US2177018A - Electrolytic condenser - Google Patents

Description

Oct. 24, 1939- A. F. P. J. CLAASSEN ET AL 2,177,013

ELECTROLYTIC CONDENSER .Filed 001:. 23, 1936 Patented Oct. 24, 19 39 2 Claims.

This invention relates to wet electrolytic condensers, and more particularly to electrodes for 350 volts and more.

Such condensers usually have a container of conductive material acting as the cathode, and an anode whose surface area is made as large as possible to obtain a maximum capacity for a given size container; this surface area, which is 4 provided with an insulating oxide-coating dielectric, determining the capacity of .the condenser. To provide the large surface area 'the anode is formed in various manner, for instance as a heIically-wound aluminium strip apertured .v at various points to permit free passage of the electrolyte, or as a plate of film-forming material however, have the serious drawback that the paths cathode-container are different for different points of the anode, which results in the series resistance of the entire condenser being extremely unfavorable. v Although in the so-called dry electrolytic confabric. absorbing a pasty electrolyte the paths are the same, such condensers have several disthe oxide film is self-healing to only a very limited extent, and thus after a breakdown the short circuit between the electrodes will remain.

an electrolytic condenser with a meander-shaped anode surrounded by a cathode-container equidistantly spaced therefrom, such a construction is mechanically weak and thus subject to variations in series-resistance. Moreover the great danger of short circuit between anode and cathode container as a consequence of the weak construction exists. Although this can be eliminated number of pointsgsuch a construction is very complicated, expensive and unsuitable for massproduction.

One object of the present invention is' to eliminate the abovedifliculties and to provide a wet electrolytic condenser which is of simple construction, of large capacity for a given volume, and of low internal resistance.

Another object is .to provide a large surfacearea electrode which can be inexpensively producedin" mass production.

In accordance with thednvention, at least one of the electrodes is formed as a plate having a bent in the shape of a star. Such constructions,

- from the anode through the, electrolyte to the densers having strip electrodes separated by advantages over wet condensers, including that While it has also been suggested to construct by supporting the anpde and container at a large UNITED STATES PATENT OFFICE.

ELECTROLYTIC CONDENSER Anthonius Frederik Peter Johan Claassen, and

Cornelis de Lange, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfahrieken, Eindhoven, Netherlands Application October 23, 1936, Serial No. 107,290 In Germany October 26, 1935 I ing perpendicularly thereto. condensers operating on voltages of the order of 7 By making the plate. and the rings in one piece, additional supporting means or means for attaching the rings to the plate are unnecessary,

by the operation of the condenser is very favor--.

able.

In another embodiment only one electrode, preferably the anode, is provided with projecting rings, and these rings are diametrically slotted to decrease the series-resistance.

Further advantages and features of the invention will appear as the -description progresses.

Inorder that the invention may be clearly understood and readily carried into effect, it will be described in more detail with reference to th accompanying drawing, in which:

Figure l is a sectional view of a condenser having a large surface electrode according to the prior art;

Fig. 2 is a sectionized side view of a condenser according to the invention:

Fig. 3 is a sectionized side view of a condenser according to another embodiment of the invention;

Fig. 4 is a sectional view taken along lines H of Fig. 3. I

The disadvantages of using electrodes spaced apart at unequal distances will be explained'in more ,detail in connection with Fig. 1, in which an anode 3| having a star-shaped section 3|, is disposed within a cylindrical cathode-container 34.

As the distances between the anode 3| and. the cathode-container 34 are not the same throughout, the partial capacities, i. e., the capacities from which the total-capacityof the condenser fairly large, For example, consider a condenser having a total capacity of 18 mid., and an electrolyte having a specific resistance of about 10,000 ohms per cubic centimeter at 20 0., intended to operate on 500 volts, 50 C., and consider another electrolyte with specific resistance of about 15,000 to 20,000 ohms per 'cubic centi' meter at 20 C., intended to operate on 550 volts,

.50 G. Such a condenser may have a partial capacity corresponding to 6 mfd. as supplied by a surface area of about 100 square centimeters lying at a distance of 2 cm. from the cathodewhich may readiiyoccur in the usual constructions of wet electrolytic condensers. With a specific resistance of the electrolyte of 15,000 ohms per cubic centimeter the resistance in series with the'6 mfd. will amount to 15,000 X f =aoc ohms This means a very high power factor loss, since the impedance of 6 mfd. at 100 cycles will amount to about 260 ohms.

