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CDM Cornell Dubilier • 140 Technology Place • Liberty, SC 29657 • Phone: (864)8

CDM Cornell Dubilier • 140 Technology Place • Liberty, SC 29657 • Phone: (864)843-2277 • Fax: (864)843-3800 1 Aluminum Electrolytic Capacitor Application Guide This guide is a full handbook on aluminum electrolytic capacitors, of course with emphasis on Cornell Dubilier’s types. It covers construction in depth and discloses the latest information on performance and application for the major aluminum electrolytic types made worldwide. We encourage you to tell us what more you’d like to know, so we can improve this guide. CONTENTS PAGE Capacitor Construction 2 Other Types of Capacitors Comparison 4 Characterization and Circuit Model 5 TABLES PAGE Temperature Range 6 Capacitor Parameter Formulas 6 Capacitance 7 Base Lives and Max Core Temperatures 14 Dissipation Factor (DF) 7 Thermal Resistance Screw Terminal Capacitors 17 Equivalent Series Resistance (ESR) 8 Thermal Resistance for Snap-in Capacitors 19 Impedance (Z) 8 Pressure Relief Device Clearance 21 Low-Temperature Impedance 8 Screw Tightening Torque for Screw Terminals 21 DC Leakage Current (DCL) 8 Maximum Currents for Screw Terminals 21 Voltage Withstanding 9 Tightening Torque for Nylon Mounting Nuts 22 Ripple Current 10 Inductance 10 Self-Resonant Frequency 10 Dielectric Absorption 11 Insulation and Grounding 11 Elevation & External Pressure 11 Vibration Withstanding Capability 11 Safety Considerations 11 Capacitor Bank Configurations 12 Non-Polar and Motor Start Capacitors 13 Reliability and Lifetime 13 Cooling and Thermal Resistance 16 Process Considerations 19 Mounting 20 Disposal of Capacitors 22 ALUMINUM ELECTROLYTIC CAPACITOR OVERVIEW Except for a few surface-mount technology (SMT) aluminum electrolytic capacitor types with solid electrolyte systems, an aluminum electrolytic capacitor consists of a wound capacitor element, impregnated with liquid electrolyte, connected to terminals and sealed in a can. The element is comprised of an anode foil, paper separators saturated with electrolyte and a cathode foil. The foils are high-purity aluminum and are etched with billions of microscopic tunnels to increase the surface area in contact with the electrolyte. While it may appear that the capacitance is between the two foils, actually the capacitance is between the anode foil and the electrolyte. The positive plate is the anode foil; the dielectric is the insulating aluminum oxide on the anode foil; the true negative plate is the conductive, liquid electrolyte, and the cathode foil connects to the electrolyte. However, just as the anodic-oxide dielectric insulates the anode foil from the electrolyte, so too the cathode is insulated from the electrolyte by the low voltage air oxide on the cathode foil and the double-layer ionic barrier. This makes the cathode a capacitor in series with the anode. In high voltage capacitors the cathode capacitance is hundreds of times the anode capacitance and does not measurably affect the overall capacitance, but in capacitors of less than about 50 V the anode capacitance begins to approach the value of the cathode capacitance and requires use of higher capacitance cathode to avoid needing to increase the anode length to achieve the rated 2 CDM Cornell Dubilier • 140 Technology Place • Liberty, SC 29657 • Phone: (864)843-2277 • Fax: (864)843-3800 Miniature, Radial-Leaded Type Lead Wire Aluminum Tabs Rubber Sleeve over Aluminum Can Capacitor Element Snap-in Type Sleeve over Aluminum Can Terminal Aluminum Tabs Phenolic/ Rubber Disc Capacitor Element Rivet Tape capacitance. Aluminum electrolytic capacitor construction delivers colossal capacitance because etching the foils can increase surface area more than 100 times and the aluminum- oxide dielectric is less than a micrometer thick. Thus the resulting capacitor has very large plate area and the plates are intensely close together. These capacitors routinely offer capacitance values from 0.1 µF to 3 F and voltage ratings from 5 V to 550 V. Up to 700 V are commercially available. They are polar devices, having distinct positive and negative terminals, and are offered in an enormous variety of styles which include molded and can-style SMT devices, axial- and radial-leaded can styles, snap-in terminals styles and large-can, screw-terminal styles. Representative capacitance-voltage combinations include: 330 µF at 100 V and 6,800 µF at 10 V for SMT devices, 100 µF at 450 V, 6,800 µF at 50 V and 10,000 µF at 10 V for miniature-can styles, 1200 µF at 450 V and 39,000 µF at 50 V for snap-in can styles and 9000 µF at 450 V and 390,000 µF at 50 V for large-can, screw-terminal styles. If two, same-value, aluminum electrolytic capacitors are connected in series with the positive terminals or the negative terminals connected together, the resulting single capacitor is a non-polar capacitor