WO2022238720A1

WO2022238720A1 - Battery charging and voltage supply system

Info

Publication number: WO2022238720A1
Application number: PCT/GB2022/051225
Authority: WO
Inventors: Barry GLEAVE
Original assignee: Intelligent Clean Energy Ltd
Priority date: 2021-05-14
Filing date: 2022-05-16
Publication date: 2022-11-17
Also published as: GB202207120D0; GB202106907D0

Abstract

There is provided a circuit including a controller. The circuit comprises a first set of terminals Gen +V, Gen 0V electrically couplable to an electrical power source; a second set of terminals +ve, -ve electrically couplable to a load Load 1; a third set of terminals electrically couplable to a set of nickel- metal hydride secondary cells comprising a first cell BAT 1 and a second cell BAT X; and a set of multi-pole changeover relay switches respectively electrically coupled to cells of the set of secondary cells. The respective terminals of the third set of terminals are electrically couplable to respective cells of the set of secondary cells. The controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a first configuration and a second configuration. In the first configuration, the first cell BAT 1 and the second cell BAT X are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals Gen +V, Gen 0V, whereby the first cell BAT 1 and the second cell BAT X are arranged to be charged by the power source. In the second configuration, the first cell BAT 1 and the second cell BAT X are mutually electrically coupled in series via the third set of terminals to the second set of terminals +ve, -ve, whereby the first cell BAT 1 and the second cell BAT X are arranged to drive the load Load 1. The controller is configured to receive a measurement of a voltage supplied to the load via the second set of terminals +ve, -ve. The controller is configured to electrically couple the set of secondary cells in one of the configurations in response to the measurement. The controller is configured to transmit a signal to cause a subset of the relay switches to switch the set of secondary cells between configurations.

Description

1

BATTERY CHARGING AND VOLTAGE SUPPLY SYSTEM

Technical Field

The present invention relates to a circuit including a controller and a method of controlling the circuit performed by the controller.

Background to the Invention

Conventional battery charging systems are generally based around standard battery voltages, such as 12V, 24V and 48V, as these voltages are used by the majority of direct current (DC) apparatuses. Lead-acid batteries, for instance, are typically 6V, 12V or 24V. To charge batteries at these voltages, it is necessary to generate slightly higher than the nominal voltage. For instance, to charge a 12V battery, 13.8V needs to be generated. No energy is put into the battery until the charging voltage is reached. Lead-acid batteries must be charged with constant voltage.

Consequently, if energy to charge the battery is generated using a renewable energy source, such as a wind energy, tidal energy or solar energy, there may be times during which the charging voltage is not reached despite the availability of the relevant energy source. For example, though there may be some wind, the strength of the wind may not be sufficient to generate the charging voltage.

Batteries are generally made up of cells of 1.2V placed in series, meaning that a 12V battery could be made up of 10 cells of 1.2V connected in series to give the required voltage. For example, the nominal voltage of a nickel-cadmium ora nickel-iron electrochemical cell is 1.2V. Nickel-metal hydride batteries must be charged with constant current and are more efficacious than lead-acid batteries. Other types of cell may have different nominal voltages. Therefore, one approach to addressing the problem of reaching the charging voltage could be to charge each of the cells individually and, once charged, manually arrange the cells in useful configurations. However, such an approach is impractical and inefficient. Moreover, as the cells became drained, they would need to be individually removed from the configuration in which they had been arranged in order to be recharged. Removing cells in order to recharge them is not possible for critical applications, where a constant power supply must be maintained. 2

Hence, there is a need to charge batteries at the lowest possible voltage in order to maximise use of the energy from the environment whilst also maintaining a useful operating voltage for most DC apparatus (e.g., 12, 24 and 48V).

Summary of the Invention

It is one aim of the present invention, amongst others, to provide a circuit including a controller which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified here or elsewhere. For instance, it is an aim of the present invention to provide a circuit including a controller that enables charging of cells at low voltages without having to charge the cells individually. For instance, it is further an aim of the present invention to enable a constant power supply to be maintained when cells are recharged.

Detailed Description of the Invention

According to the present invention there is provided a circuit including a controller, as set forth in the appended claims. Also provided is a method of controlling the circuit performed by the controller. Other features of the invention will be apparent from the dependent claims and the description that follows.