Below are the calculations for a theoretical case in which the total capacity of the condenser is 18 mfd., (real value as would be measured by ballistic methods) and in which the distances be- 'r m1 ca T r 1 0 paco a series Frequency ity resistance Micrnfnmds Ohms 50 cycles 16.8 131 100cyclcs 13.0 103 500 cycles 7.7 6%

tween the anode and cathode of the parallelconnected partial capacities" have such values that the partial capacities are in series with the following resistances:

Partial capacities Resistances at 20 C.

Ohms 2 Microfarads 4 Microl'arads. 200 6 Microfarads. 400 6 Microiarads 800 'A condenser having the above partial capacities and resistances in series will have the following total capacities and total series resistances depending upon the frequency used:

large changes in the specific resistance of the electrolyte with temperature. Although this does not apply to such an extent to aqueous electrolytes, it ioes apply to high-voltage condensers in which an electrolyte in a glycerol solution is preferably used.

This temperature dependency of the electrolyte is so great that at about 45 C. for instance, the specific resistance of the electrolyte is V; the resistance at 20 C, Thus, when the values of Table I are calculated at 45 (2., all of the series resistances will be reduced to one-quarter a follows:

With the partial resistances of Table III, the condenser would have the following total capacities and total resistances at the given frequencies:

' Total Total Frequences capacity resistance Microfurads Ohms 50 cycles i7. 4 30 100 cycles l7. 0 34 50') cycles 12. 2 24 Comparison of Tables II and IV clearly brings out the high temperature dependency of the series resistance and of the capacity.

From the above it clearly appears that it is of great importance in an electrolytic condenser to make the series-resistance between every point of the formed electrode'and the counter-electrode as equal and as small as possible.

In the embodiment of the invention illustrated in Fig. 2 the condenser comprises a positive electrode i, a negative electrode 9, and a liquid electrolyte 30 for example a mixture of 200 gr. boric acid (HzBOa), 1000 gr. glycerol, and cc. ammonia (N'HrOH) 10% by weight. The electrode l comprises a plate portion 3| and a plurality of projecting concentric rings 32, and is provided with an insulating oxide coating. The electrodes are preferably made of a film-forming metal such as aluminum, which can be extruded into a onepiece body, and their active surfaces may be etched to increase the capacity.

The electrode I is secured to a base 4 of insulating material, for instance a moldable material containing synthetic resin, by' means of a metal pin 2 extending through a central bore in the plate portion 3| and base 4. The pin 2 has a flanged upper end 33 bearing upon the upper surface of plate 3|, whereas its lower end is riveted over the base 4 with the interposition of a terminal I. The base 4 is provided with an externally-threaded projecting portion 5 for mounting the condenser, and a gasket 3, for instance of rubber, is disposed between the base 4 and circular corrugations on the adjacent surface of plate 3| to form a liquid-tight seal.

A cup-shaped member 34, whose closed end surface forms a dome 20 provided with one or more apertures 22, has its lower edge bent over the edge of the base 4 with the interposition of gasket 3 to effect a liquid-tight seal. the member l4 by means of a ring-shaped indentation, formed by rolling, is the electrode 9, which is similar to electrode I and is provided with a plurality of ring-shaped projections ll spaced so as to telescope with the rings 32 of electrode i.

Electrode 9 is provided with a plurality oi bores 19 to allow the electrolyte 30 to flow into the space formed between the rings 32 and II, and with a central counterbore into which is secured the'top of a porcelain tube- It! extending with a snug fit into the space formed by the inner ring 32. A gasket 0, for instance of rubber, is disposed between the top of pin 2 and the bot- Secured to.

tom of tube l0, whereas a gasket I 4 extends between member 9 and the top inner ring 32 and partly within the spaces I5.

