: ALEXANDER M. OKGI KH Electrolytic capacitors play vital oles in the operation of practically every radio-electr nic device, and their applications in the vast electrica industry are increas- ing by leaps and bounds. This b ok, written by an in- ternationdJIy knawn authority, Ifescribes trie design, construction [\rnariufacture, functi L and testing of dry ing characterises of the varioujjjjyffes arid indicates both their useful applications and their limitations. $3.00 THE ELECTROLYTIC CAPACITOR by ALEXANDER M. GEORGIEV Member, American Institute of Electrical Engineers This is a practical book which will be of value not only to engineers concerned with the actual design and manufacture of electrolytic capacitors (annual production now amounts to tens of millions) but also to that larger group of engineers, techni- cians, and maintenance men concerned with equipment in which electrolytic ca- pacitors are used, e.g., radio receivers and transmitters; sound systems and other elec- tronic apparatus; telephone circuits; elec- tric welding equipment; and single-phase induction motors such as those used in refrigerators, air-conditioning units, pumps, oil burners, washing machines, etc. It will also be a useful reference book for aca- demic and industrial research workers in the electrical and electrochemical field, and physicists and chemists may find of interest the recorded observations and experimental data on electrolytic cells. The author's primary objective is to describe the design, construction, manu- facture, function, and testing of dry and wet electrolytic capacitors, to explain the operating characteristics of various types, and to indicate both their useful appli- cations and their limitations. In addition, (Continued on bock flap) Technical Division MURRAY HILL BOOKS, INC. Publishers NewYork The Electrolytic Capacitor ALEXANDER M. GEORGIEV Member, American Institute of Electrical Engineers Technical Division MURRAY HILL BOOKS, INC. NEW YORK TORONTO COPYRIGHT, 1945, BY ALEXANDER M. GEORGIEV PRINTED IN THE UNITED STATES OF AMERICA BY THE FERRIS PRINTING COMPANY, NEW YORK ALL RIGHTS RESERVED Preface The origin of the electrolytic capacitor or condenser can be traced to the second half of the 19th century when the discovery was made (Wheatstone, Buff, Ducretet) that a film can be formed on aluminum electrochemically and that it will exhibit unidirectional electrical con- ductance and other peculiar properties. One of the early attempted applications of the electrolytic capacitor was in conjunction with the starting of single-phase induction motors; efforts were also made to utilize it for power factor correction in alternating current circuits. It appears that no extensive use had been made of this device until the early twenties, when its utility in filter circuits supplying rectified plate current to radio tubes was definitely established. These capaci- tors were "polarized" and of the "wet" type. Several years later "dry" electrolytic condensers of a low voltage rating and large capacitance found a limited application in A-battery eliminators (comprising a rectifier and a filter circuit) which furnished filament current for d.c. radio tubes. By 1929 the high-voltage dry electrolytic capacitor was developed and soon found very extensive and diversified applications in several fields. The annual production of dry and wet electrolytic capacitors amounts now to tens of millions and they are used in radio receivers and transmitters, sound systems and other electronic appa- ratus, in telephone circuits, in conjunction with electric motors and, to a smaller extent, in a number of other applications. The main object of this book is to describe the construction, manu- facture, function and testing of dry and wet electrolytic capacitors, to explain the operating characteristics of the various types and to indi- cate both their useful applications and their limitations. To make clearer the peculiarities of these devices, a comparison has been drawn between them and the nonelectrolytic capacitors, the latter being known for a much longer time. It has been endeavored, otherwise, to limit this text to the subject matter that is specifically related to the electrolytic type. The discussion of the theory underlying capacitors in general (electrolytic and nonelectrolytic) has been omitted, as far as possible, because it is covered by the literature on this subject. Several of the known theories on the nature of the dielectric film have been briefly outlined. The properties of the film, however, have vi PREFACE been treated in detail, as they determine to a very large extent the characteristics of the electrolytic capacitor. Only a few commercial dry and wet capacitors have been described, but they are typical and representative of most electrolytic capacitors now in use. The description of the numerous minor constructional variations has been considered unnecessary. In writing this book, the author has used extensively his observa- tions and experience acquired in the development and manufacture of electrolytic capacitors during the past fifteen years. It is hoped that the information presented in the text will be of interest to manufac- turers and users of electrolytic capacitors and also to workers con- cerned with the development of capacitors and related apparatus. There are many patents on electrolytic capacitors and a list of some of the more interesting among them has been appended. 