According to a first aspect of the present invention, there is provided a circuit including a controller. The circuit comprises a first set of terminals electrically couplable to an electrical power source; a second set of terminals electrically couplable to a load; a third set of terminals electrically couplable to a set of nickel-metal hydride secondary cells comprising a first cell and a second cell; and a set of multi-pole changeover relay switches respectively electrically coupled to cells of the set of secondary cells. The respective terminals of the third set of terminals are electrically couplable to respective cells of the set of secondary cells. The controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a first configuration and a second configuration. In the first configuration, the first cell and the second cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, whereby the first cell and the second cell are arranged to be charged by the power source. In the second configuration, the first cell and the second cell are mutually electrically coupled in series via the third set of terminals to the second set of terminals, whereby the first cell and the second cell are arranged to drive the load. The controller is configured to receive a measurement of a voltage supplied to the load via the second set of terminals. The controller is configured to electrically couple the set of secondary cells in one of the configurations in 3 response to the measurement. The controller is configured to transmit a signal to cause a subset of the relay switches to switch the set of secondary cells between configurations

In one example, the controller is a programmable logic controller (PLC), microcontroller, computer or microprocessor. In one example, the first, second and third sets of terminals are sets of electrical contacts. The load is an electrical load, meaning that the load is a portion of the circuit that consumes active power, for example an electrical appliance. Secondary cells can be charged, discharged into a load, and recharged many times, as opposed to disposable or primary cells, which are supplied fully charged and discarded after use. In one example, each of the secondary cells is replaced by a secondary battery. In one example, the measurement of voltage supplied to the load is made by a voltmeter (i.e., the voltage across the load is measured by a voltmeter).

By charging the first cell and the second cell in parallel, the first cell and the second cell can be charged simultaneously at low voltages. For example, if the electrical power source is a wind turbine, the first cell and the second cell can both be charged even when the wind strength is low. For example, if the electrical power source is a solar panel, the first cell and the second cell can both be charged even at low lights levels (e.g., dawn or dusk). By the first cell and the second cell driving the load in series, the sum of the charge of the first cell and the second cell is discharged to the load. By coupling the set of secondary cells in one of the configurations in response to the measurement, the set of secondary cells is automatically configured to charge or drive the load as necessary.

In one example, the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a third configuration. In the third configuration, the first cell is electrically coupled via the third set of terminals to the first set of terminals, and the second cell is electrically coupled via the third set of terminals to the second set of terminals. The third configuration results in the first cell being charged while the second cell is driving the load.

In one example, the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a fourth configuration. In the fourth configuration, the second cell is electrically coupled via the third set of terminals to the first set of terminals, and the first cell is electrically coupled via the third set of terminals to the second set of terminals. The third configuration results in the second cell being charged while the first cell is driving the load.

In one example, the set of secondary cells further comprises a third cell, and the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a fifth configuration. In the fifth configuration, the first cell and the second cell are mutually electrically 4 coupled in parallel via the third set of terminals to the first set of terminals, and the third cell is electrically coupled via the third set of terminals to the second set of terminals. The fifth configuration results in the first cell and the second cell being charged in parallel, such that the first cell and the second cell are charged simultaneously at low voltages, while the third cell drives the load. In this way, more than one cell can be charged at a low voltage while another cell drives the load.

In one example, the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in a sixth configuration. In the sixth configuration, the first cell and the third cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, and the second cell is electrically coupled via the third set of terminals to the second set of terminals. The fifth configuration results in the first cell and the third cell being charged in parallel, such that the first cell and the second cell are charged simultaneously at low voltages, while the second cell drives the load. In this way, more than one cell can be charged at a low voltage while another cell, different to the cell driving the load in the fifth configuration, drives the load.

In one example, the controller is configured to switch the set of secondary cells between the first configuration and the second configuration. By switching the set of secondary cells between the first configuration and the second configuration, the first cell and second cell can be alternately charged/recharged and used to drive the load.

In one example, the controller is configured to switch the set of secondary cells between the first configuration, the second configuration, the third configuration and the fourth configuration. By switching the set of secondary cells between the first configuration, the second configuration, the third configuration and the fourth configuration, the first cell and second cell can be charged/recharged simultaneously, used to drive the load simultaneously, or respectively charged and used to drive the load.

In one example, the controller is configured to switch the set of secondary cells between the first configuration, the second configuration, the third configuration, the fourth configuration, the fifth configuration and the sixth configuration. By switching the set of secondary cells between the first configuration, the second configuration, the third configuration and the fourth configuration, the set of secondary cells can switch between configurations with the aforementioned benefits of charging at low voltage and/or driving the load.

