between adjacent stator coils in order for the thermistor to accurately respond to the actual operating temperature of the coils. With increases in temperature, the resistance of the negative temperature coefficient thermistor will decrease, lowering the resistance of the motor circuit and maintaining the L/R time constant of the system. The opposite effect will occur with decreasing tempreature. To adjust for the fact that thermistors that accurately reflect the changes in resistance of the wire used to wind the coils with changes in temperature are not available, a resistor is wired in parallel with the thermistor, the resistor having a value chosen to modify the total resistance represented by the thermistor network to the coils so that the compensation is accurate over a wide range of changes in temperature and motor design. The shunt resistor allows flexibility in motor design, as it can have any selected value from zero to infinity to compensate for variations in motor design.