Abstract:
A charge/discharge device composed of low cost passive component, which allows charge/discharge a pack of supercapacitors for automotive applications without any risk for operators and without danger of damaging neighboring devices, materials and supercapacitors is disclosed. It contains an inner electric charge line connected to a supply terminal of the device; an inner electric ground discharge line connected to a ground terminal of the device; an inner electric output line connected to an output terminal of the device; an on-off-on toggle switch, and a passive bipolar resistive circuit having an overall resistance comprised between 0.1 Ohms and 10 Ohms and inserted in the inner electric output line, having a power resistor installed on a heat sink.

Description:
TECHNICAL FIELD 
       [0001]    The present invention concerns charge/discharge devices of accumulators and more particularly a charge/discharge device of a pack of supercapacitors for applications in the automotive field. 
       BACKGROUND 
       [0002]    Supercapacitors, which are capacitors with a capacity in the order of many Farads used in place of or in addition to batteries, are becoming increasingly used in the automotive field, thanks to the ease with which they are charged and discharged, to the high number of charge/discharge cycles and to their low weight. 
         [0003]    The supercapacitors are increasingly emerging in applications where a high power is required at short time intervals, as for example during the ignition of an internal-combustion engine. For this reason, packs of supercapacitors are increasingly used in order to supply the engine starter and to provide the required peak current by limiting the current absorbed by the battery, thus prolonging its life. 
         [0004]    Since the mechanism of energy storage of supercapacitors is not a chemical reaction, as it happens instead in the batteries, the operations of charge/discharge occur at the same speed. Furthermore, supercapacitors have a very low equivalent series resistance, so that they can be charged and discharged at much higher speeds than the usual batteries, which makes them ideal for recovering energy, as for example in recovery braking systems. 
         [0005]    Since supercapacitors have an extremely low equivalent series resistance, they pose problems for the usual charging systems for the common batteries because they appear as a virtual short circuit and this may damage the charging circuit. For this reason, supercapacitors are currently charged and discharged only through charge/discharge systems based on switching regulators. 
         [0006]    For example, a pack of supercapacitors for applications in the automotive field, which typically has a total capacity of at least 100 F, can be charged/discharged through DC-DC constant current regulators or through buck regulators or also through boost regulators, which are suitable to provide a substantially constant current by gradually increasing/decreasing the output voltage used to charge the pack of supercapacitors, so as to adjust it to the charge voltage of the pack of supercapacitors. 
         [0007]    However, when charged, they represent a danger for the operators. Even if the typical charge voltage of a pack of supercapacitors for automotive applications is in the order of ten or a few tens of Volts (typical voltages are 12, 24 or 48V), they, unlike batteries, can deliver very high currents of several thousand Amperes, even higher than those of arc welders, so that they are capable of instantly melt metal items such as screwdrivers and tools of considerable section, sheet metals, carbon fibers, bracelets, chains and electric cables, so as to accidentally cause severe burns and/or starts of fire caused by the induces combustion of insulating materials such as sheaths, paints, etc. For this reason, they should be installed (or removed) discharged, and be charged (or discharged) only when they are on the motor vehicle. 
         [0008]    Currently, the operation of charge/discharge of a pack of supercapacitors installed on a motor vehicle is quite inconvenient because it is performed with complex, relatively bulky and expensive electronic devices, typically supplied by mains at 220 V and which are difficult to transport from one motor vehicle to another. However, for the reasons stated above, it is dangerous to charge a pack of supercapacitors on a charge bench and then install it already charged on a motor vehicle. 
         [0009]    A device for charging/discharging a pack of supercapacitors would be desirable, in particular for applications in the automotive field, which is simple to be produced with low cost components, which can be easily transported from one motor vehicle to another and handled safely by an operator, while protecting him from the risk of electrocution. 
         [0010]    US 2012/133309 A1 discloses a charge/discharge device according to the preamble of claim  1 . 
       SUMMARY 
       [0011]    Although it is commonly known and reported even in the technical documentation of supercapacitors (as for example indicated in Application Note 1008981 of Maxwell Technologies) that they must be charged (and consequently also discharged) by using switching regulators or other specific and complex devices, such as electronic apparatuses with a programmed resistive load which adapt themselves to the needs of the supercapacitors, the applicant has verified that, with a particular choice of the discharge circuit, it is possible to quickly and safely charge/discharge a pack of supercapacitors for automotive applications, which typically has a capacity of the magnitude of about one hundred Farads and a nominal charging voltage of about ten Volts, without using voltage switching regulators. 
