GB2047488A - Battery charger fault detector - Google Patents

Battery charger fault detector Download PDF

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Publication number
GB2047488A
GB2047488A GB8001486A GB8001486A GB2047488A GB 2047488 A GB2047488 A GB 2047488A GB 8001486 A GB8001486 A GB 8001486A GB 8001486 A GB8001486 A GB 8001486A GB 2047488 A GB2047488 A GB 2047488A
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GB
United Kingdom
Prior art keywords
circuit
battery
charger
load
oscillator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8001486A
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GB2047488B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thomas Ashworth and Co Ltd
Original Assignee
Thomas Ashworth and Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomas Ashworth and Co Ltd filed Critical Thomas Ashworth and Co Ltd
Priority to GB8001486A priority Critical patent/GB2047488B/en
Publication of GB2047488A publication Critical patent/GB2047488A/en
Application granted granted Critical
Publication of GB2047488B publication Critical patent/GB2047488B/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/005—Testing of electric installations on transport means
    • G01R31/006—Testing of electric installations on transport means on road vehicles, e.g. automobiles or trucks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits

Abstract

A fault detector for detecting faults in a circuit comprising a battery charger 2 connected in parallel with a battery 4 across a load 1. The oscillation of an oscillator is monitored, the oscillator having a first tuned circuit 5, 6 connected in series circuit with the battery charger 2, a diode 7 and the battery 4, a second tuned circuit 10, 11 transformer coupled to the series circuit, and a feedback circuit 12 connected between the first and second tuned circuits. The oscillator is constructed such that it oscillates if and only if current can flow through the said series circuit. A fault indication is provided at 13 in the event of oscillation ceasing. <IMAGE>

