GB2050721A

GB2050721A - Battery charging apparatus

Info

Publication number: GB2050721A
Application number: GB8011815A
Authority: GB
Original assignee: Burka V A
Current assignee: Burka V A
Priority date: 1979-04-10
Filing date: 1980-04-10
Publication date: 1981-01-07
Also published as: IT8021309A0; GB2050721B; DE3013709A1; DE3013709C2; FR2454209A1; IT1148815B; SU868921A1; FR2454209B1; JPS5612823A

Abstract

In a battery charger of the kind in which pulsating d.c. is supplied to the battery (6) from the rectified output of transformer (1) until a threshold device 15 detects the battery is charged, a bimetallic strip (9, 10) responds to the charging current. If the battery draws high current, say upon initial charging, then resistor 9 heats up strip 10 causing it to break the circuit until the strip cools. The resistor and bimetal strip are chosen so as to allow an average current flow within the capabilities of transformer 1, thus obviating the need for a current limit resistor, and protecting the circuit. Once the battery has charged sufficiently, the bimetallic strip ceases to operate. The device is said to enhance reliability and to permit a smaller and lighter transformer to be used. <IMAGE>

Description

SPECIFICATION Battery charging apparatus The present invention relates to apparatus for transformation of the electrical energy and is specifically concerned with a battery charging apparatus.

The invention may find the most advantageous application in the field of motor transport for charging and service recharging of motor vehicle storage batteries.

According to the invention, there is proposed a battery charging appartus comprising a matching transformer whose primary is connected to the apparatus' input terminals, a battery charging circuit connected to the secondary of the matching transformer and formed by a semiconductor rectifier intended to produce a unidirectional pulsating voltage in the circuit; a threshold circuitry to detect the charging completion moment, which circuitry utilizes a silicon controlled rectifier connected to the output of said semiconductor rectifier, by the cathode to the negative terminal, and a resistive voltage divider whose centre point is connected to the gate electrode of the silicon controlled rectifier, and the end points, to the apparatus' output terminals; and a charging current switching, means which includes a bimetallic strip, a breaking contact mechanically coupled to the bimetallic strip and incorporated in series with the latter into the battery charging circuit between the point of connection of the positive terminal of the semiconductor rectifier with the threshold circuitry and the apparatus' positive output terminal as well as a wire-wound resistor intended to heat the bimetallic strip and interposed between the anode of the silicon controlled rectifier and the positive terminal of the semiconductor rectifier.

The use in the apparatus of a charging current switching means in the form of a bimetallic strip mechanically coupled with a breaking contact and incorporated in series with the latter into the battery charging circuit allows during the initial period of storage battery charging the charging current to be pulse width modulated to a present value not exceeding its average value over the second, prolonged, bat'tery charging period. Thus, at the expense of somewhat extending the initial period of battery charging (by about 10-15%), the apparatus allows the rating of the matching transformer to be reduced down to the level of the average power consumed over the second period of the charging and hence obviates the need for a current-limiting resistor.

Thvs permits reducing both the weight and the size of the apparatus as a whole.

The proposed apparatus, in its preferable modification, finds an application mainly in transformer means where a need for charging storage batteries from an A.C. power source often arises. This modification of the proposed battery charging apparatus comprises a matching transformer 1 (Fig. 1) whose primary 2 is connected to appartus' input terminals 3, 4 and whose secondary 5 is connected to the charging circuit of a storage battery 6. The circuit is formed by a semiconductor rectifier 7 which produces a unidirectional pulsating voltage in the circuit and by a charging circuit switching means 8. The diode shown in the Figure represents one of the possible forms of the semiconductor rectifier and gives a half-wave rectification of voltage.It will be apparent to those skilled in that art that the diode may be substituted by a full-wave rectifier employing, e.g., a bridge circuit.

According to the invention, the switching means 8 includes a bimetallic strip 9 whose one end is connected to the positive terminal of the rectifier 7, while the other end of the strip is mechanically coupled to a breaking contact 10.

The bimetallic strip 9 jointly with the breaking contact 1 () is series-connected into the charging circuit of the storage battery 6 between the point of connection of the positive terminal of the rectifier 7 with a threshold circuitry 11 and an apparatus' positive output terminal 1 2. An apparatus' negative terminal 1 3 is connected to the secondary 5 of the matching transformer 1.

The switching means 8 includes also a wirewound resistor 14 intended to heat the bimetallic strip 9. The resistor may be wound on the strip 9, placed thereon, etc. so as to ensure a thermal contact therebetween. The electrical connections of the resistor will be described below.

The threshold circuitry 11 to detect the charging completion moment comprises a SCR 15 whose cathode is connected to the appartus' negative terminal 13 and whose control or gate electrode is connected to the centre point of a resistive voltage divider 1 6. The end points of the divider 1 6 are connected to the apparatus output terminals 12, 13.

