DE102013109348A1 - Accumulator with monitoring device - Google Patents

Abstract

The invention relates to an accumulator (10) with a monitoring circuit having a fuse (14) in the main current path for interrupting the flow of current in the event of an overload, and to means (16, 18) for measuring the current in the main current path, wherein the device (16, 18) Current measurement is coupled to the fuse (14) to use the voltage drop across the fuse (14) for current measurement.

Description

The invention relates to an accumulator, with a device in the main current path for interrupting the flow of current in case of overload, and with a device for measuring current in the main current path.

The invention further relates to a power tool with such a rechargeable battery.

Modern accumulators usually have elaborate electronics to protect the individual cells from overcharging and undervoltage. For this purpose, the voltages of the individual cells or the total voltage of the accumulator pack are monitored. This is especially true for lithium-ion based storage systems. Due to the known characteristic of the cells, it is possible to deduce the state of charge and the current flow through the cell from the cell voltage.

However, such a model-based current determination is very inaccurate, since the cell properties are significantly scattered and are highly temperature- and age-dependent.

For safety reasons, accumulator systems often have a fuse as short-circuit protection in the main current path. This limits the maximum possible current. As fuses fuses or semiconductor devices are known.

When operating power tools with such rechargeable batteries, it must be ensured that the fuse of the rechargeable battery does not trip during normal operation of the power tool. On the other hand, the maximum possible power should be exploitable. For this purpose, an accurate current measurement in the accumulator is required.

In the prior art, an additional measuring resistor in the main current path is used for this purpose.

Thus, for example, reveals US 2011/0228136 A1 an accumulator having a fuse and a sense resistor connected in a current path over which a charge or discharge current flows, wherein a fuse control switch is provided to monitor the fuse. Furthermore, the device has a Schottky diode, which is connected at one end to the measuring resistor and at the other end to the fuse control switch. In this way, a destruction of the measuring resistor is detected, whereby a melting of the fuse is effected.

Also according to the US 2012/0008246 A1 and according to the US 2010/0127663 A1 In each case one measuring resistor is used in the main current path to monitor the current flow.

However, an additional measuring resistor has the disadvantage that it always represents an additional heat source and the accumulator is hereby unnecessarily burdened. Furthermore, the measuring resistor leads to corresponding component costs and additional wiring effort.

The invention is therefore an object of the invention to provide an accumulator, in which a current monitoring is carried out in the simplest and most cost-effective manner. Furthermore, a power tool to be specified with such a battery.

This object is achieved according to the invention in an accumulator according to the aforementioned type in that the means for measuring current is coupled to the means for interrupting the flow of current to use the voltage drop across the device for interrupting the current flow for current measurement.

The object of the invention is achieved in this way.

According to the invention, the voltage drop is used on the already existing device for interrupting the flow of current in the accumulator in order to determine the current. In this way, an additional measuring resistor in the main current path becomes superfluous. The circuit is simplified and made cheaper. Also, no additional measuring resistor has to be monitored for its failure.

The means for interrupting the flow of current may be a fuse whose voltage drop is monitored. This results in a particularly simple structure.

Alternatively, the device for interrupting the flow of current may also comprise a semiconductor component, in particular a MOSFET.

This has the advantage that normally no replacement is necessary in response to the overload protection thus realized, but the MOSFET simply blocks, without later a component must be replaced. However, this is associated with higher component costs.

In this case, the device for interrupting the flow of current may comprise two counter-series-connected MOSFETs in the main current path. This results in a particularly reliable structure. This version is especially for Accumulators suitable that have no separate charging port.

According to a further embodiment of the invention, the means for interrupting the flow of current to a MOSFET in the main current path and a MOSFET in the charging path. Such a design is particularly suitable for batteries with a separate charging port. While the MOSFET for the main current path must be designed for the full current, the second MOSFET for the charging path can be designed for a correspondingly low current, which means however an increased wiring effort.

In an advantageous development of the invention, the device for measuring the current at an output of the accumulator provides a signal (ENABLE) which can be evaluated by a load connected to the accumulator, in particular a power tool, in order to indicate a correct state of the accumulator (OK), as long as a certain limit value of the current is not exceeded, and to indicate an error of the accumulator when reaching or exceeding the limit value (NOK).

By providing the signal ENABLE to the consumer, it is possible to ensure that the consumer, in particular the power tool, can not be put into operation at all, if a release of the fuse is to be feared.