         [0012]    This result has been obtained with a charge/discharge device essentially made up of low cost passive components, which allows to charge/discharge a pack of supercapacitors for automotive applications without any risk for the operators of the facilities and neighboring equipment and without any danger of damaging the supercapacitors, comprising: 
         [0013]    an inner electric charge line connected to a supply terminal of the device; 
         [0014]    an inner electric ground discharge line connected to a ground terminal of the device; 
         [0015]    an inner electric output line connected to an output terminal of the device; 
         [0016]    an on-off-on toggle switch, configured so that:
       in a first extreme position, it connects said inner charge line to said inner output line,   in a central position, it leaves said inner lines mutually disconnected,   in a second extreme position, is connects said inner output line with said inner ground discharge line;       
 
         [0020]    a passive bipolar resistive circuit having an overall resistance comprised between 0.1 Ohms and 10 Ohms and inserted in said inner electric output line, comprising at least one power resistor mounted on a heat sink. 
         [0021]    According to one embodiment, the bipolar resistive passive circuit comprises two power resistors having a resistance of about 1 Ohm each and being suitable to dissipate a maximum power of about 150 W, connected in parallel and mounted on a heat sink made of an anodized aluminum finned plate. 
         [0022]    The claims as filed are an integral portion of this description and are incorporated herein by express reference. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a basic first embodiment of a charge/discharge device according to the present disclosure. 
           [0024]      FIG. 2  illustrates how to connect the device of  FIG. 1  to a battery and to a terminal of a pack of supercapacitors connected to a starter of a motor. 
           [0025]      FIG. 3  shows a charge/discharge device according to the present disclosure with three power resistors in parallel, equipped with a digital panel meter and signaling LEDs. 
           [0026]      FIG. 4  shows a resistive bipolar circuit alternative to the one shown in  FIG. 3 , which consists of two power resistors in parallel mounted on a heat sink. 
           [0027]      FIG. 5  shows a detailed circuit diagram of a charge/discharge device according to the present disclosure having a green LED and a red signal LED, and provided with diodes to protect against accidental reverse polarity connections to the vehicle battery and to ground. 
           [0028]      FIG. 6  is a perspective view of the chassis of the charge/discharge device of this disclosure, with a telescopically extendable hook represented in a retracted position, to hang the device to the bodywork of a motor vehicle. 
           [0029]      FIG. 7  is a perspective view of the device shown in  FIG. 6  with the hook in an extended position. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Contrary to what is commonly accepted by the technical experts and commonly held true in practice, it is possible to quickly and safely charge and discharge a pack of supercapacitors for automotive applications, which typically has a total capacity of at least 100 F and a nominal charge voltage of 12 V, without using voltage or current switching regulators, which are expensive and bulky, but simply by using passive and low cost components. 
         [0031]    A basic embodiment of a charge/discharge device according to the present disclosure is shown in  FIG. 1 . The device comprises essentially an internal electric charge line connected to a terminal POS of a power supply, an inner electric ground discharge line connected to a ground terminal GND, an inner electric output line connected to an output terminal UCAP, a bipolar resistive passive circuit D, RP inserted in the inner electrical output line, and an on-off-on toggle switch SW. In a first extreme position ON 1 , the switch SW connects the charge line to the output line by circulating current from the supply terminal POS to the output terminal UCAP in order to charge the pack of supercapacitors connected to it; in a central position OFF, as shown in the figure, it mutually insulates the inner electric lines; in a second extreme position ON 2 , it connects the output line to the ground discharge line, by circulating current from the output terminal UCAP to the ground terminal GND of the device in order to discharge the pack of supercapacitors. 
         [0032]    The device according to the present disclosure charges/discharges under conditions of total safety the pack of supercapacitors on the bipolar resistive circuit without using active and passive switching regulators, possibly providing also full comprehensive information on the state of charge/discharge. 
         [0033]    The applicant has found that it is possible to carry out in total safety for the operators the operations of charging/discharging the pack of supercapacitors by using the device shown in  FIG. 1 , provided that the bipolar resistive passive circuit has an overall equivalent resistance Req comprised between 0.1 Ohms and 10 Ohms and has power resistors mounted on a heat sink. Surprisingly, it has been experimentally verified, with a working prototype, that a bipolar resistive circuit thus constructed is able to withstand the exponential charge/discharge currents of a pack of supercapacitors for applications in the automotive field without the supercapacitors themselves being damaged by the charge/discharge current and in an extremely simple, controllable and safe manner, with no harm to operators and devices. 
