GB2192306A - High sensitivity relay for switching high currents - Google Patents

Abstract

A relay for operation by TTL and switching 80 amps and 240 volts a.c., comprises a low voltage coil (1) surrounding a circular armature (2) having a large end disc (3). A U-shaped yoke (4) has a permanent magnet (6) and pole plate (7) attached to one limb (4A) of the U. Energisation causes repulsion between the pole plate (7) and the disc (3) coupled with attraction towards the yoke, to move the armature into its operate position. Upon de- energisation the flux from the permanent magnet (6) acting on the armature disc presents a greater force across the small area gap (b) than across the large area gap (B) so the armature moves towards the plate (7) and remains against it in the de-energised state. <IMAGE>

Description

SPECIFICATION High sensitivity relay for switching high currents This invention relates to high sensitivity relay capable of switching high currents.

Sometimes it is necessary to switch high currents for example 80 amps at 240 volts a.c. by means of a relay which is operated by TTL circuitry. In addition it may be required that the relay should only provide a low current drain while it is operated. One such situation is in switching equipment on and off during off-peak electricity supply periods. For example a consumer may wish to switch on electrical central heating during a "white meter" supply period and since the relay will be under the control of the Electricity Supply Board, any electricity "drain" through the relay winding will be a potential loss to the Electricity Supply Board.

Therefore it is necessary to minimise this loss and provide a relay which takes only minimal power to switch such large currents. For example a half-watt winding would meet this requirement.

It is an object of the present invention to provide an electrical relay which is highly sensitive and has a low power consumption and able to switch relatively high currents e.g. 80 amps at mains voltage.

According to the present invention there is provided an electro-magnetic relay comprising an armature carrying a plate-like magnetic member moveable between a first co-operating pole face and a second co-operating pole face to operate contacts, said first and second pole faces being of permanently-induced opposite polarity, and wherein in its rest position the plate-like member is closer to the first pole face than to the second pole face, and wherein when the relay is energised the plate-like member has the same polarity as the first pole face which thereby repels the armature towards the second pole face.

According to another aspect of the present invention there is provided a relay comprising a low voltage coil, and high current, high voltage switching contacts, a plunger-type armature having a plate-like member at one end which moves in a space between a yoke which completes the magnetic circuit of the relay, and a separate pole face, said yoke and said pole face being permanently magnetically polarised in the opposite sense, said armature member lying closer to the pole face than the yoke in the deenergised state of the relay.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings in which: Fig. 1 shows schematically a relay according to an embodiment of the present invention, Fig. 2A to 2C show various views of a relay and contactor set incorporating the principles outlined in Fig. 1, according to another embodiment of the invention.

Referring to Fig. 1 the relay comprises a low voltage coil 1 compatible with Transistor-Transistor Logic (TTL) surrounding an internal armature 2 having a circular cross-section and which has a large area plate or disc-like member 3 extending normal to the armature axis and located at the right hand end of the armature as viewed in Fig. 1 of the drawings. A U-shaped yoke 4 completes the magnetic circuit. The armature movement is longitudinal. A permanent magnet 6 and pole plate 7 are attached to the right hand end of the yoke as viewed in Fig. 1.

The space 8 between the yoke limb 4A and the pole plate 7 allows the armature disc 3 to move from the yoke to the plate when operating and the broken line 9 indicates a mechanical linkage connected to a contact set for switching high current e.g. 80 amps at high voltage e.g. 240 volts a.c.

In the de-energised state, the flux from the permanent magnet 6 acting on the armature disc 3 presents a greater force between pole plate 7 and disc 3 than between limb 4A and disc 3 because the effective common area of the disc 3 and the plate 7 is smaller than that of disc 3 and limb 4. Thus the flux from the permanent magnet 6 provides the normally-open force biasing the armature towards the position shown generally in Fig. 1, so the armature moves towards the pole plate 7 which is a south pole as shown in the drawing, and remains against it. When the coil is correctly energised the armature disc 3 is made a south pole which is then repelled by the pole plate 7 (which is a south pole) and attracted by the limb 4A of the yoke which becomes a north pole and also attracted at the end 2A of the armature to the limb 4B of the yoke.

On closure of the contact set a large force is produced at the end 2A and the relay is so designed to achieve very little latching by having a small gap remaining at B when the gap A has closed.

The longitudinal movement of the armature 2 is transmitted as indicated by the broken line via an insulating member to a single make switch contact set which is capable of switching 80 amps at 240 volts a.c.

Referring now to Fig. 2 the relay there shown embodies the same principles of design and operation as the one described in Fig. 1. A moulded bobbin 20 has end cheeks 20A and 20B and a tubular portion 20C accommodating the armature 30.

