Circuit for constant voltage power source

• US 4,207,511 A
• Filed: 09/15/1978
• Issued: 06/10/1980
• Est. Priority Date: 09/15/1978
• Status: Expired due to Term

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Motor Company
• Inventors: Radtke, Gerald W.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/943,254
• Time in Patent Office: 634 Days
• Field of Search: 320/2-6, 320/15, 320/56, 320/61
• US Class Current: 320/126
• CPC Class Codes: H02J 7/1423 with multiple batteries
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y10S 320/11 Prioritized supply of power or power supply compensation

Abstract

This specification discloses a circuit for a constant voltage power source. The circuit includes a vehicle charging means, such as an alternator, which charges a main battery designed for operating main vehicle electrical loads such as a starter motor and a secondary battery, designed for operating secondary vehicle electrical loads such as electronic components particularly sensitive to voltage variations and typically requiring a constant voltage input for operation. A resistor in series with the vehicle charging means and the secondary battery limits the rate of charging of the secondary battery. The main vehicle loads can be selectively connected to the circuit for operation by the vehicle charging means and/or the main battery. A diode in series with the secondary battery prevents the secondary battery from discharging through any path but the secondary vehicle loads. The secondary vehicle loads are connected across the secondary battery but can also receive current from any of the main battery, secondary battery and the vehicle charging means. When sufficient current and voltage is not available for the secondary vehicle loads from the main battery and the vehicle charging system, such as during cold cranking of the starter motor, the needed power can be supplied from the secondary battery. This is particularly advantageous because the secondary vehicle loads can include electronic circuits necessary for proper ignition of the vehicle engine.

Claims

1. A circuit for a constant voltage power source for operating a vehicle electrical load including:

a series connection including a vehicle charging means, a vehicle ignition switch, a diode, a resistive means for developing thereacross a portion of the voltage drop from said vehicle charging means, and a secondary battery having polarities such that current can flow from said vehicle charging system through said diode to charge said secondary battery;

a main battery connected in parallel across said vehicle charging means so that current can flow from said vehicle charging means and charge said main battery;

a secondary vehicle load requiring a substantially constant applied voltage connected in parallel across said secondary battery;

a main vehicle load connected in parallel across the series combination of said ignition switch and said main vehicle battery;

said secondary battery and said main battery having a common ground and said resistive means and said diode being connected in series between said ignition switch and said secondary battery so that said resistive means does not draw current from said main battery and said vehicle charging means when said ignition switch is open and said secondary battery does not substantially discharge through said main vehicle load;

said main battery having a substantially higher voltage and amperage capacity than said secondary battery; and

said resistive means having a current carrying capacity of about 10% of the ampere-hour rating of said secondary battery.

2. A circuit as recited in claim 1 wherein said secondary vehicle load includes voltage sensitive electronic components which are supplied by a sufficiently high voltage for normal operation by said secondary battery even when the voltage across said main battery is substantially reduced from the voltage of said voltage charging means.

3. A circuit as recited in claim 2 wherein said secondary battery is of the rechargeable nickle cadmium type.

4. A circuit as recited in claim 3 wherein said diode is a semiconductor device.

5. A circuit as recited in claim 3 wherein said main vehicle load includes a vehicle starter motor.

6. A circuit for a constant voltage power source for use in a motor vehicle including:

a vehicle charging means for providing a current source for charging a secondary vehicle battery and a main vehicle battery, said secondary vehicle battery being adapted to provide a substantially constant voltage source;

said main battery being connected across said vehicle charging means and having a sufficient ampere hour rating to supply current for the operation of a vehicle starter motor;

a series combination connected across said vehicle charging system including an ignition switch having a first and second terminal, said first terminal being connected to a node between said main battery and said vehicle charging means, said main battery having a positive and negative terminal, said negative terminal being connected to ground, and the series combination of a diode and a resistor being connected between the positive terminal of said main battery and the second terminal of said ignition switch;

a main vehicle load, including the vehicle starter motor, being connected between said second terminal of said ignition switch and ground;

a secondary vehicle load, including elements requiring a constant voltage, being connected between said positive terminal of said first battery and ground; and

said resistor having a sufficient magnitude to permit only trickle charging of said secondary battery by said vehicle charging means and said diode being connected so as to prevent discharging of said secondary battery through any of said main vehicle load, said main battery and said vehicle charging means.