GB563491A - Improvements in circuit arrangements for electromagnetic relays - Google Patents

Abstract

563,491. Electric control systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and FORMBY, W. L. Feb. 10, 1943, No. 2206. [Class 38 (iv)] [Also in Groups XXXVI and XXXVII] A relay particularly suitable in combination with similar relays for battery charging systems automatic voltage regulation or voltage indicating, has two windings ab and de connected in parallel or series and acting in opposition, one winding being associated with a non-linear resistance such as NLR2, the resistance of which varies with applied voltage while the temperature remains the same. By this arrangement one winding will overpower the other at certain voltages, but will itself be overpowered at other voltages. Fig. 2 shows a, system for battery charging, contacts c2 being operated to provide a high voltage charging current when the voltage of the battery falls to 48 volts and a low voltage charging current when the voltage of the battery rises to 54. The contacts c2 are operated by relay C a resistance R3 of which is normally short-circuited by contact b1 of relay B, the non-linear resistance NLR2 of which is short-circuited at c1 by operation of relay C. With parts in the position shown, a battery voltage between 48 and 54 will operate relay e over contact b1. Relay C will operate c2 for high charging and will short-circuit NLR2 so that relay B operates and contacts b1 open. Relay C remains operated, since although winding de is opposed by winding ab it overpowers it. When voltage reaches 52, the relative strength of ab has increased owing to non-linear resistance NLR3 so that the relay C releases, and the low rate of charging is set up, till the voltage 48 is reached when the relay B, under the differential action of its windings releases, whereupon C operates. The cycle continues similarly. The material used for the non-linear resistance may be silicon carbide together with carbon and for tungsten and molybdenum, agglomerated under pressure and baked, and it may take the form of a disc. Selenium or copper oxide may also be used and sensitivity may be further increased by having a resistance with a negative characteristic in circuit with one winding and one with a positive characteristic in circuit with the other winding.