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Thermistor protection for a wire feed motor

Image Number 3 for United States Patent #6204479.

A system for arc welding includes a welding power supply and a wire feeder. The wire feeder includes a dc wire feed motor and a dc wire feed power supply in electrical communication with the wire feed motor. A PTC thermistor is disposed electrically between the power supply and the wire feed motor. Current flows from the power supply, through the PTC thermistor, and then to the motor. Under normal current conditions the PTC thermistor allows current to be provided to the wire feed motor from the power supply, but under excessive current conditions the PTC thermistor inhibits current from being provided to the wire feed motor from the power supply. A diode is connected in anti-parallel with the motor. A pulse width modulation switch control current delivered to the motor. A normally open relay is closed when welding is to be performed to provide current to the motor, and a normally closed relay, connected in parallel with and shunting the motor, is opened when welding is to be performed. The normally closed relay acts as a brake on the motor when it is closed. The PTC thermistor is not shunted by a resistor and/or a varistor, and/or is not in parallel with a relay.

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