Description

SPECIFICATION Battery charger fault detector The present invention relates to battery charger fault detectors, and in particular to fault detectors which can detect faults occurring in circuits where a battery charger is permanently connected to a battery and a load.
It is well known to connect a battery charger and a battery in parallel across a standing load. In such a circuit it is necessary to give a fault indication in the event of the charger failing, the battery becoming disconnected, or the battery discharging owing to a load demand beyond the capacity of the charger.
One known system monitors the voltage output of the charger. Such a system cannot detect disconnection of the batteries and can give a false indication when the charger is charging flat batteries in a correct manner.
A second known system monitors the current charging the battery. This is done by measuring the voltage across a resistor of low ohmic value (e.g. 20 ohms) connected in series with the battery. Two diodes of opposed polarities are connected across the resistor so that high charging and discharging currents can bypass the resistor. Such a system is not satisfactory however as small voltages (e.g. 40 mV) across the resistor must be accurately measured if the system is to perform reliably, and large amounts of power are dissipated in the diodes when charging or discharging currents are large. A voltage drop of about one volt also occurs across the diodes and is therefore not available to the load.
It is an object of the present invention to provide a battery charger fault detector which is an improvement on the detector systems described above.
According to the present invention, there is provided a fault detector for detecting faults in a circuit comprising a battery charger connected in parallel with a battery across a load, comprising an oscillator having a first tuned circuit connected in series circuit with the battery charger, a diode and the battery, a second tuned circuit coupled to the said series circuit, and a feedback circuit connected between the first and second tuned circuits such that the oscillator oscillates if and only if current can flow through the said series circuit, means being provided to provide a fault indication in the event of oscillation ceasing.
The diode prevents current flowing in the series circuit when the charger output voltage is less than the battery voltage.
Preferably the second tuned circuit is transformer-coupled to the series circuit. The first tuned circuit may comprise an inductor connected in parallel with a capacitor in the series circuit, the second tuned circuit comprising the primary of a transformer across which a capacitor is connected. The transformer secondary winding is connected in said series circuit, and the feedback circuit comprises an amplifier.
Where the fault detector is to be used to monitor a system powering a standing load of large capacitance, it may be necessary to connect an inductor in series with the load to ensure that the oscillator can oscillate in normal conditions.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing.
The drawing shows a circuit in which a standing load 1 is powered from a constant voltage battery charger 2. The capacitance of the load is represented by capacitor 3. A battery 4 is connected in parallel with the charger 2 so that in the event of the charger failing the load 1 will be powered from the battery 4.
A first tuned circuit comprising capacitor 5 and inductor 6 is connected in series circuit with the charger 2, a diode 7, the battery 4 and the secondary winding 8 of a transformer 9. The primary 10 acts as an inductor which forms a second tuned circuit with a capacitor 11.
The first and second tuned circuits are connected by a feedback circuit including amplifier 1 2 so as to form an oscillator. The effective oscillator input appears across the first tuned circuit and the oscillator appears across the secondary 8 of the transformer 9.
When current can flow in the series circuit formed by the charger 2, the diode 7, the battery 4, the secondary 8 and the first tuned circuit, the oscillator oscillates. Accordingly the oscillator frequency is modulated on the current flowing in the series circuit. When current can no longer flow in the series circuit, for example as a result of the battery becoming disconnected or the diode becoming reversed biased after failure of the charger, the oscillator can no longer oscillate.
Suitable detecting means (not shown) are connected to the terminal 1 3 so that a fault indication may be given whenever the oscillator fails to oscillate.
If the capacitance of the load 1 as represented by capacitor 3 is so large that it prevents oscillation of the detector circuit even in no-fault conditions, an inductance in the form of for example a saturable inductor 1 4 may be connected in series with the load.
1. A fault detector for detecting faults in a circuit comprising a battery charger connected in parallel with a battery across a load, comprising an oscillator having a first tuned circuit connected in series circuit with the battery charger, a diode and the battery, a second tuned circuit coupled to the said series circuit, and a feedback circuit connected between the
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Battery charger fault detector The present invention relates to battery charger fault detectors, and in particular to fault detectors which can detect faults occurring in circuits where a battery charger is permanently connected to a battery and a load. It is well known to connect a battery charger and a battery in parallel across a standing load. In such a circuit it is necessary to give a fault indication in the event of the charger failing, the battery becoming disconnected, or the battery discharging owing to a load demand beyond the capacity of the charger. One known system monitors the voltage output of the charger. Such a system cannot detect disconnection of the batteries and can give a false indication when the charger is charging flat batteries in a correct manner. A second known system monitors the current charging the battery. This is done by measuring the voltage across a resistor of low ohmic value (e.g. 20 ohms) connected in series with the battery. Two diodes of opposed polarities are connected across the resistor so that high charging and discharging currents can bypass the resistor. Such a system is not satisfactory however as small voltages (e.g. 40 mV) across the resistor must be accurately measured if the system is to perform reliably, and large amounts