JP2004364362A - System and method for supplying power to load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sustain the charging capacity of a sub-battery over a long term. <P>SOLUTION: At least the second load voltage Vs of a sub-battery 13 under full-charge state is set lower than the first load voltage Vm of a main battery 11 under full-charge state by providing step-down elements 19 and 21, e.g. diodes, or by lowering the concentration of electrolyte, e.g. dilute sulfuric acid, in the sub-battery 13. Difference between the second load voltage Vs and the first load voltage Vm is preset depending on a voltage drop incident to the lowering of the charging capacity of the main battery 11. The sub-battery 13 is prevented from running out before the charging capacity of the main battery 11 is lowered by a dark current, or the like, to cause a voltage drop. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a load power supply system including a sub-battery serving as a backup power supply in addition to a main battery, and a power supply method thereof.
[0002]
[Prior art]
A vehicle is generally equipped with a battery and supplies power not only to audio and car navigation but also to basic functions such as power steering and an electronically controlled suspension that are essential for the running of the vehicle.
[0003]
By the way, the charge capacity of a battery generally decreases each time discharge is repeated. If the battery is overcharged when fully charged, or overdischarged (completely discharged) until all of the active material serving as the electrode of the battery is changed to lead sulfate, the charge capacity of the battery is significantly reduced and the power supply is greatly reduced. The voltage will drop.
[0004]
In this case, the battery needs to be replaced. Until this battery is replaced, a sub-battery is mounted separately from the main battery as a temporary emergency backup power supply.
[0005]
It should be noted that the prior art documents relating to the above-mentioned conventional technology could not be found.
[0006]
[Problems to be solved by the invention]
As described above, when the power supply voltage applied to the load is reduced due to the decrease in the charging capacity of the main battery, the sub-battery is supplied with the voltage from the sub-battery as a backup power supply to the load, and the sub-battery is provided for safety of the vehicle. Will play a crucial role. Therefore, it is necessary to keep the power supply voltage of the sub-battery as fully charged as possible at the time when the charging capacity of the main battery is reduced and the power supply voltage is reduced. There is a need for techniques to maintain across.
[0007]
Therefore, an object of the present invention is to provide a load power supply system and a power supply method thereof that can easily maintain the charge capacity of a sub-battery as a backup power supply for a main battery over a long period of time.
[0008]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 provides a main battery for supplying a first load voltage to a load to drive the load, and a second battery as a backup power supply when the voltage of the main battery drops. A sub-battery that applies a load voltage to the load, wherein at least the second load voltage in a fully charged state of the sub-battery is set lower than the first load voltage in a fully charged state of the main battery. Things.
[0009]
The invention according to claim 2 is the load power supply system according to claim 1, wherein the second load voltage is lower than the first load voltage between the sub-battery and the load. The voltage step-down element is connected.
[0010]
The invention according to claim 3 is the load power supply system according to claim 1, wherein each of the main battery and the sub-battery is charged and discharged by a chemical reaction between the electrolyte and the electrolyte. And an electrode plate made of an active material for performing the following. The concentration of the electrolytic solution of the main battery is set such that the concentration of the electrolytic solution of the sub-battery makes the second load voltage lower than the first load voltage. It is set lower.
[0011]
The invention according to a fourth aspect is the load power supply system according to any one of the first to third aspects, wherein a difference between the second load voltage and the first load voltage is the main load voltage. It is set in advance according to a voltage drop due to a decrease in the charge capacity of the battery.
[0012]
According to a fifth aspect of the present invention, in the load power supply system according to any one of the first to fourth aspects, the second load voltage in the fully charged state of the sub-battery is equal to the voltage of the main battery. It is set to be equal to the first load voltage in a completely discharged state.
[0013]
According to a sixth aspect of the present invention, a main battery for applying a first load voltage to a load to drive the load, and applying a second load voltage to the load as a backup power supply when the voltage of the main battery drops. A power supply method for a load power supply system including a sub-battery, wherein at least the second load voltage in the fully charged state of the sub-battery is lower than the first load voltage in the fully charged state of the main battery. , Is set lower.
[0014]
The invention according to claim 7 is the power supply method of the load power supply system according to claim 6, wherein the second load voltage is provided by a step-down element provided between the sub-battery and the load. Is lower than the first load voltage.
