GB2276990A

GB2276990A - Method of charging lead storage batteries having fixed or immobilized electrolyte

Info

Publication number: GB2276990A
Application number: GB9406308A
Authority: GB
Inventors: Franz-Josef Glasner
Original assignee: VARTA Batterie AG
Current assignee: VARTA Batterie AG
Priority date: 1993-04-08
Filing date: 1994-03-30
Publication date: 1994-10-12
Also published as: ITMI940476A0; IT1269550B; GB9406308D0; ITMI940476A1; DE4311586A1; FR2703835B1; FR2703835A1

Description

2276990 1 METHOD OF CHARGING LEAD STORAGE BATFERIES HAVING FIXED OR

IMMOBILIZED ELECTROLYTE The invention relates to a method of charging tightly sealed, maintenance- free lead storage batteries having fixed or immobilized electrolyte.

Such storage batteries use sulphuric acid as electrolyte. In order that the sulphuric acid electrolyte is immobilized, it is preferably present as a thixotropic gel. Alternatively the electrolyte may be immobilized by being absorbed in or sucked up by glass-mat separators, with no freely mobile electrolyte present.

It has been found that known charging methods suitable for lead storage batteries having liquid electrolyte (i.e. electrolyte which is not fixed or immobilized) give rise to difficulties when attempts are made to use them to charge lead storage batteries having fixed or immobilized electrolyte.

An objective of all charging methods is to achieve complete charging of the battery in a short time. This can be done, for example, in accordance with an IV characteristic line, charging initially being carried out with a high constant current until the gassing voltage is reached, the current then being allowed to drop to the very low value of a permissible limit current with the voltage being kept constant.

DE-PS 1233 934 discloses a charging method in which the charging current is reduced several times in steps as soon as the gassing voltage is reached.

According to E. Nann (Photovolt. Solarenergie, Supplm. 4th Nat. Symp., 13. 3.1989, 1.1.1-1.1.24), charging and float charging of sealed lead storage 2 batteries having an electrolyte fixed with a mat requires regulated charging units which limit the charging voltage in accordance with an IV or WV characteristic line. In use of a charging unit which limits the charging voltage in accordance with a VN characteristic line, the charging takes place in a first phase with a falling current (charging characteristic line W) which is due to the fact that the charging unit delivers constant power. Since this produces an increasing countervoltage at the battery, the current drops parabolically.

W.H. Deluca et a. (25th Proc. Intersoc. Energy Convers. Eng. Conf., IECEC 1990,3,320-325) report on the charging of lead battery modules of the type having absorbed electrolyte and of the gel-electrolyte type in accordance with an IV procedure. 105% charge may be absorbed within 8 hours with a voltage upper limit of 2.35 V/cell. If 105% charge is not achieved by the charging in accordance with the IV procedure, then such charge should be ensured by a voltage-limited additional charging in accordance with an extended IVI procedure.

Such a charging method, namely in accordance with an IVI,, charging characteristic line and suitable in particular for lead storage batteries having thixotropic gel electrolyte has also been disclosed in EP-A-339 446. However, this charging method is not free of defects since, in a parallel treatment of lead cells having liquid electrolyte and those having gel electrolyte, the variation in the end-of-charge voltages around the specified voltage of 2.3 V was found to be approximately twice as large in the case of the latter (cf. H. Tuphorn, Revue G6neral de UEletricit6 (RGE) 48/No. 3, March 1990,45-49). Consequently it can be concluded that the cell voltages drift apart after a prolonged operating time, and the cells having lower cell voltage are no longer fully charged and consequently fail prematurely.

3 An object of the invention is to provide a charging method for lead storage batteries having fixed electrolyte which ensures a uniform charge acceptance and a full charging of all the cells and which prolongs or does not diminish the service life of the cells.

In accordance with the present invention there is provided a method of charging a sealed, maintenance-free lead storage batteries having fixed electrolyte, comprising; at least two Primary charging phases in each of which constant current is supplied to the battery and charging is carried out until limit voltage value is reached, in each primary phase, except the first, the current being reduced as compared with the preceding phase; and a further or additional charging phase wherein charging is carried out with a constant charging current for a limited period of time.

In practice the supply of current to the battery is not interrupted between phases in order to mininise the time required to charge the battery.

Preferably there are three of said primary phases, in each of which charging current is supplied to the battery, the current in each said phase except the first being lower than the current in the preceding phase.

In the further or additional charging phase, the current is preferably of the same value as the current in the last of the primary charging phases. The duration of the further or additional charging phase may be determined by a timing element. A voltage criterion does not terminate the further charging phase and thus the further charging phase cannot be terminated prematurely. The further charging phase provides a charge equalization of all the cells with the battery and ensures their uniform conditioning.

4 The method of the invention comprises multi-stage charging having an IIII, , charging characteristic line with consecutive constant-current charging phases I, which are voltage-limited, and a subsequent, time-limited equalization charging phase la with free-wheeling voltage.

The voltage at the end of the I phases (i.e. the primary phases) is preferably between 2.3 and 2.4 V and is determined as a function of the battery temperature. The latter is measured in the interior of the cell or one of the cells of the battery, between two cells of the battery or on a connector between two cells of the battery.

The charging currents I and la are based on the five-hour rated current of the battery (15) and are preferably chosen as follows:

0.4 to 1.0 times 15, more preferably 0.7 x 15, in the first phase; 0.2 to 0.5 times 1.5, more preferably 0.25 x Is, in the second phase; 0.05 to 0. 2 times 1.5, more preferably 0.1 x I., in the third phase; and 0.05 to 0.2 times Is, more preferably 0.1 x l., in the further or additional charging phase.

