Dual battery system

Details Dual battery system Dual battery system

1999-09-16

2001-05-08

Wong, Peter S. (Department: 2838)

Electricity: battery or capacitor charging or discharging

One cell or battery charges another

Vehicle battery charging

C320S126000, C307S010100, C429S009000

Reexamination Certificate

active

06229279

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an improved dual-battery system and a method for its operation.
BACKGROUND OF THE INVENTION
A known dual-battery system includes a starter battery and a vehicle electrical system battery, e.g., see: German Patent 40 28 242 A1. Arranged between the starter battery and the vehicle electrical system battery is a starter battery switch that is closed during a starting operation so that both batteries are connected to one another. Primary and secondary loads are then powered via both batteries. “Primary load” is understood to be loads essential for starting and driving capability or for vehicle safety, and “secondary load” to be for comfort components. In order to prevent any discharge of the starter battery, a control device senses the charge states of each of the starter battery and the vehicle electrical system battery. If the charge state of the starter battery drops below that of the vehicle electrical system battery, so that charging of the vehicle electrical system battery would take place at the expense of the starter battery, the control device will break the connection between the batteries by opening the starter battery switch. The known dual-battery system is disadvantageous firstly because the starter battery is on-load even after the starting operation has taken place, and secondly because the complexity of measuring and sensing the charge states of the two batteries is quite substantial.
OBJECTS AND SUMMARY OF THE INVENTION
An object of this invention is therefore to provide a dual-battery system in which the starter battery is on-load only in the starting phase and the starter battery can nevertheless be charged at any time when the load state permits, and which requires little investment in terms of circuit engineering.
The present invention provides a dual-battery system, which comprises: a starter battery, a generator, a primary load, a vehicle electrical system battery, a starter, a power switch connected between the starter battery and vehicle electrical system battery so that the starter battery and vehicle electrical system battery can be connected together in parallel during operation of the starter, and a controllable electronic switch connected in parallel to the power switch.
The present invention further provides a method for controlling a dual-battery system of the type described in the preceding paragraph, which involves, a) sensing the charge balance of the starter battery and the vehicle electrical system battery by the current profile at the controllable electronic switch, preferably a MOSFET, and b) making the electronic switch conductive whenever a charging current can flow from the vehicle electrical system battery to the starter battery.
Because a controllable electronic switch, in particular a MOSFET, is arranged parallel to the power switch, it is very easy to sense, by way of the internal current measurement capability of the MOSFET, whether the charge state of the starter battery and vehicle electrical system battery allows charging of the starter battery. By generating a gate voltage of the correct sign, in such a situation a charging path can be enabled and the starter battery can be charged. Otherwise, the MOSFET disconnects the starter battery from the primary and secondary load so that the starter battery is on-load exclusively in the starting operation. Since all the control data are already available internally in the MOSFET, separate measurement shunts are unnecessary and the configuration of the control device can also be very simple. Further advantageous embodiments of the invention are evident from the dependent claims.
In a preferred embodiment, there is arranged between the vehicle electrical system battery and the primary load a switch with which, prior to the starting operation, the supply of power to the primary load can be selectably switched over between the vehicle electrical system battery and the starter battery, preferably, this switch is also a MOSFET.
Preferably the two, above-mentioned, MOSFETs are polarized oppositely to one another, so that either the two source or the two drain terminals are connected to one another, so that a short-circuit path cannot occur via the parasitic diodes of the MOSFETs.


REFERENCES:
patent: 5316868 (1994-05-01), Dougherty et al.
patent: 5325038 (1994-06-01), Banzai et al.
patent: 5488283 (1996-01-01), Dougherty et al.
patent: 5726553 (1998-03-01), Waugh
patent: 5764032 (1998-09-01), Moore
patent: 5962928 (1999-10-01), Schenk
patent: 38 41 769 C1 (1990-06-01), None
patent: 40 28 242 A1 (1992-03-01), None
patent: 196 51 612 A1 (1998-06-01), None
patent: 0 583 630 A1 (1994-02-01), None

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