WO2004077636A2

WO2004077636A2 - Charging apparatus, system and method for charging an accumulator

Info

Publication number: WO2004077636A2
Application number: PCT/NL2004/000141
Authority: WO
Inventors: Taco Wijnand Neeb; Edward Frederik Geert Vuijk
Original assignee: Tendris Solutions B.V.
Priority date: 2003-02-26
Filing date: 2004-02-25
Publication date: 2004-09-10
Also published as: WO2004077636A3; NL1022784C2

Abstract

A charging apparatus for charging an accumulator, is provided with at least one supply terminal for supplying an alternating feed current; a rectifier circuit for rectifying a supplied alternating feed current; and an output stage with terminal means for supplying the rectified current to poles of the accumulator to be charged. The charging apparatus is further provided with an input stage connected between the supply terminals and rectifier circuit, which input stage, in use, confers upon the charging apparatus a substantially reactive input impedance.

Description

Charging apparatus, system and method for charging an accumulator.

The invention relates to a charging apparatus for charging an accumulator, which charging apparatus is provided with at least one supply terminal for supplying an alternating feed current ; a rectifier circuit for rectifying a supplied alternating feed current ; and an output stage with terminal means for supplying the rectified current to poles of the accumulator to be charged.

The invention also relates to a system for charging an accumulator, comprising an accommodation construction for placing an accumulator to be charged and such an accumulator charging apparatus .

The invention additionally relates to a method of charging an accumulator, wherein use is made of such a charg- ing apparatus.

Examples of a charging apparatus, system and method as described above are known from GB 2 197 551. This publication concerns a battery charger which can only be used for charging miniature batteries. Furthermore, the input impedance of the known battery charger is substantially resistive in nature. The known battery charger has an input stage with a capacitor, connected in series between the rectifier circuit and the current supply terminals. In the known battery charger, the capacitor serves to bring about a voltage drop, in order that the voltage across the poles of the battery does not become too high.

A disadvantage of the known apparatus is that the charging an accumulator takes a relatively long time.

It is an object of the invention to provide a charg- ing apparatus, system for charging an accumulator and method of charging an accumulator which enable an accelerated and relatively efficient charging.

This object is achieved by means of the charging apparatus according to the invention, which charging apparatus is provided with at least one supply terminal for supplying an alternating feed current; a rectifier circuit for rectifying the supplied alternating feed current; and an output stage with terminal means for supplying the recti- fied current to poles of the battery to be charged, wherein the charging apparatus is further provided with an input stage connected between the supply terminals and rectifier circuit, which input stage, in use, confers upon the charging apparatus a substantially reactive input impedance. The charging apparatus, in use, thus has an input impedance of which the reactive component is higher than the resistive component. By using the input stage, it is possible to supply more power to the charger, without the apparent power uptake increasing appreciably. By using a reactive input i - pedance in combination with power supply from an alternating feed current, a pulsating power is supplied to the accumulator. An additional effect of the use of the charging apparatus according to the invention is that the accumulator is somewhat regenerated. This means that the capacity of an accumulator, which has decreased through prolonged use of the accumulator, increases again. It is believed that this is a consequence of the fact that a pulsating power is supplied to the accumulator.

Preferably, the input stage comprises at least one capacitor connected in series between the supply terminals and the rectifier circuit, and more particularly, the input stage is comprised of a capacitor bank, which comprises one or more capacitors connected in parallel .

In this manner an almost purely reactive input imped- ance may be obtained, as a result of which the advantageous effects of the charging apparatus according to the invention manifest themselves in an enhanced manner.

The supply terminals are suitable for connection of the charging apparatus to the mains network, amongst others. If the charging apparatus circuit is connected directly to the mains network, it is simple to use in many places. Therefore, no separate alternating current power source is needed. According to another aspect of the invention, there is provided a system for charging an accumulator, comprising an accommodation construction for placing an accumulator to be charged and a charging apparatus according to the invention. This system has the same advantageous effects as the charging apparatus. The accommodation construction ensures correct placement of the accumulator.

The system is particularly suitable for loading accumulators comprising one or more electrode plates. Preferably, the system further comprises means for making vibrate at least one or more electrode plates of an accumulator to be charged placed in the accommodation construction.

By making the electrode plates of an accumulator to be charged vibrate, and simultaneously charging by means of the charging apparatus according to the invention, a synergis- tic effect arises. This manifests itself in the shape of improved regeneration of charged accumulators and shortened charging times. It is believed that the pulsating power and the vibrations enhance each other, as a result of which depos- its on the electrode plates, for example sulphate deposits on the plates of a lead sulphate accumulator, are removed. An additional effect is that any crystallised electrolyte dissolves again more rapidly. Thus a regenerative effect is achieved which is particularly advantageous if the accumulator has been used in a relatively cold environment for a prolonged period of time, as crystallisation occurs most often in that case. Preferably, the system is suitable for charging an accumulator having one or more electrode plates immersed in an electrolyte solution, and the system further comprises means for generating pressure waves in the electrolyte solution.