[0015]
The invention according to claim 8 is the power supply method of the load power supply system according to claim 6, wherein the main battery and the sub-battery are charged and discharged by a chemical reaction between the electrolyte and the electrolyte. And an electrode plate made of an active material for performing the following, and the concentration of the electrolytic solution of the sub-battery is previously set lower than the concentration of the electrolytic solution of the main battery, whereby the second load voltage is reduced. The first load voltage is set lower than the first load voltage.
[0016]
According to a ninth aspect of the present invention, there is provided the power supply method for the load power supply system according to any one of the sixth to eighth aspects, wherein a difference between the second load voltage and the first load voltage is provided. Is set in advance according to a voltage drop due to a decrease in the charge capacity of the main battery.
[0017]
According to a tenth aspect of the present invention, in the power supply method of the load power supply system according to any one of the sixth to ninth aspects, the second load voltage in a fully charged state of the sub-battery is: The first load voltage is set to be equal to the first load voltage in a completely discharged state of the main battery.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
<< 1st Embodiment >>
FIG. 1 is a diagram showing a load power supply system according to a first embodiment of the present invention.
[0019]
This load power supply system is mounted on a vehicle, and as shown in FIG. 1, a main battery 11 for supplying a normal power supply for driving a vehicle-mounted load 10 such as a power steering or an electronic control suspension. A sub-battery 13 which is used as a temporary emergency backup power supply when the power supply voltage of the main battery 11 is lowered, and converts the power of the rotational driving of the wheels into electric energy when the automobile is running to convert the main battery 11 into electric energy. (AG) 15 for supplying a regenerative voltage to the power supply, and a DC / DC converter 17 for reducing the power supply voltage from the main battery 11, the sub-battery 13, and the generator 15 to the power supply voltage of the control circuit (ECU) 16 In particular, in the configuration including Because, it is set lower than the power supply voltage of the power supply voltage from the sub-battery 13 from the main battery 11. More specifically, in this embodiment, the load 10 is provided with step-down elements 19 and 21 for reducing the power supply voltage from the sub-battery 13 to the power supply voltage from the main battery 11.
[0020]
The main battery 11 and the sub-battery 13 are, for example, a general paste-type lead battery which is charged and discharged by a chemical reaction between an electrode plate using lead as an active material and dilute sulfuric acid as a paste-like electrolyte. Etc. are used. The same battery voltage is used for both batteries 11 and 13. The voltage (+ B) of the main battery 11 is applied to the DC / DC converter 17 as shown in FIG. 1, and the voltage Vs0 of the sub-battery 13 is reduced by the first step-down element 19 as shown in FIG. Is applied. Further, the load 10 is connected with backflow prevention diodes 23 and 25 for preventing backflow of current from the batteries 11 and 13, respectively. Therefore, as shown in FIG. ) Is supplied with a voltage (first load voltage) Vm stepped down by the forward voltage of the backflow prevention diode 23. As shown in FIG. 2, the voltage Vs0 of the sub-battery 13 is reduced by the step-down elements 19, 21 and the backflow. Voltage (second load voltage) Vs stepped down by prevention diode 25 is applied. Actually, when the voltage (+ B, Vm) from the main battery 11 and the voltage (Vs1, Vs) from the sub-battery 13 are applied to the DC / DC converter 17 and the load 10, respectively, a relay or a power MOSFET is used. It is desirable to perform switching control between the main battery 11 side and the sub-battery 13 side using the switches described above. However, here, for simplicity of description, the voltage (+ B, Vm) from the main battery 11 and the sub-battery 13 It is assumed that the voltages (Vs1, Vs) are applied in parallel to the DC / DC converter 17 and the load 10, respectively.
[0021]
The main battery 11 regenerates upon receiving a voltage from the generator (AG) 15, but the sub-battery 13 is basically used as an emergency backup power source, so Is maintained in a fully charged state, and is not connected to the generator 15 so that overcharging in this fully charged state is not performed.
[0022]
The DC / DC converter 17 mainly stabilizes the voltage of the main battery 11 while decreasing the voltage.
[0023]
The step-down elements 19 and 21 set the voltages (Vs1, Vs) applied from the sub-battery 13 to the DC / DC converter 17 and the load 10, respectively, lower than the voltages (+ B, Vm) applied from the main battery 11. It is provided for the purpose.
[0024]
In general, the charge capacity of an automobile battery decreases every time discharge is repeated. Particularly, when a dark current flows through the load 10, excessively deep discharge, that is, so-called "battery discharge" is performed, the charge capacity of the battery is significantly increased. Will decrease. In particular, in a recent automobile, even if a main switch (not shown) of the load 10 is turned off, a small current called a dark current continues to flow to the load 10, so that the automobile is operated for a long time. If left unattended, a situation may occur in which the charging capacity of the battery is reduced by the dark current.
