Abstract:
A low energy electromagnetic relay and method of reducing power consumption in electromagnetic relays. The electromagnetic relay includes an electrical coil having a first end connected to a first contact and a second end connected to first side of a normally closed switch, a second side of the switch connected to a second contact; a resistor connected between the first end of the coil and the second contact; and an armature configured to move to an actuated position and open the first switch when power is applied across the first and the second contacts.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of electromagnetic relays; more specifically, it relates to electromagnetic relays with reduced power consumption and methods of reducing power consumption in electromagnetic relays. 
       BACKGROUND 
       [0002]    The coil of electromagnetic relays can consume relatively large amounts of power when powered. Various methods currently employed to reduce power consumption are mechanically complex or require complex power control circuits external to the relay. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove. 
       SUMMARY 
       [0003]    A first aspect of the present invention is a device, comprising: an electrical coil having a first end connected to a first contact and a second end connected to first side of a normally closed switch, a second side of the switch connected to a second contact; a resistor connected between the first end of the coil and the second contact; and an armature configured to move to an actuated position and open the first switch when power is applied across the first and the second contacts. 
         [0004]    A second aspect of the present invention is a method, comprising: applying power to a coil of an electro-mechanical actuator through a normally closed switch; the actuator opening the normally closed switch so all power to the coil is supplied through a resistor connected between the normally closed switch and the coil; maintaining the switch in the open position as long as power is applied to the coil through the resistor; and returning the switch to the closed position when power is turned off to the coil. 
         [0005]    These and other aspects of the invention are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0007]      FIG. 1A  is a side view partly in section illustrating an exemplary electromagnetic relay assembly according to an embodiment of the present invention; 
           [0008]      FIG. 1B  is a top view partly in section of the exemplary electromagnetic relay assembly of  FIG. 1A ; 
           [0009]      FIG. 1C  is an end view partly in section through line  1 C- 1 C of  FIG. 1A  of the exemplary electromagnetic relay assembly of  FIG. 1A ; 
           [0010]      FIG. 1D  is an end view partly in section of the exemplary electromagnetic relay assembly of  FIG. 1A ; 
           [0011]      FIG. 1E  illustrates the functional switch of the exemplary electromagnetic relay assembly of  FIG. 1A ; 
           [0012]      FIG. 2A  is a schematic circuit diagram of the exemplary electromagnetic relay of  FIGS. 1A through 1E  with no power applied to the coil of the relay; 
           [0013]      FIG. 2B  is a schematic circuit diagram of the exemplary electromagnetic relay of  FIGS. 1A through 1E  while power is applied to the coil of the relay; and 
           [0014]      FIG. 3  illustrates exemplary switchable elements that may be used in electromagnetic relays according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Electromagnetic relays of the embodiments of the present invention utilize a resistor in series with the coil of the relay and a normally closed switch in parallel with the resistor to reduce power consumption of the coil when the coil is powered. Initially power is applied to the coil both directly and also through the resistor. This opens the switch, so power to the coil is then supplied only through the resistor. When power is turned off, the switch resets. 
         [0016]      FIG. 1A  is a side view partly in section illustrating an exemplary electromagnetic relay assembly according to an embodiment of the present invention. In  FIG. 1A , a relay assembly  100  includes a coil assembly  105 , an armature  110  (which can pivot about a pivot  115 ), a first switch  120 , a resistor  125  and a spring  130 . First switch  120  includes a electrically conductive and rigid first contact strip  135  having an electrically conductive first contact  140  physically and electrically attached and an electrically conductive second contact strip  145  having rigid portion  150  and a flexible portion  155 . An electrically conductive second contact is  160  is electrically and physically attached to flexible portion  155 . Second contact  160  is positioned opposite first contact  140 . Second contact strip  145  and a third contact strip  165  are the power supply inputs to coil assembly  105 . First switch  120  is a normally closed (NC) switch and  FIG. 1A  depicts relay assembly  105  in the off state with contacts  140  and  160  in physical and electrical contact. Relay assembly also includes a second switch  170 , which is illustrated in  FIGS. 1A ,  1 B and  1 E and described in detail infra with respect to  FIG. 1E .  FIG. 1B  is a top view partly in section of the exemplary electromagnetic relay assembly of  FIG. 1A . 
         [0017]    First, second, third, fourth and fifth contact strips  135 ,  145 ,  165 ,  175  and  190  coil assembly  105  and armature  110  are held in position in a housing  200  by dielectric supports  195 A and  195 B. Second, third, fourth and fifth contact strips,  145 ,  165 ,  175  and  190  extend through a dielectric base  205  which seals (optionally hermetically seals) the relay assembly  100 . First contact strip  135  is connected directly (by electrically conductive wire  230 ) to a first end of an electrically conductive wire coil  210  wound around a dielectric tube containing a core  215 . (If an insulated wire is used to make coil  210 , dielectric tube may be eliminated.) Third contact strip  165  is electrically connected to a second and opposite end of coil  210 . Resistor  125  is electrically connected between second contact strip  145  and the first end of coil  210 . In one example, core  215 A is formed from a ferromagnetic material. Suitable resistor types for resistor  125  include but are not limited to carbon composite resistors, thin film resistors and wire-wound resistors. 