Relative to other means for making the electrode plates vibrate this system has the advantage that no further operations on the accumulator to be charged are necessary, and that it functions to a large extent independent of the manner in which the electrode plates are accommodated in the accumulator. Furthermore, the concentration of dissolved gases that arise in the electrolyte solution of the accumulator during charging decreases . In a preferred embodiment, the accommodation construction comprises a fluid bath, and the system is provided with means for generating pressure waves in the fluid bath when filled with fluid. This is a highly effective manner of transmitting pressure waves, as the impedance of the fluid and electrolyte solution are in the same range, so that more power is transmitted.

According to yet another aspect the invention pro- vides a method of charging an accumulator, wherein use is made of a charging apparatus according to the invention.

This method has the advantage of being of relatively short duration and to bring about an increase in the life span of the accumulator. In a preferred embodiment, an accumulator having one or more electrode plates immersed in an electrolyte solution is charged, wherein furthermore the electrode plates are made to vibrate during charging, preferably by generating pressure waves propagating in a direction parallel to the electrode plates.

It has been established experimentally that with this mutual orientation of the accumulator and pressure waves the advantageous effect on life span and charging time of the accumulator is biggest . The invention will now be explained in further detail with reference to the accompanying drawings, wherein: in Fig. 1A and IB schematic top and side plan views, respectively, are shown of an example of a system according to the invention; and in Fig. 2 a circuit diagram of an embodiment of the charging apparatus according to the invention is shown.

The system according to the invention, of which Fig. 1A and IB schematically show an example, comprises a charging apparatus and a vessel 2 filled with water 1 forming a fluid bath. In the fluid bath, an accumulator 3 to be charged has been placed. The accumulator 3 comprises an accumulator tank 4, with a plurality of plane, parallel electrode plates 5 therein, which are immersed in an electrolyte solu- tion 6. The electrode plates 5 form a number of cells, connected in series, which are connected to positive and negative poles 7,8 of the accumulator 3. The invention is particularly suitable for charging lead sulphate batteries, such as are used in cars and lorries, for instance. There, the problem occurs that through repeated charging and discharging sulphate is deposited on the electrode plates 5, as a result of which the capacity of the accumulator 3 decreases over its life span. By means of the system according to the invention this effect can be reversed and prevented.

In use, the accumulator 3 is placed on a pedestal 9 in the vessel 2 filled with water 1, wherein the fluid level is set such that the poles 7,8 just surface above the water 3. The poles 7,8 are connected to leads 10,11, for example by means of alligator clips (not shown) or other suitable connection means. The electronics of the charging apparatus according to the invention, of which a generalised example is shown schematically in Fig. 2, are accommodated in a housing 12. Thus, the system according to the invention in this example is comprised of the charging apparatus, the housing 12 with the electronics accommodated therein, and the fluid bath, of which the function will be described in more detail further on.

The charging apparatus according to the invention is preferably powered from the mains, although another source of alternating current could be used in principle, which in the context of the invention should also be taken to mean sources of polyphase current (three-phase current) , such as a power current network. An example of a suitable source is an alternating current generator such as a car dynamo or an emergency backup power generator. In principle, the charging apparatus according to the invention is usable separately from the fluid bath, for example in a vehicle, to charge the accumulator whilst driving. Such an application is not limited to cars, but also extends to other vehicles, such as electric trains, trams, wheelchairs, boats or aeroplanes, for instance.

Returning to the example of Fig. 2, the depicted charging apparatus is provided with plugs 13,14, which constitute a supply terminal for supplying the alternating current from the socket. The supplied alternating current is first passed through an input stage, which in this example is comprised of a capacitor bank 15. The capacitor bank 15 comprises a first and second row of capacitors 16,17 connected in paral- lei. It is observed that the second row of capacitors 17, with the associated row of switches 19, is optional. By using the capacitor bank 15, no separate transformer is needed, and conferment of an almost completely reactive input impedance by the input stage upon the charging apparatus, when supplied from the mains (that is to say with alternating current having a frequency in the range between 40 and 60 Hz) , is also attained. Thus, current and voltage are almost 90° out of phase, as a result of which the apparent power consumed is almost equal to zero. The capacitor bank 15 makes the use of a sepa- rate transformer superfluous. The switches 18,19 make it possible to control the impedance of the input stage, whilst a control circuit, discussed in more detail below, takes care of a last voltage adjustment, in order that the voltage over the positive and negative poles 7,8 of the accumulator 3 does not become too large.

