Charge equalization of series connected cells or batteries

• US 5,594,320 A
• Filed: 09/09/1994
• Issued: 01/14/1997
• Est. Priority Date: 09/09/1994
• Status: Expired due to Fees

• Current Assignee: Bank of New York Mellon Corporation
• Original Assignee: Rayovac Corp (Spectrum Brands Holdings, Inc.)
• Inventors: Ebner, Walter B., Pacholok, David R., Fouchard, David T.
• Primary Examiner(s): NAPPI, ROBERT E
• Application Number:
  US08/303,703
• Time in Patent Office: 858 Days
• Field of Search: 320/4, 320/6, 320/8, 320/15, 320/19, 320/21
• US Class Current: 320/103
• CPC Class Codes: H02J 7/0018 using separate charge circuits

Abstract

An equalizer for equalizing the charge on several series-connected cells includes a transformer having plural windings on a core corresponding to the number of cells. The windings are tightly coupled to one another. A switching device such as a MOSFET is connected to each of the windings, and a winding and a switching device are connected across each of the cells. The switching devices are simultaneously switched at a relatively high frequency, e.g., 20 Hz, and the voltage across the highest charged cell appears across each of the windings when the switching devices are on. Current flows from the most highly charged cell to a cell or to cells of lower charge, with the charging current being proportional to the difference in voltage between the highest charged cell and each of the lesser charged cells. Equalization is carried out with very little power consumption by the equalizer, allowing charging to take place in a rapid manner.

Claims

1. An equalizer for equalizing the charge on two or more cell units connected in series comprising:

(a) a transformer having plural windings on a core corresponding to the number of cell units, each of the windings having the same number of turns and being tightly coupled to one another;

(b) a controllable switching device connected in series with each winding, each series combination of switching device and winding connectable in parallel across one of the cell units; and

(c) an oscillator connected to the switching devices to provide a control signal to each switching device to turn each of the switching devices on and off simultaneously at a high switching frequency, whereby the voltage across each winding of the transformer will be the voltage of the cell unit having the highest voltage such that energy is transferred from the highest charged cell unit to one of lower charge.

2. The equalizer of claim 1 wherein the switching devices are power MOSFETs having gates, and wherein the oscillator is connected to supply the control signal to the gates to turn the MOSFETs on and off simultaneously.

3. The equalizer of claim 2 wherein the oscillator provides a square-wave output signal to the gates of the MOSFETs.

5. The equalizer of claim 1 wherein the oscillator switches at a switching frequency which is above an audible frequency.

6. The equalizer of claim 1 including means for turning off the oscillator when no current is being supplied by a battery charger to the cell units so that the switching devices are turned off and for turning on the oscillator and the switching devices when current is supplied from a battery charger to the cell units.

7. The equalizer of claim 6 in combination with a battery charger connected to supply charging current to the series combination of cell units.

8. The equalizer of claim 1 wherein the windings on the transformer are multifilar windings which are wound together on the core of the transformer having substantially no gap.

4. An equalizer for equalizing the charge on two or more cell units connected in series comprising:

(a) a transformer having plural windings on a core corresponding to the number of cell units, each of the windings having the same number of turns and being tightly coupled to one another, and wherein the windings of the transformer have inductance;

(b) a controllable switching device connected in series with each winding, each series combination of switching device and winding connectable in parallel across one of the cell units, and wherein the switching devices are power MOSFETs having gates and wherein each MOSFET has a drain to source capacitance which forms a resonant circuit with the winding to which the MOSFET is connected; and

(c) an oscillator connected to the switching devices to provide a control signal at a switching frequency lower than a resonant frequency of the resonant circuit to the gates of each switching device to turn each of the switching devices on and off simultaneously at a high switching frequency, whereby the voltage across each winding of the transformer will be the voltage of the cell unit having the highest voltage such that energy is transferred from the highest charged cell unit to one of lower charge.

