Overload protection arrangement for an electric motor, especiall

Details Overload protection arrangement for an electric motor, especiall Overload protection arrangement for an electric motor, especiall

1981-05-22

1984-02-07

Moose, Jr., Harry E.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Motor protective condition responsive circuits

310 68C, 318783, H02H 7085

Patent

active

044306814

ABSTRACT:
An overload protection arrangement for an electric motor, especially of a hand-held power tool, includes an electronic speed of rotation control arrangement which is, in turn, controlled by an overload circuitry which includes a positive temperature coefficient resistor situated in the winding of the electric motor and incorporated in a voltage divider. The output of the PTC-resistor is amplified by an amplifier and, when the temperature of the winding increases above an acceptable level, the maximum current which can be drawn by the electric motor is reduced to a level at which the winding cannot burn out even if the rotor of the electric motor is blocked. If the rotor can rotate freely, the speed of rotation thereof even at the reduced power input will be sufficient to assure rapid cooling of the device powered by the electric motor. A time-delay member consisting of a capacitor and a resistor is arranged in parallel with the operational amplifier.

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