of power are dissipated in the diodes when charging or discharging currents are large. A voltage drop of about one volt also occurs across the diodes and is therefore not available to the load. It is an object of the present invention to provide a battery charger fault detector which is an improvement on the detector systems described above. According to the present invention, there is provided a fault detector for detecting faults in a circuit comprising a battery charger connected in parallel with a battery across a load, comprising an oscillator having a first tuned circuit connected in series circuit with the battery charger, a diode and the battery, a second tuned circuit coupled to the said series circuit, and a feedback circuit connected between the first and second tuned circuits such that the oscillator oscillates if and only if current can flow through the said series circuit, means being provided to provide a fault indication in the event of oscillation ceasing. The diode prevents current flowing in the series circuit when the charger output voltage is less than the battery voltage. Preferably the second tuned circuit is transformer-coupled to the series circuit. The first tuned circuit may comprise an inductor connected in parallel with a capacitor in the series circuit, the second tuned circuit comprising the primary of a transformer across which a capacitor is connected. The transformer secondary winding is connected in said series circuit, and the feedback circuit comprises an amplifier. Where the fault detector is to be used to monitor a system powering a standing load of large capacitance, it may be necessary to connect an inductor in series with the load to ensure that the oscillator can oscillate in normal conditions. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing. The drawing shows a circuit in which a standing load 1 is powered from a constant voltage battery charger 2. The capacitance of the load is represented by capacitor 3. A battery 4 is connected in parallel with the charger 2 so that in the event of the charger failing the load 1 will be powered from the battery 4. A first tuned circuit comprising capacitor 5 and inductor 6 is connected in series circuit with the charger 2, a diode 7, the battery 4 and the secondary winding 8 of a transformer 9. The primary 10 acts as an inductor which forms a second tuned circuit with a capacitor 11. The first and second tuned circuits are connected by a feedback circuit including amplifier 1 2 so as to form an oscillator. The effective oscillator input appears across the first tuned circuit and the oscillator appears across the secondary 8 of the transformer 9. When current can flow in the series circuit formed by the charger 2, the diode 7, the battery 4, the secondary 8 and the first tuned circuit, the oscillator oscillates. Accordingly the oscillator frequency is modulated on the current flowing in the series circuit. When current can no longer flow in the series circuit, for example as a result of the battery becoming disconnected or the diode becoming reversed biased after failure of the charger, the oscillator can no longer oscillate. Suitable detecting means (not shown) are connected to the terminal 1 3 so that a fault indication may be given whenever the oscillator fails to oscillate. If the capacitance of the load 1 as represented by capacitor 3 is so large that it prevents oscillation of the detector circuit even in no-fault conditions, an inductance in the form of for example a saturable inductor 1 4 may be connected in series with the load. CLAIMS
1. A fault detector for detecting faults in a circuit comprising a battery charger connected in parallel with a battery across a load, comprising an oscillator having a first tuned circuit connected in series circuit with the battery charger, a diode and the battery, a second tuned circuit coupled to the said series circuit, and a feedback circuit connected between the first and second tuned circuits such that the oscillator oscillates if and only if current can flow through the said series circuit, means being provided to provide a fault indication in the event of oscillation ceasing.
2. A fault detector according to claim 1, wherein the second tuned circuit is transformer-coupled to the series circuit.
3. A fault detector according to claim 2, wherein the second tuned circuit comprises the primary af a transformer across which a capacitor is connected, the secondary of the transformer being connected in said series circuit.
4. A fault detector according to claim 3, wherein the first tuned circuit comprises an inductor connected in parallel with a capacitor in said series circuit.
5. A fault detector according to claim 4, wherein the feedback circuit comprises an amplifier the input of which is connected to the first tuned circuit and the output of which is connected to the second tuned circuit.
6. A fault detector according to any preceding claim, wherein an inductor is connected in series with the load to ensure oscillation of the oscillator despite a high capacitance load.
7. A fault detector substantially as hereinbefore described with reference to the accompanying drawing.
GB8001486A 1979-04-17 1980-01-16 Battery charger fault detector Expired GB2047488B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8001486A GB2047488B (en) 1979-04-17 1980-01-16 Battery charger fault detector

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7913318 1979-04-17
GB8001486A GB2047488B (en) 1979-04-17 1980-01-16 Battery charger fault detector

Publications (2)

Publication Number Publication Date
GB2047488A true GB2047488A (en) 1980-11-26
GB2047488B GB2047488B (en) 1983-04-20

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB8001486A Expired GB2047488B (en) 1979-04-17 1980-01-16 Battery charger fault detector

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GB (1) GB2047488B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0067589A1 (en) * 1981-06-05 1982-12-22 Firing Circuits Inc. Method and apparatus for testing a battery

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4396880A (en) 1981-06-05 1983-08-02 Firing Circuits Inc. Method and apparatus for charging a battery

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0067589A1 (en) * 1981-06-05 1982-12-22 Firing Circuits Inc. Method and apparatus for testing a battery
US4433294A (en) * 1981-06-05 1984-02-21 Firing Circuits, Inc. Method and apparatus for testing a battery

Also Published As

Publication number Publication date
GB2047488B (en) 1983-04-20

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