In assembling the condenser the member 9 with tube l0 secured thereto is pressed down so as to compress the gasket 8, which prevents the electrolyte. from reaching the top of pin 2 and passing between pin 2 and base I; thus preventing corrosion of pin 2. If pin 2 is of a material which does not form an oxide layer, gasket 8"-also serves to prevent short-circuiting between the electrodes through the electrolyte. The gasket [4 serves to space the electrodes I and 9 at the correct distance and also to prevent the electrolyte contained in space l5 from creeping upward along tube Ill. The electrodes I and 9 are telescoped to such an extent that the distance between the ends of rings ll and the surface l2 of plate 3| is substantially equal to the distance 13 between adjacent surfaces of rings 32 and II.

Bearing upon the top of the dome 20 and secured to member 34 by a rolled indentation at 36 is a cup-shaped cover 23 provided with a vent hole 25. Surrounding the dome 20 so as to cover the apertures 22 is a band of flexible material, for instance rubber, which in known manner serves to vent the gases developed during the operation of the condenser. It will be noted that by forming a dome 20 on the member 34 and locating the vent holes 22 therein, these holes are located well above the surface of the electrolyte 30, thereby minimizing the possibility of the electrolyte being carried out with the escaping vent gases.

To completely prevent the escape of electrolyte with the venting gases, and thus to prevent corrosion of objects mounted in the vicinity of the condenser, the space formed between the members 23 and I6 is filled with a suitable liquid-absorbing material 23 such as sawdust, whereby only the gases will escape through the aperture 25.

The condenser shown in 'Figs. 3 and 4 has in general a construction similar to that of Fig. 8 with the exception that only the anode is shaped according to the invention; the container itself acting as the cathode. In the construction shown in Figs. 3 and 4 the anode 5| is similar to that of electrode I with the exception that the rings 52 are provided with a plurality of, preferably about 10 to 15, diametr'ical slots 53 (see Fig. 4), which may be saw cuts. The slots 53 serve to reduce the series resistance and by giving them a width less than the thickness of the rings 52, the active surface and thus the'capacity of the electrode is increased, whereas the-series resistance retains a suitable value. An electrolytic condenser with an anode according to the invention with five concentric rings of utmost diameter of 24 mm. and a height of 55 mm., surface of the anode 275 square centimeters, has for 320 volt a capacity of 32 mid, and a series resistance of only 10 ohms. This latter value may be reduced to 5 ohms by mounting in the center of the container a metal bar fixed to the container thus serving as an inner cathode-container. The series-resistance for a condenser of similar electric properties but with an anode as drawn in Fig. 1 is about 15 ohms or more.

While we have described our invention in connection with specific examples and constructions, we do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

1. An electrolytic condenser comprising a liquid electrolyte, two electrodes each consisting of a one-piece body having a plate-shaped bottom portion and a plurality of concentric ring-shaped portions extending perpendicularly to said bottom portion, said bodies being arranged with the ring-shaped portions interlapping with their opposing surfaces equidistantly spaced apart and parallel, the ring-shaped portions of one electrode alternating with the ring-shaped portions of the other electrode.

2. An electrolytic condenser comprising a liquid electrolyte, a container, an electrode having a bottom portion and a plurality of concentric rings extending perpendicularly to said portion, a second electrode having a bottom portion, and a plurality of rings extending perpendicularly to said portion and telescoping with the rings of said first electrode, means to insulate said electrodes from each other and to space said rings apart, said means comprising a member of insulating material secured to one electrode and extending within the inner ring of the second electrode, and

a gasket of insulating material extending around said member and between said electrodes, said gasket also preventing creepage of the electrolyte along said member. ANTHONIUS FREDERIK PETER JOHAN CLAASSEN. CORNELIS n1: LANGE.

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