As far as a fuse is used, the product is preferably determined as the limit of the square of the measured current and time.

In a fuse, the limiting factor leading to (thermal) tripping is the product of the square of the current and the time (heating power times the line: I ² t). By determining this product, a precise monitoring of the fuse is ensured, on the one hand to be able to exploit a maximum possible current, on the other hand to reliably avoid a premature release of the fuse.

According to a further advantageous embodiment of the invention, a calibration device is provided to detect component scatters prior to initial startup.

Since the individual components, in particular the accumulator cells and the components for current monitoring, have a component distribution, it makes sense to provide a calibration prior to initial startup, so that an exact current measurement can be made in later use.

According to a further embodiment of the invention, the device for measuring current comprises a microprocessor.

In this way, a simple and inexpensive monitoring of the accumulator is possible.

According to a further feature of the invention, the microprocessor has an input for a nominal voltage which is indicative of a nominal current of the accumulator, wherein the microprocessor comprises a comparator which compares the target voltage with the actual value of the voltage supplied to the microprocessor at the nominal current of the accumulator to determine a correction value.

In this way a simple and precise calibration is possible.

According to a further feature of the invention, the means for interrupting the flow of current is coupled to an operational amplifier whose output is coupled to the microprocessor.

In this way, the very small voltage drop across the means for interrupting the flow of current can be sufficiently amplified to be evaluated directly by the microprocessor can.

According to a further embodiment of the invention, the device for interrupting the flow of current is designed so that a short-term operation in the overload range is possible, however, in the case of a short circuit, tripping takes place.

In this way, the necessary short-circuit protection is ensured, while short-term overload conditions are made possible without tripping occurs.

According to a further embodiment of the invention, the device for interrupting the flow of current is installed with a fuse such that after tripping a repair and recalibration is possible or required.

As far as the device for interrupting the flow of current is designed as a fuse, it does not make sense to install them interchangeable in an exchangeable, since this can lead to large variations in the series resistance of the fuse, which can also change during operation. After the fuse has tripped, it is repaired and recalibrated to ensure precise monitoring of the current value during further operation.

A power tool operated with such a rechargeable battery preferably has a control which allows the power tool to be switched on only when the signal ENABLE is OK.

In this way it is ensured that the power tool can only be switched on when the current flow through the accumulator does not assume any impermissible values.

It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the invention.

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings. Show it:

1 a first circuit of an accumulator according to the invention with an associated consumer in the form of a power tool, which is powered by the accumulator;

2 an accumulator according to 1 with a coupled calibration device;

3 a second circuit of an accumulator according to the invention, wherein the means for interrupting the flow of current in case of overload is formed by counter-series-connected MOSFETs and

4 a modification of the embodiment according to 3 with a MOSFET in the main current path and a MOSFET in a charging circuit.

In 1 is an inventive accumulator in total with the numeral 10 designated.

The accumulator 10 has a series of battery cells connected in series 12 on. In the main current path of the positive pole is a fuse 14 , The outputs of the accumulator 10 for power supply are with 24 (Plus pole) and 26 (Negative pole). The current of the accumulator 10 is through a microprocessor 18 measured and monitored. For this purpose, the at the fuse 14 falling voltage tapped and from an operational amplifier 16 reinforced and an entrance 20 of the microprocessor 18 fed. The voltage of the accumulator 10 is also via a voltmeter 28 whose output is connected to another input 22 of the microprocessor 18 is coupled.

The microprocessor 18 is also with the positive pole 24 and the negative pole 26 coupled for voltage.

Is a consumer 40 to the outputs 24 . 26 of the accumulator 10 connected, as in 1 with the two entrances 46 . 48 is indicated, the accumulator causes 10 a current flow through the consumer 40 , Supplies the accumulator 10 a current, so falls at the fuse 14 a voltage from the operational amplifier 16 is amplified and the microprocessor 18 is supplied.

The microprocessor 18 calculates from this the current I and the product of the square of the current I with the time t (I ² t). This is the limiting factor for the release of the fuse 14 ,

As long as the product I ² t is below a predetermined limit value, no release of the fuse is to be feared, and the microprocessor supplies to the output 30 of the accumulator 10 a signal ENABLE that is OK. If the product I ² t exceeds the predetermined limit, the microprocessor delivers 18 at the exit 30 as signal ENABLE NOK (error).

