Starter motor protection circuit with relay protection
AssigneeElectro-Tech, Inc.
InventorChester C. Quantz
Life of this patent
Estimating the term…
Abstract
A starter motor energized through a relay is protected from low voltages by a circuit which senses low voltages and turns off the motor relay via a transistor switch. A generator voltage sensing circuit also turns off the relay via the same switch when a generator voltage threshold is reached. For operation over a wide system voltage range, the coil of the relay is protected against high voltages by a chopper circuit which operates the transistor switch at a duty cycle of 100% at low voltages across the coil and lower duty cycles at high voltages. For a 12 volt relay the average current at higher voltages is maintained at a value approximating that obtained at a steady state 12 volts.
Claims6
A starter motor protection circuit for protecting a starter motor and relay coil over a wide range of coil voltages during starter operation, comprising:
- low voltage sensing means for de-energizing the relay coil in response to a low coil voltage to protect the starter motor;
- and
- a relay protection circuit for reducing the average current through the relay coil in response to a high coil voltage to protect the relay coil.
A relay protection circuit, comprising:
- a switch for selectively applying a voltage to a relay coil;
- and
- a chopper circuit coupled to the switch for operating the switch at a duty cycle that reduces the average current in the relay coil when the coil voltage exceeds a desired value, the chopper circuit including;
- a comparator;
- a first voltage divider subject to the coil voltage and a reference voltage for providing a first voltage input to the comparator;
- and
- a second voltage divider having a pair of resistors connected across the coil and subject to the coil voltage and having a capacitor connected across one of the resistors to establish a time constant, the second voltage divider providing a second voltage input to the comparator as a function of the time constant;
- wherein the first and second voltage inputs to the comparator establish a duty cycle that decreases from 100% as the coil voltage increases above the desired value.
Dependencies are inferred from the claim text.