Nickel-metal hydride battery life measuring circuit

Abstract

The utility model belongs to the technical field of electronic circuits, and discloses a nickel-metal hydride battery life measuring circuit. Comprising a battery input control circuit, a constant-current discharge circuit, a voltage sampling circuit and a control module, the control module is used for outputting a control signal to the battery input control circuit, and the battery input control circuit is used for connecting a battery to be tested with the constant-current discharge circuit under the control of the control signal; the constant-current discharge circuit is used for performing constant-current discharge on the battery, and the voltage sampling circuit is used for measuring the voltage of the battery. According to the utility model, constant-current discharge can be carried out on the battery, the voltage of the battery can be accurately measured, quantitative data can be provided for the evaluation of the service life of the battery, circuit components are few, the cost is low, and a special chip is not needed.

Description

Technical Field

[0001] The utility model belongs to the technical field of electronic circuits, and particularly relates to a nickel-metal hydride battery life measurement circuit. Background Art

[0002] As a backup power source, batteries are usually used to provide power for terminal products to continue working when the power supply in the substation area is cut off, so as to save and report important data and events. At present, most power collection terminal products use nickel-metal hydride batteries as backup power sources. Nickel-metal hydride batteries have a lifespan problem. Generally speaking, the battery life is much lower than that of other parts of the product. Therefore, it is necessary to regularly and accurately evaluate the battery usage status to avoid the loss of key data. At present, the battery voltage is mostly sampled to judge the battery status. This judgment method is not accurate enough. According to on-site feedback, it often occurs that when the battery has failed, the sampled voltage reading of the battery is still normal, and the sampled voltage is only a virtual voltage.

[0003] Therefore, a new measurement circuit needs to be proposed to accurately evaluate the battery life. Summary of the Utility Model

[0004] The utility model overcomes the deficiencies existing in the evaluation of battery life in the prior art. The technical problem to be solved is: to provide a nickel-metal hydride battery life measurement circuit, which realizes the measurement of battery internal resistance and battery capacity by performing constant current discharge on the battery.

[0005] To solve the above technical problem, the technical solution adopted by the utility model is: a nickel-metal hydride battery life measurement circuit, including a battery input control circuit, a constant current discharge circuit, a voltage sampling circuit and a control module; the control module is used to output a control signal to the battery input control circuit, and the battery input control circuit is used to connect the battery to be measured with the constant current discharge circuit under the control of the control signal.

[0006] The constant current discharge circuit includes a resistor R3, a triode V2, a load resistor R1, and a voltage regulator TS1. The positive electrode of the battery to be measured is connected to the collector of the triode V2 through the battery input control circuit. The base of the triode V2 is connected to the collector of the triode V2 through the resistor R3, and the emitter is grounded through the load resistor R1. The cathode of the voltage regulator TS1 is connected to the base of the triode V2, the anode is grounded, and the reference electrode is grounded with the emitter of the triode V2.

[0007] The voltage sampling circuit includes a resistor R6 and a resistor R7. One end of the resistor R6 is connected to the positive electrode of the battery to be measured, and the other end is grounded through the resistor R7; the other end of the resistor R7 is also connected to the input end of the control module.

[0008] The battery input circuit includes resistor R4, resistor R5, triode V3, resistor R2, and field effect transistor V1. One end of resistor R4 is connected to the control signal output terminal of the single-chip microcomputer, and the other end is connected to the base of triode V3. The emitter of triode V1 is grounded, and the collector is connected to the gate of field effect transistor V1. One end of resistor R3 is connected to the base of triode V3, and the other end is connected to the emitter of triode V1. The source of field effect transistor V1 is connected to the battery to be tested, and the drain is connected to the input terminal of the constant current discharge circuit.

[0009] The battery input control circuit further includes capacitor C1, and capacitor C1 is connected in parallel with resistor R5.

[0010] The field effect transistor V1 is a PMOS transistor.

[0011] The control module is a single-chip microcomputer.

[0012] The input terminal of the battery input control circuit is connected to the GPIO of the single-chip microcomputer.

[0013] The resistance value of the constant current resistor R1 is 10 Ω.

[0014] The resistance values of resistor R6 and resistor R7 are 51 kΩ and 47 kΩ respectively.

