Method for arc suppression in relay contacts

In a circuit having an electro-mechanical relay, the contacts of which are subject to arcing, bridging across the electro-mechanical relay in a manner configured to begin conducting electrical current around the electro-mechanical relay prior to closing the electro-mechanical relay and to continue conducting electrical power around the electro-mechanical relay for a predetermined time after the onset of separation of contacts of the electro-mechanical relay pursuant to discontinuance of current flow through the electro-mechanical relay. An optical coupler is provided to ascertain a current flow through the relay coil effected to close the electro-mechanical relay contacts, and activates a shunt device in bridging electrical current flow around the electro-mechanical relay. The shunt device is provided to be substantially non-load carrying while the electro-mechanical relay is closed. Utility is found in protecting electro-mechanical relay contacts against damage due to arcing.

FIELD OF THE INVENTION 
This invention relates to electrical circuits and, more particularly, to 
the prevention of damage to components employed in such electrical 
circuits. More specifically this invention relates to means for 
suppressing arcing across contacts within an electro-mechanical relay 
during opening and closing of the electro-mechanical relay to establish or 
discontinue electrical current flow within the circuit employing the 
relay. 
BACKGROUND OF THE INVENTION 
The use of electro-mechanical relays in electrical circuits for initiating 
and discontinuing the flow of electrical current through such a circuit is 
well-known. Electro-mechanical relays have established the capability for 
conducting relatively large quantities of electrical current while 
associating with conductance of these large currents a relatively minimal 
penalty in the form of a voltage drop across current conductors within the 
relay. This relatively low voltage drop is engendered, primarily, by dint 
of solid, generally metallic conductor to solid, generally metallic 
conductor within the electro-mechanical relay while the electro-mechanical 
relay is configured for conducting electrical current therethrough. 
Electro-mechanical relays, historically, have been subject to damage as a 
result of arcing of electrical current between current conductors within 
the relay as the conductors are separated to discontinue electrical 
current flow through the relay or as the conductors approach physical 
contact one with the other to initiate the flow of electrical current 
electrical through the relay. These typically metallic conductors subject 
to such arcing damage are frequently termed "contacts". Electro-mechanical 
relay contacts frequently sustain damage as a result of electrical arcing, 
and the damage functions typically to alter the geometry and metallic 
properties of the contacts, thereby introducing resistance to electrical 
current flow through the relay. This resistance to electrical flow can 
contribute to a more elevated voltage drop than would otherwise be 
desirable being associated with electrical current flow through the 
conductor and, unchecked, can result in further, progressive deterioration 
of the contact and eventually result in a failure of the relay by dint of 
excessive heat build-up associated with the passage of electrical current 
through the deteriorated contact(s). In voltage sensitive circuits, a 
significant voltage drop across an electro-mechanical relay in the circuit 
can adversely impact the performance of any sensitive circuitry relying 
upon a particular voltage being available from the relay where such 
available voltage is reduced by reason of elevated resistance in the relay 
associated with damaged contacts. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
for suppressing arcing within an electro-mechanical relay during the 
opening or closing of the electro-mechanical relay. More particularly, it 
is an object of the invention to provide a method for suppressing such 
arcing characterized by negligible power dissipation upon closure of the 
electro-mechanical relay to a full, electrically conductive mode and upon 
separation of the electromechanical relay contacts to place the relay in a 
non-conducting mode. 
Accordingly, in the present invention, wherein an electrical circuit 
includes an electro-mechanical relay activated by a flow of electrical 
current through an activating coil associated with and typically a 
component of the electro-mechanical relay to close the electro-mechanical 
relay for the transmission, from time to time, of electrical current 
therethrough or thereacross, and wherein electrical current carrying 
contacts within the electro-mechanical relay are subject to damage by dint 
of arcing of electrical current between the contacts upon opening or 
closing of the contacts during operation of the electro-mechanical relay, 
an arc suppressing means is provided in the circuit. In providing the arc 
suppressing means, the electro-mechanical relay is bridged by providing a 
solid state electrical switching means or shunt configured to carry 
electrical current around the electro-mechanical relay within the circuit 
and configured to be activated to conduct electrical current around the 
electro-mechanical relay by the application of a desired electrical signal 
to a sensing electrode associated with the solid state electrical 
switching means. 
A condition within the circuit enabling a flow of electrical current 
through the relay activating coil is detected, and upon detection, the 
desired electrical signal is applied to the sensing electrode of the solid 
state electrical switching means while the condition is detected. 
