CA2380586A1 - Fast pulse battery charger - Google Patents

Abstract

A battery charger comprises a source of electrical power, and at least one semiconductor switch having a characteristic to be able to close for a duration of 10 -6 to 10 -8 seconds, and to withstand a pulse voltage of up to 20,000 volts. There is a pulse generator operating with a pulse frequency in the range of 1 kHz to 1 mHz, and with a pulse duration per cycle of 10 -6 to 10 -8 seconds. The pulse generator has a pulse output voltage of 12 to 20,000 volts.
There is also a circuit controller having terminal voltage sensing means for a battery to be charged, and a pulse controller for controlling the frequency and pulse duration characteristics of the pulse generator during a charging operation. Typically, the battery charger operates to charge lead acid or alkaline zinc manganese dioxide batteries.

Description

FAST PULSE BATTERY CHARGER
FIELD OF THE INVENTION:
[0001 ] This invention relates to battery chargers, and particularly to battery chargers for lead acid batteries. Specifically, the present invention provides a battery charger for lead acid batteries, where the charging energy which is delivered to the battery is delivered in very fast, short duration pulses, usually having a high voltage.
BACKGROUND OF THE INVENTION:

[0002] Pulse pattern battery charging is well known. In particular, it is known that pulse pattern battery charging will provide numerous advantages over continuous direct current charging, including extending the battery cycle life, and increasing the permissible recharge rate of a battery.
Of course, recharge efficiency may be significantly increased, as is well known to those skilled in the battery art, by the use of pulse pattern battery charging.
~=0003] Moreover, it has been found that, in some cases, primary cells such as alkaline batteries which are generally considered to be non-rechargeable, may be recharged at least to a limited extent by the use of low voltage, pulsed battery charging techniques.
~=0004] Typically, however, in the past, the duration of individual charging pulses has been l n the millisecond range - say, in the range of 10 ' 3 to 10 ' a seconds.
However, typically such charge pulses have been delivered at relatively low voltage. For example, charging pulses delivered to a l2 volt lead acid battery might be in the range of up to 48 volts, having a duration of 10 ' 3 to 10 -a seconds, and a frequency of 1 Hz to l KHz.
[:0005] Of course, for such battery systems and cells as ordinary alkaline cells - whether of the typical non-rechargeable type, or the more recent rechargeable type - the charge pulse voltage must be limited to being only several times greater than the nominal terminal voltage of the cell, due to the risks of zinc dendrite formation, separator "punch through", and electrolyte "boil off'.
[0006] On the c>ther hand, known pulse pattern battery charging, techniques have been able to exploit the differential mobility between the electrode and the electrolyte, particularly in lead acid battery systems and like.

[0007] The inventor herein has unexpectedly discovered that a very substantial improvement in overall charging capability may be obtained by the use of ultra short charging pulses. Moreover, it has been unexpectedly discovered that the use of ultra short reverse (discharge) pulses also leads to a substantial improvement in overall charging capability - particularly for lead acid batteries.
[0008] The duration of charging pulses, and indeed, discharging pulses, that has been found to be advantageous, is in the microsecond and sub-microsecond range - 10 - 6 to 10 ' 8 seconds. By having very short charging pulses, or discharge pulses, it is possible to permit those pulses to have relatively high voltage -- in the range of kilovolts - with a relatively high pulse frequency, which may be in the range of 1 kHz to 1 mHz. 'this gives a duty cycle of up to 10%, at high voltage, thereby providing significant energy transfer without undesirable heat loss effects, and the like.
[0009] Moreover, by using a pulse duration in the range 10 ' 6 to 10 - 8 seconds, with a pulse Frequency in the range of 1 kHz to 1 mHz, advantage is taken of ionic mobility, or more particularly, the lack thereof. In other words, minimum contribution due to ionic mobility effects will occur.
:However, at the same time, the time constant characteristic of the boundary layer between the electrode and the electrolyte will come into play. This, of course, is in contradistinction to the time constant of a conductive electrode.
~=0010] Thus, a reverse pulse - application of a load - having a short duration as discussed above, will depolarize the boundary layer between the electrolyte and an electrode, and thereby discharge the capacitive storage of the boundary layer.
~=0011 ] On the other hand, a forward pulse of the sort being discussed, in the range of 10 ' 6 t:o 10-8 seconds, and having a pulse output voltage of up to 10,000 or 20,000 volts, will dramatically effect the solubility of lead sulphate. This is as a consequence of hyperpressure solubility, and voltage gradient effects, of the lead sulphate and sulphuric acid.
[:0012] In order for the ultra-fast, high voltage charging pulses in keeping with the present invention to be attainable, the inventor herein has taken advantage of the fact that economical semiconductors which have high power, ultra-fast operating characteristics, with very high operating reliability, are now commercially available.
[0013] Thus, the present inventor has provided a fast pulse battery charger that is particularly adapted for use with lead acid batteries, and which takes advantage of the commercial availability of high power, ultra-fast, reliable, semiconductors which will function at the pulse switching rate and pulse voltages contemplated by the present invention.
SUMMARY OF THE INVENTION:
[0014] In accordance with one aspect of the present invention, there is provided a battery charger for lead acid batteries which comprises a source of electrical power, and at least one semiconductor switch having a characteristic such that it is able to close for a duration of 10 - 6 to - g seconds, and to withstand a pulse voltage of up to 20,000 volts.
[0015] A pulse generator is provided, having a characteristic pulse frequency in the range 10 .of 1 kHz to 1 mHz and a pulse duration per cycle of 10 ' 6 to 10 - 8 seconds.
[0016) In the battery charger of the present invention, the pulse generator has a pulse output voltage ranging from 12 up to 20,000 volts.
[0017] There is also provided a circuit controller having terminal voltage sensing means for .a lead acid battery to be charged, and also having a pulse controller for controlling the frequency and ;pulse duration characteristics of the pulse generator during a charging operation.
[0018] Moreover, the circuit controller may also be such as to provide a load to a battery to be charged, so as to precondition the battery. If so, the load to be applied to the battery to be charged is a pulsed load, having a pulse frequency in the range of 1 kHz to 1 mHz, and a pulse duration per load cycle of 10 -6 to 10 - 8 seconds.
DRIEF DESCRIPTION OF THE DRAWINGS:
x;0019) The novel features which are believed to be characteristic of the present invention, ~~s to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example. It is expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. Embodiments of this invention will now be described by way of example in association with the accompanying drawings in which:

[0020] Figure 1 provides a functional schematic of a battery charger in keeping with the present invention, as connected to a source of alternating current power and to a battery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0021 ] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.
[0022] As noted above, a principle purpose of the present invention is to provide a battery charger which has high voltage, short duration charged pulses, thereby minimally affecting electrolyte ionic mobility, while at the same time affecting the boundary layer between the electrolyte and an electrode, as a consequence of hyperpressure solubility and voltage gradient effects thereat, so as to specifically improve the solubility of lead sulphate.
[0023] Of course, as noted previously, a reverse pulse of short duration may have the effect of discharging the capacitive storage of the boundary layer, so as to thereby depolarize the boundary layer.
~=0024] Referring to Figure 1, a fast pulse battery charger in keeping with the present invention is indicated generally at 10.
~-0025] The battery charger 10 comprises several principal components, identified at 12, 14, <~nd 16, respectively. Those components, their purposes, and characteristics, are described in greater detail hereafter.
x:0026] It will be seen in Figure 1 that the fast pulse battery charger 10 is connected to a source of alternating current 20, and to a battery 30.
[:0027] While the present invention is particularly directed to lead acid batteries, it will be v.mderstood to those skilled in art that other battery systems may also be charged in keeping with the present invention, with appropriate pulse width, pulse frequency, and voltage control.
[;0028] The first component is a rectifier and voltage amplifier, shown generally at 12. The specific characteristics of the rectil-ier/voltage amplifier are beyond the scope of the present invention, and are known to those skilled in the relevant art in any event.

[0029] The next component is shown generally at 14, and it includes a pulse generator indicated at 22 and a switch indicated generally at 24. The particular features of component 14, and its constituent elements including a pulse generator 22 and a semiconductor switch 24, are described hereafter.
[0030] Finally, a circuit controller 16 is shown. The circuit controller has voltage sensing means included therein, for sensing the terminal voltage of the lead acid battery 30 which is to be charged. Moreover, the circuit controller 16 also functions as a pulse controller for controlling the :frequency and pulse duration characteristic of the pulse generator 22 during a charging operation.
[0031 ] The pulse generator 22 and the semiconductor switch 24 each have a characteristic that they are capable of operating at ultra short pulse widths, relatively high pulse frequencies, and high pulse voltage outputs.
~=0032] Specifically, the semiconductor switch 24 is such as to have the characteristic that it will close for a duration of 10 -6 to 10 ' ~ seconds, and that it will withstand a pulse voltage of up to 20,000 volts.
x:0033] The pulse generator 22 is such that it has a characteristic pulse frequency in the range of 1 kHz to 1 mHz. Moreover, the pulse generator 22 is capable of producing pulses having a duration of only 10 ' 6 to 10 - 8 seconds.
[:0034] However, the pulse generator/switch module 14 is also capable of delivering output pulses to the battery 31), with a pulse output voltage of 12 to 20,000 volts.
Typically, the pulse output voltage will be in the range of 1,000 to 10,000 volts, but lower voltages may be employed at <;ertain times during a charging cycle. and may be employed even in a "trickle charge" condition, so as to assure a substantially completely charged battery.
[0035] It is known that the charging efficiency of lead acid batteries, in particular, can be improved by partially discharging them while at the same time charging the battery, or as an initial step during a charging operation.
[0036] Accordingly, the circuit controller module 16 also is such as to provide a load to the battery 30, when connected thereto, so as to precondition the battery.
however, the load is also a fast pulse load, and it is such that the pulse frequency of the load as it is applied to the battery 30 is in the range of 1 kHz to 1 mHz, having a pulse duration per load cycle of 10 -6 to 10' g seconds.

