The present invention relates ^' to a circuit arrangement for enabling simultaneous operation of independent AC circuits, particularly for enabling an array of independent lamps or relays to he tested or for enabling motors to be operated εim- ultaneously in parallel, avoiding capacitive feedback.

Previously, a common test facility for an array of indep¬ endent AC circuits was achieved by relays, the movable contacts of which were provided for enabling energisation of the independent circuits simultsineously. However, such arrangements have the disadvantage that relays are generally expensive, and are prone to wear and breakdown, and therefore are not as reliable as would be desired.

Accordingly, it is an object of the present invention to ^: provide a circuit arrangement for enabling parallel testing of independent AC circuits avoiding the use of relays.

According to the present invention there is provided a circuit arrangement for enabling simultaneous operation of independent AC circuits, comprising diode means connected bet¬ ween each independent AC circuit and a power supply, via switch means, which switch means when closed enables power to be supplied simultaneously in parallel to all of the AC circuits, said diode means being arranged to ensure that the AC circuits are independent from one another during normal operation.

The circuit arrangement of the present invention may be applied to any appropriate circuit arrangement requiring routing of a common AC signal to otherwise independent units, which may for example be lamps or relays or other circuit arrangements. The diode means may be pairs of discrete diodes

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or full wave rectifiers, details of which will be described later.

A further application of a circuit arrangement of the present invention would be in the power supply of capacitor split phase motors driven in parallel and avoiding the poss¬ ibility of capacitor generated feedback overriding end-of- travel switches for such motors.

The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 illustrates a basic circui-fc arrangement for testing lamps utilising diodes;

Fig. 1a illustrates a circuit arrangement, according to the prior art, utilising relays;

Fig. 2 illustrates a circuit arrangement similar to Fig.

1 for testing relays utilising a full wave rectifier;

Fig. 5 illustrates diode arrangements for enabling capacitor split phase motors to be driven in parallel according to the present invention;

Fig. 3 ^~~ - illustrates a conventional arrangement for driving capacitor split phase motors in parallel via relays; and

Fig. 3D illustrates the difficulties in driving capacitor split phase motors directly in parallel.

Referring first to Figures 1 and 1a, a pair of lamps L1 and L2 are connected to an AC supply and can be activated by means of respective switches S1 and S2, each lamp circuit

being normally isolated from the other lamp circuit. Pairs of diodes ^~ Q. , D.., and D - ) are connected respectively to each of said lamp circuits, one of each pair being connected to a first test line A and the other of said diodes of each pair being connected to a second test line B. The test lines A and B can be connected to the AC supply via a test push-button T, the contacts of which are open during normal operation of the lamp circuits, so that if one or other of the lamps L1 and L2 is energised, then there is no current path via the diodes

"^ ₁ ' ^1 _b ' ^ _? * "* _b ^an<3 * *k ^e ^ ^eB ^ lai ¹¹ © ¹³ A ^{3 i} ά B, thereby maintain ^¬ ing electrical isolation of the lamp circuits.

However, if it is desired to test the lamps simultaneously, then this may be achieved by operating the test push-button T, thereby supplying AC currents to the lamps L1 and L2 via the diodes D„ , I , _> -D_ » and D_- and if any of the lamps fails to 1a ⁷ 1b 2a 2b ^J be illuminated then it can be identified and replaced. Obviously, whilst Figure 1 illustrates the example with only two lamps, the arrangement of Figure 1 can be extended to any number of lamps and any failure can be easily identified for replacement.

The arrangement of Figure 1 replaces the prior art arrange¬ ment shown in Figure 1a, wherein the lamps L1 and L2 may be simultaneously energised in a test condition by means ^' of contacts C1 and C2 of a test relay R upon actuation of lamp test push-button T. However, with arrangements utilising the arrays, the relays and their moving contacts are subject to wear and possible failure to a much larger extent than with diodes and with large arrays of lamps-multiple relays would be required and such are considerably more expensive than diodes.

Coning now to the arrangement of Fig. 2, an alternative arrangement to that shown in Fig. 1 is shown, this time for testing relays R1 and R2, again normally operated by means of

switches S1 and S2 respectively, wherein in this case, instead of pairs of diodes connected to each test circuit, a full wave rectifier is provided for each pair of test circuits, connected as shown.

Turning now to Figures 3 _» 3-a and 3 ^" b _» a pair of capacitor split phase motors driven in parallel are shown, the motors K1 and M2 having respective capacitors C1 and C2 connected across their forward and reverse inputs. Each motor is provided with end-of-travel switches ET.. , ET^ -E p ' ^Sϊ 2b ^£θT ^-P-P^S their respective motors at an appropriate end-of-travel position in either a forward or backward direction.

In Fig. 3 _ι "the respective inputs of each motor are connected via a pair of diodes in parallel to an AC input via forward and reverse switches „ and T respectively thereby r - enabling the motors to be driven in parallel without the risk of capacitor generated feedback overriding the end-of-travel switches.

Fig. 3 illustrates a prior art arrangement of capacitor split phase motors driven in parallel conventionally via relays which achieve ^" the same degree of isolation between the motors to avoid capacitor feedback, but are open to the same disadvantages as previously described for the arrangements of Figures 1 and 2 due to "the lower reliability of relays and increased maintenance and cost involved when compared with diode arrangements for performing the same function. Figure 3b illustrates how capacitor feedback occurs if motors are driven directly in parallel without the use of relays or diodes to isolate the motors from one another and it can be seen that if the motors M ₁ and K_ are both driven in the forward direction by closing the switch S_,, if the motor M is. stopped by end-of-

J. I travel switch E..l3r which opens, since motor ϊl C_m is still running, a capacitor feedback signal is induced which is supplied to

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the motor M. via the closed end-of-travel switches E.., and

E_, and the capacitor C_ of motor M„ -and the end-of-travel switch 2b -.

E_ , and capacitor C,, thereby allowing motor K to run after the end-of-travel switch E.. has opend and damage to motor K _i can result. Thus, the need for isolation of the motors M_. and ML can be clearly seen.