Application of the desired electrical signal to the sensing electrode of 
the solid state electrical switching means is continued for a desired time 
period following the discontinuance of the flow of electrical current 
through the activating coil. 
The solid state electrical switching means is configured to be possessed of 
a resistance to the passage of electrical current therethrough whereby 
during flow of electrical current through the electro-mechanical relay 
within the circuit, a flow of electrical current through the solid state 
electrical switching means results in negligible power dissipation 
internal to the switching means. 
The above and other features and advantages of the invention become more 
apparent when considered in light of a detailed description invention 
together with the drawing which follow, together forming a part of the 
specification.

BEST EMBODIMENT OF THE INVENTION 
Referring to the drawing, FIG. 1 depicts an electrical circuit 10. The 
electrical circuit includes a source of direct current (DC) power 12 and a 
source of elevated DC power 14. By a source of elevated DC power 14 what 
is meant is a DC power source supplying a DC power voltage in excess of 
the voltage available at the source of DC power 12. The extent of the 
excess of the DC power voltage supplied by the source of DC power 14 is 
primarily dependent upon the voltage requirements of the particular 
configuration of components within the electrical circuit 10 in order to 
enable operation of the electrical circuit 10. 
The electrical circuit 10 is configured for the application of an 
electrical current from the source of DC power 12 through a load 16, 
typically having an electrical resistance associated therewith, to a point 
of low reference voltage 18 within the circuit, that is, a path for the 
return of electrical current to the source of DC power 12. 
It should be understood that the load 16, while depicted in FIG. 1 as a 
resistor, can be any combination of electrical or electronic components 
configured to consume power available from the source of DC power 12 for 
purposes of performing a useful function or useful for work. By the term 
electrical component what is meant is electrically operated equipment; by 
the term electronic component what is meant is devices in which conduction 
is principally accomplished by electrons moving through a vacuum, gas, or 
semiconductor. 
In the circuit depicted in FIG. 1, the load 16 is contemplated as being an 
electrothermal de-icer or anti-icer positioned typically on or straddling 
a leading edge of an aircraft component for purposes of either de-icing 
the aircraft component or prevent the accumulation of ice upon the 
component. Such de-icers or anti-icers are well-known in the art of 
aircraft ice protection engineering and typically comprise electrical 
resistance elements in the form of metallic wires or ribbons embedded 
between plies of a supportive material, typically coated fabric and 
rubber, to define a structure typically laminatably applied to surfaces 
such as a leading edge of aircraft. Such a de-icing element is shown and 
described in U.S. Pat. No. 4,386,749 the specification of which is 
incorporated herein as if fully set forth herein. 
The circuit 10 includes an electromechanical relay 20 having a moveable 
contact 22 configured to bridge between stationary contacts 22', 22" to 
establish a flow of current from the source of DC power 12 to the point of 
low reference voltage 18 through the load 16 and the electro-mechanical 
relay 20. An electro- mechanical relay coil 24 is associated with the 
electro-mechanical relay configured upon application of electrical current 
through the relay coil to draw the moveable relay contact 22 into intimate 
contact with the stationary relay contacts 22', 22" to establish a flow of 
electrical current through the electro-mechanical relay contacts 22, 22', 
22". The act of drawing the moveable relay contact 22 into intimate 
physical contact with the stationary contacts 22', 22" is conventionally 
known as closing the relay. 
Conversely, the elimination of electrical current flow through the relay 
coil 24 functions to release the relay moveable contact 22 from intimate 
physical contact with the stationary contacts of 22', 22". Typically the 
moveable, relay contact 22 is spring or otherwise biased to becomes 
physically distanced from the stationary relay contacts 22', 22" rapidly 
upon discontinuance of the flow of electrical current through the relay 
coil 24. This distancing of the moveable relay contact 22 from the 
stationary contacts 22', 22" is known conventionally as opening the relay. 
A solid state switch 26 is provided within the circuit 10. The switch 26 is 
configured to permit a flow electrical current between the source of DC 
power 12 and the point of low reference voltage 18 through the relay coil 
24, closing the relay 20 by dint of movement of the moveable relay contact 
22 into contact with the stationary contacts 22', 22" to establish a flow 
of electrical current through the relay 20. In the embodiment of FIG. 1 it 
should be apparent that power to the relay coil 24 could be applied 
employing the switch 26 from a source other than the source of DC power 
12. Equally, the switch 26 could be of any suitable or conventional nature 
including manual or electro-mechanical switches. Accordingly, the switch 
26 is thereby configured to control electrical current flow through the 
load 16 to the point of low reference voltage 18. 
