Technical Library

Recent Technology Trends in Aluminum Electrolytic Capacitors
for Onboard Automotive Use

NICHICON CORPORATION

1.Introduction

Aluminum electrolytic capacitor products with high capacitance are relatively inexpensive, and at 2-700V the rated voltage ranges are high. For this reason, these products are used in many different markets and products. To meet the needs of these different markets, they are available in different form factors, including chip type, radial lead type, snap-in terminal type and screw terminal type.

Due to the increasing demand for electronics in automobiles, the use of aluminum electrolytic capacitors has grown remarkably. In particular, chip-type and radial lead-type products are most often used. (These two types are discussed below). Automotive applications require high levels of safety, excellent comfort and environmental friendliness. To meet these requirements, a variety of electronic control systems must be used in the vehicle. Additionally, the advances in safety and comfort are occurring at remarkable speed. The number of electronic control units (ECUs) is growing so quickly that to where recently produced vehicles may have 100 or more ECUs. Integration and high-density mounting are making progress due to the functional aggregation of ECUs, but the number of ECUs mounted in vehicles is expected to continue rising. ECUs are essential to automobiles, but ECUs’ roles differ; and the performance requirements of the components that accompany them vary widely, as well. For example, the aluminum electrolytic capacitors in the battery monitoring units used in electric vehicles/hybrid vehicles (EVs/HVs) require high withstand voltages of as much as 400V. At the same time, capacitors used in the control units that activate airbags in emergencies typically have relatively low rated voltages, typically 25–35V. At the same time, however, these capacitors require high capacitances of more than 10,000μF. ECUs placed in the engine compartment are exposed to high temperatures, so they must be able to withstand temperatures of 125˚C or 135˚C. They must also have vibration-resistant structures capable of withstanding engine vibrations. Furthermore, as ECUs grow increasingly compact, in order to supply higher current to the power supply circuit, capacitors must be smaller and require high ripple current. In some cases, products used in colder climates must have certain guaranteed characteristics for use in low-temperature environments.

2.Industry Requests and Nichicon Responses For Aluminum Electrolytic Capacitors In the Transportation Industry

(1) Resistance to Vibration
When capacitors are used that do not have measures in place the counter vehicle vibrations, the supporting surface of the board and the terminal can act as a fulcrum, as a result vibration may cause the product to dislodge from the board. Alternatively, sealed rubber and leads can act as a fulcrum to transmit vibration to internal elements, resulting in internal disconnections. There have been two (2) main improvement made to avoid this type of problem. Chip-type products use variable-height base plate side walls to control the vibration of the capacitors themselves. Adherence is increased between the base plate and the PC board by using auxiliary electrodes. These improvements are shown in [Photo 1] with a comparison of typical products and the vibration-resistant products. The enhanced products allow for a vibration resistance guarantee of 30G(10–2,000Hz).

(2) Response to Miniature Size, High Ripple Current Requirements
The growing trend of smaller ECU’s, the space inside them becomes more limited. Providing aluminum electrolytic capacitors with the required levels of capacitance presents a major issue: capacitors must be both smaller and have higher capacitance. There are three different techniques for achieving the required smaller size and higher capacitance: high-capacitance foil, thinner material or revised structural surface. Aluminum electrolytic capacitors need to respond to high ripple currents when they are used in power supplies in high current applications. In general, ripple current flowing through a capacitor generates heat, causing electrolyte transpiration or deterioration, reducing capacitor life. For this reason, the amount of ripple current each product can withstand is shown as rated ripple current. Capacitors capable of withstanding high ripple currents have been adjusted to handle high specified values. There are three main techniques for achieving these high ripple currents: reducing the product’s ESR (the higher the ESR, the higher the ripple current heat generation temperature), increasing heat dissipation performance to allow heat to escape from the capacitor interior, and using materials capable of withstanding heat generation.
The UBY and UCV series: smaller, higher capacitance and higher ripple current series.
(2)-1. UBY Series of Radial Leaded High Temperature, High Ripple Current Type Aluminum Electrolytic Capacitors with High Capacitance
The UBT Series is used frequently automotive market. In response to market requirements, we have developed the UBY Series [Photo 2]. This product meets some of the industry’s highest requirements for high ripple current, high temperature and higher capacitance.

◆Characteristics

With the increasing use of electronic controls in automobiles, electronic components and equipment mounting locations are being shifted from the passenger cabin and its vicinity to the engine compartment, requiring them to be more space-saving and responsive to higher temperatures. To meet these requirements, we have as much as tripled the capacitance from our current UBT Series. This has been done by using high-magnification anode foil. In addition, the UBY series more than doubles the ripple current when compared to the UBT series. This is accomplished by employing electrolytes that provide excellent stability in high-temperature regions and using extremely durable rubber end seal. Using the UBY Series allows various control units to be made more space-saving and offer higher levels of efficiency[Table 1].