It will be appreciated that the first, second and third phases are the primary phases.

Disconnection at the end of, or termination of each of the first, second and third phases, is preferably determined or indicated by a voltage signal. Termination of the end of the additional or further charging phase in accordance with time elapsed and is not in accordance with any voltage criterion.

1 1 t The duration of the further or additional phase is preferably 1 to 5 hours. If the time incurred for the primary or I phases is less than six hours in total, as may be the case if the battery is already substantially charged at the start of charging by the method of the invention, one hour may be sufficient for the additional charging phase.

The invention is further described below by way of example with reference to the accompanying drawing, which shows the current and voltage applied to a battery being charged as a function of time.

Referring to the drawing, a gel battery module of rated capacity 180 Ah and having five-hour rated current 1.5 of 36 A. The thick unbroken line shows the variation of the charging current with time and the thin unbroken line shows the variation of the charging voltage with time.

The voltage limitation for each charging step or phase is 2.4 V/cell.

In the drawing tl, t2, t3denote the duration of the first three charging phases, which are the primary charging phases. Each primary charging phase is terminated on a disconnection voltage of 2.4 V being reached. The duration t4of the additional-charging phase is fixed at 1 hour.

In the first phase, charging is carried out with a current of 15 A. In the second phase, the charging current is reduced to 8A, and in the third phase the charging current is reduced to 4 A. After a voltage-limited disconnection, the charging is continued immediately thereafter in the additional charging phase with a constant current of 4 A in a timelimited manner.

6 The charging method of the invention, which is in accordance with an IIIIa charging procedure, is particularly suitable for lead batteries having fixed electrolyte. It comprises only charging phases wherein a constant current is applied to the battery. The additional charging phase I,, provides for charge equalization between the battery cells after exhaustive charge acceptance. Cells having lower capacity can be replaced by new cells without the remaining cells suffering damage.

The degree of discharge of the battery does not have to be known. If a fully charged battery is subjected to the method of the invention, the battery is overcharged at most only for 1 hour with a current I equal to 0.1 x 15 and the charge applied is only 2% of the rated capacity Is.

Charging methods comprising IV stages are unable to keep the cell voltage of older cells at the necessary level and the cells fail after a few cycles.

In the method of the invention, a recombination heat produced during the catalytic recombination of the charging gases can be utilized particularly advantageously by using the response of a recombiner present on the storage battery as a signal for the charge control.

It may be very beneficial for carrying out the method of the invention to fit the storage battery additionally with a two-way valve in accordance with German Offenlegungsschrift 4108 491. Such a valve is specially adapted in its function to the gassing behaviour of storage batteries having fixed electrolyte.

The invention may be summarized as follows:

7 1. Method of charging tightly sealed, maintenance-free lead storage batteries having fixed electrolyte, characterized in that at least two charging phases with constant current are provided, in each of which charging is carried out until a limit voltage value is reached and the further charging is carried out in the next phase with a stepwise reduced constant current, and in that additional charging is carried out in a further charging phase with a constant current in a time-limited manner, without disconnection in accordance with a voltage criterion.

2. Method according to Summary 1, characterized in that it comprises three charging phases having constant currents reduced one after the other.

3. Method according to Summary 2, characterised in that the charging currents 1 for the first three charging phases and for a constant limit voltage between 2.3 and 2.4 V are chosen in such a way that they amount to 0.4 to 1.0 times the rated current 15 in the first phase, 0.2 to 0.5 times the rated current 15 in the second phase and 0.05 to 0.2 times the rated current 15 in the third phase, and in that the constant current 1,., provided for the additional charging amounts to 0.05 to 0.2 times the rated current 15.

4.

Method according to Summary 3, characterized in that the constant charging currents used are I = 0.7 x 15 in the first phase, I = 0.25 x I. in the second phase and 1 = 0.1 x Is in the third phase, and in that the constant additional charging current I,, amounts to 0.1 times the rated current I..

5. Method according to one of Summary 1 to 4, characterized in that the duration of the additional charging is 1 to 5 h.

8

Claims

1. A method of charging a sealed lead storage battery having fixed electrolyte, comprising; at least two primary charging phases wherein a constant current is supplied to the battery and charging is carried out until a limit voltage value is reached, in each primary phase, except the first, the current being reduced as compared with the preceding phase; and a further or additional charging phase wherein charging is carried out with a constant current for a limited or predetermined period of time.

2. A method according to Claim 1, wherein there are three of said primary charging phases, in each of which a constant current is supplied to the battery, the current in each said phase, except the first, being lower than the current in the preceding phase.

3. A method according to Claim 2, wherein the constant limit voltage is between 2.3 and 2.4 V, the current in the first phase is 0.4 to 1.0 times a rated current 15, the current in the second phase is 0.2 to 0.5 times the rated current 15, the current in the third phase is 0.05 to 0.2 times the rated current IS, and the current I,, in the further charging phase is 0.05 to 0.2 times the rated current 15.

4. A method according to claim 3, wherein the current I in the first phase is 0.7 x I,,, the current in the 1 in the second phase is 0.25 x 1. and the current I in the third phase is 0.1 x I. and the current I. in the further charging phase is 0.1 X IS.

5. A method according to any of claims 1 to 4, wherein said limited or predetermined period of time of the further charging phase is 1 to 5 hours.

1 9

6. A method according to any preceding claim, wherein the limit voltage in each of the primary charging phases has a common value.

7. A method of charging a lead storage battery, substantially as described herein with reference to and as illustrated in the accompanying drawings.