1 The author wishes to express his appreciation to Delco Products and Delco-Remy Divisions of General Motors Corporation, The Crosley Corporation, The Aluminum Research Laboratories, The Aerovox Corporation, P. R. Mallory & Co., Inc., Sprague Electric Company, and the Solar Manufacturing Corporation for the illustra- tions they have furnished him. A. M. G. Dayton, Ohio January, 1945 1 A few of the listed patents do not specifically refer to electrolytic capacitors. However, the subject matter presented therein is directly or indirectly related to such capacitors. Contents PAGE Preface v CHAPTER I General Information on Capacitors 3 II Electrolytic vs. Nonelectrolytic Capacitors 7 III Dry vs. Wet Electrolytic Capacitors 13 IV The Electrodes of Electrolytic Capacitors 20 V The Dielectric Film—Theoretical Considerations 29 VI The Dielectric Film—Practical Considerations 36 VII The Filming Electrolyte 40 VIII The Filming Process and Equipment. Re-forming 44 IX The Etching of Aluminum Electrodes 55 X The Electrode Spacer 62 XI The Operating Electrolyte 66 XII The Winding of Capacitor Sections and Their Con- nections 77 XIII The Impregnation of Dry Electrolytic Capacitors 85 XIV The Capacitor Container and Its Vent. Assembling the Capacitor 91 XV Electrical Measurements and Routine Tests on Elec- trolytic Capacitors 104 XVI Special Tests for Electrolytic Capacitors 115 XVII Troubles in Electrolytic Capacitors, Their Causes and Detection. Emergency Repairs. Replacements 120 XVIII The Design of Electrolytic Capacitors 130 XIX Trends in the Development of Electrolytic Capaci- tors 143 XX Semi-electrolytic Capacitors 146 XXI Some of the Uses for Electrolytic Capacitors 149 Glossary 161 Bibliography 169 Patents 175 Index 181 List of Figures FIGURE PAGE 1. Two-plate fixed capacitor 4 2. Wound capacitor section 6 3. Graph showing the leakage current vs. voltage in a polar- ized capacitor 10 4. Schematic drawing of a wet electrolytic capacitor 13 5-A. Wax-impregnated paper capacitor, ignition type 16 5-B. Dry electrolytic capacitor section 16 6. Three-section dry electrolytic capacitor 17 7. Polarized wet electrolytic capacitor 18 8. The essential component parts of a dry polarized electro- lytic capacitor 20 9. Microstructure of 99.8% aluminum foil 24 10. Microstructure of 99.2% aluminum foil 25 11. Rolled or spirally wound anode for wet polarized capacitor 26 12. Pleated anode for wet polarized capacitor 27 13. Schematic drawing of a wet electrolytic capacitor with intermeshed plate electrodes 28 14. Electrolyte bath for the formation of capacitor anodes, batch method 29 15. Schematic drawing of a machine for the continuous filming of aluminum foil 47 16. Illustration of the formation of a pre-wound capacitor 52 17-A. Cross section of two samples of 99.8% aluminum foil (light vs. deep etching) showing the microconstituents 56 17-B. Cross section of a lightly etched and a deeply etched sample of 99.8% aluminum foil after its formation as a condenser anode 56 18-A. Machine for etching of aluminum foil for electrolytic capacitors 59 18-B. Illustration of the continuous method of etching of foil 59 19-A. Photomicrograph of a sample of .0012" absorbent con- denser paper 63 x LIST OF FIGURES FIGURE PAGE 19-B. Photomicrograph of a sample of .0005" uncalendered con- denser linen paper 63 20-A. Graph showing the leakage current vs. temperature in a polarized wet capacitor 69 20-B. Graph showing the capacitance vs. temperature in a polar- ized wet capacitor 69 21. Graph showing the power factor vs. temperature in a polar- ized wet capacitor 69 22. Graph showing the leakage current vs. temperature in a polarized dry capacitor 70 23. Graph showing the capacitance vs. temperature in a polar- ized dry capacitor 70 24. Graph showing the power factor vs. temperature in a polarized dry capacitor 70 25-A. Capacitor winding machine 78 Schematic presentation of the winding of capacitor sections 78 Section wound on a large arbor and subsequently shaped to fit containers of various proportions 79 Integral tab for a heavy foil electrode 81 Integral tab for a thin foil electrode 81 Telescoped section : the beginning of the winding 81 Telescoped section ; completed 81 Two capacitors in one section. Two anodes and one com- mon cathode 82 31. Series combination of two a.c. capacitors having a wide common foil and wound into one section 82 32-A. Series combination of two a.c. capacitors having a long common foil and wound into one section 83 32-B. Equipment for the impregnation of electrolytic capacitors 89 33. Vent for wet capacitor 92 34. Venting arrangement for dry capacitor 92 35. Weak-spot vent for dry capacitors 92 36. Vent for dry capacitors with a pierced rubber membrane 92 37.