US 3074013 A
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Jan. 15, 1963 R. N. BOWDEN DEVICE FOR INDICATING SHORT CIRCUITS Filed Sept. 23, 1958 BATTERY BATTERY United States Patent Gfifice 3,074,613 Patented Jan. 15, 1963 3,074,013 DEVHIE FGR WDICATING SHORT CIRCUITS Roy N. Eowden, 143 Washington St, Morristown, N1, Filed Sept. 23, 1958, Ser. No. 762,819 2 (Jiaims. (31. 324-51 This invention relates to a safety device for electrical lighting systems and more particularly to a device for locating a short circuit in the lighting system of a vehicle, which device also is useful for effecting a correction of certain types of short circuits and also for providing a warning that a short circuit exists.
Although the device is adaptable for use in various specific applications, it will be described herein with reference to the lighting system of an automobile.
In the lighting system of an automobile, a single lead wire connects one side of each lamp filament to the positive terminal of the battery. The other side of each lamp filament is grounded to the chassis as is the negative terminal of the battery. The electrical circuit between the battery and a selected group of lamp filaments, such as the tail lights, headlights, etc., is completed upon closure of a manually operable switch connected in the lead wire. Due to factors such as vibration, accidents, etc., the insulation on the lead wire often is damaged and the bare lead wire makes contact with the chassis, resulting in a short circuit. Under such condition, an abnormally large current flows through the lead wire between the battery and the point at which the lead wire is grounded to the chassis, resulting in a charring of the insulation which necessitates replacement of the lead wire. In fact, the spark resulting from the grounding of the lead wire often ignites flammable material resulting in a fire. To prevent such dangerous conditions, a fuse, or a circuit breaker, is incorporated in the lighting system to open the circuit to the battery When the current in the lead wire reaches a preselected magnitude. Although such safety devices serve a useful purpose, there are other troublesome aspects of a short circuit, or ground, developing in the lighting system of an automobile. Specifically, once the fuse burns out, or the breaker opens, the automobile is without lights and, therefore, the vehicle can not safely be driven at night to a ganage or service station. Further, in many instances, it is difficult and time consuming for the service man to locate the point where the lead wire actually is in electrical contact with the chassis. Still further, if the short circuit occurs in the lead wire at a point between the battery and the fuse (or breaker) such safety device is ineffective and there results a condition conducive to the starting of a fire. The device described herein, which may be used in conjunction with, or in place of, the fuse or breaker, affords a scope of protection beyond that provided by the fuse and such device also facilitates the location and correction of the short circuit.
An object of this invention is the provision of a simple and effective device for providing a warning when a short circuit develops in an electrical lighting system.
An object of this invention is the provision of a device which facilitates the tracing of a short circuit in an electrical lighting system.
An object of this invention is the provision of a device useful for correcting certain short circuits in an electrical lighting system.
An object of this invention is the provision of a device adapted for more or less permanent installation in the lighting circuit of a vehicle, said device providing a visual warning when a ground develops in a lead connected to a single light bulb and maintaining circuit continuity to other light bulbs in the lighting circuit.
These and other objects and advantages will become apparent from the following detailed description when taken with the accompanying drawings illustrating several embodiments of the invention. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.
In the drawings wherein like reference characters denote like parts in the several views:
FIGURE 1 is a simplified diagram of the electrical headlight system of an automobile;
FIGURE 2 is similar to FIGURE 1 and showing my device as used to locate and possibly correct a. short circuit in such lighting system; and
FIGURE 3 is a diagram showing the device connected to provide a warning when a short circuit develops in the lighting system.
Referring specifically to FIGURE 1, a typical headlight system of an automobile comprises the two headlight bulb ltl, 10, disposed in suitable sockets through which one side of each bulb-filament is grounded to the automobile body. The other side of each filament is connected to the battery 11 through a switch 12 and an automatic circuit-breaker, illustrated as a fuse 13, the latter being supported in conventional terminals or fuse clips 14. Closure of the switch completes the electrical circuit between the battery and the bulbs. In the event a short circuit develops anywhere in the leads 15, 16, 17, 18, as, for example, at one or the other of the points identified S, S S closure of the switch 12 results in an opening of the circuit through or a blowing out of the fuse l3 acting as an automatic circuit-breakers, since the current-limiting resistance of the bulbs 10, 10 is no longer effective in the system. Generally, such short circuit develops at a point where the lead wire is mechanically secured to the body of the automobile or at a point where the insulation is damaged by vibration, thereby permitting the lead wire to contact the body.
