US2297669A

US2297669A - Electrolytic condenser

Info

Publication number: US2297669A
Application number: US316033A
Authority: US
Inventors: Robinson Preston; Burnham John
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-01-27
Filing date: 1940-01-27
Publication date: 1942-09-29
Anticipated expiration: 1959-09-29

Description

sept- 1942. P. ROBINSON T 2,297,669

ELECTROLYTIC CONDENSER Filed Jan. 27, 1940 PRESTON ROBINSON AND JOHN BURNHAM BY m (3 4, 5L ga/r M/ ATTORNEY 5 Patented Sept. 29, 1942 ELECTROLYTIC CONDENSER Preston Robinson, Williamstown, and John Burnham, North Adams, Mass.

Application January 27, 1940, Serial No. 316,033

7 Claims.

The present invention relates to electrolytic condensers suitable for operation in alternating current circuits. More particularly our invention relates to a new and novel electrolytic condenser of the so-called A. C. dry type suitable for continuous operation in A. C. circuits.

Prior condensers of this type usually comprise as their main elements two electrodes of a filming metal on which is electrolytically formed a dielectric film. As is well known, the two filmed electrodes of an A. C. electrolytic condenser are always charged positive with respect to the electrolyte and because of this such electrodes are referred to as anodes. Disposed between the anodes is a spacer of an absorbent material which also serves as a carrier-for the electrolyte. The anodes, together with their interposed spacers are usually wound to form a condenser roll, although they may be assembled as a stack. The electrolyte used may have a viscosity ranging from that of a viscous fluid to that of a semisolidpaste.

Heretofore dry electrolytic condensers have been restricted in their use to circuits involving their intermittent operation only. For example, condensers of this type have been used to a considerable extent as starting condensers of capacitor motors, where in such application, they are subjected to short intermittent use and to comparatively low voltages.

Attempts to use dry electrolytic condensers for continuous operation and/or at higher voltages, have not been successful, as the prior condensers fall after short periods of operation, and the higher the voltages the shorter these periods. The main reason for this is the heating up of the condenser, due primarily to its comparatively high and unstable power factor; such heating up causing a progressive and rapid deterioration of the condenser. While artificial means to increase the heat dissipation of the condenser have been suggested, for example, by means of oil cooling, as described in U. S. Patent #1,992 .545 to Preston Robinson, such means are comparatively expensive and not always practical.

Another solution of this problem, namely the use of a series combination of a plurality of such condensers, has been described in U. S. Patent #2,0l1,l26 to Robert C. Sprague. However, series operation of electrolytic condensers introduces the outstanding difficulties of a reduction in capacity to a value inversely proportional to the number of condensers connected in series, and an increase in the number of condenser units requlred.

The present invention which will be described in connection with a wound condenser, obviates the difficulties of prior condensers, and permits the operation of A. C. electrolytic condensers in continuous service and at high voltages and this without requiring a plurality of condensers being operated in series arrangement.

The novel A. C. electrolytic condenser of our invention is characterized by a very low and stable power factor and low electrical losses, whereby such losses as exist are easily dissipated by the condenser and the heating up and consequent destruction thereof is prevented.

As a result of a comprehensive investigation of prior A. C. electrolytic condensers, in an effort to determine the causes bringing about the very high and unstable power factors and losses thereof we have found the following:

The general assumption that the current flows from one anode to the other in a straight line path through the electrolyte, and that the series resistance and hence the power factor of the condenser is determined by the length of this straight line path, is erroneous. We have found on the contrary, that in the proximity of and at the edges of the anodes there exists a fringe eifect, causing the current path in the electrolyte at these edge zones to be many times longer than the distance between the anodes.

This fringe effect we have found, is greater the greater the distance between the anodes, and iurthermore all other factors being equal, the power factor of the condenser increases with the fringe effect. 1

The fringe effect manifests itself both at the side edge zones and the end edge zones of the anodes. This is due to the fact that at the end edge zones of the anodes there is no immediately adjacent portion of the other anode. At the side edges of the anodes a similar condition exists because of the dielectric film formed on the surface of the edge portions.

While as a rule because of the length of the anode strips, the area of the side edge zones is greater than that of the end edge zones, we have found that the influence of the fringe eifect caused by the latter alone is unexpectedly high.

As a result of our investigations we have found that a substantial reduction of the power factor of an A. C. dry electrolytic condenser can be achieved by eliminating the fringe effect and causing all of the current to flow through the electrolyte in a path substantially perpendicular to the surface of the anodes.

In accordance with our invention we achieve the above results by interposing between the anodes floating electrodes having surface dimensions greater than those of the anodes and extending well beyond the corresponding edges of the anodes and preferably even beyond the electrolyte, respectively the electrolyte carrying spacer. Thus the edges of the floating electrodes extend not only beyond the side edges of the anodes but also beyond the end edges thereof whereby they overlap at least one anode turn at the inner and outer ends of the condenser roll. This provides that every portion of each anode is opposed by a corresponding portion of a floating electrode.

To get the full benefits of our invention, the floating electrodes should be of a non-filming character, for example, made of a non-filming metal such as chromium, nickel, silver, tin or lead, and which do not form soluble salts in the particular condenser electrolyte used.

Instead of using the metals themselves they may be applied as a plating or coating on other metals, for example, on aluminum or iron.