Rated
voltage(V)
Case Size
φD×L(mm)
Capacitance(μF) Ripple
Tolerance(mAms)
(at 125℃ 100kHz)
UBT UBY Increase
in
Capacitance
UBT UBY Increase
in
Capacitance
25 12.5 X 25 1,000 3,000 X 3.0 1,750 3,480 X 2.0
18 X 31.5 3,300 8,200 X 2.5 2,710 5,600 X 2.1
35 16 X 25 1,000 3,000 X 3.0 2,010 4,260 X 2.1
18 X 35.5 2,200 6,200 X 2.8 2,790 6,280 X 2.3
50 12.5 X 25 470 820 X 1.7 1,650 3,350 X 2.0
16 X 31.5 1,000 1,800 X 1.8 2,430 5,130 X 2.1
【Table1】Comparison of Electrical Characteristics for UBY and UBT Series of
the Same Size

◆Specifications

The principal specifications of the UBY Series are: Case sizes: 15 sizes, φ12.5x20L–φ18x40L; category temperature range: -40 to 135˚C; life: 3,000 hours; rated voltage range: 25–50V; rated capacitance range: 620–12,000μF.

(2)-2. UCV Series of Low-Impedance Chip-Type Aluminum Electrolytic Capacitors is rated to 105°C. The 105˚C, low-impedance UCM Series meets device requirements for the increasing demands for smaller and higher performance and has been frequently used in the past. However, we have developed the UCV Series [Photo 3] to offer the industry’s highest level of compactness in response to miniature size and higher capacitance requirements.

◆Characteristics

Demands for chip-type aluminum electrolytic capacitors are growing as onboard applications require increasingly high-density mounting. These capacitors are required to offer lower impedance, smaller size and higher capacitance. To meet these requirements, we have employed high-magnification anode foil, thinner cathode foil and thinner electrolysis paper. By optimizing the combination of materials used, we have succeeded in increasing the capacitance a notch above our current UCM
Series105˚C low-impedance chip-type aluminum electrolytic capacitors. Using the UCV Series reduces personnel requirements and enables space savings [Photo 4].

◆Specifications

The principal specifications of the UCV Series are: Case sizes:, φ6.3x7.7L–φ10x10L; category temperature range: -55–105˚C; life: 2,000 hours at 105˚C; rated voltage range: 25–35V; rated capacitance range: 220–1,000μF.

(3) Responding to Reduced ESR Requirements
One technique to increase ripple current is to reduce ESR, but in recent years onboard applications are requiring low ESR at ambient temperatures of -40˚C. In colder regions, ambient temperatures may be as low as -40˚C, and starting engines at these ambient temperatures can be a matter of life or death. Also, as capacitors deteriorate due to age their ESR typically increases. Major fluctuations in ESR that might prevent equipment from starting must be avoided. Instead of developing a product with an initial ESR value at low temperatures of -40˚C, we have produced a series of products whose values are guaranteed following life tests.
(3)-1. The UCH Series Chip-Type Aluminum Electrolytic Capacitors with ESR Rating after Life Testing at 125˚C
In our current UCZ Series, offer a lineup of low-temperature ESR rated products after life testing at 125°C. However, for further control over ESR variations we have developed the UCH Series [Photo 5], which achieves the highest levels in the industry.

◆Characteristics

As was mentioned earlier, more and more of the electronic modules are being shifted from the passenger cabin to the engine compartment. The harsh environment of the engine compartment subjects the components and modules to radiant heat from the engine as well as extremely cold ambient temperatures when used in cold climates. As a result these products must be capable of spanning from low to high temperatures and offer lower ESR. In response to these requirements, we have developed a proprietary low-transpiration and low-resistance electrolyte and optimized the internal structure to produce a product that offers an even more reduced ESR than our current 125℃ low-ESR chip-type product, the UCZ Series[Figure 1].

◆Specifications

The principal specifications of the UCH Series are:
Case sizes: φ6.3x7.7L; category temperature range: -40–125˚C; life: 2,000 hours at 125˚C; rated voltage: 35V; rated capacitance range: 47–100μF.

3.Future Developments in Aluminum Electrolytic Capacitors for Onboard Automotive Use

Nichicon anticipates that future development in aluminum electrolytic capacitors to be for use in the transportation industry. This is expected because of an increase in the number of vehicle types employing electrical drives—ie. fuel cell vehicles (FCVs) as well as EVs and HVs. Against this backdrop, the control of electronic devices is forecast to become increasingly important. In the face of these technology trends involving aluminum electrolytic capacitors for onboard automotive use, to meet user expectations we will go beyond current conditions and continue to develop new products.

 

NICHICON CORPORATION
From the Dempa Shimbun, Aug. 18, 2016

 
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