Although FIGURE 1 includes only the headlight lamps 1t), lit, those skilled in this art will know that other vehicle lights, such as tail lights, are similarly protected by the fuse 13*. As is clear from FIGURE 1, once the fuse is blown, the vehicle is without lights. If the short circuit develops when the car is being driven at night, the sudden loss of headlights is dangerous to a degree depending upon the genenal visibility and the speed at which the vehicle is tnaveling Also, the vehicle cannot safely be driven to a service station. Further, as is apparent from FIGURE 1, if the ground develops in the lead 19, between the battery and the fuse, the headlights may go out completely or burn very dimly. If such short circuit develops at a time when the lights are off, the battery may become discharged and/or the hot lead 19 may cause a fire. In either case, the operator is not aware of actually what happened. In any event, in modern vehicles, it is becoming increasingly difficult to locate the precise point of the short circuit within a reasonable time.
FIGURE 2 illustrates the use of my device to facilitate the location of a short circuit and to correct certain types of short circuits without disturbing the wiring. The device comprises a plurality of lamp bulbs identified by the nrunerals 20 to 25, inclusive, carried by a suitable housing 26 in such manner that the lamps are visible to the operator of the device. These lamps preferably are 6 volt automobile bulbs of the double filament type with the filaments of each bulb connected in parallel. To facilitate replacement of burned out or otherwise defective bulbs, each bulb may be carried in an individual socket, as is well known. A three-pole, double throw switch 27 is operable to one position when the device is used for locating a short circuit in a vehicle having a 6 volt battery and to another position to condition the device for operation on a 12 volt system.
Assuming now that a short circuit is suspected to exist in a 6 volt system the switch 27 is thrown to the 6 volt position and the device is connected across the fuse clips 14 by means of relatively heavy cables 28. Such cables may be provided with alligator type clips for this purpose. The mechanic then closes switch 20 which connects the test lamp 29 into the electrical circuit in place of the burned-out, or removed fuse. This places substantially the full battery voltage across the test lamp 20, except for the voltage drop in the leads and across the ground S. If the test lamp lights up brightly, it is known that a short circuit does in fact exist. If, however, the test lamp only glows dimly, the test may not be conclusive since the test lamp is in series with both headlight lamps and all three of these lamps may have somewhat les than /2 the battery voltage impressed thereacross. The operator then closes the test switches 21 and 22' which connect the test lamps 21 and 22 in parallel with the test lamp 20. The resistance now introduced into the lighting circuit by the test device is relatively low compared to that of the headlight lamps 10, 10. If there is no shortcircuit in the system, the voltage across the test set is too low to cause the test lamps to light up perceptibly whereas the voltage across the headlight lamp is only a little lower than normal and these lamp will burn at almost full brilliance. However, if a ground exists, as, for example. at the point S, substantially the full battery voltage is applied across each of the test lamps whereupon these lamps burn brilliantly. I
In some cases, the ground is intermittent. In this case the mechanic leaves the test device connected into the circuit as described, (with the test switches 2b, 21 and 22 closed) and drives the car over relatively rough terrain. When the test lamps remain energized, a heavy current flows through the lead wires to the ground point S. In fact, the current flow, using 3, 32 candle-power test lamps each with double filaments, normally is suflicient to heat the test leads significantly. Thus, the mechanic need merely run his fingers along the lead wire until he comes to a cold portion of wire. The transition from hot to cold occurs at the ground point S.
Further, it often happens that a sliver of metal protruding from the body or chassis punctures the insulation of the lead wire causing a ground. In such case, the heavy current caused to flow through the lead wire by the test device is often sufficient to burn out the metal sliver, thereby correcting the difficulty.
From the description given to this point, it is apparent that my test device serves several purposes, namely, to provide a visual indication when a short circuit exists, to provide a closed electrical circuit of a selected low re sistance value so as to heat the lead wires to facilitate loeating the precise point of the short circuit, and to burn out and correct certain types of short circuits.
When testing a 12 volt lighting system, the switch 27 is closed in the 12 volt position. This connects the test lamps 23, 24, 25 individually in serie with the test larnps 22, 21 and 20, respectively, and the test device is used as described hereinabove.
