Charge monitor for electric battery

• US 4,086,524 A
• Filed: 09/09/1976
• Issued: 04/25/1978
• Est. Priority Date: 10/02/1974
• Status: Expired due to Term

• Current Assignee: Still Gesellschaft Mit Beschrã¤Nkter Haftung (Superlift Holding SARL)
• Original Assignee: Still Gesellschaft Mit Beschrã¤Nkter Haftung (Superlift Holding SARL)
• Inventors: Kremer, Manfred
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/722,064
• Time in Patent Office: 593 Days
• Field of Search: 320/32, 320/48, 320/9, 320/13, 320/33, 320/40, 340/249
• US Class Current: 320/136
• CPC Class Codes: G01R 17/10 AC or DC measuring bridges
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: H02J 9/002 in which a reserve is maintained in an energy source by disconnecting non-critical loads, e.g. maintaining a reserve of charge in a vehicle battery for starting an engine
• CPC Class Codes: Y10S 320/21 State of charge of battery
• CPC Class Codes: Y10S 320/32 Voltage divider having diverse elements other than merely plural resistors
• CPC Class Codes: Y10S 320/34 Robot, hybrid, recreational or emergency vehicle

Abstract

An electric battery, such as that of an automotive vehicle, is continuously tested for its state of charge by a bridge circuit in parallel with a voltage stabilizer such as a Zener diode which forms part of a voltage divider connected across the battery terminals, the other part of that divider being a resistance circuit. The bridge circuit has an output diagonal with one corner connected to the battery terminal which is tied to the resistance circuit so that a reduction of battery voltage unbalances the bridge in one sense, a compensatory change in the opposite sense being brought about by a sensor responsive to the load current drawn from the battery. The current sensor may be a small resistor inserted between two adjoining bridge arms. An integrating operational amplifier connected across the output diagonal of the bridge controls a pulse generator which steps an associated pulse counter whenever the amplifier output passes a threshold indicating a predetermined degree of depletion of the battery; the counter, after measuring a cumulative time interval during which this depletion condition is present, triggers a switch which generates an alarm signal, e.g. by eliminating certain options in the operation of the vehicle. The operational amplifier and/or pulse generator also work into visual charge indicators. The resistance circuit of the voltage divider may include a transistor designed to compensate changes in battery current due to the de-energization of a switcing relay. A feedback connection between the counter and the pulse generator causes continuing stepping of the counter after the switchover to maintain the alarm signal until the counter resets itself after an extended period, such resetting also occurring upon reclosure of the load circuit after a prolonged interruption.

Claims

1. A method of monitoring the state of charge of an electric battery supplying current to a load connected across its terminals, comprising the steps of simultaneously measuring the terminal voltage and the load current of the battery, deriving from the values so measured a resultant test parameter, comparing said test parameter with a predetermined threshold designating the transition from a normal range indicative of a state of effective charge to an off-normal range indicative of a state of approaching depletion, generating counting pulses during periods in which said test parameter falls into said off-normal range, storing the resulting pulse counts during intervals of return to said normal range, and switching off at least a significant part of said load upon the cumulative pulse count reaching a predetermined magnitude.

2. The method defined in claim 1, comprising the further step of automatically reconnecting the full load across the battery a predetermied length of time after the switching-off step.

3. The method defined in claim 2 wherein the generation of said coating pulses is continued regardless of the state of charge of the battery during said predetermined length of time until the cumulative count reaches a fixed limit whereupon the load is reconnected.

4. The method defined in claim 1, comprising the further step of producing a warning signal concurrently with the generation of said counting pulses.