In the embodiment of the invention shown in FIG. 1, the switch 26 is a 
solid state device having a sensing electrode 28 and a pair of conducting 
electrodes 29, 30. The conducting electrodes 29, 30 are configured to 
conduct electricity through the switch 26 to the point of low reference 
voltage thereby establishing a current pathway through the relay coil 24 
from the source DC power 12 to activate the relay 20 by closing the 
moveable relay contact 22 against the stationary contacts 22', 22". The 
sensing electrode 28 is configured to receive an electrical signal. 
Receipt of an electrical signal at the sensing electrode 28 typically 
causes the solid state switch 26 to establish electrical current flow 
through the solid state switch 26 employing the electrodes 29, 30. 
A second solid state switching means or shunt 32 is provided having a 
sensing electrode 33 and current conducting electrodes 34, 35. The current 
conducting electrodes 34, 35 are positioned within the circuit whereby, 
with respect to a direction of current flow through the relay to the point 
of low reference voltage 18, the electrode 34 is connected to the circuit 
10 prior to the relay 20 and the electrode 35 is connected to the circuit 
10 subsequent to the relay 20. When the solid state switching shunt 32 is 
activated, electrical current can flow through the electrodes 34, 35 to 
bypass the relay 20 and establish a current flow from the source of DC 
power 12 through the load 16 to the point of low reference voltage 18. The 
sensing electrode 33 of the solid state switching means or shunt 32 is 
configured to respond to an electrical signal which signal is appropriate 
to the particular embodiment, that is, the electrical condition of the 
signal is capable of being changed to either enable or inhibit the passage 
of electrical current through the electrodes 34, 35 of the solid state 
switching means 32, typically between a 0 volts, 0 ampere condition and 
another voltage/amperage condition. 
Typically the solid state switching means or shunt 32 is a suitable or 
conventional current conducting solid state device configured to be 
activated upon receipt of an altered electrical signal at a sensing 
electrode and to apply a current through the switching means or shunt 32 
by the electrodes 34, 35. Preferably the switching means or shunt 32 is an 
FET transistor. 
A means 37 is provided in the circuit 10 of FIG. 1 for detecting the onset 
of a flow of electrical current through the coil 24 by activation 
concurrently therewith and is configured for altering an electrical signal 
applied to the sensing electrode 33 while electrical current flows through 
the relay coil 24, that is an electrical signal altered from the 
electrical signal, if any, applied to the sensing electrode 33 while 
electrical current is not being applied to the relay coil 24. In preferred 
embodiments, this means 37 is a so-called optical coupler. Suitable 
optical couplers for practicing the invention are readily commercially 
available. 
Also known as optoisolators, optical isolators, optically coupled 
isolators, optocouplers, optoelectronic isolators, photocouplers, or 
photoisolators, these optical couplers are characterized by a light 
emitting diode (LED) energized by electrical current passed through the 
LED, optically coupled to a light sensitive output diode, transistor, 
silicone controlled rectifier or other photo detector. 
An optical coupler such as the means 37 in FIG. 1 responds to a flow of 
electrical current through the LED 38 to provide an optical signal which 
activates an opto detector 34 to provide an electrical signal altered from 
the electrical signal, if any, provided by the optical coupler while 
electrical current is not flowing through the relay coil 24 and LED. In 
the embodiment of FIG. 1, the switching means 32 requires an electrical 
potential sensed at the electrode 33 of a greater voltage than that 
available from the source of DC power 12 as provided to the electrode 34 
in the circuit 10. Accordingly, a source of elevated DC power 14 is made 
available to the optical coupler 37 enabling the optical coupler 37 to, in 
conjunction with an electrical current flow through the relay coil 24, 
apply an elevated voltage to the sensing electrode 33 in excess of that 
available at the electrode 34 from the source of DC power 12. 
A resistor 44 is provided to protect the optical coupler 37 against exces 
current flow. It should be apparent that while electrical current flows 
through the relay coil 24 as enabled by activation of the switch 26, such 
activation will also cause a current flow through the resistor 44, the LED 
of the optical coupler 37, and then through the diode 46. When the solid 
state switch 26 is opened, electrical flow is also discontinued through 
the diode 46 to the point of low reference voltage 18. 
It is desirable that the shunt or solid state switching means 32 be 
activated for a time period extending beyond the point in time at which 
electrical current flow through the relay coil 24 is terminated. 