[0025]
Therefore, as described above, when the battery voltage applied to the DC / DC converter 17 or the load 10 decreases due to the decrease in the charging capacity of the main battery 11, the sub-battery 13 uses the voltage from the sub-battery 13 as a backup power supply. It is provided to the DC / DC converter 17 and the load 10, and plays an extremely important role in the safety of the automobile. Therefore, it is desirable that the charging capacity of the sub-battery 13 be maintained for a longer period than the main battery 11 that is frequently replaced.
[0026]
In consideration of this, in the present embodiment, while the main battery 11 has a normal charging capacity, the dark current of the load 10 that is likely to cause the battery to run down is supplied to the power supply from the main battery 11 particularly. Therefore, as described above, the voltage applied from the sub-battery 13 to the load 10 and the DC / DC converter 17 is applied from the main battery 11 using the step-down elements 19 and 21. It is set smaller than the voltage.
[0027]
Specifically, as shown in FIG. 2, the first step-down element 19 converts the power supply voltage Vs0 from the sub-battery 13 into a lower voltage Vs1. For example, a general resistor is applied. The voltage Vs1 means a voltage supplied from the backup power supply unit 22 to the DC / DC converter 17, and the voltage Vs1 is reduced from a voltage (+ B) from the main battery 11 in a normal state (full charge state). Then, the flow of current from the sub-battery 13 to the DC / DC converter 17 is stopped. As a result, it is possible to prevent a situation where the charging capacity of the sub-battery 13 is reduced before the main battery 11 is reduced.
[0028]
The first step-down element 19 is desirably unitized as a backup power supply unit 22 together with the sub-battery 13 as shown in FIGS.
[0029]
The second step-down element 21 sets the voltage Vs applied from the sub-battery 13 to the load 10 to be lower than the voltage Vm applied from the main battery 11 so that the current (dark current) Is stopped, thereby preventing a situation in which the charging capacity of the sub-battery 13 is reduced before the main battery 11 is reduced. For example, a diode is used as the second step-down element 21. The anode of the second step-down element 21 is connected to a connection intermediate point between the first step-down element 19 and the DC / DC converter 17, and a cathode is provided. The voltage output from is dropped by the forward voltage. That is, the voltage Vs1 applied from the sub-battery 13 to the DC / DC converter 17 is stepped down from Vs0 by only the first step-down element 19, whereas the voltage to the load 10 is the first step-down voltage. After the voltage is reduced from Vs0 to Vs1 by the element 19, the voltage is further reduced to Vs2 by the second step-down element 21 to be set lower. This is because there is a high possibility that the dark current of the load 10 is a main cause of the rising of the battery (mainly the main battery 11). In particular, considering that a large number of loads 10 are mounted on an automobile as a recent tendency, DC / DC This is because current leakage from the sub-battery 13 to the load 10 (particularly, prevention of dark current from the sub-battery 13) is more important than to the DC converter 17 and the ECU 16.
[0030]
Although FIGS. 1 and 2 show the second step-down element 21 as a single element, a plurality of diodes may be connected in series to adjust the voltage drop due to the forward voltage. . For example, when the voltage drop by the second step-down element 21 requires about 1 to 2 volts, and when the forward voltage of a single diode is 0.6 volt, two to three diodes are connected in series. Just connect it to.
[0031]
The operation of the load power supply system having the above configuration will be described. As described above, the voltage (+ B, Vm) from the main battery 11 and the voltages (Vs1, Vs) from the sub-battery 13 are supplied to the DC / DC converter 17 and the load 10 in parallel.
[0032]
FIG. 3 shows the relationship between the charged capacity of each of the batteries 11 and 13 and the voltage, and the symbol Vm in FIG. 3 shows the voltage applied from the main battery 11 to the load 10 as described above. Further, the symbols Vsa to Vsc all indicate the voltage (the voltage corresponding to the symbol Vs in FIGS. 1 and 2) applied from the sub-battery 13 to the load 10, but it is particularly assumed that the voltage levels are different. FIG. Generally, as shown in FIG. 3, the output voltage of each of the batteries 11 and 13 tends to decrease as the charging capacity decreases.