         [0018]    When power is supplied across second and third contact strips  145  and  165  coil  210  current flow is through contract strip  145 , contact  160 , contact  140  and contact strip  135  thereby magnetizing core  215  and attracting button  220  to a protruding portion  215 A of core  215  causing armature  110  to rotate in the counter-clockwise direction. Rotation of armature  110  causes dielectric button  225  to physically contact and push on flexible portion  155  of contact strip  145  forcing contacts  140  and  160  apart as well as compressing spring  130 . Note, in the example of  FIG. 1 , contacts  180  and  185  will be forced together into physical and electrical contact. When contacts  140  and  160  are forced apart, current flow is only though contact strip  145  and resistor  125  to coil  210 . The resistance value of resistor  125  is selected so sufficient current is supplied to coil  210  to keep button  220  attracted to core  215 A and contacts  140  and  160  apart. Because the power supply voltage to coil  210  now passes through resistor  125 , the amount of current through coil  210  is reduced thus saving power. When power to second and third contact strips  145  and  165  are turned off, spring  130  rotates armature  110  clockwise resetting first and second switches  120  and  170  to their original states. 
         [0019]    When relay assembly  100  is designed for a direct current (DC) power supply, optional diode  240  may be electrically connected between the first and of coil  210  and second contact strip  165  for arc suppression across first and second contacts  140  and  160 . (See also  FIGS. 2A and 2B .) When relay assembly  100  is designed for an alternating current (AC) power supply, no diode is required. 
         [0020]      FIG. 1B  is a top view partly in section of the exemplary electromagnetic relay assembly of  FIG. 1A .  FIG. 1B  illustrates that switches  120  and  170  are located next to one another. The straight dashed lines illustrate the ends of first contact strip  135  and the dashed circles the first, second, third and fourth contacts  140 ,  160 ,  180  and  185 . 
         [0021]      FIG. 1C  is an end view partly in section through line  1 C- 1 C of  FIG. 1A  of the exemplary electromagnetic relay assembly of  FIG. 1A . In  FIG. 1C , the relative positions of resistor  125 , first, second, third, fourth and fifth contact strips  135 ,  145 ,  165 ,  175  and  190  and optional diode  240  within housing  200  are illustrated. 
         [0022]      FIG. 1D  is an end view partly in section of the exemplary electromagnetic relay assembly of  FIG. 1A . In  FIG. 1D , the relative positions of second, third, fourth and fifth contact strips  145 ,  165 ,  175  and  190  external to housing  200 . 
         [0023]      FIG. 1E  illustrates the functional switch of the exemplary electromagnetic relay assembly of  FIG. 1A . Second switch  170  includes a electrically conductive and rigid fourth contact strip  175  having an electrically conductive third contact  180  physically and electrically attached and an electrically conductive fifth contact strip  190  (see also  FIG. 1E ) having rigid portion  235  and a flexible portion  240 . An electrically conductive fourth contact is  185  is physically and electrically attached to flexible portion  240 . Fourth contact  185  is positioned opposite third contact  180 . Fourth contact strip  175  and a fifth contact strip  190  are switch inputs to switch  170 . Second switch  170  is a normally open (NO) switch. 
         [0024]      FIG. 2A  is a schematic circuit diagram of the exemplary electromagnetic relay of  FIGS. 1A through 1E  with no power applied to the coil of the relay. In  FIG. 2A , an electromagnetic relay  100 A includes a solenoid section  255  and a switch section  260 . Solenoid section  255  includes resistor R, optional diode D, coil L, a NC single-pole single throw (SPST) switch SW 1  and power terminals P 1  and P 2 . The coil L, the heavy vertical line and the horizontal small dashed line through switches SW 1  and SW 2  represent an electro-mechanical actuator. Power terminal P 1  is electrically connected to a first end of resistor R and to a first terminal of switch SW 1 . Power terminal P 2  is electrically connected to a first end of coil L. The second end of resistor R, the second end of coil L and the second terminal of SW 1  are electrically connected to each other. Switch section  260  includes a NO SPST switch SW 2 . Resistor R is electrically connected in parallel with switch SW 1 . Switch SW 2  includes an input terminal A and an output terminal B. Switches SW 1  and SW 2  are ganged together so both switches change state when power is applied to coil L. The type of switch illustrated for switch SW 2  is exemplary. If the power supply is DC, then P 1  is electrically connected to the positive side of the power supply and P 2  is electrically connected to the negative side of the power supply. The anode of an optional diode D is electrically connected to terminal P 2  and the cathode of diode D is electrically connected to the second terminal of switch SW 2 . Diode D is electrically connected in parallel with coil L. 
