US2427751A

US2427751A - Capacitor closed relay having reduced holding current

Info

Publication number: US2427751A
Application number: US714827A
Authority: US
Inventors: Frederick D Snyder
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-03-29
Filing date: 1946-12-07
Publication date: 1947-09-23
Anticipated expiration: 1964-09-23

Description

P F. p. SNYDER 2,427,751

CAPACITOR CLOSED RELAY HAVING REDUCED HOLDING CURRENT Original Filed larch 29, .1945

WITNESSES: INVENTOR Fredmcu'usn du.

BY M TIORNEY Patented 23, 194

UNITED STATES PATENT OFFICE cnraorroa CLOSED RELAY navmcnnnucan nonnme CURRENT Frederick n. Snyder, Milton, Masa, admin to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application March 29, 1945, Serial No. 585,515. Divided and this application Decembet 7, 1940, Serial No. 114,827

My invention relates electromagnetic relays and represents a division from my copending application Serial No. 585,515, filed-March (29, 1945.

1 claim. (Cl. 175-320) to control systems for It is an object of the invention to provide relay ii -obtained without the use of a separate self-sealing contact and holding circuit usually required for such relays. I I

-Another object of the invention is to devise a low voltage relay which requires only a two-wire a control circuit and thereby affords simplifying the appertaining control system. The latter object, more specifically, is intended to permit obtaining low voltage protection in magnetic starters for motors when using a two-wire master control system for the motor. Such two-wire control systems are used, for instance, when a limit switch, thermostat or some similarly simple contact device is employed for governing the operation of a motor. Two-wire systems for obtaining low voltage control are also of advantage where the control apparatus proper is installed at a long distance away from a push button or the like control contact. In such cases the possibility of affordlng low voltage protection by means of a twowire relay circuit permits saving one control wire between the control equipment and the appertaining push button contact.

-In order to achieve the above-mentioned objects and in accordance with my invention, I interconnect the two input terminals of the relay circuit by resistance means in series connection with a rectifier and a capacitor so that the capacitor is charged through the resistance means and the rectifier when the terminals are energized. The relay to be controlled has a control coil connected across the capacitor; and a, control contact is disposed between the coil and the capacitor. In conjunction with the just-mentioned circuit arrangement, the resistance means and the relay coil are rated relative to each other so that the continuous current which flows through the resistance means and coil when the control contact is closed, is lower than the pickup value required by the relay coil for closing the relay. It is rurther essential in conJunction with the above-mentioned requirements that the capacitor be rated for providing, when the control contact is closed, a. temporary discharge current which fiows through the relay coil and exceeds the critical or pickup'value and hence causes the relay to close.

It is understood in the foregoing that the electromagnetic relay incorporated in the control system has a marked difierence between the current value necessary for causing the relay to pick up and the minimum value of current required for holding the relay in closed condition once it has picked up. Such a difference exists, for instance, in clapper type relays where the armature gap is large when the relay is in dropped-oil condition and is small or fully closed after the relay has picked up. The above-mentioned conditions are also present in relays of the latched-in type in which no continuous holding current is required for securing the relay in the closed position.

, The above-mentioned and other objects and, features of my invention will be apparent from the following description in conjunction with the embodiment illustrated in the drawing which represents the circuit diagram of an ordinary, i. e., nonretentive relay, especially designed for afiording low voltage protection by means oi! a twowire connection.

According to the drawing, the two wires or terminals Li and L! of the energizing circuit are cross connected by means of a resistor It in series with a rectifier I1 and a capacitor Ill. The relay IQ of this system is of the nonretentive type. That is, it requires a continuous holding or sealing current in order to be maintained in the closed position in opposition to its armature bias. The relay field structure is denoted by 20, the appertaining armature by 2|, and the contact assembly of the armature by 23. The control coil 22 of the relay is connected across the capacitor it through a control contact 24. The resistor l6 and the coil 22 are rated relative to each other so that the continuous current which flows through the coil v22, when the contact 24 is closed,

is lower than the current magnitude required for.

closing the relay to pick up. However, when the two terminals are energized, the capacitor It assumes a charge which upon closure of contact 24 is discharged through the coil 22. The current surge exceeds the pickup value and hence causes the armature 2| to move against the structure 20. Thereafter the continuous current is effective to hold the armature closed since its value is sufliciently above the critical holding value.

In this manner the relay It stays closed as long voltage iailure occurs at the terminals oi the system. Upon occurrence of voltage failure, the contact 24 must first be opened and then reclosed in order to charge the capacitor II and thereafter discharge it through therelay coil. The holding effect is produced within the energizing circuit 01' the relay coil so that no separate sealing contact and sealing circuit are necessary to achieve low voltage protection.

While I have especially described an embodiment of my invention for use in connection with alternating current circuits. it will be understood from the foregoing that the same devices can also be used for direct current, it being merely necessary to omit the rectifier I! in such cases of application. v

Other modifications and changes as to detail will be apparent t those skilled in the art upon the study 01' the foregoing disclosure. I, therefore, wish this specification to be understood chiefly as illustrative while the essential features and scope or my invention are intended to be defined by we claim annexed hereto.

. I claim as my invention:

A relay control system comprising two terminal means [or connection to a single phase alternating current circuit, a connection between said terminals having a resistor and a rectifier and a capacitor series-connected with one another so that said capacitor is charged when said terminals are energized, an electro-magnetic relay having a relatively high pickup current value and a relatively low holding current value and being provided with a control coil connected across said capacitor, a control contact disposed between said coil and said capacitor, said resistor and coil being rated so that the continuous current normallv flowing therethrough when said contact is closed is above said h'oldlng value and below said pickup value, and said capacitor being rated for providing, when said contact is closed, a tem- FREDERICK D. SNYDER.