[0037] Typically, high voltage pulses of the sort described above are produced indirectly, through the use of step up "pulse" transformers, tapped inductors, and the like. Thus, a semiconductor switch 24 is required to have the capacity to handle the speed and power which is involved, but not necessarily the voltage per se. As an example, the combination of the pulse generator 22 and the semiconductor switch 24 may employ field effect transistors (FETs) which are rated at 500 to 600 volts. However, at the frequencies and pulse widths described above, pulses will be routinely generated that are in the 10,000 to 20,000 volt range.
[003 8] It should also be noted that the present invention may be equally applicable to alkaline batteries such as zinc manganese dioxide batteries - which are typically found in the market in sizes ranging from AAA and AA, up to C and D. This may be particularly advantagous where the pulse duration is maintained at a short pulse length of the magnitude described above. Moreover, reverse pulses have shown to be effective in the suppression of zinc dendrite growth in such batteries.
[0039] This is because reverse pulses will have multiple effects. Not only will they depolarise the boundary layer, they also act to briefly discharge the cell.
Zinc dendrites have an abnormally large surface to volume ratio, so they are selectively soluble in the alkaline electrolyte of the cell, during discharge.
[0040] Still further, reverse pulses will planarize a surface, which will also have the effect of inhibiting zinc dendrite growth.
[0041 ] It should also be noted that in some circumstances, for example the charging of lead acid batteries, a very fast, very high voltage forward pulse can be deliberately added to the leading edge of a slower charging pulse, and this aids in the control of sulfation within the battery.
[0042] It will also be apparent to those skilled in the art that control of current intervals in a pulse pattern may have useful equilibration or re-equilibration effects; and may also provide an opportunity for zero current voltage measurement as may be required in many different forms of charge management, charge monitoring, and feedback control.
[0043] Moreover, reverse pulses in the millisecond range can be employed to lower the barrier height in such systems as, particularly, lead acid batteries, thereby reducing power requirements and cell heating. This, in turn, will generally lead to a more rapid charging effect, with faster charge acceptance.

[0044] The principals of fast pulse battery chargers have been described above, and are set forth in the appended claims. Specific charging and discharging frequencies, pulse widths for charging pulses and discharged pulses, and pulse output voltages, have been discussed. However, alterations and modifications may become suggested or known to those skilled in the art, without departing from the spirit and scope of the appended claims.
[0045] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises"' or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not to the exclusion of any other integer or step or group of integers or steps.
[0046] Moreover, the word "substantially" when used with an adjective or adverb is intended to enhance the scope of the particular characteristic. Thus, substantially charged, in respect of a battery, means effectively fully charged, to within a very high percentage of the total charge capacity of the battery.

Claims (3)

1. A battery charger for batteries, comprising:
a source of electrical power;
at least one semiconductor switch having a characteristic to be able to close for a duration of 10 -6 to 10 -8 seconds, and to withstand a pulse voltage of up to 20,000 volts;
a pulse generator having a characteristic pulse frequency in the range of 1 kHz to 1 mHz, and a pulse duration per cycle of 10 -6 to 10 -8 seconds;
wherein said pulse generator has a pulse output voltage of 12 to 20,000 volts;
and a circuit controller having terminal voltage sensing means for a lead acid battery to be charged, and a pulse controller for controlling the frequency and pulse duration characteristics of said pulse generator during a charging operation.

2. The battery charger of claim 1, wherein said circuit controller is such as to provide a load to a battery to be charged so as to precondition the battery, where the load to be applied to the battery to be charged is a pulsed load having a pulse frequency in the range of 1 kHz to 1 mHz, and a pulse duration per load cycle of 10 -6 to 10 -8 seconds.

3. The battery charger of claim 1, when used to charge batteries chosen from the group consisting of lead acid batteries and alkaline zinc manganese dioxide batteries.