In one example, the controller is configured to switch the set of secondary cells between configurations based on at least one of: the measurement of voltage supplied to the load; a length of 5 time the set of secondary cells has been in one of the configurations; and a charge level of one of the cells. In one example, the controller is configured to switch the set of secondary cells between configurations cyclically. In one example, controller is configured to switch the set of secondary cells to another configuration when the measurement of the voltage supplied to the load falls below a predetermined threshold. For instance, the controller may be configured to switch the set of secondary cells from the third configuration to the fourth configuration or from the fifth configuration to the sixth configuration when the measurement of the voltage supplied to the load falls below a predetermined threshold. In one example, the controller is configured to alternate between configurations after a preset period of time. For instance, the controller may be configured to switch the set of secondary cells from the third configuration to the fourth configuration or from the fifth configuration to the sixth configuration after T seconds. In one example, controller is configured to switch the set of secondary cells to another configuration when based on a charge level of one of the cells. For instance, the controller may be configured to switch the set of secondary cells from the third configuration to the fourth configuration when it is determined that the charge level of the first cell falls below a predetermined low level or when the charge level of the second cell reaches a predetermined upper level. By the controller being configured to switch the cells according to one or more of the metrics of measurement of voltage supplied to the load; length of time the set of secondary cells has been in one of the configurations; and charge level of one of the cells, a constant discharge drives the load. For instance, simultaneously decoupling a cell with a charge level below the predetermined low level from the second set of second terminals and coupling a cell with a charge level at or above the predetermined upper level to the set of second terminals facilitates maintenance of a constant discharge to the load.

In one example, the controller is configured to be powered by the power source.

In one example, the controller comprises a transmitter and a receiver. In one example, when the controller switches set of secondary cells from the first configuration to the second configuration, the controller transmits a signal to cause a first switching device coupled to the first cell and a second switching device coupled to the second cell. In one example, when the controller switches the set of secondary cells from the fifth configuration to the sixth configuration the controller transmits a signal to the second switching device and a third switching device coupled to the third cell. In one example, transmission of a signal to a respective switching device causes the corresponding one of the set of secondary cells to couple to the second set of terminals, and the absence of transmission of the signal to a respective switching device causes the corresponding one of the set of secondary cells to couple to the first set of terminals. 6

In one example, the switching devices are three- pole changeover relay switches.

In one example, the circuit further comprises a set of current limiting devices configured to prevent excessive current being delivered by the power source to a corresponding cell or cells of the set of secondary cells.

In one example, the circuit further comprises a set of blocking diodes configured to prevent current from leaving a corresponding cell or cells of the set of secondary cells when the corresponding cell or cells are electrically coupled to the first set of terminals.

In one example, the power source is a renewable energy source. In one example, the renewable energy source is at least one of: wind energy, tidal energy, solar energy, hydroenergy, geothermal energy and biomass energy.

In one example, the power source is one or more photovoltaic cells.

According to a second aspect of the present invention, there is provided a method of controlling a circuit performed by a controller, the circuit comprising: a first set of terminals electrically couplable to an electrical power source; a second set of terminals electrically couplable to a load; a third set of terminals electrically couplable to a set of nickel-metal hydride secondary cells comprising a first cell and a second cell; and a set of multi-pole changeover relay switches respectively electrically coupled to cells of the set of secondary cells. The respective terminals of the third set of terminals are electrically couplable to respective cells of the set of secondary cells. The method performed by the controller comprises electrically coupling the set of secondary cells, via the third set of terminals, in a first configuration or a second configuration. In the first configuration, the first cell and the second cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, thereby charging the first cell and the second cell by the power source. In the second configuration, the first cell and the second cell are mutually electrically coupled in series via the third set of terminals to the second set of terminals, thereby driving the load by the first cell and the second cell. The method also comprises receiving a measurement of a voltage supplied to the load via the second set of terminals, electrically coupling the set of secondary cells in one of the configurations in response to the measurement and transmitting a signal to cause a subset of the relay switches to switch the set of secondary cells between configurations. Each feature of the second aspect is as described with reference to the first aspect. The method of the second aspect comprises any of the steps described with reference to the first aspect. 7

According to a third aspect of the present invention, there is provided a computer program comprising instructions for implementing the method of the second aspect. Each feature of the third aspect is as described with reference to the first aspect.

Definitions

Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term “consisting essentially of” or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like.

The term “consisting of” or “consists of” means including the components specified but excluding other components.

Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to include the meaning “consists essentially of” or “consisting essentially of”, and also may also be taken to include the meaning “consists of” or “consisting of”.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein, are also applicable to all other aspects or exemplary embodiments of the invention where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.

Brief Description of the Drawings

For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

Figure 1 schematically depicts a battery charging and voltage supply system comprising two secondary cells according to an exemplary embodiment; 8

Figure 2 schematically depicts a battery charging and voltage supply system comprising more than two secondary cells according to an exemplary embodiment;

Figure 3 schematically depicts a simplified representation of the system of Figure 1 or Figure 2; and

Figure 4 schematically depicts a method of controlling a circuit performed by a controller according to an exemplary embodiment.

Detailed Description of the Drawings

Figure 1 schematically depicts a battery charging and voltage supply system according to an exemplary embodiment. Figure 1 shows a first set of terminals Gen +V Gen 0V electrically couplable to a power source and a second set of terminals +ve -ve electrically couplable to a load Load 1. A third set of terminals is shown electrically coupled to a set of nickel-metal hydride secondary cells. In Figure 1 , two secondary cells are shown BAT 1, BAT X. However, as indicated by the notation “BAT X”, the system may comprise more than two secondary cells (see Figure 2). Typically, X is equal to several hundred. The number of secondary cells included in the system depends on the voltage required by the load Load 1, for instance.

Each secondary cell BAT 1, BAT X is coupled to a corresponding switching device, each switching device being a multi-pole changeover relay switch. Secondary cell BAT 1 is coupled to a first switching device comprising a main switch SW1, a coil RL1 and subsidiary switches S1 , S2, S3 to form a first combination of secondary cell BAT 1 and the first switching device. Secondary cell BAT X is coupled to an x^th switching device comprising a switch SWX, a coil RLX and subsidiary switches S1 , S2, S3 to form an x^th combination of secondary cell BAT X and the x^th switching device.

Figure 1 shows both switching devices de-energised, which is the default position of the switching devices. The switching devices are both de-energised, because each of the main switches SW1 and SWX are open. Resultingly, the secondary cells BAT 1, BAT X are mutually charged in parallel by the power source in the configuration shown in Figure 1. The configuration of the system shown in Figure 1 in which the secondary cells BAT 1, BAT X are mutually charged in parallel is termed a first configuration.

In the first configuration, the positive terminal of each of the secondary cells BAT 1 , BAT X is respectively fed a charging current by Pin 1 via Pin 4, Pin 4 connecting to Gen +V. The negative 9 terminal of each of the secondary cells BAT 1, BAT X respectively completes the charging circuit by Pin 11 via Pin 8, Pin 8 connecting to Gen 0V.

In the first configuration, Pin 4 of each of the switching devices is respectively connected to the power source via a current limiting device IL1, ll_X and a blocking diode D1 , DX. The current limiting devices IL1 , I LX prevent excessive current being delivered to respective secondary cells BAT 1 , BAT X. Nickel-metal hydride cells could be destroyed if the current is not limited. The blocking diodes prevent current leaving the respective secondary cells BAT 1 , BAT X and prevent current exchange between secondary cells BAT 1, BAT X when the secondary cells BAT 1, BAT X are being charged.

The switching devices enable the system to be switched between the first configuration shown in Figure 1 and other configurations. For instance, the switching devices enable the system to be switched to configurations in which one or both of the secondary cells BAT 1, BAT X are driving the load Load 1. For example, the system may be switched to a second configuration in which both secondary cells BAT 1, BAT X are mutually electrically coupled in series and drive the load Load 1. For example, the system may be switched to a third configuration in which secondary cell BAT 1 is coupled to the power source and secondary cell BAT X is coupled to the load Load 1, or a fourth configuration in which secondary cell BAT 1 is coupled to the load Load 1 and secondary cell BAT X is coupled to power source.

The use of relay switches is particularly advantageous. Relay switching is associated with volt free contacts with zero losses across the switch, which is crucial for cells charged at low voltages. Semi conductor switches (e.g., MOSFETs), for instance, have an inherent voltage drop across them when on, typically 1V to 3V, leading to power losses. MOSFETs are technically viable when charging conventional battery voltages (e.g., 6V, 2V, 24V). However, MOSFETs are not technically viable for single cell charging at 1.2V, because when a MOSFET is turned on the forward voltage drop across the MOSFET is similar to the voltage that it is feeding. Therefore, during charging as much power is consumed by the MOSFET as is delivered to the cell. Resultingly, the charging voltage needs to be increased to compensate. Use of relay switches facilitates charging at the lowest possible voltage.

