Large can-type aluminum electrolytic capacitors use aluminum for the electrode, which gives them excellent characteristics. The aluminum anodic oxide film has a high relative permittivity and therefore yields high capacitance. Aluminum is also one of the most available valve metals and is relatively inexpensive, this makes production costs that are lower than that of other capacitors.
The internal structure of an aluminum electrolytic capacitor (hereinafter called an “element”) consists of separator paper between an anodic aluminum electrode foil and a cathodic aluminum electrode foil. These layers are wound into a cylindrical shape. Note that merely wrapping it cylindrically does not cause it to function like a capacitor or give it the necessary capacitance value. The winding must be impregnated with an electrolytic solution having electrical conduction properties to allow it to function like a capacitor. To the end of this cylinder (winding) a terminal plate is attached which allows electrode foils to be attached. The element is sealed in an aluminum case, and covered with an exterior sleeve to complete its structure as a capacitor.
There are many types of aluminum electrolytic capacitors: chip type, lead type, snap-in terminal-type, and screw-terminal type. Here we will discuss technology trends and market needs for the snap-in and screw-terminal-type capacitors. These are also known as large can-type aluminum electrolytic capacitors.
Large can-type aluminum electrolytic capacitors are used in a wide range of applications and markets, including energy, ecology, medical equipment; as well as automotive and railway-car related appliances; household electrical appliances and industrial inverters; and information and communications equipment. The main usage is for smoothing the input voltage on power supplies, with the capacitors being used in switching power supply circuits and inverter circuits. Inside the circuit, the aluminum electrolytic capacitor plays the crucial role of providing stable electricity.
Users demand large can-type aluminum electrolytic capacitors that are increasingly compact and low profile, to meet the end products shrinking size.
Due to advances in the efficiency and energy saving requirements of industrial machinery, systems are requiring increasingly higher in voltage to meet the trends. The need is for capacitors that can withstand the high voltage demands of control circuits and other inverter power supplies. In the renewable energy market such as solar and wind power, more and more users are demanding capacitors that have high withstand voltage.
In addition to being used to improve the capabilities of the products, high-withstand-voltage capacitors are used to smooth input voltage fluctuations in regions with unstable power supplies. In these regions, the machinery must be designed to take into account large voltage fluctuations, manufacturers of this machinery need capacitors that are able to withstand increasingly higher voltages.
In response to these needs, Nichicon developed the compact LGM Series (the industry’s smallest class) and the 600-V rated, high-withstand-voltage LGN Series.
We are also developing a new electrolytic solution that will achieve a 105°, 750-V rated aluminum electrolytic capacitor (the industry’s highest).
An aluminum electrolytic capacitor’s capacitance is proportional to the surface area of the aluminum electrode foil.
To enlarge the surface area of the aluminum electrolytic foil, a chemical process called etching is carried out to roughen the surface.
The key to developing smaller capacitors lies in using high-amplification anodic aluminum electrode foil, which has a higher effective surface area which is made possible by etching technology.
By increasing the surface area through etching, the diameter of the holes (pits) on the foil surface is made an optimal size so that the number of pits can be increased and the length of each pit is increased. The result is a significant increase in capacitance value.
In addition, the separator part of the element is a thinner, high-withstand-voltage type. Through the use of this thin separator, the same capacitance can be achieved with less element volume. As a result of using this high-capacity electrode foil and high-withstand-voltage separator, the LGM is smaller than Nichicon’s current smallest capacitor series.
The LGM Series is up to 14% smaller by volume than our current smallest product, the LGL Series, and is the industry’s smallest class of snap-in terminal-type aluminum electrolytic capacitor.
Figure 1 LGM Series of snap-in terminal-type aluminum electrolytic
capacitors, the industry’s smallest
In addition to using the same electrode foil and separator as in the compact capacitor series, the key to developing a high-withstand-voltage capacitor lies in the performance of the electrolytic solution.
The LGN Series uses anodic aluminum electrode foil, which is formed from high-withstand-voltage oxide film,and high-withstand-voltage electrolytic paper. It has long-term stability, and with the newly developed electrolytic solution with enhanced oxide film restoring capacity at high voltages. The result is the industry’s highest rating of 600V.
The newly developed electrolytic solution has an optimal make-up of ingredients compared to our current electrolytic solution. We also developed and added an agent that improves voltage resistance without affecting heat resistance and conductivity, resulting in the ability to withstand voltages that are 20-30% higher than our current product.
Figure 2 Nichicon added a 600-V rating, the industry’s highest, to the LGN
Series of snap-in terminal-type aluminum electrolytic capacitors
When using multiple aluminum electrolytic capacitors connected in a series, fewer of the 600-V rated LGN Series capacitors are needed. For example, a 1,200-V system would require three 400-V capacitors in series, but only two of Nichicon’s 600-V capacitors.
Figure 3 1,200V circuit example
We have talked about our 105°, 600-V-rated capacitors, however; to achieve a higher withstand voltage, we are developing a new electrolytic solution that will achieve a rating of 105°, 750-, the highest in the industry.
For example in main circuit capacitors for industrial machinery inverters and servo amps, a series of two 400-V capacitors are used for 400-V AC input power supplies. But if there were a capacitor able to withstand 750V or higher, it would provide significant benefits to customers, making possible fewer components and reducing balance resistance, and allowing compatibility with safety tests (one side short circuit tests)
Nichicon got an early start on the development of high-withstand-voltage capacitors, in 2005 by achieving mass-production of 85°, 750-V screw-terminal type aluminum electrolytic capacitors.
With more powerful and efficient machinery, and the need to withstand higher voltages, it became crucial that capacitors be more reliable and able to withstand higher temperatures.
To meet market needs for an electrolytic solution capable of withstanding high voltages, our idea was to design and synthesize at the molecular level. Joint research conducted with Japan’s Mie University resulted in the development of a new electrolytic solution capable of withstanding voltages of 750V or higher while operating at 105°C.
By analyzing voltage resistance and heat resistance at the molecular level, designing and synthesizing an optimal structure, we realized this newly developed electrolytic solution using breakthroughs in conventional technology.
To allow normal electrolytic solutions to withstand higher voltages, we had to make them less concentrated, but this caused problems, such as reducing the oxide film restoring capacity at high voltages and accelerating the thermal decomposition of the dicarboxylic acid structure. The new electrolytic solution combines the basic structure of dicarboxylic acid and a molecular structure of diacid incorporating multiple ethers. This achieved the ability to withstand higher voltages and high temperatures.
Figure 4 Molecular structure of new 105°, 750-V electrolytic solution
While we currently plan to release 750-V products, we see the potential for even higher withstand voltage and are aiming for 800V and higher.
Figure 5 Withstand voltage characteristics of electrolytic solution
Large can-type aluminum electrolytic capacitors are used in a wide range of fields. To meet today’s growing needs for energy efficiency and environmental performance, Nichicon will contribute to products that provide society with abundance, safety, and peace-of-mind.