JPS604949B2 - Storage battery overdischarge detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an overdischarge detection device for a storage battery.

Storage batteries are widely used in many other fields, including as a power source for electric vehicles such as battery-powered forklifts, but over-discharging of storage batteries is an issue that must be constantly monitored, as it can degrade the performance of storage batteries. , should be avoided as much as possible as it shortens lifespan.

The most reliable way to determine the discharge status of a storage battery is to measure the specific gravity of the electrolyte, but in normal electric vehicles, this requires stopping operation and is time-consuming.■ Voltage Monitoring the terminal voltage of a storage battery using a meter■ If the terminal voltage falls below a certain set voltage level,
Efforts are made to prevent overdischarge by cutting off the power supply and installing devices that issue alarms.

Incidentally, in general, the apparent internal resistance RB of a storage battery gradually increases as discharge progresses, as shown in FIG. Further, as the discharge rate Q increases, the no-load voltage also decreases, so the change in terminal (output) voltage with respect to the load (output) current is as shown in FIG. Here, internal resistance RB
is expressed as a value obtained by dividing the terminal voltage change ΔVB by the load current change ΔD for each discharge rate Q. RB=△
Kaizo------.

'In this way, depending on the value of load current IB, terminal voltage VB
Since the voltage changes, the above-mentioned monitoring using the voltmeter requires the driver to know from experience the state in which the discharge should be stopped, which requires skill.

In addition, based on the comparison with the reference level VT (see Figure 2) in (2) above, if the reference voltage level VT is set to a high value, even if it is still possible to discharge sufficiently, it will operate with a large load current for a short time. On the other hand, if you set it to a low value, it will only operate when the load current is large, so
It does not necessarily serve the purpose of protecting the storage battery. None of the conventional methods can be said to be suitable for preventing over-discharge of storage batteries. The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an overdischarge detection device for a storage battery that can accurately detect an overdischarge state regardless of the magnitude of the load current. 3rd below
Embodiments of the present invention will be described in detail with reference to the drawings to FIG.

In FIGS. 3 and 4, the required no-load voltage VI is applied as one input of the subtracter 1.

As this voltage VI, for example, the discharge rate Q=
The no-load voltage at 100(%) is selected. On the other hand, as another input to the subtractor 1, a voltage V2 proportional to the load current IB flowing into the load 7 is provided from the current detector 2 via the amplifier 5. V2=K・IB
[2] The coefficient K is the total gain of the current detector 2 and the amplifier 5.

Here, if the gain K is set to be equal to the internal resistance RB of the storage battery 6 when the no-load voltage is VI, then the second equation becomes V2;RB・Ta...'3
} becomes.

That is, V2 corresponds to the voltage drop due to the internal resistance RB. Upon receiving these two inputs V1 and V2, subtracter 1 outputs V3=VI-V2=VI-RB・IB...
. . . A voltage of 41 is sent to the comparator 3 as a reference voltage.

The comparator 3 constantly compares the reference voltage V3 given from the subtracter 1 and the terminal voltage VB of the storage battery 6, and determines that V3>VB...
...{51, an output signal is generated to activate a power circuit breaker or alarm 4, etc.

The combination of V1 and V2 that are input to the subtracter 1 can be arbitrarily set depending on the discharge characteristics of each storage battery.

In addition, it is also possible to set the discharge state of the storage battery at which it is operated. For example, in a storage battery-powered electric vehicle, if the work place and the charging place are far apart, the discharge state that is somewhat lower than 100% may be set. It is also possible to match the characteristics of the rate. Power circuit breaker or alarm 4
Needless to say, various methods can be applied depending on the usage condition of the storage battery. An example of a specific configuration of the circuit shown in FIG. 3 is shown in FIG.

Changes in the load current IB of the storage battery 6 are input to the operational amplifier 51 via the shunt 21 connected in series with the load 7 and amplified to an appropriate level. The output voltage E2 of the amplifier 51 becomes an anti-phase input to the operational amplifier 11. On the other hand, a constant voltage of R13 EI = Amehaba Amon Vcc .

These two inputs EI and E2 of the multiplier 11 correspond to the no-load voltage VI and the voltage drop V2 due to the internal resistance RB in a predetermined discharge state of the storage battery 6, respectively. The level of each input voltage E1, E2 is adjusted by the amplification factor of the amplifier 11 and the voltage division ratio of equation (2). Amplifier 11 acts as a differential amplifier, E3=
Equipment (EI-E2)...・Perform the operation '7'.

The output E3 of the amplifier 11 becomes the positive phase input of the operational amplifier 31, which corresponds to the reference voltage V3. The multiplier 31 receives the terminal voltage VB of the storage battery 6 as a negative phase input.
However, R3384-R320R powder/VB...
・The pressure is divided into {8) and given.

This voltage division ratio is determined according to the level of voltage 83.
Therefore, when E4 is lower than the reference voltage E3, that is, E3>E4...
- side, the output of the intensifier 31 is obtained, the transistor 42 is turned on, and the alarm lamp 41 is lit.

Note that R12, R13, R14, R15, R32, and R33 are resistors 12, 13, 14, 15, 32, and 3
3, respectively. Further, in the circuit shown in FIG. 5, a lamp 41 is used as an alarm, but this can be easily changed to a lamp flasher, a buzzer, or a power circuit breaker. As described above, the storage battery overdischarge detection device according to the present invention includes a load current detector that detects the load current of the storage battery, and a preset internal resistance value of the storage battery at a discharge rate that should be considered as overdischarge. A multiplier circuit that outputs a voltage representing the product of the load current and a subtraction circuit that subtracts the output voltage of the multiplier circuit from the preset no-load voltage of the storage battery at a discharge rate that should be considered overdischarge and outputs a reference voltage. Because it has a circuit,
A reference voltage equal to the terminal voltage of the storage battery at a discharge rate that is considered to be overdischarge, that is, a reference voltage representing the lower limit of the terminal voltage of the storage battery within a usable range, can be obtained in accordance with the load current.

Then, the comparison circuit compares the reference voltage with the terminal voltage of the storage battery, and when the terminal voltage becomes lower than the reference voltage, an overdischarge detection signal is output, so regardless of the magnitude of the load current, It is possible to accurately detect the over-discharge state of the storage battery.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between discharge rate and internal resistance, Figure 2 is a graph showing the relationship between discharge rate and internal resistance.
The figure is a graph showing the relationship between load current and terminal voltage, Figure 3 is a block diagram showing an embodiment of the invention, Figure 4 is a graph explaining the operation of the circuit shown in Figure 3, and Figure 5 is a graph showing the relationship between load current and terminal voltage. 4 is a circuit diagram showing an example of a specific configuration of the block diagram shown in FIG. 3. FIG. 1...Subtractor, 2...Load current detector, 3
... Comparator, 6 ... Storage battery, 7 ... Load. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A load current detector that detects the load current of a storage battery, a multiplier circuit that outputs a voltage representing the product of the detected load current and a preset internal resistance value of the storage battery at a discharge rate that should be considered overdischarge, and an overdischarge. From the preset no-load voltage of the storage battery at the discharge rate that should be considered as
A subtraction circuit that subtracts the output voltage of the multiplier circuit to output a reference voltage, and a comparison between the reference voltage output from the subtraction circuit and the terminal voltage of the storage battery, and overdischarge occurs when the terminal voltage becomes lower than the reference voltage. A storage battery overdischarge detection device comprising a comparison circuit that outputs a detection signal.