The above-mentioned resistor 14 is interposed between the anode of the SCR 1 5 and the positive terminal of the semiconductor rectifier 7.

To compensate for the discharge of the battery 6 on the resistive voltage divider 1 6 with the contact 10 open by providing a trickle maintenance charge, a resistor 1 7 may be incorporated in parallel to the breaking contact 1 7.

A charging completion indicator, such as a lamp 18, may be incorporated into the anode circuit of the SCR 1 5.

A rectifier bridge 1 9 (Fig. 2) may be substituted for the diode 7 as the semiconductor rectifier.

To enable the voltage to which the battery 6 is charged to be varied within a predetermined range, the resistive voltage divider 1 6 is preferably composed of a variable resistor 20 and two fixed resistors 21 and 22, one of which, namely the resistor 22, is connected in parallel with the gate electrode of the SCR 1 5.

A thermal compensation is preferably accomplished with the use of a thermistor 23 connected in parallel with the fixed resistor 22 of the resistive voltage divider 1 6 and with the control or gate electrode of the SCR 1 5.

The apparatus functions as follows.

When the charging current flows through the bimetallic strip 9, electric losses cause the strip to heat and hence to change its configuration: the strip bends and opens the breaking contact 10.

The duration of the open and the closed state of the breaking contact 10 depends on the intensity of the charging current flowing through the bimetallic strip 9. The higher the charging current, the more rapidly the bimetallic strip 9 opens the contact 10 and the longer will be the off state of the apparatus.

The closing and opening of the contact 10 of the switching means 8 by the charging current as a result of heating and cooling of the bimetallic strip 9 follows the principle of pulse width modulation in such a way that the higher is the effective value of the charging current, the shorter is the time of its flowing through the bimetallic strip, and vice versa (see Fig. 3, curve "a"). The charging circuit being switched in such a manner, the matching transformer 1 (Fig. 1) operates in a mode which allows varying its average power and dispensing with a current-limiting resistor, and hence retakes it possible to reduce its weight and size. The operational dependability of the apparatus' components is at the same time enhanced, since a possibility of a prolonged flow therethrough of a current under the conditions of a short-circuit is in principle excluded.

As the charging current decreases to the preset value, the temperature of the bimetallic strip 9 becomes insufficient for developing the effort to open the contact 10.

When the voltage across the battery 6 and hence also across the resistive voltage divider 1 6 has reached the preset value, the SCR 1 5 is triggered into conduction to feed voltage to the indicating lamp 18 and wire-wound resistor 14.

The latter heats the bimetallic strip 9, with the result that the strip opens the contact 10.

In normal operation of the apparatus, the indicating lamp 1 8 in the course of charging a storage battery is out. At the end of the charging, as the SCR 1 5 is turned on, the indicating lamp goes on again.

The leakage from the battery 6 through the divider 16 is compensated by that, with the contact 10 open, a trickle maintenance charging current flows via the resistor 10 whose resistance is great enough (on the order of several kiloohms), When the apparatus passes from the trickle charging mode to the charging mode, the indicating lamp 1 8 will go on and out respectively.

The use of the bimetallic strip 9 makes it possible to dispense with a current-limiting resisitor, and the extension of the battery charging time at the first portion of the performance curve I =f(t) (Fig. 3, curve "a") allows reducing the average electric power drawn by a storage battery from the mains as against that of the prior art apparatus (curve "b") and hence enables the rating of the matching transformer to be selected on the basis of the average power consumption over the main period of charging and thereby the weight and size thereof to be reduced.

An absence of a current limiting resistor and smaller weight and size of the matching transformer result in smaller size and weight of the apparatus.

The' above-described embodiments of the invention are merely illustrative, and various modifications and alterations may be made therein without departing from the invention as set forth in the appended claims.

Claims

1. A battery charging appratus comprising a matching transformer whose primary is connected to the apparatus' input terminals, a battery charging circuit connected to the secondary of the matching transformer and formed by a semiconductor rectifier intended to produce a unidirectional pulsating voltage in the circuit; a threshold circuitry to detect the charging completion moment, which cicuitry utilizes a silicon controlled rectifier connected to the output of said semiconductor rectifier, by the cathode to the negative terminal, and a resistive voltage divider whose centre point is connected to the gate electrode of the silicon controlled rectifier, and the end points, to the appartus' output terminals; and a charging current switching means which includes a bimetallic strip, a breaking contact mechanically coupled to the bimetallic strip and incorporated in series with the latter into the battery charging circuit between the point of connection of the positive terminal of the semiconductor rectifier with the threshold circuitry and the apparatus' positive output terminal as well as a wire-wound resistor intended to heat the bimetalic strip and interposed between the anode of the silicon controlled rectifier and the positive terminal of the semiconductor rectifier.

2. A battery charging appartus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.