9. A method of equalizing the charge on two or more cell units connected in series, comprising the steps of:

(a) providing a transformer having plural windings on a core corresponding to the number of cell units, each of the windings having the same number of turns and being tightly coupled to one another;

(b) simultaneously electrically connecting each of the windings to one of the cell units for a selected period of time such that the voltage at the highest charged cell unit appears across each of the windings to transfer energy from the most highly charged cell unit to a cell unit of lower charge, and then simultaneously disconnecting the windings from the cell units, and repeating the steps of connecting and disconnecting the windings from the cell units at a selected frequency thereby to equalize the charge on the cell units.

10. The method of claim 9 wherein the step of connecting and disconnecting the windings to the cell units is carried out at a frequency above an audible frequency.

11. The method of claim 9 including the additional step of providing charging current through the cell units connected in series.

12. The method claim 9 wherein the step of connecting and disconnecting the windings is carried out only when charging current from a battery charger is supplied to the cell units.

13. A method of equalizing the charge on two or more cell units connected in series, comprising the steps of:

(a) providing a transformer having two windings on a core for each cell unit, the two windings for each cell unit connected in parallel to such cell unit, the two windings for each cell unit comprising a first winding and a second winding, each of the first windings having the same number of turns and being tightly coupled to one another and each of the second windings having the same number of turns and being tightly coupled to one another; and

(b) simultaneously electrically connecting each one of the first or second windings to one of the cell units for a selected period of time such that the voltage at the highest charged cell unit appears across each of the windings to transfer energy from the most highly charged cell unit to a cell unit of lower charge, and then simultaneously disconnecting the windings from the cell units, wherein the step of simultaneously electrically connecting and disconnecting is carried out alternatively for the first windings and then the second windings, and repeating the step of connecting and disconnecting the windings from the cell units at a selected frequency thereby to equalize the charge on the cell units.

14. An equalizer for equalizing the charge on two or more cell units connected in series comprising:

(a) a transformer having first and second windings on a core, the number of first and second windings corresponding to the number of cell units, each of the first windings having the same number of turns and being tightly coupled to one another and each of the second windings having the same number of turns and being tightly coupled to one another;

(b) a first controllable switching device connected in series with each first winding and a second controllable switching device connected in series with each second winding, each series combination of a first switching device and a first winding connectable in parallel with a series combination of a second switching device and a second winding across one of the cell units; and

(c) an oscillator connected to the switching devices to provide a control signal to each switching device to turn each of the first switching devices on and off simultaneously and to turn each of the second switching devices on and off simultaneously at a high switching frequency, and wherein the second switching devices are off when the first switching devices are on and the second switching devices are on when the first switching devices are off, whereby the voltage across each winding of the transformer will be the voltage of the cell unit having the highest voltage such that energy is transferred from the highest charged cell unit to one of lower charge.

15. The equalizer of claim 14 wherein the first and second switching devices are power MOSFETs having gates and wherein the oscillator provides a noninverted output signal and an inverted output signal which is the complement of the noninverted output signal, the noninverted output signal connected to the gates of the first MOSFETs and the inverted output signal connected to the gates of the second MOSFETs.

16. The equalizer of claim 15 wherein the noninverted and inverted output signals of the oscillator are square-waves.

17. The equalizer of claim 15 wherein the windings of the transformer have inductance and each MOSFET has a drain to source capacitance which forms a resonant circuit with the winding to which the MOSFET is connected, and wherein the oscillator provides a control signal at a switching frequency lower than a resonant frequency of the resonant circuit.

18. The equalizer of claim 14 wherein the oscillator switches at a switching frequency which is above an audible frequency.

19. The equalizer of claim 14 including means for turning off the oscillator when no current is being supplied by a battery charger to the cell units so that the switching devices are turned off and for turning on the oscillator and the switching devices when current is supplied from a battery charger to the cell units.

20. The equalizer of claim 19 in combination with a battery charger connected to supply charging current to the series combination of cell units.

21. The equalizer of claim 14 wherein the first windings on the transformer are multifilar windings and the second windings are multifilar windings and wherein the multifilar windings are wound together on the core of the transformer having substantially no gap.