The advantage of using double filament lamps in the test device lies in the fact that both filaments of a lamp are unlikely to be burned out or damaged simultaneously so that the operator cannot be misled. Also, lamp filaments have a relatively low resistance when cold, and the resistance increases substantially when hot. Thus, in the case of a partial, or incomplete short circuit, the voltage drop across the test device is very low so that a maximum current momentarily flows through the lead wires and across the short circuit point, thereby rendering such point of a more permanent character facilitating the location thereof. Conversely, in the case of a good short circuit, or one rendered more permanent, as just mentioned, the application of substantially full battery voltage across the test device raises the temperature of the test lamps to the point of incandencence thereby increasing the effective resistance and limiting the current drain from the battery.
My test device is also useful for more or less permanent connection in the lighting circuit to serve as a warning and safety device. Such arrangement is illustrated in FIGURE 3. In this case, the number of bulbs incorporated in the device is such that the resistance across the terminals T is very low compared to that of the headlight lamps 10, 19'. Although only three bulbs are shown in FIGURE 3, additional bulbs or resistors may be incorporated therein all bulbs and resistors being connected in parallel. In any event, it is preferable that the total resistance of the device 26 be about to that of the headlight bulbs 14 10. Under such condition, the voltage drop across the terminals T, upon closure of the switch 12,, is only .3 to .6 volt so that the headlight lamps normally burn at substantially full brilliance. The device 26' replaces the conventional fuse and may be insorted into the main line at any point although I prefer to connect the device between the battery and the light switch 12. The leads 33 preferably are of a heavier gauge than the lighting circuit wires in order to carry relatively large currents and these leads are covered with high quality insulation to eliminate the possibility of grounding. The device 26 may be disposed under the dashboard of the vehicle, or other suitable area, so that the operator can see when the lamps 3t), 31, 32 are illuminated.
In the event a ground develops in the main lead wire, as at the point S, the lamps of the device 26' will light up brightly, as has already been described. In such case, the vehicle is Without headlights but the operator knows why. However, when a ground develops in a branch lead, as at the point S, in the lead 17, the headlight bulb 10 is shorted out of the circuit, the voltage increases across the terminals T and the lamps 3t 31, 32 light up. The circuit to the battery is not opened, as in the case of a fuse, and under certain conditions, the headlight lamp It) will remain lighted at a level which will permit the vehicle to be driven to a service station. The level to which the bulb 10' will light up depends upon the relative resistance of the branch lead 17 between the main lead wire and the ground point S Obviously, if the point S is proximate to the joint between the main lead wire 16, both of the lamps 10, 10 will be shorted out of the circuit. More often, however, the ground point S occurs at the headlight, in which case the resistance of the branch leads 17 and 18 approaches that of the device 26' and the non-grounded bulb 10' will produce a useful level of illumination.
Having now described my invention in detail, it will be apparent that the net elfective resistance of my device will depend upon the number and rating of the bulbs used in a particular vehicle. Since the lighting systems of modern vehicles are fairly well standardized, particularly the headlight systems of cars, this presents no particular problem. The effective resistance of the device must be of a relatively low order to permit the flow of sufficient current to heat the lead wires when the device is used to locate a ground point. In the use of the device for safety and warning purposes, its resistance must be of a still lower order, so that the headlight lamps normally will burn at substantially full brilliance. These resistance parameters can readily be calculated. It is preferable that the device incorporate at least two single filament bulbs or a single, double filament bulb so that the device is not rendered inoperative for the intended purposes upon the burning out of a filament.
What I desire to protect by Letters Patent of the United States is set forth in the following claims.
1. A device for connection into the main lead of a vehicle lighting system to complete the circuit between a battery and the vehicle light bulbs, said device comprising a pair ofterminals; a first group of resistance elements at least one of which is an incandescent lamp filament, a second group of resistance elements; a switch operable to a first position and to .a second position; a lead connecting one side of each element of the first group to one of said terminals; a lead connecting one side of each element in the second group to the other of said terminals; circuit elements connecting the other side of the elements of the first group to the said other terminal when the switch is in the first position; leads connecting the other side of individual elements in the first group to the corresponding side of individual elements in the second group when the switch is in the second posi tion.
2. The invention as recited in claim 1, including indi- References Cited in the file of this patent vidual switches inserted between each of the elements of 5 2,447,736
the first group and the lead that is connected to the said one terminal.
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