[0033]
In such a situation, the voltage of the sub-battery 13 in the fully charged state (point P1 in FIG. 3) is compared with the voltage Vm (point P1 in FIG. 3) of the main battery 11 in the fully charged state (charging capacity = 100%). (Point P2 in FIG. 3) is considered. In this case, since the two voltages Vm and Vsa are applied to the load 10 in parallel, a current flows through the load 10 by a relatively high voltage. That is, since the voltage value of the point P2 related to the voltage Vsa of the sub-battery 13 is higher than the voltage value of the point P1 related to the voltage Vm of the main battery 11, the current from the main battery 11 does not flow. Current will flow through the load 10. This state continues until the voltage Vsa of the sub-battery 13 decreases to the state of the point P3. When the voltage Vsa falls below the state of the point P3, the voltage Vm of the main battery 11 and the voltage of the sub-battery 13 are thereafter changed. A current flows from both Vsa to the load 10 (however, when the main battery 11 and the sub-battery 13 are switched by a switch, the switch is switched to the sub-battery 13 side at this time).
[0034]
Such an operation mode of the two batteries 11 and 13 cannot be said to secure the function as the backup power supply of the sub-battery 13, and the sub-battery 13 is likely to be consumed earlier than the main battery 11.
[0035]
Further, when the voltage level of the sub-battery 13 is, for example, the symbol Vsb in FIG. 3, when the charging capacity of the sub-battery 13 is 0% (point P4), the voltage Vsb (= Lv1) indicates that the main battery 11 is fully charged. It is equal to the voltage Vm (= Lv1) at the point P1 in the state (charge capacity = 100%). In this case, when the sub-battery 13 is dead (point P4), a current (including a dark current) flows from the main battery 11 in the state of the point P1 to the load 10 for the first time. In this case, it means that the sub-battery 13 always becomes dead (overdischarged) when the main battery 11 functions as a power source, and it is no longer expected that the sub-battery 13 functions as a backup power source. Impossible.
[0036]
On the other hand, in this embodiment, the voltage Vs applied from the sub-battery 13 to the load 10 by the two step-down elements 19 and 21 is in a fully charged state (charging capacity = 100%) as indicated by a symbol Vsc in FIG. Therefore, since the sub-battery 13 is set sufficiently lower than the voltage Vm from the main battery 11, it is possible to prevent the sub-battery 13 from being discharged earlier than the main battery 11. Specifically, when the voltage supplied from the main battery 11 to the load 10 is at the state of the point P1 (voltage Vm = Lv1), the load 10 is at the point P5 from the sub-battery 13 (the voltage Vsc = Lv2 <Lv1). Therefore, the current from the sub-battery 13 does not flow to the load 10, and the current from the main battery 11 exclusively flows to the load 10.
[0037]
Then, the main battery 11 repeats discharging due to dark current or the like to reduce the charge capacity, and the voltage Vm applied to the load 10 becomes the state at the point P6 in FIG. 3 (voltage Vsc = Lv2). A current flows to the load 10 from both the voltage Vm of the battery 11 and the voltage Vsa of the sub-battery 13 (however, when the main battery 11 and the sub-battery 13 are switched by a switch, the switch is set at this point. It will be switched to the battery 13). That is, the voltage Vs (reference sign Vsc in FIG. 3) applied from the sub-battery 13 to the load 10 is sufficiently lower than the applied voltage Vm from the main battery 11 by the two step-down elements 19 and 21. Until the applied voltage Vm from the main battery 11 decreases to the voltage Lv2 in FIG. 3, the sub-battery 13 can be maintained in the fully charged state (charge capacity = 100%), and the main battery 11 Even if the charging capacity of the sub-battery 13 decreases to some extent, the function of the sub-battery 13 as a backup power supply can be sufficiently ensured.
[0038]
Here, the difference (Lv1−Lv2) between the voltage Lv1 and the voltage Lv2 in FIG. 3 is suitable for switching from the main battery 11 to the sub-battery 13 when the main battery 11 is consumed by the dark current. It is appropriately set in consideration of the degree of consumption of the main battery 11, that is, the degree of decrease in the charge capacity of the main battery 11 to be switched to the sub-battery 13. It has been empirically found that in a real vehicle, the voltage Vm applied to the load 10 fluctuates by about 1 to 2 volts due to a large fluctuation in the charging capacity of the main battery 11. Therefore, a difference (Lv1−Lv2) between the voltage Lv1 and the voltage Lv2 is set in consideration of the voltage difference of 1 to 2 volts, and a voltage drop corresponding to the difference (Lv1−Lv2) is set by the step-down elements 19 and 21. If it is ensured, it is possible to prevent a situation in which the charging capacity of the sub-battery 13 is reduced before the main battery 11 is consumed by the dark current, whereby the backup power function of the sub-battery 13 can be maintained. In this case, in addition to the first step-down element 19 as a resistor disposed on the current path from the sub-battery 13 to the DC / DC converter 17, the number of series-connected diodes as the second step-down element 21 is appropriately set. Thus, the voltage of sub-battery 13 in the fully charged state can be set to desired voltage value Lv2.
