Motor vehicle battery disconnect switch circuits

Abstract

A disconnect switch (30, 30SA) is placed in circuit between a battery bank (12) and a distribution point (30B) for the entire electrical system load except the engine cranking motor (24). This allows the circuit between the battery bank and a cranking motor solenoid (22) that operates the cranking motor to be switch-free. A switch-free circuit allows a continuous cable to connect the battery bank to the cranking motor solenoid, significantly reducing the electrical resistance between the battery bank and the cranking motor solenoid.

Description

FIELD OF THE INVENTION [0001] This invention relates generally to electrical systems of motor vehicles. More particularly, the invention relates to battery disconnect circuits for preventing battery drain when the engine does not run for extended periods of time. BACKGROUND OF THE INVENTION [0002] Certain motor vehicles, heavy trucks that are powered by diesel engines for example, may be parked for extended periods of time. If its engine is allowed to keep running after a vehicle has been parked, the alternator should be effective to keep the battery bank charged. If the engine is shut down, either intentionally by the driver, or automatically by a device such as an idle shutdown timer, while the circuits for electric devices remain on, the battery bank will begin to drain. For example, an ignition switch will typically remain on after an idle shutdown timer has timed out, and certain circuits that are left on may continue to draw current. [0003] Because the battery bank must be abl...

AI Technical Summary

Benefits of technology

[0006] The present invention relates to disconnect switch circuits that are believed to offer better solutions for avoiding inadvertent battery draining when a vehicle is parked for an extended period of time. Rather than placing a disconnect switch in circuit between a battery bank and a distribution point for the entire electrical system load, the invention places the disconnect switch between the battery bank and a distribution point for the entire system load except the engine cranking motor. This allows the circuit between the battery bank and the contacts of a cranking motor solenoid that is energized to run the cranking motor to be switch-free. The cranking motor solenoid is often integrated with the cranking motor itself, rather than being a discrete component that is separate from the cranking motor so as to have a battery terminal connected by a heavy conductor to the ungrounded battery bank terminal and a load terminal connected by another heavy conductor to a terminal on the cranking motor. When the cranking motor solenoid is integrated with the cranking motor, the integrated assembly has a terminal connected to the ignition switch start contact, either directly or through a relay, and a terminal to which one termination of such a switch-free circuit is connected. Such a switch-free circuit, whether connected to a cranking motor solenoid that is separate from the cranking motor or one that is integrated with the cranking motor, provides important advantages.

[0008] Another advantage of removing the disconnect switch from the battery feed to the cranking motor solenoid is that the electrical resistance between the battery bank and the cranking motor solenoid is significantly reduced. A switch-free path eliminates the contact resistance that is inherently present in a switch. And although some might consider that resistance small, it is significant when the large amperage of the cranking current is considered. Large current flowing through even a small resistance creates a non-trivial voltage drop and attendant heating. Avoidance of such losses is believed especially significant and beneficial when one recognizes the difficult task of starting a diesel engine, which is most noticeable in sub- zero weather.

[0010] The invention is therefore believed to provide a cost-effective improvement for avoiding unintended battery draining in a motor vehicle when parked for an extended period of time, and the possible inconvenience of having to jump-start the engine, to replace one or more batteries, or perhaps even to tow the vehicle.

[0015] One more aspect of the invention relates to a method for avoiding draining a battery bank of one or more storage batteries in an engine-powered land vehicle to a point where the battery bank is incapable of operating an electric cranking motor to crank the engine at starting while providing a switch-free path for current flow from the battery bank to the cranking motor solenoid during engine cranking. The method comprises placing a disconnect switch that can be operated to respective ON and OFF positions in circuit between the battery bank and multiple circuit protection devices that distribute current to individual circuits in the vehicle, including a cranking motor solenoid circuit through which the cranking motor solenoid is energized to connect the cranking motor solenoid to the battery bank for operating the cranking motor to crank the engine at starting, so that the circuit protection devices are connected to the battery bank when the disconnect switch is in ON position and disconnected from the battery bank when the disconnect switch is in OFF position. The cranking motor solenoid is connected to the battery bank through a switch-free current path for carrying cranking current from the battery bank to the cranking motor via the cranking motor solenoid when the disconnect switch is in ON position and the cranking motor solenoid is being energized by the cranking motor solenoid circuit.

Problems solved by technology

And although some might consider that resistance small, it is significant when the large amperage of the cranking current is considered.

Large current flowing through even a small resistance creates a non-trivial voltage drop and attendant heating.

First, operation of the cranking motor is quite likely to be noticed unless a person is totally deaf.

Second, ignition switches that are presently in widespread use require maintained contact by the driver against a return spring force when placed in START position for cranking the engine.

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