The end cheeks 20A and 20B are slotted as indicated by reference numerals 22A and 22B to accommodate, respectively, the limbs 21A and 21 B of the yoke 29 so the yoke can be inserted into the moulded bobbin from above.

The permanent magnet 23 and pole plate 24 also fit in the slot 22B of the end cheek 20B of the bobbin 20. It has at its right hand end the armature disc 25 and a projecting spiggot 26 with barbs 26A which hold to the armature 21 an insulating actuating member 27 which is coupled to the moveable contact arm 28 by means of a reduced diameter portion 27A passing through hole 28A in the contact arm 28 and spring 29 retains contact arm 28 against the shoulder 27B on the member 27.

Contact arm 28 carries contact 28B which cooperates with fixed contact arm 30 carrying contact 30A. Contact arm 28 is pivotally mounted at 28C.

The relay is shown in its rest position, unenergised with the contacts 28B and 30A open. Upon energisation the armature moves to the left as viewed in Fig. 2A, the disc 25 being repelled from the plate 24 and attracted to the limb 21 B and the limb 21A. This closes the contacts 28B and 30A.

The coil 32 in this particular embodiment has a resistance of 320 ohms and operates at 5 volts. It has 7500 turns of 0.164 wire.

Fig. 2B is an end view of the relay of Fig. 2A but viewed behind the contact set, along the line indicated by X-X, and with part of the end cheek housing 20B removed so that the shape of the plate 24 is visible. As can be seen the plate 24 is U-shaped with legs 24A, 24B and the amount of effective common area between disc 25 and legs 24A, 24B can be seen, represented by the portions of disc 25 in broken line behind the legs 24A, 24B.

Fig. 2C shows the slots 22A, 22B.

In manufacturing the relay, the bobbin 31 is wound with the coil 32. The yoke 31 is then inserted into the bobbin with limbs 21A, 21 B located in slots 22A, 22B. The armature 21 disc 25, member 27 and spiggot 26 are then inserted longitudinally through the cheek 20B via holes 20C and 21 C and the magnet 23 and plate 24 are then inserted and the magnet magnetised in situ. The magnet and plate locate in slots 22B against shoulders 22C, 22D (Fig. 2B).

The contact set 28 and 30 is then assembled.

The relay described will operate at 5 volts and provide a contact force in the range 100 to 300 grams, average 200 grams and an open contact gap no less than 12 mm and of the order of 21 mm.

In the embodiment of Fig. 2 the common effective area between the disc 25 and the plate 24 is about half the common effective area betwen the disc 25 and the limb 21 B, allowing for the aperture 21C. This is found to be approximately the optimum ratio of common effective areas to provide a force which is about 50% stronger in the direction of the plate 24. If the size of the legs 24A, 24B is reduced much more than the total flux is reduced too much and the net longitudinal force is reduced. The effective area at A is about 13 sq mm butthe area ofthe disc25 is not too critical. Its diameter in this embodiment is about 10 mm.

The relay consumes about 70 mW of electrical power, and no more than 100 mW.

Claims (9)

1. An electro-magnetic relay comprising an armature carrying a plate-like magnetic member moveable between a first co-operating pole face and a second co-operating pole face to operate contacts, said first and second pole faces being of permanently-induced opposite polarity, and wherein in its rest position the plate-like member is closer to the first pole face than to the second pole face, and wherein when the relay is energised the plate-like member has the same polarity as the first pole face which thereby repels the armature towards the second pole face.

2. A relay comprising a low voltage coil, and high current, high voltage swiching contacts, a plungertype armature having a plate-like member at one end which moves in a space between a yoke which completes the magnetic circuit of the relay, and a separate pole face, said yoke and said pole face being permanently magnetically polarised in the opposite sense, said armature member lying closer to the pole face than the yoke in the deenergised state of the relay.

3. A relay as claimed in claim 1 or claim 2 wherein said yoke is U-shaped and wherein one limb of the U limits the movement of the armature to preventing the armature member contacting the other limb of the yoke on energisation of the relay.

4. A relay as claimed in claim 2, wherein the armature passes through an aperture in one limb of the yoke.

5. A relay as claimed in any preceding claim, wherein the contacts are provided by a moveable contact which is pulled into contact with a fixed contact when the relay is energised.

6. A relay as claimed in any preceding claim, wherein the yoke is U-shaped and the limbs of the U slot into respective slots in end cheeks of a moulded plastics bobbin.

7. A relay as claimed in any preceding claim, wherein the common effective area between the armature member and the pole face is less than that between the armature member and the yoke.

8. A relay as claimed in claim 7 wherein the common effective area between the armature member and the pole face is about half that between the armature and the yoke.

9. A relay substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.