         [0034]    Since the power dissipated on the bipolar resistive circuit is inversely proportional to its total equivalent resistance Req, the latter will be suitably dimensioned so as not to be less than 0.1 Ohms. This minimum value has been identified by the applicant considering that a pack of supercapacitors for applications in the automotive field has a nominal charge voltage of 12 V. With an equivalent resistance Req lower than the minimum identified above, the bipolar resistive circuit should dissipate a power much higher than a kilowatt, which would cause an excessive heating of the charge/discharge device with risks for the operator and for the electronic circuitry, if present in it, and charge/discharge currents exceeding about one hundred Amperes, which, if continued for several seconds, may damage the conventional batteries and overcharge the AGM (Absorbent Glass Mat) batteries for high currents. 
         [0035]    Conveniently, the minimum value of the equivalent resistance Req can be correspondingly increased for nominal charge voltages higher than 12V. 
         [0036]    Since the total capacity of a pack of supercapacitors for applications in the automotive field is higher than about one hundred Farads, conveniently the equivalent resistance Req of the bipolar resistive circuit will not be greater than 10 Ohms, to avoid unacceptably long charge/discharge times. 
         [0037]    When increasing the total capacity of the pack of supercapacitors, it is convenient to reduce in an inversely proportional manner the maximum value of the equivalent resistance Req. For example, if using a pack of supercapacitors with a capacity in the order of one KiloFarad, the equivalent resistance Req will conveniently not exceed 1 Ohm. 
         [0038]    Thus, contrary to what has been commonly held true, there is a narrow range of values in which the equivalent resistance Req of the bipolar resistive passive circuit can dimensioned and for which it is possible to carry out in total safety operations of charge/discharge of the packs of supercapacitors currently used in the automotive field, which have a charge voltage in the order of ten Volts and a capacity in the order of several hundred Farads. 
         [0039]    According to one embodiment, the bipolar resistive circuit will have an equivalent resistance Req of 0.5 Ohms. This value represents an excellent compromise between the conflicting demands of limiting the power dissipated during the charge/discharge operations and quickly complete the latter. 
         [0040]      FIG. 2  shows how to connect the device of this disclosure to a terminal J 2  of a pack UM of supercapacitors UC 1 , . . . , UC 6  connected to the starter ES of a motor M, connected to a line SK of a circuit of a key ignition circuit of the motor vehicle, to a terminal J 1  of a battery B of the motor vehicle and to ground. The figure also indicates the alternator A charging the battery B, connected to an inner line PW of the motor vehicle, the charge distributor AUX on the supercapacitors, which acts in such a way that the supercapacitors are charged and discharged together, and its relevant control circuit CON 5  that controls the closure of a switch K 3  through a relay to connect directly the pack of supercapacitors in parallel to the battery, which occurs when the pack of supercapacitors is charged and must provide the high peak currents absorbed at the ignition, thus saving a stress of the battery. The battery, when the ignition has occurred, along with the alternator works as a reservoir of energy, thus compensating for relatively long times the voltage drop of the supercapacitor, which acts instead as a reservoir of power by delivering in short times very high currents and powers. 
         [0041]    When the pack of supercapacitors is discharged and must be charged, or when it is charged and must be discharged, switch K 3  is opened and the charge/discharge device of this disclosure is connected as shown in the figure, thus keeping the three-positions switch in the center position OFF so as not to generate sparks or electric discharges. Then, the switch is moved to the extreme position ON 1  or ON 2  depending on whether the pack of supercapacitors must be charged or discharged. 
         [0042]    The central-zero switch can for example be of the type with one pole with 30 A contacts, or even with two poles, with 15 A or 20 A contacts connected in parallel. 
         [0043]    An embodiment of a charge/discharge device according to the present disclosure is shown in  FIG. 3 . The bipolar resistive circuit is in this case made up of three power resistors electrically connected in parallel and mounted on a heat sink D, for example a finned plate made of anodized aluminum with a high surface exposure to the environment. The power resistors can have a resistance of 1.5 Ohms and be constructed for dissipating a maximum power of 100 W each, while the heat sink D may have a size of 160 mm×100 mm×40 mm. Alternatively, the bipolar resistive circuit can be composed of two 1 Ohm resistors in parallel constructed to dissipate a maximum power of 150 W each, as shown in  FIG. 4 , also mounted on the heat sink D. 
