Supercapacitors Start application in the automotive

l Introduction

Car battery is the key electrical components, which directly affects the car boot. Now start the car, without exception, start motor starting methods used. During the startup process, especially in the moment of starting, by activating the motor speed is zero, does not produce induced electric potential, so start current: I = E / (RM + RS + RL); where: E is the battery no-load terminal voltage, RM To start the motor armature resistance, RS for the battery internal resistance, RL the line resistance. As the RM, RB, RL are very low, starting current is very large. For example, use 12 V, 45 Ah battery to start the installation 1.9 L diesel engine car, the battery voltage is 12.6 V at the moment of starting down from the approximately 3.6 V, the startup process of the battery voltage waveform shown in Figure 1. Start the instantaneous current up to 550 A, about 12C battery discharge rate> start the process of battery current waveform shown in Figure 2. Current Sensor current / voltage conversion ratio of 100 A / V. Although the car battery is to start special battery, can be high-rate discharge, can be seen from Figure l, 10 times more when high-rate discharge becomes very poor battery performance, and that such a high rate discharge of the battery damage is very obvious of. Dramatic changes in the voltage during startup is a very strong electromagnetic interference, electrical equipment can result in power-down, forcing electrical equipment in the generator after the re-start the process of power, the computer in this process is very easy to hang. Therefore, to improve the vehicle electrical equipment from the electromagnetic environment, improving the car's boot performance and extended battery performance or battery life to consider, to improve the car power performance during the startup process is necessary. One solution to the problems increase the battery's capacity, but need to increase a lot, and increase its volume, this is not a good option. And the super capacitor in parallel with the battery can solve this problem.

Supercapacitors Start application in the automotive

2 Principles and characteristics of supercapacitors

2.1 The principle of super-capacitor

Super-capacitor is an electrical capacity of up to thousands of great capacity Farah capacitor. United States Cooper Cooper's super capacitor, for example, according to the principle of capacitor, capacitance depends on the distance between electrodes and electrode surface area, in order to get such a large capacitance, super-capacitors to minimize the distance between electrodes to increase electrode surface area, To this end, double-layer theory and the porous carbon electrode.

Super capacitor structure shown in Figure 3. Electric double layer capacitor dielectric in two electrode voltage is applied, the dielectric near the electrode interface to generate the charge carried by the electrode of opposite polarity to the charge and was binding on the medium interface to create a de facto two capacitors electrode. Shown in Figure 3, it is clear that the distance between two electrodes is very small, only a few nm. Porous activated carbon electrode while the electrode surface area to great, can reach 200 m2 / g. Therefore this structure has great power super capacitors to store large capacity and the electrostatic energy. The storage, the super capacitor between this characteristic between traditional capacitors and batteries. When the electric potential between two electrodes under electrode potential of the redox electrolyte, the electrolyte interface, the charge will not be from electrolyte, super capacitors in normal condition (usually in the 3 V below), if the terminal voltage capacitor 2 Over the redox electrolyte electrode potential, then the electrolyte will be decomposed, in a non-normal state. With the super-capacitor discharge, positive and negative charge is outside the circuit board vented electrolyte interface to reduce the charge response. It can be seen super-capacitor charge-discharge process is always the physical process, no chemical reaction, so the performance is stable, and the use of different chemical reactions of batteries.

Supercapacitors Start application in the automotive

2.2 The main features of super-capacitors

Although the super-capacitor battery energy density is 5% or less, but this energy storage method can be applied to the inadequacies of the traditional battery and short-term peak currents. Compared with batteries, super capacitors that have the following advantages:

First, large capacitors, supercapacitors using activated carbon powder and activated carbon fiber used as the polarization of electrodes, and electrolyte contact area greatly increased, according to the formula for calculating capacitance, the greater the surface area of two plates, the greater the capacitance Therefore, general electric double layer capacitor capacity easy 超过 1 F, it appears the scope of ordinary capacity of the capacitor suddenly jumped by 3 to 4 orders of magnitude, now the largest single super-capacitor capacitance up to 5000 F;

Second, charge-discharge life is very long, up to 500 000 or 90000h, while the battery charge and discharge more than l 000 times life is difficult;

Third, can provide high discharge current, such as the 2700 F super capacitor discharge current rating of not less than 950 A, peak discharge currents up to 1 680 A, general battery usually can not have such a high discharge current, a number of high discharge current battery, in such a high discharge current, shorten life;

Fourth, in tens of seconds to minutes quick charge, while the battery in such a short period of time would be extremely dangerous to full power or nearly impossible;

5 is a very wide working temperature range (-40 ℃ ~ +70 ℃), the battery is difficult, especially at high temperatures in the low-temperature environment;

Sixth, the supercapacitor is safe and nontoxic materials, and lead-acid batteries, nickel-cadmium batteries are toxic, and, super-capacitors can be used to increase any parallel capacitance, if the pressure to take all measures can also be used in tandem.

3 super capacitor start the application in the automotive

3.1 The improvement of electrical properties

Super capacitor in parallel with the battery, the car boot process shown in Figure 4 the voltage waveform, current waveform shown in Figure 5. And Figures 1 and 2 compared to instantaneous voltage drop from the start only when using 3.2V battery upgrade to 7.2V; starting current from 560 A up to l200 A; start the instantaneous power output power from 2 kW up to 8.7kW; smooth startup voltage from 7 V up to 9.4 V; start the process of steady current from 280 A up to 440 A; start the process of smooth power output increased from 2.44 kW to 4.12 kW.

Supercapacitors Start application in the automotive

3.2 start-up performance improvement

Application of super capacitors and batteries in parallel can improve the startup performance of locomotive. The super capacitor (450 F/16.2 V) and 12 V, 45Ah batteries connected in parallel to start the installation of 1.9 liters of diesel engine cars, a smooth start at 10 ℃. Although in this case super-capacitors are not connected battery can also start, but the use of super capacitors in parallel with the battery starts the motor speed and performance are very good. As the power supply output power increases, the starting speed by the battery only when the 300 r / m to 450 r / m. In particular, super-capacitor can improve the car in cold weather start-up performance (higher starting torque), in -20 ℃, due to significantly decrease the battery performance is likely to be several times the normal start or start to ignition, and super-capacitor only one battery in parallel with the ignition, the advantage is obvious.

Supercapacitors Start application in the automotive

3.3 Application of the state to improve battery

Super capacitor in parallel with the battery, because super-capacitor equivalent series resistance (ESR) is far lower than the battery's internal resistance, therefore, start an instant, 1 200 A starting current of 800 A current is provided by the supercapacitor, the battery is only available 400 A current, significantly lower than using only battery 560 A, effectively reducing the polarization of the battery plate and prevent the battery internal resistance increases, the steady voltage to start the process is improved. The most important thing is to reduce battery plate polarization is not only beneficial to extend the battery life, but also can eliminate the frequent start of the life of storage battery.