[0039]
Most preferably, the sub-battery 13 is set so that the voltage Vs in the fully charged state of the sub-battery 13 (the voltage Vsd at the point P7 in FIG. 3) becomes equal to the voltage Vm (Lv3) in the fully discharged state of the main battery 11. Is set so as to lower the voltage Vs. This makes it possible to prevent the sub-battery 13 from being discharged at all until the main battery 11 is completely discharged, thereby making it possible to easily maintain the charging capacity of the sub-battery 13 for a long period of time. .
[0040]
In this embodiment, in addition to the diode serving as the second step-down element 21, a resistor serving as the first step-down element 19 is used. Although the voltage Vs for 10 is set to be lower than the voltage Vm from the main battery 11, one of them, for example, only a diode may be used.
[0041]
In the above embodiment, a resistor is used as the first step-down element 19 and a diode is used as the second step-down element 21. However, any element that can perform voltage drop can be used. Can be used.
[0042]
<< 2nd Embodiment >>
In this embodiment, elements having the same functions as those in the first embodiment will be described with the same reference numerals.
[0043]
In the first embodiment, the voltage Vs with respect to the load 10 from the sub-battery 13 is changed from the main battery 11 by the voltage drop of the first step-down element 19 which is a resistor and the second step-down element 21 which is a diode. However, in the load power supply system according to the second embodiment of the present invention, the concentration of the dilute sulfuric acid, which is the electrolytic solution of the sub-battery 13, is adjusted by the main battery 11 and the sub-battery 13. Thus, the voltage Vs from the sub-battery 13 to the load 10 is set to be lower than the voltage Vm from the main battery 11.
[0044]
FIG. 4 is a schematic diagram showing an internal configuration of a general battery. Generally, inside the battery, an anode plate 31 and a cathode plate 33 each using lead as an active material are opposed to each other with a separator 35 interposed therebetween, and they are immersed in dilute sulfuric acid 37 which is a paste-like electrolyte. Have been. Specifically, the anode plate 31 is made of lead peroxide, and the cathode plate 33 is made of spongy lead.
[0045]
When the load 10 is connected to this battery and discharge is performed, the lead peroxide of the anode plate 31 and the spongy lead of the cathode plate 33 respectively react with sulfuric acid in the dilute sulfuric acid 37 to be changed to lead sulfate. Turns into water. In this case, the higher the concentration of sulfuric acid in the diluted sulfuric acid 37 is, the more the chemical reaction of the anode plate 31 and the cathode plate 33 is activated, so that the extracted voltage is higher. On the other hand, when the concentration of sulfuric acid in the diluted sulfuric acid 37 is low, the voltage taken out of the battery becomes low.
[0046]
Utilizing this, the second step-down element 21 (diode) is omitted from the configuration of the load power supply system described in the first embodiment (FIG. 1) (FIG. 5), and By setting the concentration of dilute sulfuric acid 37 (FIG. 4), which is an electrolytic solution, lower than the concentration of dilute sulfuric acid (electrolytic solution) in the main battery 11, the voltage Vs applied from the sub-battery 13 to the load 10 is reduced. 11 is set lower than the voltage Vm.
[0047]
As described above, since the concentration of the dilute sulfuric acid 37 of the sub-battery 13 is set lower than that of the main battery 11, the same as in the first embodiment without using the second step-down element 21 such as a diode. In addition, it is possible to prevent the sub-battery 13 from running out of battery earlier than the main battery 11.
[0048]
【The invention's effect】
According to the first and sixth aspects of the present invention, at least the second load voltage in the fully charged state of the sub-battery is set lower than the first load voltage in the fully charged state of the main battery. In addition, it is possible to prevent the sub-battery from running out of battery before the charging capacity of the main battery decreases due to dark current or the like and the voltage decreases. Therefore, the charging capacity of the sub-battery as a backup power source for the main battery can be easily maintained for a long period of time.