         [0025]    With no power applied SW 1  is closed and switch SW 2  is open. When power is applied to terminals P 1  and P 2  current flow is instantaneously through coil L and switch SW 1 . If the resistance of coil L is Rc then the current through coil L is given by Ii=V/Rc where Ii is the initial current through coil L and V is the power supply voltage. Thus  FIG. 2A  also illustrates the state of relay  100 A with no power applied and immediately (or instantaneously) after power is supplied to the coil of the relay. However, since applying power to the coil, causes SW 1  to change state (from closed to open) the maintaining current flow Im through coil L is determined from  FIG. 2B . 
         [0026]      FIG. 2B  is a schematic circuit diagram of the exemplary electromagnetic relay of  FIGS. 1A through 1E  while power is applied to the coil of the relay. The difference between  FIG. 2A  and  FIG. 2B  is SW 1  is open in  FIG. 2B  (it was closed in  FIG. 2A ) and SW 2  is closed in  FIG. 2B  (it was opened in  FIG. 2A ). If the resistance of resistor R is Rr then the current through coil L is given by Im=V/(Rc+Rr) where Im is the maintaining current through coil L and V is the power supply voltage since the resistor R and coil L are in series. Comparing the equations for Ii and Im it is clear that Im must be less than Ii. It should also be understood that, in general, a higher voltage must be applied to coil L to initially activate the solenoid then that current required to maintain the solenoid in the activated state. 
         [0027]    Taking an example, assume a relay designed for a 12 volt DC power supply having a 500 ohm coil and a 250 ohm resistor. It will take about 10 volts to activate the solenoid initially. After SW 1  opens it will take about six to about eight volts to maintain the solenoid in the active state. Ii=12 v/500 ohm=24 ma. Im=12 v/(500 ohm+250 ohm)=16 ma which is about a 30% savings on power consumption. In one example, it is preferred that electromagnetic relays according to embodiments of the present invention have a resistor whose resistance that is about ⅓ the resistance of the coil. In one example, it is preferred that electromagnetic relays according to embodiments of the have a resistor whose resistance is between about ⅕ and about ⅖ the resistance of the coil. When the resistance of the resistor is less than about ⅕ that of the coil, not very much power is saved. When the resistance of the resistor is greater than about ⅖ that of the coil, the solenoid is likely to “chatter” because the maintenance voltage being dropped across the coil is insufficient to generate a strong enough magnetic field in the core to overcome the force of the spring. Chatter occurs when switch SW 1  continuously cycles between closed and open while power is supplied to the solenoid section. 
         [0028]    In summary the operation of the solenoid sections of electromagnetic relays according to embodiments of the present invention is as follows:
       1. Power is applied to the coil through the normally closed switch.   2. The powered coil electro-mechanically opens the normally closed switch so all power to the coil is then supplied through the resistor connected to the hot side of the normally closed switch.   3. The switch is electro-mechanically maintained in the open state (e.g., latched) as long as power is applied.   4. When power is turned off, the normally closed switch mechanically returns to the closed state.       
 
         [0033]      FIG. 3  illustrates exemplary switchable elements that may be used in electromagnetic relays according to embodiments of the present invention.  FIG. 3  illustrates seven types of switches that may be used for SW 2  of switch section  260  of  FIGS. 2A and 2B . A first type of switch is a NO SPST switch having an input A and an output B. This is the type of switch illustrated in  FIGS. 1A ,  1 E,  2 A and  2 B. A second type of switch is a NC SPST witch having an input A and an output B. A third type of switch is a single pole double throw switch having an input C, a first output A and a second output B. A fourth type of switch is a NO double pole single throw (DPST) switch having a first input A 1  and corresponding first output B 1  and a second input A 2  and corresponding second output B 2 . A fifth type of switch is a NC DPST switch having a first input A 1  and corresponding first output B 1  and a second input A 2  and corresponding second output B 2 . A sixth type of switch is a NO/NC DPST switch having a first input A 1  and corresponding first output B 1  and a second input A 2  and corresponding second output B 2 . A seventh type of switch is a double pole double throw (DPDT) switch having an first input C 1 , corresponding first and second outputs A 1  and B 1  and n second input C 2 , corresponding third and fourth outputs A 2  and B 2 . Double throw switches may come in break-before-make or make-before-break types. When the SPDT switch illustrated is a make-before-break switch, input C is connected to output B before being disconnected from output A. When the SPDT switch illustrated is a break-before-make switch, input C is disconnected from output A before being connected to output B. Similarly, each side of the DPDT switch illustrated may be independently a break-before-make or make-before-break type. 
         [0034]    Thus the embodiments of the present invention provide electromagnetic relays with reduced power consumption and methods of reducing power consumption in electromagnetic relays. 
         [0035]    The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.