         [0044]    The maximum total value of power of 300 W which can be dissipated, in this case described as an example, is adapted to a pack of supercapacitors having a capacity in the order of several hundred Farads and having a nominal charge voltage of 12 V. By respecting the constraint of the maximum and minimum values of the equivalent resistance Req and by using power resistors to achieve the bipolar resistive circuit, the technical expert will be able to choose the material of the heat sink D as well as its size to dissipate the energy accumulated in a pack of supercapacitors having different capacity and nominal charge voltage, so as to avoid reaching temperatures dangerous for the operators. 
         [0045]    In the embodiment of  FIG. 3 , the charge/discharge device comprises a DC-DC voltage regulator REG, supplied by the battery voltage available on the supply terminal POS, which generates a regulated DC voltage VCC on an inner distribution line. A digital voltmeter with a luminous display, for example a digital panel meter DPM, having a positive supply pin V+ connected to the inner distribution line, a negative power supply V− pin connected to the ground terminal of the device, is configured to measure the charge voltage of the pack of supercapacitors. To this end, a resistive divider R 1 , R 2  connected between the output terminal UCAP and the ground terminal GND will generate on its central pin a scaled voltage repetition of the charge voltage of the pack of supercapacitors, which will be applied on a measurement pin Vin of the digital panel meter DPM. The resistive divider R 1 , R 2  is always connected between the output terminal UCAP and the ground terminal GND, so that the charge/discharge device detects the charge voltage of a pack of supercapacitors even if the switch SW is in the central position OFF. 
         [0046]    Conveniently, the resistors R 1  and R 2  will be of high value, typically in the order of kΩ and beyond, in order to absorb a practically negligible current from the pack of supercapacitors. 
         [0047]    Optionally, but not necessarily, the DC-DC voltage regulator REG can be equipped with low-pass filtering capacitors C 1 , C 2 , to reduce any fluctuations of the regulated voltage VOUT. 
         [0048]    The device shown in  FIG. 3  has also a control circuit U 2  of signaling LEDs. This control circuit is supplied with the regulated voltage VOUT, receives in input a scaled repetition of the charge voltage of the pack of supercapacitors provided by a resistive divider, which can be identical to the resistive divider R 1 , R 2  of the digital panel meter or be actually the same, and which is configured to turn on, turn off, and possibly blink at least one LED to indicate a state of complete/incomplete charge/discharge of the pack of supercapacitors. Such control circuit can optionally be enabled/disabled by a jumper J 4 . 
         [0049]    It should be noted that the DC-DC voltage regulator REG shown in  FIG. 3  is only used to provide a regulated voltage VOUT of lower value than the battery voltage of the motor vehicle: it only has to supply the digital panel meter DPM and the electronic circuit U 2  to control the LEDs. In fact, the battery (and thus also the pack of supercapacitors) typically provides a voltage of 12V at full charge, so it cannot be directly connected to the circuit blocks DPM and U 2 , which typically operate with a voltage of 5V. Such a regulator is therefore much simpler to implement and is subject to considerably less stringent design constraints than the voltage switching regulators that are currently used to charge or discharge the pack of supercapacitors, as it is basically a very low power device. As will be shown later, it may consist of a simple voltage follower. 
         [0050]      FIG. 5  shows a detailed circuit diagram of a working prototype of a charge/discharge device according to the present disclosure, suitable to charge/discharge a pack of supercapacitors with a nominal charge voltage of 12V. The components of  FIG. 5  which also appear in  FIG. 4  are indicated with the same references. The numerical values of the resistors and the capacitors, as well as the codes of the electronic components used, must be considered purely illustrative. 
         [0051]    Optionally, also a thermal switch RT 1  is present in series with the bipolar resistive circuit, which switch, when open, interrupts the charge/discharge of the pack of supercapacitors when the temperature of the bipolar circuit exceeds a predetermined maximum temperature. Preferably, this maximum temperature is 55° C., which is considered the maximum temperature for withstanding a prolonged contact. 
         [0052]    In the embodiment shown in the figure, the voltage regulator that generates the regulated voltage VOUT and supplies the digital panel meter DPM, is an operational amplifier U 1 A configured as a voltage follower which generates a regulated repetition VOUT of the voltage supplied on the median pin of a resistive divider with three pins R 4 , R 5 , R 6 , R 7  coupled between the supply terminal POS and the ground terminal GND of the charge/discharge device. Unlike what is described with reference to  FIG. 4 , the low-pass filter capacitor C 2  is connected to an input of the operational amplifier U 1 A instead than on its output, as it is typical in the topologies of the voltage followers. 