The signal ENABLE at the output 30 is with an entrance 50 of the consumer 40 coupled in the form of a power tool. The consumer 40 has a microprocessor 44 for controlling an engine 42 on. The ENABLE signal is for the microprocessor 44 of the consumer 40 fed. The microprocessor 44 is programmed so that the engine 42 can only be put into operation if the ENABLE signal is OK. If the signal NOK, this indicates an overload condition, so that the engine 42 can not be put into operation.

The fuse 14 is designed as a slow-acting fuse and dimensioned so that it allows a certain overload condition for a certain time before the fuse 14 triggers. That from the microprocessor 18 measured product I ² t is such that the accumulator 10 can be operated until reaching the maximum current, without triggering the fuse 14 is to be feared.

Based on 2 will be briefly a calibration 60 which can be used to perform a calibration prior to initial start-up. The calibration device 60 includes a microprocessor 72 , by means of which a load resistance 62 can be controlled so that when applying the load resistance 62 over the two entrances 66 . 68 to the voltage outputs 24 . 26 of the accumulator 10 a predetermined current of z. B. 1 A flows.

For this purpose, the calibration device 60 with two voltage inputs 66 . 68 to the voltage outputs 24 . 26 of the accumulator 10 coupled. Further, the output becomes 30 ENABLE with a corresponding input 70 a microprocessor 72 , The microprocessor 72 also provides a setpoint voltage at an output 64 ready, over an entrance 32 of the accumulator 10 an input of the microprocessor 18 of the accumulator 10 is supplied.

The microprocessor 72 controls the load resistance 72 such that a certain nominal current of z. B. 1 A adjusts. At the same time the microprocessor delivers 72 a nominal voltage to the input 32 of the microprocessor 18 that corresponds to such a current flow. If, for example, the nominal resistance of the fuse in the cold state is 1 milliohm and the operational amplifier amplifies nominally 1000 times, then the nominal voltage is 1 volt. The value for the nominal voltage 32 is with the actual value at the entrance 20 of the microprocessor 18 which results in a correction value stored in the microprocessor.

Such a calibration becomes unique before the battery is started up 10 carried out.

The fuse 14 is in the accumulator 10 Firmly mounted on a printed circuit to ensure a secure connection with the circuit, so that the internal resistance of the fuse 14 which is typically about 1 milliohm when cold, does not change. At the fuse 14 typically accumulate about 70 millivolts in nominal mode.

In 3 is a respect to the execution according to 1 modified version of an accumulator according to the invention shown and in total with 10a designated.

The accumulator is hereby provided with three connections, one connection 24 for the positive pole, a connection 26 for the negative pole and a connection 30 for the input ENABLE according to 1 , In the main current path of the negative pole are two counter-current in series MOSFETs 80 . 82 whose gates G are each of terminals 81 . 83 of the microprocessor 18 be controlled.

Commercially available MOSFETs additionally have a diode between source S and drain D, which is additionally shown here. The diode blocks in the forward direction of the MOSFET, but conducts in the opposite direction as soon as the threshold voltage is exceeded. In the forward direction with the gate turned on, the voltage Rds (depending on the current) drops across a MOSFET, which in principle is monitored here.

The total voltage drop across the MOSFETs 80 . 82 is the two entrances 85 . 86 an operational amplifier 84 supplied to amplify the voltage dropped as a result of the internal resistance voltage as a measurement voltage.

The output of the operational amplifier 84 is a connection 87 of the microprocessor 18 fed. When the voltage at the connection 87 of the microprocessor 18 exceeds a predetermined value, is at the output 30 the signal NOK output and the previously switched MOSFETs 80 . 82 will be closed.

In 4 is a further modification of the accumulator over the embodiment according to 3 represented us in total with 10b designated. Here, the accumulator 10b in addition to the connections according to FIG. 10a a fourth connection 88 on, which only serves for charging (charging connection), while the connection 26 is intended exclusively for unloading. In the main current path is here in a modification to the execution according to 3 only a MOSFET 82 , whose voltage drop Rds by means of an operational amplifier 90 is monitored, at its two entrances 95 . 96 with the mosfet 82 is coupled to tap and monitor the voltage Rds in case of load or overload. The output of the MOSFET 90 is with the entrance 87 of the microprocessor 18 coupled. A MOSFET 80 lies between the charging port 88 and the input of the MOSFET 82 at its output with the accumulator cells 12 is coupled.