[0015] Compared with the prior art, the present utility model has the following beneficial effects: The present utility model provides a nickel-metal hydride battery life measurement circuit. The battery can be discharged with a constant current through the constant current discharge circuit, and the voltage sampling circuit can be used to measure the voltage of the battery after a certain discharge time. This voltage value can be used to calculate the internal resistance of the measured battery. In addition, the battery input control circuit can be used to control the automatic discharge of the battery. At the same time, the battery voltage can be measured through the voltage sampling circuit. By measuring the discharge time of the fully charged battery to the cut-off voltage under the condition of constant current discharge, the battery capacity can also be measured. Therefore, the present utility model can not only achieve constant current discharge, but also accurately measure the battery voltage, and further provide quantitative data for battery life assessment. Moreover, its circuit components are few, the cost is low, and no special chip is required. Description of the Drawings

[0016] Figure 1 It is a circuit principle block diagram of a nickel-metal hydride battery life measurement circuit provided by an embodiment of the present utility model;

[0017] Figure 2 It is a circuit schematic diagram of the battery input control circuit and the constant current discharge circuit in an embodiment of the present utility model;

[0018] Figure 3 It is a circuit schematic diagram of the voltage sampling circuit in an embodiment of the present utility model. Detailed Embodiments

[0019] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be described clearly and completely below. Apparently, the described embodiments are some but not all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without making creative efforts shall fall within the protection scope of the present utility model.

[0020] As Figure 1 shown, an embodiment of the present invention provides a nickel-metal hydride battery life measurement circuit, including a battery input control circuit, a constant current discharge circuit, a voltage sampling circuit and a control module; the control module is used to output a control signal to the battery input control circuit, and the battery input control circuit is used to connect a battery under test to the constant current discharge circuit under the control of the control signal; the constant current discharge circuit is used to perform constant current discharge on the battery, and the voltage sampling circuit is used to measure the battery voltage.

[0021] Further, as Figure 2 shown, in this embodiment, the constant current discharge circuit includes a resistor R3, a triode V2, a load resistor R1, and a voltage regulator TS1. The positive electrode of the battery under test is connected to the collector of the triode V2 through the battery input control circuit. The base of the triode V2 is connected to the collector of the triode V2 through the resistor R3, and the emitter is grounded through the load resistor R1. The cathode of the voltage regulator TS1 is connected to the base of the triode V2, the anode is grounded, and the reference electrode is grounded to the emitter of the triode V2;

[0022] Further, as Figure 3 shown, in this embodiment, the voltage sampling circuit includes a resistor R6 and a resistor R7. One end of the resistor R6 is connected to the positive electrode of the battery under test, and the other end is grounded through the resistor R7; the other end (NiH-Batt_AD) of the resistor R7 is also connected to the input end of the control module.

[0023] Specifically, as Figure 2 shown, the battery input circuit includes a resistor R4, a resistor R5, a triode V3, a resistor R2, and a field effect transistor V1. One end (Batt_discharge) of the resistor R4 is connected to the control signal output end of the single-chip microcomputer, and the other end is connected to the base of the triode V3; the emitter of the field effect transistor V1 is grounded, and the collector is connected to the gate of the field effect transistor V1; one end of the resistor R3 is connected to the base of the triode V3, and the other end is connected to the emitter of the triode V1; the source of the field effect transistor V1 is connected to the battery under test, and the drain is connected to the input end of the constant current discharge circuit.

[0024] Furthermore, in this embodiment, the battery input control circuit further includes a capacitor C1, and the capacitor C1 is connected in parallel with a resistor R5. The field effect transistor V1 is a PMOS transistor.

[0025] Specifically, in this embodiment, the control module is a single-chip microcomputer. The input end of the battery input control circuit is connected to the GPIO port of the single-chip microcomputer. That is to say, one end of the resistor R4 is connected to the GPIO port of the single-chip microcomputer.

[0026] Specifically, the single-chip microcomputer uses a 12-bit ADC, and the sampling resolution reaches 0.000732422 V / bit. If the internal resistance of the battery is 100 mR under normal conditions and it discharges at a constant current of 250 mA, the corresponding real-time sampled voltage fluctuation is V = (0.1×0.25÷(51 + 47)×47) = 0.012 V, and the contrast resolution fully meets the requirements.

[0027] Specifically, in this embodiment, the resistance value of the constant current resistor R1 is 10 Ω. In addition, the resistance value of the constant current resistor R1 can be set according to the required discharge current, for example, set to 1 - 100 Ω.

[0028] Specifically, in this embodiment, the resistance values of the resistors R6 and R7 are 51 kΩ and 47 kΩ respectively.

[0029] The measurement principle of the present invention is introduced below.

[0030] The working principle of the present invention is as follows: When the GPIO port of the single-chip microcomputer outputs a high level, at this time, the triode V3 reaches the conduction condition, pulling down the gate of the field effect transistor V1. At this time, the gate-source voltage Vgs of the field effect transistor V1 reaches the turn-on condition of the field effect transistor V1, and the field effect transistor V1 conducts, and the battery input constant current discharge circuit is turned on. After the battery is input, it is limited by the resistor R3 to provide a regulated working current for the voltage regulator TS1. At this time, a 2.5 V voltage is generated between the reference terminal of the voltage regulator TS1 and the ground, and the discharge current can be adjusted by adjusting the resistance value of the resistor R1; if the resistor R1 selects a 10R resistor at this time, the current is constant at I = 2.5 V / 10R = 0.25 A. During the discharge process, the voltage is adjusted by the triode V2. The voltage across the triode V2 is the battery voltage minus 2.5 V. If the battery voltage is 4.8 V at this time and it discharges at 250 mA, the heat dissipation power borne by the triode V2 is approximately: P = (4.8 - 2.5) * 0.25 = 0.575 W. Therefore, the selection of the triode should be comprehensively considered in combination with the discharge current, etc., to prevent the temperature rise of the triode from being too high during the discharge process, and at the same time, pay attention to the heat dissipation design in the PCB design.