In other applications the input impedance is always adjusted to the frequency of the power supply. For power current or current from a car dynamo, the frequency will be much higher, for example around 600 Hz. The input impedance of the charging apparatus according to the invention is then again substantially reactive, through an appropriate choice of capacitors 16,17. The input stage is thus always adapted to the properties of the alternating feed current (which should also be taken to mean polyphase current) , such that the input stage confers upon the circuit a substantially reactive input impedance in use .

After the input stage the current is only rectified by a bridge circuit 20 connected to the input stage. The rectified current is supplied to the accumulator 3 through termi- nal clips 21,22, which are connected to the positive and negative poles 7,8 of the accumulator 3. Because the charging apparatus, except for the control circuit, is essentially comprised of the input stage with an almost purely reactive input impedance and the bridge circuit 20, a pulsating power is supplied to the accumulator 3.

It is observed that other rectifier circuits than the bridge circuit 20 shown in Fig. 2 are possible within the scope of the invention. In principle a half-wave rectifier circuit is possible, but it is preferable, with a view to faster and more efficient charging, to use a full-wave rectifier circuit. The choice of rectifier circuit, in addition to the nature of the electrochemical process, determines whether and which harmonics of the alternating current frequency are passed. In an electrochemical process, such as the charging of an accumulator, only even harmonics are involved. This is an additional advantageous effect of the circuit according to the invention, as odd harmonics are undesirable. Those harmonics are usually responsible for problems such as overheating. The harmonic components enhance the accelerating effect on the electrochemical process in the accumulator.

It has just been observed that the charging apparatus further comprises a control circuit for controlling the voltage across the poles 7,8 of the accumulator 3 connected through the terminal clips 21,22. In particular, the control circuit carries out a comparison between this voltage and an adjustable reference voltage, and the current supply is interrupted upon exceeding of the reference voltage. Thus, the voltage at which the accumulator 3 is completely charged can be adjusted. The charging apparatus automatically switches off upon attainment of this voltage. The user of the charging apparatus can therefore then safely detach the terminal clips 21,22 from the poles 7,8, without the danger of spark- over .

The control circuit in the example of Fig. 2 comprises a window discriminator 23, for comparing the voltage across the poles 7,8 of the accumulator to a reference value set by means of a potentiometer 25. A memory circuit 25 oper- ates on a first light emitting diode (LED) 26, a second light emitting diode (LED) 27 and a relay 28. By means of the relay 28, the charging current is interrupted if the voltage across the poles 7,8 exceeds the reference value. Simultane- ously, the first LED 27, which lights up during charging, goes out. The second LED 27 goes on, as a sign that the accumulator has been recharged.

The use of the relay 28 further has the advantage that the charging current only begins to flow after the poles 7,8 of the accumulator have been connected to the charging apparatus. This is so, because the relay is powered by the accumulator 3. By inclusion of a switch that passes the charging current upon closure to the terminal means of the charging apparatus and is powered by the accumulator to be charged, the safety level of the charging apparatus is increased.

The charging apparatus according to the invention is continuously adjusted to the capacity of the accumulator to be charged. In particular, the charging apparatus is configured to limit the maximum charging current to a value numerically equal to the capacity of the accumulator to be charged. It is has been determined experimentally that the risk of explosion of the accumulator is then negligibly low.

Returning to Figs. 1A and IB, the function of the fluid bath will now be described. During charging, the electrode plates 5 are made to vibrate, by means of which any deposited sulphate is detached and dissolves in the electrolyte solution 6 more easily. Although the vibrations could also be generated by other means, for example by means of a vibratory pad, pressure waves are preferably generated in the water 1, by means of an actuator 29 attached to the vessel 2. The actuator 29 can, for example, be a piezo actuator, but specially adapted loudspeakers driven by means of a magnet and solenoid are equally possible. Preferably, ultrasonic pressure waves are generated, preferably with a frequency of 20 kHz or more.

The range above 25 kHz has proved to be particularly advantageous. It has been established experimentally that the effect of the pressure waves is largest between 20 kHz and 50 kHz. When using an electrolyte solution with water as component, the range of 38-46 kHz, and within that range 41-43 kHz in particular, is best. This is connected with the fact that the resonance frequency of water molecules lies at about 42 kHz. It is has further become apparent that the regenerative effect is advanced by generating pressure waves that propagate in a direction parallel to the electrode plates 5. In Fig. 1A, this direction has been indicated by means of ar- row A, and the wave fronts of the propagating pressure wave is indicated by reference numeral 30. Note that the wave fronts run almost parallel to the wall of the accumulator tank 4 that is perpendicular to the direction A of propagation.