The MOSFET 80 voltage dropping during charging can (optionally) additionally by a second operational amplifier 92 be monitored, with its two inputs 94 . 95 on the one hand with the charging port 88 and on the other hand with the supply voltage 97 is coupled. The output of the second operational amplifier 92 is with another entrance 93 of the microprocessor 18 coupled. Exceeds the on one of the two MOSFETs 80 . 82 decreasing voltage Rds a predetermined value so the microprocessor locks 18 the relevant MOSFET 80 respectively. 82 and gives at the exit 30 the signal NOK off.

The monitoring by means of the second operational amplifier 92 for the MOSFET 80 in the charging circuit is optional, as shown by the dashed design.

While in the circuit according to 3 both MOSFETs 80 . 82 must be designed for the maximum current is in the execution according to 4 only the mosfet 82 for the maximum current, while the other MOSFET 80 only for the lower charging current must be designed, which compared to the design according to 3 a cost and weight saving means. On the other hand, there is an increased complexity and increased wiring costs.

Both circuits according to 3 and 4 are usefully calibrated before first use, to compensate for component variations, similar to previously based on 2 described. In principle, this is a known discharge current through the accumulator 10b generated and the falling voltage at the entrance 87 recorded (discharge). The relevant voltage value is stored in a value table. In the same way can with the charging current through the charging port 88 be moved and the voltage value at the input 93 captured and stored in a lookup table.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2011/0228136 A1 [0008]
• US 2012/0008246 A1 [0009]
• US 2010/0127663 A1 [0009]

Claims (15)

Accumulator, with a device ( 14 ) in the main current path to interrupt the flow of current in the event of an overload, and with a device ( 16 . 18 ) for current measurement in the main current path, characterized in that the device ( 16 . 18 ) for current measurement with the device ( 14 ) to interrupt the flow of current to the voltage drop across the device ( 14 ) to use for power interruption for current measurement. Accumulator according to Claim 1, characterized in that the device ( 14 ) is designed to interrupt the flow of current as a fuse. Accumulator according to claim 1, characterized in that the device ( 14 ) for interrupting the flow of current, a semiconductor device ( 80 . 82 ). Accumulator according to claim 3, characterized in that the device ( 14 ) to interrupt the flow of current a MOSFET ( 80 . 82 ). Accumulator according to Claim 4, characterized in that the device ( 14 ) for interrupting the flow of current two counter-series-connected MOSFETs ( 80 . 82 ) in the main current path. Accumulator according to Claim 4, characterized in that the device ( 14 ) to interrupt the flow of current a MOSFET ( 82 ) in the main current path and a MOSFET ( 80 ) in the charging path. Accumulator according to one of the preceding claims, characterized in that the device for current measurement ( 16 . 18 ) a signal (ENABLE) at an output ( 30 ) of the accumulator ( 10 ) from one to the accumulator ( 10 ) connected consumers ( 40 ), in particular a power tool, can be evaluated to indicate a proper state of the accumulator (OK), as long as a predetermined limit is not exceeded, and to indicate an error of the accumulator when the limit value is reached or exceeded (NOK). Accumulator according to Claim 7, characterized in that the device for measuring current ( 16 . 18 ) determines as limit the product of the square of the measured current and the time (I ² t). Accumulator according to one of the preceding claims, characterized in that a calibration device ( 60 ) is provided to detect component scatters prior to initial startup. Accumulator according to one of the preceding claims, characterized in that the device for measuring current is a microprocessor ( 18 ). Accumulator according to Claims 9 and 10, characterized in that the microprocessor ( 18 ) an entrance ( 32 ) for a nominal voltage which is suitable for a nominal current of the accumulator ( 10 ) indicative, and that the microprocessor ( 18 ) has a comparator, the actual value of the microprocessor ( 18 ) compares the voltage supplied to the setpoint current of the accumulator with the setpoint voltage to determine a correction value. Accumulator according to Claim 7 or 8, characterized in that the device ( 14 ) for interrupting the flow of current with an operational amplifier ( 16 ; 84 ; 90 . 92 ) whose output is connected to the microprocessor ( 18 ) is coupled. Accumulator according to one of the preceding claims, characterized in that the device ( 14 ) is designed to interrupt the flow of current so that a short-term operation in the overload range is possible, however, in the case of a short circuit, tripping takes place. Power tool with an accumulator according to one of claims 1 to 12. Power tool with an accumulator according to one of claims 7 to 13, with a control ( 44 ), which involves switching on an engine ( 42 ) of the power tool ( 40 ) only allowed if the ENABLE signal is OK.

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