[0031] Specifically, the measurement method of the DC impedance of the battery is as follows: First, measure the open-circuit voltage U1 of the battery before connecting the load through the voltage sampling circuit, then connect the load and discharge at a constant current I. After discharging for a period of time (not exceeding 500 ms), measure the battery voltage U2 through the voltage sampling circuit, then the internal resistance R = (U1 - U2) / I. The measurement method of the battery capacity is as follows: First, fully charge the battery, then discharge it at a constant current until the cut-off voltage of the battery, and record the discharge time t, then the capacity C = I * t. In addition, it should be noted that if the battery voltage drops at a speed exceeding the threshold during the constant-current discharge process, it is determined that the battery fails.

[0032] Specifically, the battery life is closely related to the internal resistance and capacity. If the change in the battery internal resistance compared to the rated value is not significant, it indicates that the battery is still in normal use. If there is an obvious change, it means that the battery is about to fail, an alarm needs to be issued, and the battery needs to be replaced. Generally, the internal resistance of a nickel-metal hydride four-cell battery is about 200 mΩ. If the measured internal resistance increases significantly through calculation, it can be considered that the battery has failed or is about to fail. The calculation of the battery capacity is used as an auxiliary basis for judging the battery life. If it is much smaller than the rated capacity and at the same time the internal resistance also increases significantly, it indicates that the battery life is about to expire and the battery is about to fail.

[0033] In summary, the present invention provides a constant-current discharge circuit measurement. Through the constant-current discharge circuit, the battery can be discharged at a constant current, and the voltage sampling circuit can be used to measure the voltage of the battery after a period of discharge time, so that the internal resistance and capacity of the battery can be calculated, and then the battery life can be evaluated. In addition, the battery input control circuit can realize the automatic control of the constant-current discharge of the battery.

[0034] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nickel-metal hydride battery life measurement circuit, characterized in that It includes a battery input control circuit, a constant current discharge circuit, a voltage sampling circuit and a control module; the control module is used to output a control signal to the battery input control circuit, and the battery input control circuit is used to connect the battery under test to the constant current discharge circuit under the control of the control signal. The constant current discharge circuit includes a resistor R3, a triode V2, a load resistor R1, and a voltage regulator TS1. The positive electrode of the battery under test is connected to the collector of the triode V2 through the battery input control circuit. The base of the triode V2 is connected to the collector of the triode V2 through the resistor R3, and the emitter is grounded through the load resistor R1. The cathode of the voltage regulator TS1 is connected to the base of the triode V2, the anode is grounded, and the reference electrode is grounded to the emitter of the triode V2. The voltage sampling circuit includes a resistor R6 and a resistor R7. One end of the resistor R6 is connected to the positive electrode of the battery under test, and the other end is grounded through the resistor R7; the other end of the resistor R7 is also connected to the input end of the control module.

2. The nickel-metal hydride battery life measurement circuit according to claim 1, wherein The battery input control circuit includes a resistor R4, a resistor R5, a triode V3, a resistor R2, and a field effect transistor V1. One end of the resistor R4 is connected to the control signal output end of the single-chip microcomputer, and the other end is connected to the base of the triode V3; the emitter of the field effect transistor V1 is grounded, and the collector is connected to the gate of the field effect transistor V1; one end of the resistor R3 is connected to the base of the triode V3, and the other end is connected to the emitter of the triode V1. The source of the field effect transistor V1 is connected to the battery under test, and the drain is connected to the input end of the constant current discharge circuit.

3. The nickel-metal hydride battery life measurement circuit according to claim 2, characterized in that, The battery input control circuit further includes a capacitor C1, and the capacitor C1 is connected in parallel with the resistor R5.

4. The nickel-metal hydride battery life measurement circuit according to claim 2, characterized in that, The field effect transistor V1 is a PMOS transistor.

5. A nickel-metal hydride battery life measurement circuit according to claim 1, characterized in that, The control module is a single-chip microcomputer.

6. The nickel-metal hydride battery life measurement circuit according to claim 5, characterized in that, The input end of the battery input control circuit is connected to the GPIO of the single-chip microcomputer.

7. The nickel-metal hydride battery life measurement circuit according to claim 1, wherein The resistance value of the load resistor R1 is 10 Ω.

8. A nickel-metal hydride battery life measurement circuit according to claim 1, characterized in that, The resistance values of the resistor R6 and the resistor R7 are 51 kΩ and 47 kΩ respectively.

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