Continuing electrical current flow through the shunt 32 facilitates an 
elimination of arcing as the moveable relay contact 22 disengages from the 
stationary contacts 22', 22" as the relay coil 24 ceases to be energized. 
Accordingly, a capacitor 48 is provided which enables continued electrical 
current flow through the resistor 44 and the optical coupler 37 to charge 
the capacitor 48 after termination of electrical current flow through the 
diode 46 and the solid state switch 26 as the solid state switch 26 opens 
to terminate electrical current flow through the relay coil 24. The 
capacitor 48 is sized to require a charge time sufficient to maintain 
electrical current flow through the LED portion of the optical coupler 37 
and therefore to maintain the desired altered electrical signal at the 
sensing electrode 33 for a time period sufficient to assure that the 
moveable relay contact 22 has sufficiently disengaged from the stationary 
contacts to 22', 22" to assure a minimization or hopefully a total 
elimination of arcing associated with such disengagement. As the capacitor 
48 becomes fully charged, electrical current flow through the optical 
coupler 37 drops to an extent where the desired altered electrical signal 
is no longer made available by the optical coupler 37 to the sensing 
electrode 33 of the switching means or shunt 32 and electrical conductance 
through the shunt 32 is thereby terminated. 
It should be apparent, in operation of the circuit 10 shown and described 
in FIG. 1, that the switching means or shunt 32 also provides a fail-safe 
backup function to the mechanical relay 20. In the event that the relay 
coil 24 becomes defective or the mechanical relay, for any reason, fails 
to close upon activation of the relay coil 24, while the switch 26 is 
activated enabling the flow of electrical current therethrough, electrical 
current will flow through the resistor 44, the optical coupler 37, and the 
diode 46 to provide the desired altered electrical signal at the sensing 
electrode 33 of the shunt 32 and thereby engage the shunt to provide an 
electrical flow through the load 16. 
The switching means 32 is provided to be possessed of a resistance to the 
flow of electrical current therethrough in a quantity sufficient to 
activate the load 16 whereby, while the relay contacts 22, 22', 22" are 
engaged, a sufficiently low value of electrical current flows through the 
switching means 32 via the electrodes 34, 35 to assure that a negligible 
power dissipation occurs from within the switch as a result of the 
switching means 32 being present in the circuit 10. By negligible power 
dissipation, what is meant is that the switching means 32 does not require 
protection by a heat dissipating device such as a heat sink. Heat 
protection is typically not required when a temperature rise associated 
with operation of the shunt 32 over an extended time period does not 
exceed about 20.degree. C. in excess of a temperature associated with the 
circuit 10 while no current flows therethrough. More typically this 
limiting temperature rise is associated with 8.degree. C. maximum. 
In use, DC power is supplied from the source of DC power 12 and elevated DC 
power is supplied from the source of elevated DC power 14. The switch 26 
is closed by application of an electrical signal to the electrode 28 to 
initiate electrical current flow through the relay coil 24 coincidentally 
with electrical current flow through the resistor 44, the LED portion of 
the optical coupler 37, and the diode 46. Electrical current flow through 
the relay coil 24 activates the electro-mechanical relay 20 by closing the 
contacts 22, 22', 22"; however before the moveable relay contact 22 can 
close, a result of the time delay inherent in such a mechanical closing 
function, the solid state switching means 32 initiates current flow around 
the electro-mechanical 20 to an extent sufficient whereby, as the moveable 
relay contact 22 closes against the stationary contacts 22', 22", arcing 
is substantially minimized or eliminated between such contacts. 
Once the relay contacts 22, 22', 22" close, by dint of a resistance 
associated with the passage of electrical current through the solid state 
switching means 32, the preponderance of the electrical current flowing 
from the source of DC power 12 through the load 16 passes through the 
relay 20 and not the shunt 32. Accordingly, the solid state shunt 32 
itself does not dissipate meaningful quantities of power. As the switch 26 
disengages, and the moveable relay contact 22 begins to disengage from the 
stationary contacts 22', 22", the capacitor 48 functions to hold the 
optical coupler 37 in the circuit by continuing the flow of electrical 
current through the LED portion thereof for sufficient time to provide the 
desired altered electrical signal to the sensing electrode 33 of the shunt 
32 and thereby hold the shunt 32 in the circuit sufficiently long to 
conduct electrical current around the electro-mechanical 20, and 
substantially reduce or eliminate arcing as the contacts 22, 22', 22" 
separate. 
While a preferred embodiment of the invention has been shown and described 
in detail, it should be apparent that various modifications may be made 
thereto without departing from the scope of the claims that follow.