[0049]
In this case, for example, the second load voltage is made lower than the first load voltage by the step-down element provided between the sub-battery and the load as in the second and seventh aspects. The second load voltage can be easily set lower than the first load voltage of the main battery.
[0050]
Alternatively, the second load voltage of the sub-battery can be reduced by setting the concentration of the electrolyte of the sub-battery in advance to be lower than the concentration of the electrolyte of the main battery. It can be easily set lower than the first load voltage.
[0051]
According to the fourth and ninth aspects of the present invention, the difference between the second load voltage and the first load voltage is set in advance according to the voltage drop due to the decrease in the charging capacity of the main battery. Therefore, there is an effect that the operation timing of the sub-battery can be freely set according to the characteristics of the main battery.
[0052]
Most desirably, the second load voltage in the fully charged state of the sub-battery is set to be equal to the first load voltage in the fully discharged state of the main battery. Until the battery is completely discharged, it is possible to prevent the sub-battery from being discharged, thereby making it possible to easily maintain the charging capacity of the sub-battery for a long period of time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a load power supply system according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a sub-battery and both step-down elements of the load power supply system according to the first embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between charging capacity and voltage of a main battery and a sub battery.
FIG. 4 is a schematic view showing a structure of a general battery.
FIG. 5 is a block diagram showing a load power supply system according to a second embodiment of the present invention.
[Explanation of symbols]
10 Load
11 Main battery
13 Sub-battery
15 Generator
16 ECU
17 DC / DC converter
19, 21 Step-down device
22 Backup power supply unit
31 Anode plate
33 cathode plate
37 Dilute sulfuric acid
Vm, Vs Load voltage

Claims (10)

A main battery for applying a first load voltage to the load and driving the load;
A sub-battery that applies a second load voltage to the load as a backup power supply when the voltage of the main battery drops,
A load power supply system, wherein at least the second load voltage in the fully charged state of the sub-battery is set lower than the first load voltage in the fully charged state of the main battery. The load power supply system according to claim 1, wherein
A load power supply system, wherein a step-down element for lowering the second load voltage to be lower than the first load voltage is connected between the sub-battery and the load. The load power supply system according to claim 1, wherein
Inside each of the main battery and the sub-battery, an electrolytic solution, comprising an electrode plate made of an active material that performs charging and discharging by a chemical reaction with the electrolytic solution,
A load power supply system, wherein a concentration of the electrolyte in the sub-battery is set lower than a concentration of the electrolyte in the main battery such that the second load voltage is lower than the first load voltage. The load power supply system according to claim 1, wherein:
A load power supply system, wherein a difference between the second load voltage and the first load voltage is set in advance according to a voltage drop due to a decrease in a charging capacity of the main battery. The load power supply system according to claim 1, wherein:
The load power supply system, wherein the second load voltage in the fully charged state of the sub-battery is set to be equal to the first load voltage in the completely discharged state of the main battery. A load power supply, comprising: a main battery for supplying a first load voltage to a load to drive the load; and a sub-battery for supplying a second load voltage to the load as a backup power supply when the voltage of the main battery drops. A system power supply method,
A power supply method for a load power supply system, wherein at least the second load voltage in a fully charged state of the sub-battery is set lower than the first load voltage in a fully charged state of the main battery. . A power supply method for a load power supply system according to claim 6, wherein
A power supply method for a load power supply system, wherein the second load voltage is lower than the first load voltage by a step-down element provided between the sub-battery and the load. A power supply method for a load power supply system according to claim 6, wherein
The main battery and the sub-battery each include therein an electrolytic solution and an electrode plate made of an active material that performs charging and discharging by a chemical reaction with the electrolytic solution,
A load power supply system, wherein the second load voltage is lower than the first load voltage by previously setting the concentration of the electrolyte of the sub-battery lower than the concentration of the electrolyte of the main battery. Power supply method. A power supply method for a load power supply system according to any one of claims 6 to 8, wherein
A power supply method for a load power supply system, wherein a difference between the second load voltage and the first load voltage is set in advance according to a voltage drop due to a decrease in a charging capacity of the main battery. A power supply method for a load power supply system according to any one of claims 6 to 9, wherein
A power supply method for a load power supply system, wherein the second load voltage in the fully charged state of the sub-battery is set to be equal to the first load voltage in the fully discharged state of the main battery.

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