Maxwell Technologies BMOD0083-48.6V Ultra capacitorsThe BMOD0083 module was chosen for our application because of its cost and the fact that it has a maximum capacity of 83 Farads. In order to supply 1000W of power for 18 seconds at 48V a capacitor needs a minimum of 44 Farads.fig3. Module Voltage vs. Time characteristicsULTRACAPACITORSMarvell Mukongolo11-5-2008ECE 480Executive Summary:Energy and Renewable energy in today’s world make up two of the most researched and influential parts of the field of electrical engineering. Finding new sourcesof energy and optimizing old technologies to fit today’s demands has created a multibillion dollar industry that promises to be the backbone of our economy for years to come. One of those optimizations has been the use of Double Layer Capacitors or ultra capacitors in hybrid power systems in-order to increase longevity and reduce cost and size. This document will introduce readers to the application of ultra capacitors in battery-ultra capacitor hybrid systems. Key Words: Energy Density, Power Density, DC-DC converter, Buck ConverterObjective:This application note will provide instruction on calculating and designing the proper parameters for use of a 48.6V ultra capacitor module. This application note will also give instruction on voltage regulation between the battery and ultra capacitor.Introduction:Compared to regular electrolytic capacitors, ultra capacitors have to the capacity to hold a larger amount of energy. This higher energy density makes it possible to have thousands of farads in a single cell. Although they have a higher energy density than regular electrolytic capacitors they still lag behind conventional batteries in the amount ofenergy they can store.Fig.1 Power/Energy density chartUltra capacitors have a high power density when compared to conventional batteries which makes them ideal for use in applications that require quick boosts of power or applications that require a power supply to receive a large amount of power in a shortamount of time for example regenerative braking. A major drawback to ultra capacitors isthere inability to handle higher voltages per cell unit and their voltage decays linearly making them highly unstable for use as a primary energy supply. DC-DC ConverterDC-DC Converter’s are devices that are used to change dc voltage levels. A DC-DC converter can be used to step up or step down an input voltage depending on the application. There are three different types of DC-DC converters; the Buck Converter is used to step down voltage, the Boost Converter is used to step up voltage and the Buck-Boost converter is used for both operations. Fig. 2 Buck ConverterFor the ultra capacitor-battery hybrid operation a buck converter will be used to step down the battery voltage of 51.8V to a voltage of 48.6V which would match the nominal voltage of the ultra capacitor module. This is done to protect the ultra capacitor module from damage that can be sustained by a higher voltage from the batteries. Conversely a DC-DC converter placed between the battery and ultra capacitor module protects the battery from high surge currents that can be released by the ultra capacitor module. Maxwell Technologies BMOD0083-48.6V Ultra capacitorsThe BMOD0083 module was chosen for our application because of its cost and the fact that it has a maximum capacity of 83 Farads. In order to supply 1000W of power for 18 seconds at 48V a capacitor needs a minimum of 44 Farads. fig3. Module Voltage vs. Time characteristicsWith this module we will be able to sustain a voltage between 48.6V and 40V in the 18 seconds of peak demand. Also for cost saving purposes we decided to create a system which can recharge the ultra capacitor module after every cycle. This route allows us to save thousands of dollars and as well as reducing the overall mass of the power plant. In order to have a system that could handle ten cycles on a single charge we would need a 400 farad module. This would require three 165 farad modules placed in parallel with each other, the cost of such a module would be around $6000. Using one module for one cycle saves us over $4000 in total cost. This route will reduce the amount of battery life that would have been saved if the power plant had two stand alone power supplies. In astand alone system the battery would take 5hours to discharge under our parameters. Since the ultra capacitor module will require recharging every cycle the battery will be used to provide 1000W of power. This equals a discharge of 1C, at this rate for an hour the battery would lose charge. Since the batteries will only recharge the ultra capacitors for a short amount of time battery life can still be spared. But the amount of money and space saved makes up considerably for the loss in battery life. This route also requires theaddition of active circuit components that will switch the flow of power between the battery and the ultra capacitor module, to the load. RecommendationsThis system deals with a high amount of current, caution should be exercised whenever the system is on. All components placed in this system should be rated to handle relatively large voltages and currents. Ultra capacitors can discharge energy at a fast rate, when placing them into circuits precautionary measures should be taken in orderto protect other circuit components.Conclusion Ultra capacitors are quickly becoming an alternative to conventional power sources. With their high power densities they have the ability to provide power rapidly. When selecting ultra capacitors the type of application must be taken into consideration. For use in hybrid systems there has to be a system in place to regulate the voltage between the battery and ultra capacitors. Unbalanced voltage can lead to damage of the system and can cause bodily harm to those operating the system. When handling high currents great precaution must always be taken in order to insure no one is harmed or killed.ReferencesECE320 notes by Elias G.
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