         [0053]    Furthermore, diodes D 1 , D 5 , preferably Schottky diodes with a very low conduction drop, are present and respectively inserted in the inner electric charge line of the device and between this line and the ends of the bipolar resistive circuit, so as to prevent the circulation of current in case of a reversed polarity connection of the device terminals to the positive terminal of the battery, to the positive terminal of the pack of supercapacitors and to ground. 
         [0054]    The illustrated device also includes two LEDs, for example red R and green V, and a relevant control circuit, whose possible electrical diagram is illustrated in detail, which can turn the LEDs on/off by applying appropriate voltages on the anodes G and R. 
         [0055]    The control circuit of the LEDs comprises a first threshold comparator, composed of an operational amplifier U 1 B and of the relevant bias resistors R 3  and R 10 , which compares the charge voltage of the pack of supercapacitors, available at the output terminal UCAP, with an upper threshold, available on the upper pin of the resistive divider R 4 , R 5 , R 6 , R 7 , and a second threshold comparator, composed of the operational amplifier U 1 C and of the relevant bias resistors R 3  and R 13 , which compares this charge voltage with a lower threshold available at the bottom pin of the resistive divider R 4 , R 5 , R 6 , R 7 . The control circuit is configured to turn on in a fixed manner one of the two LEDs, typically the red LED R, when the first threshold comparator U 1 B switches to high, indicating that the charge voltage is greater than the upper threshold (so the pack supercapacitors is practically charged), and by turning on in a fixed manner the other LED, typically the green LED G, when the second threshold comparator U 1 C switches to high, indicating that the charge voltage is lower than the lower threshold (and therefore the pack of supercapacitors is practically discharged). 
         [0056]    In the embodiment shown, the control circuit of the LEDs is conditioned, in the range between the lower and upper thresholds, by a square wave oscillator composed of the operational amplifier U 1 D, of the hysteresis, positive feedback and timing resistors R 9 , R 11 , R 12  and of capacitor C 3 , which, through the circuitry Q 1 , Q 2 , R 14 , R 15 , R 16 , R 17 , produces the flashing of the LEDs corresponding to the current function of charge/discharge: flashing red LED during the charge with the switch SW in the charge position and flashing green LED during the discharge with the switch SW in the discharge position. 
         [0057]    Optionally, a portion of the control circuit, composed of the operational amplifiers U 2 A, U 2 B, diodes D 6 , D 7 , bias resistors R 8 , R 17  and capacitor C 4 , can be activated/deactivated through the jumper J 4 . Said portion is configured to allow or inhibit the flashing of the LEDs when the voltage of the pack of supercapacitors is comprised between the upper and the lower thresholds and when the switch SW is in the central position: in both these conditions, the LEDs may be inhibited by inserting the jumper J 4 , or, when the jumper J 4  is removed, they may flash red and green being modulated in time almost proportionally to the charge level of the pack of supercapacitor. 
         [0058]    In the initial condition of any operation, the digital panel accurately displays the charge status. 
         [0059]      FIG. 6  shows an embodiment of the metal chassis  1  of the charge/discharge device according to this disclosure. The lever  2  of the three-positions toggle switch, the luminous display  3  of the digital panel meter and the LEDs  4  for signaling the charge state of the pack of supercapacitors connected to it project from said chassis. A hook  5  telescopically extractable for fixing the device to the bodywork of a vehicle is also visible. The edges of the metal chassis are preferably covered with rubber bumpers  6  to prevent scratching of the bodywork of the motor vehicles on which it will be hooked. A finned heat sink  7 , arranged in the bottom portion of the chassis and in contact with the heat sink D, conveniently will have a wide dispersion surface exposed to the air to facilitate cooling of the bipolar resistive circuit. 
         [0060]    Preferably, the heat sink D on which the power resistors are mounted is the same finned heat sink  7 . 
         [0061]      FIG. 7  is similar to  FIG. 6  and shows the charge/discharge device with the hook  5  for attachment to the bodywork completely extracted. 
         [0062]    The charge/discharge device according to the present disclosure preferably will be connectable to power cables, ground cables and connection cables to the pack of supercapacitors, having at least a section of 5 mm 2 , suitable to conduct currents even of 25 A, ending with isolated pliers of different colors to identify them.