It is possible to shape the accommodation construc- tion for the accumulator 3, in this case the pedestal 9, in such a way that an accumulator placed in the accommodation construction is always correctly orientated relative to the impinging wave fronts 30.

Through simultaneous driving of the actuator 29 and supplying the charging current by means of the charging apparatus according to the invention, an enhanced regenerative effect is obtained, whilst in addition the charging apparatus ensures that the accumulator 3 is charged quickly.

The invention is not limited to the embodiments de- scribed herein, which may be modified within the scope of the accompanying claims. In particular, the system according to the invention, although pre-eminently suitable of car batteries of the lead-sulphate type, is also suitable for charging and regenerating other types of accumulators and batteries. Thus, the charging apparatus may be used for charging Nickel -Cadmum cells, Nickel Metal Hydride cells and Lithium Ion cells. In each case the charging apparatus has the advantage that charging takes place more quickly and more efficiently and that the memory effect that occurs in these types of cells is prevented. Any memory effect that has already arisen can be reversed by the use of the invention. As an aside, it is observed that when charging accumulators comprising a series of cells, the method according to the invention provides for the separate charging of each of the cells, since otherwise the voltage differences over the individual cells would differ too much, and there would be a danger of explosion.

Claims

1. Charging apparatus for charging an accumulator (3) , which charging apparatus is provided with at least one supply terminal (13,14) for supplying an alternating feed current ; a rectifier circuit (20) for rectifying a supplied alternating eed current ; and an output stage with terminal means (10 , 11 ; 21, 22) for supplying the rectified current to poles (7,8) of the accumulator (3) to be charged, wherein the charging apparatus is fur- ther provided with an input stage (15) connected between the supply terminals (13,14) and rectifier circuit (20), which input stage (15) , in use, confers upon the charging apparatus a substantially reactive input impedance.

2. Charging apparatus according to claim 1, wherein the input stage (15) comprises at least one capacitor (16,17) connected in series between the supply terminals (13,14) and the rectifier circuit (20) .

3. Charging apparatus according to claim 2 , wherein the input stage is comprised of a capacitor bank (15) , which comprises one or more capacitors (16,17) connected in parallel.

4. Charging apparatus according to any one of claims 1-3, wherein the supply terminals (13,14) are suitable for connection of the charging apparatus to the mains network.

5. Charging apparatus according to any one of claims 1-4, further comprising a control circuit (23-28) for controlling the voltage across the poles (7,8) of an accumulator (3) to be charged connected through the terminal means (10, 11 ;21,22) .

6. Charging apparatus according to claim 5, wherein the control circuit comprises means (23) for comparing the voltage across the poles (7,8) to a reference voltage, and means (28) for, in use, interrupting the current supplied to the accumulator (3) when the voltage exceeds a reference volt- age.

7. Charging apparatus according to claim 6, further comprising means (24) for setting the reference value.

8. System for charging an accumulator (3), comprising an accommodation construction (2,9) for placing an accumu- lator (3) to be charged and an accumulator charging apparatus according to any one of claims 1-7.

9. System according to claim 8, further comprising means (1,2,29) for making vibrate at least one or more electrode plates (5) of an accumulator (3) to be charged placed in the accommodation construction.

10. System according to claim 9, suitable for charging an accumulator (3) having one or more electrode plates (5) immersed in an electrolyte solution (6) , which system further comprises means for generating pressure waves in the electro- lyte solution (6) .

11. System according to claim 10, wherein the accommodation construction comprises a fluid bath (1,2), and the system is provided with means (29) for generating pressure waves in the fluid bath (1,2) when filled with fluid (1) .

12. System according to claim 10 or 11, arranged such that, in use, the generated pressure waves propagate in a direction (A) parallel to the electrode plates (5) of an accumulator (3) placed in the accommodation construction.

13. Method of charging an accumulator (3), wherein use is made of a charging apparatus according to any one of claims 1-7.

14. Method of charging an accumulator according to claim 13, wherein an accumulator (3) having one or more electrode plates (5) immersed in an electrolyte solution (6) is charged, wherein furthermore the electrode plates (5) are made to vibrate during charging.

15. Method of charging an accumulator according to claim 14, wherein the electrode plates (5) are made to vibrate by generating pressure waves propagating in a direction (A) parallel to the electrode plates (5) .

16. Method according to any one of claims 13-15, wherein a lead-sulphate accumulator is charged.