Our invention will be further described with reference to the appended drawing in which:

Figure 1 is a perspective view of an A. C. condenser in accordance with the invention.

Fig. 2 is a cross-sectional enlarged view of an element taken along the line 2--2 of Fig. 1.

Referring to the drawing, the condenser shown therein comprises two anodes I and 2 each of a filming metal and preferably of aluminum foil. Interposed between adjacent faces of the anodes I and 2 are two spacers 3-3 and between these spacers is a floating electrode 4. Similarly between the opposite faces of the anodes I and 2 there are two spacers 6-6 and between these spacers is a floating electrode 1. For their outside electrical connection the anodes I and 2 are provided with terminal tabs 8 and 9 respectively.

The anodes I and 2 may have their surfaces etched by known processes after which, whether etched or unetched, they are provided with a dielectric film by means of a suitable forming process in a suitable forming electrolyte, for example, as described in U. S. Patent #2,116,449 to Preston Robinson.

The forming voltage used depends on the voltage at which the condenser is to be operated. For example, with condensers to be operated at a voltage of 110 volts A. C., we form the anodes to a voltage of 160 volts.

The absorbent spacers may be of gauze, paper, Cellophane and the like and serve as carriers for a viscous electrolyte of the condenser.

The electrolyte 5 is as a rule viscous whereby the viscosity may vary from that of a semiviscous fluid to that of a substantially hard mass. As a rule. we prefer to use an electrolyte having at room temperature the consistency of a paste.

The impregnation of the condenser with such electrolytes takes place in well-known manner and preferably after its assembly.

The floating electrodes as previously stated, are preferably of a non-filming metal such as chromium, nickel, tin or the like, or of a filming metal such as aluminum or of a non-filming metal such as iron or copper, provided with a plating or coating of one of the first mentioned metals.

In accordance with the invention the floating electrodes have dimensions greater than those of the anodes I and 2 and extend well beyond both the side and end edges ofthe anodes and preferably overlap at least one turn thereby encircling and enclosing the anodes as shown in Fig. 1.

Fig. 2 shows the

electrodes

4 and 1 extending beyond the side edges of the anodes I and 2 and even beyond the electrode impregnated spacers 3-3 and 6-6.

Instead of rolled condensers other assemblies such as stacks may be used in which case to obtain the full benefit of the invention it is essential that the stack be terminated at each end by a floating electrode and that preferably all the floating electrodes be electrically interconnected.

The outstanding advantages achieved by the invention may be more fully realized when it is considered that a condenser of the prior art comprising etched anodes formed to 160 volts and having a capacity value of 40 microfarads, has an average life of approximately 10 hours when operated in continuous service at volts A. C. A similar condenser made in accordance with the invention operates under the same conditions in excess of 2500 hours.

While we have described our invention in a specific embodiment and by means of a specific example, we do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What we claim is:

1. An A. C. electrolytic condenser comprising two filmed anode foils, a viscous film-maintaining electrolyte and floating electrodes embedded in said electrolyte and interposed in spacial relationship between and coextensive with said anodes, said electrodes having surface dimensions greater than those of said anodes and extending beyond all edges of said anodes.

2. An A. C. electrolytic condenser comprising two filmed anode foils, a viscous film-maintaining electrolyte, and non-filming floating electrodes embedded in said electrolyte and interposed in spacial relationship between and coextensive with said anodes, said electrodes being immune against attack of the electrolyte in operation and in idleness of the condenser and having surface dimensions greater than those of said anodes and extending beyond all edges thereof.

3. An A. C. electrolytic condenser comprising two convolute filmed anode foils, a viscous filmmaintaining electrolyte, and floating electrodes of a non-film-forrning metal embedded in said electrolyte and interposed in spacial relationship between and coextensive with said anodes, said electrodes being immune against attack of the electrolyte in operation and in idleness of the condenser and having surface dimensions greater than those of said anodes whereby said electrodes extend beyond all edges of said anodes.

4. An A. C. electrolytic condenser comprising two convolute filmed anodes, a viscous filmmaintaining electrolyte and means to decrease the power factor of said condenser said means comprising floating electrodes embedded in said electrolyte and interposed in spacial relationship between and coextensive with said anodes, said electrodes having surface dimensions greater than those of said anodes whereby said electrodes extend beyond all edges of said anodes.

5. An A. C. electrolytic condenser comprising two convolute filmed anodes, a viscous film-maintaining electrolyte and means to provide a straight line current path through said electrolyte, said means comprising floating electrodes interposed between and coextensive with said anodes in said electrolyte, said floating electrodes having surface dimensions greater than the dimensions of said anodes and extending beyond all edges of the anodes.

6. An A. C. electrolytic condenser comprising two convolute filmed anode electrodes, and a viscous film maintaining electrolyte disposed between said anodes, floating electrodes interposed between said anodes and embedded in said electrolyte each of said floating electrodes having surface dimensions greater than the surface dimensions of each of said anodes, extending beyond all edges of the anodes and symmetrically interwound with said anodes, said electrodes having a length in excess of said anodes and each portion of an anode surface having opposite to it an adjacently disposed portion of a floating electrode.

7. An A. C. electrolytic condenser comprising two filmed anode foils, a film-maintaining electrolyte and floating electrodes interposed between and coextending with said anodes, said electrodes having surface dimensions greater than those of said anodes and extending beyond all edges of said anodes.

PRESTON ROBINSON. JOHN BURNHAM.