Technical Library

Technology Trends in Large Can-Type Aluminum Electrolytic Capacitors

NICHICON CORPORATION

Introduction

The markets for large can-type aluminum electrolytic capacitors can be categorized into the general fields of: household appliances, industrial inverters, transportation modules (including rail car applications), energy, medical equipment, and communications. The important core technologies required for large can-type aluminum electrolytic capacitors are: 1) smaller, lower profiles, 2) high ripple current, 3) high voltage and 4) high-speed charge-discharge.

Figure 1:Core technologies for large can-type aluminum electrolytic capacitor

[Figure 1] Core technologies for large can-type aluminum electrolytic capacitor

1.Smaller, lower profile

As equipment becomes smaller and space is reduced, the demand for smaller, lower-profile large can-type aluminum electrolytic capacitors grows.
The key to developing these smaller, lower-profile products lies in using leading-edge etching technology to increase the effective surface area of the electrode foil, raise the capacitance per unit area and reduce the amount of foil surface used, thereby making products smaller In addition, by revising the material fiber structure of the electrolytic paper we are able to use thinner paper and still improve the withstanding voltage, increasing the capacitance. By combining these with the structural components we can reduce the size of the capacitors.

2. High ripple current

As performance requirements increase, the current load increases. As a result large can-type aluminum electrolytic capacitors must be capable of withstanding high ripple current. The structure is one of the important factors in developing products with high ripple current.
Materials such as thermoplastic resin are used to fix the elements of conventional screw terminal aluminum electrolytic capacitors. By adapting a rib configuration that holds the elements without the use of resin compounds a much higher rate of heat dissipation is achieved. This reduces the rise in the temperature of the element due to ripple current. Conventional capacitors use electrolytic paper with a relatively large fiber diameter, by using low-density electrolytic paper with a small fiber diameter allows lower ESR and lowers the amount of heat generated.

Figure 2:Technology needed to achieve high ripple current.

[Figure 2] Technology needed to achieve high ripple current.

3. High voltage

The demands for high voltage large can-type aluminum electrolytic capacitors are growing due to the increasing voltage demands in the industrial sector. This is as a result of the advances in efficiencies and energy-saving applications. One of the keys in the development of high-voltage products is the advances made in electrode foil that will be highly reliable even under high-voltage conditions. Nichicon is working with chemical manufacturers to develop a new electrolyte that is resistant to thermal decomposition (heat resistant) and will offer a higher withstanding voltage.

4. High-speed charge-discharge

The increasing speed and performance of products using general-purpose inverters and servo amplifiers generate steep voltage variations. During charge and discharge (particularly discharge), the electrolytes are subjected to localized stresses that can reduce their withstanding voltage and, may ultimately lead to a short-circuit. For this reason, repeated charging and discharging of large can-type aluminum electrolytic capacitors with large differences in electric potential is known to reduce the electrolyte withstanding voltage at the lead tab of the cathode foil. Using Nichicon’s patented technology, a protective foil structure [Figure 3] dramatically reduces this potential
  As the power electronics industry adopts inverters, and the loads for the many different types of power sources and servo amplifiers get progressively more severe, this new technology is becoming increasingly important. Developing highly reliable applications is vital to the industry.

Figure 3: Nichicon’s patented “Protective foil structure” technology

[Figure 3] Nichicon’s patented “Protective foil structure” technology

We have developed new products to meet market needs: (1) ultra-miniature type snap-in terminal type aluminum capacitors, (2) 600V-rated snap-in terminal type aluminum capacitors and (3) miniature high-ripple LNU screw terminal type aluminum electrolytic capacitors.

(1) Ultra-miniature type snap-in terminal aluminum electrolytic capacitors
We are developing an ultra-miniature type of snap-in terminal type aluminum capacitor guaranteed to 105°C that is one size smaller than the current smallest LGL series. Key in the development of this smaller-sized series is the development of; high capacitance, highly reliable electrode foil and the use of thinner electrolytic paper.. The new product will be more than 20% smaller than the current LGL series, making it the smallest in the industry. When the size of a 450V/560µF, LGL series is compared to the new part one can see the size improvement. The LGL is φ35×40L, whereas the new product is φ35×35L.

Figure 4: Size comparison of Nichicon series

[Figure 4] Size comparison of Nichicon series

(2) 600V-rated snap-in terminal type aluminum capacitors
The LGN/LGX series are Nichicon’s highest rated snap-in terminal type aluminum capacitors and are guaranteed to 105°C with a maximum voltage to 500V. We are developing a new product that is guaranteed to 105°C with a maximum rated voltage of 600V. The core technology that is needed in the development of this new product includes the use of a high reliability electrode foil with high withstanding voltage as well as the use of a high withstanding voltage electrolyte (high-heat resistivity).
(3) LNU miniature high-ripple screw terminal type aluminum electrolytic capacitors
The LNU is a miniature high-ripple screw terminal type aluminum electrolytic capacitor guaranteed to 105°C. Key in the development of this series are: (1) the use of electrode foil with high withstanding voltage oxide film, (2) long-term stability, incorporating an electrolyte solution with enhanced film restoring capacity at high voltages, (3) use of low-density electrolytic paper with high withstanding voltage and, (4) an enhanced heat dissipation structure that results in a higher voltage (rated voltage: 525V) and longer life (guaranteed to 5,000 hours) over our standard LNT screw terminal type standard products that are guaranteed to 105°C. The LNU is approximately 20-30% smaller, than other products rated at 500V; this contributes to module size and weight reductions. Furthermore, the LNU series employs Nichicon’s high-speed charge-discharge technology, which has earned high marks for applications in industrial equipment where load changes are severe. This product is ideal for use in servo amplifiers and other equipment involving repeated and quick charge and discharge in short periods of time.

[Figure 5] LNU screw terminal type aluminum electrolytic capacitors

[Figure 5] LNU screw terminal type aluminum electrolytic capacitors

One of the primary uses for aluminum electrolytic capacitors is expected to continue to be for smoothing power sources, particularly in power electronics applications. However, ongoing developments in next-generation power semiconductors are prompting demand for high heat resistant, high voltage, with low ESR; all in smaller package sizes.
The Nichicon Group’s development teams are working on new materials, including electrode foils and electrolytes. Going forward, we plan to continue developing new products in response to market needs and proposing products that will satisfy our customers.
 

NICHICON CORPORATION
From the Dempa Shinbun, Jul. 1, 2015

 
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