Each of the switching devices is energised by supplying the respective relay coil RL1, RLX with an appropriate voltage (RLY V) via the corresponding main switch SW1 , SWX to Pin 2. Figure 1 shows manually operated main switches SW1 , SWX. However, these main switches SW1 , SWX are typically replaced by an electronic controller in practice. The electronic controller controls switching of the switching devices such that the configuration of the system is changed between different configurations. Switching by the controller of the configuration of the system may be responsive to, 10 for example, measurement of a voltage received by the load. When one of the switching devices is energised all three corresponding subsidiary switches S1, S2, S3 switch simultaneously.

In the second configuration and in the fourth configuration, the positive terminal of secondary cell BAT 1 is connected via Pin 1 and Pin 3 to +ve, and the x^th combination connects the positive terminal of secondary cell BAT X to the negative terminal of secondary cell BAT 1 via Pin 9 and Pin 11 of the first switching device.

In the first configuration, a shorting link is provided by Pin 5 and Pin 6. Pin 5 and Pin 6 are also connected to Pin 3 and Pin 9, respectively. Therefore, when one of the secondary cells BAT 1, BAT X is removed from the second configuration a shorting link maintains current flow to the load.

The first combination is connectable via a load switch SWL1 to +ve. The x^th combination is connectable via the same switch SWL1 to -ve. Thus, load switch SWL1 can be used to change the direction of current flow.

Table A summarises connections between components of the system of Figure 1 when the first switching device is de-energised, as is the case in Figure 1. Table B summarises the connections between components of the system of Figure 1 when the first switching device is energised, as described above. In each Table, a connection between two components is represented by ■ in a cell corresponding to the intersection of a column associated with a first of the two components and a row corresponding to the second of the two components. Note that connection to -ve is via the x^th combination. The current limiting device IL1 and the current blocking device D1 are omitted from the Tables for simplicity.

11

Figure 2 schematically depicts a battery charging and voltage supply system comprising more than two secondary cells according to an exemplary embodiment. As described in relation to Figure 1, the 12 system of Figure 1 may comprise any number of secondary cells. Figure 2 shows a case in which the system comprises four secondary cells, each coupled to a corresponding switching device as has been described for Figure 1. In Figure 2, the main switch SW1 of the first switching device is closed, hence secondary cell BAT 1 is driving the load; the main switch SW2 of the second switching device is open, hence secondary cell BAT 2 is charging; and the main switch SW3 of the third switching device is closed, hence secondary cell BAT 3 is driving the load; the main switch SWX of the x^th switching device is open, hence secondary cell BAT X is charging. Therefore, in Figure 2, two secondary cells BAT 2, BAT X are charging mutually in parallel, and two secondary cells BAT 1, BAT 3 are driving the load in series. As mentioned, use of a controller is typical in practice rather than manual operation of the main switches.

Figure 3 schematically depicts a simplified representation of the system of Figure 1 or Figure 2. Figure 3 shows the power supply as a DC power supply. In particular, the power source in Figure 3 is a wind turbine(s). The load Load 1 in Figure 3 is shown as a DC load or applications. The aforementioned controller, which would typically replace the main switches of Figure 1 and Figure 2, corresponds to the system monitoring and control module in Figure 3. A system monitoring and control module means a computer or a microprocessor, for example.

Figure 4 schematically depicts a method of controlling the system of Figure 1 , or analogously Figure 2, performed by a controller according to an exemplary embodiment. The method of Figure 4 comprises coupling (S1) the set of secondary cells in a first configuration or a second configuration. In the first configuration, the secondary cells BAT 1 , BAT X are mutually electrically coupled in parallel to the power source. In the second configuration, the secondary cells BAT 1 , BAT X are mutually electrically coupled in series to the load Load 1. The method comprises receiving (S2) a measurement of a voltage supplied to the load Load 1, and electrically coupling (S3) the set of secondary cells BAT 1 , BAT X in one of the configurations in response to the measurement.

Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

In summary, the invention provides a circuit including a controller that facilitates charging at low voltages and enables switching between configurations such that a constant discharge drives that load. Consequently, the invention provides a circuit including a controller that is particularly suitable for use with renewable energy sources. 13

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

14 Claims

1. A circuit including a controller, the circuit comprising: a first set of terminals electrically couplable to an electrical power source; a second set of terminals electrically couplable to a load; a third set of terminals electrically couplable to a set of nickel-metal hydride secondary cells comprising a first cell and a second cell, wherein respective terminals of the third set of terminals are electrically couplable to respective cells of the set of secondary cells; and a set of multi-pole changeover relay switches respectively electrically coupled to cells of the set of secondary cells, wherein the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in: a first configuration, wherein the first cell and the second cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, whereby the first cell and the second cell are arranged to be charged by the power source; and a second configuration, wherein the first cell and the second cell are mutually electrically coupled in series via the third set of terminals to the second set of terminals, whereby the first cell and the second cell are arranged to drive the load, wherein the controller is configured to receive a measurement of a voltage supplied to the load via the second set of terminals, wherein the controller is configured to electrically couple the set of secondary cells in one of the configurations in response to the measurement, and wherein the controller is configured to transmit a signal to cause a subset of the relay switches to switch the set of secondary cells between configurations.

2. The circuit according to claim 1, wherein the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in: a third configuration, wherein the first cell is electrically coupled via the third set of terminals to the first set of terminals, and wherein the second cell is electrically coupled via the third set of terminals to the second set of terminals.

3. The circuit according to claim 1 or 2, wherein the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in: a fourth configuration, wherein the second cell is electrically coupled via the third set of terminals to the first set of terminals, and wherein the first cell is electrically coupled via the third set of terminals to the second set of terminals. 15

4. The circuit according to any preceding claim, wherein the set of secondary cells further comprises a third cell, and wherein the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in: a fifth configuration, wherein the first cell and the second cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, and wherein the third cell is electrically coupled via the third set of terminals to the second set of terminals.

5. The circuit according to claim 3, wherein the controller is configured to electrically couple the set of secondary cells, via the third set of terminals, in: a sixth configuration, wherein the first cell and the third cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, and wherein the second cell is electrically coupled via the third set of terminals to the second set of terminals.

6. The circuit according to any preceding claim, wherein the controller is configured to switch the set of secondary cells between the first configuration and the second configuration.

7. The circuit according to any of claims 3 to 6, wherein the controller is configured to switch the set of secondary cells between the first configuration, the second configuration, the third configuration and the fourth configuration.

8. The circuit according to claim 5 to 7, wherein the controller is configured to switch the set of secondary cells between the first configuration, the second configuration, the third configuration, the fourth configuration, the fifth configuration and the sixth configuration.

9. The circuit according to any of claims 6 to 8, wherein the controller is configured to switch the set of secondary cells between configurations based on at least one of: the measurement of voltage supplied to the load; a length of time the set of secondary cells has been in one of the configurations; and a charge level of one of the cells.

10. The circuit according to any preceding claim, wherein the controller is configured to be powered by the power source. 16

11. The circuit according to any preceding claim further comprising a set of current limiting devices configured to prevent excessive current being delivered by the power source to a corresponding cell or cells of the set of secondary cells.

12. The circuit according to any preceding claim further comprising a set of blocking diodes configured to prevent current from leaving a corresponding cell or cells of the set of secondary cells when the corresponding cell or cells are electrically coupled to the first set of terminals.

13. The circuit of according to any preceding claim, wherein the power source is a renewable energy source.

14. The circuit of according to any preceding claim, wherein the power source is one or more photovoltaic cells.

15. A method of controlling a circuit performed by a controller, the circuit comprising: a first set of terminals electrically couplable to an electrical power source; a second set of terminals electrically couplable to a load; a third set of terminals electrically couplable to a set of nickel-metal hydride secondary cells comprising a first cell and a second cell, wherein respective terminals of the third set of terminals are electrically couplable to respective cells of the set of secondary cells; and a set of multi-pole changeover relay switches respectively electrically coupled to cells of the set of secondary cells, the method performed by the controller comprising: electrically coupling the set of secondary cells, via the third set of terminals, in: a first configuration, wherein the first cell and the second cell are mutually electrically coupled in parallel via the third set of terminals to the first set of terminals, thereby charging the first cell and the second cell by the power source; and a second configuration, wherein the first cell and the second cell are mutually electrically coupled in series via the third set of terminals to the second set of terminals, thereby driving the load by the first cell and the second cell; receiving a measurement of a voltage supplied to the load via the second set of terminals; electrically coupling the set of secondary cells in one of the configurations in response to the measurement; and transmitting a signal to cause a subset of the relay switches to switch the set of secondary cells between configurations. 17

16. A computer program comprising instructions for implementing the method of claim 15.