with half the capacitance. The two capacitors rectify the applied voltage and act as if they had been bypassed by diodes. When voltage is applied, the correct- polarity capacitor gets the full voltage. In non-polar aluminum electrolytic capacitors and motor-start aluminum electrolyte capacitors a second anode foil substitutes for the cathode foil to achieve a non-polar capacitor in a single case. Snap-in Type CAPACITOR CONSTRUCTION Tabs Phenolic / Nylon Cover w/ Centering Peg Aluminum Centering Peg Sleeve Over Aluminum Can Extended Cathode Terminals Rills Rubber Gasket Tape Aluminum Stiffening Ribs Tabs Phenolic / Nylon Cover w/ Centering Peg Aluminum Centering Peg Sleeve Over Aluminum Can Extended Cathode Terminals Rubber Gasket Tape Aluminum Stiffening Ribs Thermal Pak Construction Rilled Construction Thermal Pak Construction Rilled Construction CDM Cornell Dubilier • 140 Technology Place • Liberty, SC 29657 • Phone: (864)843-2277 • Fax: (864)843-3800 3 These figures show typical constructions of the non-surface- mount aluminum electrolytic capacitors. All Cornell Dubilier capacitors use compression-fit construction so there is no thermoplastic potting compound to interfere with safety- vent operation. Thermal Pak™ and Rilled are Cornell Dubilier’s exceptional constructions for screw terminal capacitors. Compared to conventional, potted construction, Thermal Pak operates cooler, provides longer life, withstands higher shock and vibration, delivers more reliable safety vent operation and is lighter weight. Rilled offers superior shock and vibration withstanding, typically withstanding more than 15 g acceleration forces. ETCHING The anode and cathode foils are made of high purity, thin aluminum foil, 0.02 to 0.1 mm thick. To increase the plate area and the capacitance, the surface area in contact with the electrolyte is increased by etching the foils to dissolve aluminum and create a dense network of billions of microscopic tunnels penetrating through the foil. For maximum increase in surface area in higher voltage capacitors the anode foil is 99.99% high purity, high cubicity aluminum that allows the billions of microscopic etch tunnels to be parallel and mostly perpendicular to the foil surface. Etching involves pulling the aluminum foil on rollers through a chloride solution while applying an AC, DC or AC-and-DC voltage between the etch solution and the aluminum foil. Surface area can increase as much as 200 times for foil in low-voltage capacitors and up to 60 times for high-voltage capacitors. FORMING The anode foil carries the capacitor’s dielectric. The dielectric is a thin layer of aluminum oxide, Al2O3, which is chemically grown on the anode foil during a process called “formation.” Formation is accomplished by pulling the anode foil on rollers through an electrolyte bath and continuously applying a DC voltage between the bath and the foil. The voltage is 135% to 200% of the final capacitor’s rated voltage. The thickness of the aluminum oxide is about 1.4 to 1.5 nm for each volt of the formation voltage, e.g., the anode foil in a 450 V capacitor may get a formation voltage in excess of 600 V and have an oxide thickness of about 900 nm. That’s about a hundredth of the thickness of a human hair. Formation reduces the effective foil surface area because the microscopic tunnels are partially occluded by the oxide. The tunnel etch pattern is adjusted by choice of foil and etching process so that low-voltage anodes have dense tunnel patterns compatible with thin oxide and high-voltage anodes have coarse tunnel patterns compatible with thick oxide. The cathode foil is not formed and it retains its high surface area and dense etch pattern. SLITTING Foil is etched and formed in jumbo rolls of 40 to 50 cm wide and then slit into various widths according to the lengths of the final capacitors. WINDING The capacitor element is wound on a winding machine with spindles for one-to-four separator papers, the anode foil, another set of one-to-four separator papers and the cathode foil. These are wound into a cylinder and wrapped with a strip of pressure-sensitive tape to prevent unwinding. The separators prevent the foils from touching and shorting, and the separators later hold the reservoir of electrolyte. Before or during winding aluminum tabs are attached to the foils for later connection to the capacitor terminals. The best method is by cold-welding of the tabs to the foils with tab locations microprocessor controlled during winding so that the capacitor element’s inductance can be less than 2 nH. The older method of attachment is by staking, a process of punching the tab through the foil and folding down the punched metal. Cold welding reduces short-circuit failures and performs better in high-ripple current and discharge applications in which the individual stakes may fail from high current like buttons popping uploads/Religion/ aeapp-guide.pdf