II. TECHNICAL FIELD

This invention relates to safety booster cables that only operate when the correct polarity connection is achieved, and more particularly, to such cables that include a time delay after making the physical connection for the electrical connection to be operative.

III. BACKGROUND ART

In the present patent application, a booster cable is disclosed that operates only when the correct polarity connection is observed in the connection of the electrodes of a D.C. source (a battery or generator) to a receiving battery as disclosed and claimed in U.S. patent application serial No. 609,030 filed on May 10, 1984, which is hereby incorporated by reference. However, it had the inherent inconvenience of generating sparks usually during the first few moments when making the initial connection. This happens because the user needs some time to make a solid physical connection with the alligator clips. There are some applications where this inconvenience may become a fatal problem, namely, with flammable atmospheres. This application discloses and claims the subject matter in said U.S. application and further

includes features and improvements not disclosed there. The present invention solves the problem by providing a time delay to the operation of the safety booster cables claimed in the above referenced parent application.

IV. SUMMARY OF THE INVENTION

It is the main object of the present invention to provide safety booster cables that waits a reasonable amount of time after making the initial physical connection before becoming electrically operative.

It is yet another object of the present invention to provide such a device that is inexpensive to manufacture and maintain while retaining its effectiveness.

Further objects of the invention will be brought out in the following part of the specification, wherein detailed description is for the purpose of fully disclosing the invention without placing limitations thereon.

V. BRIEF DESCRIPTION OF THE DRAWINGS

With the above and other related objects in view, the invention consists in the details of construction and combination of parts as will be more fully understood from the

following description, when read in conjunction with the accompanying drawings in which:

Figure 1 is a schematic diagram representing the safety booster cables with the time delay circuit utilized in the preferred embodiment.

Figure 2 is a representation of the safety booster cables with the circuit shown in Fig. 1 contained inside a protective box.

VI. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to Figs. 1 and 2, where the present invention is generally referred to with numeral 10, it can be seen that the safety booster cable assembly 10 includes negative cable members 31 and 41 that are electrically connected together and typically to ground. Two positive cable members, 32 and 42, are electrically connected together through the normally open contact 61 of relay 60.

Cable members 31; 32; 41 and 42 are terminated with conventional alligator clips 50 at their ends. As in any other conventional booster cable pair, like electrodes are connected to each other. For the purposes of explaining its operation, cable member 32 is connected to the positive electrode of the D.C. source (a battery or D.C. generator)

providing the electricity and cable member 42 is connected to the positive end of the battery receiving the electricity. As pointed out above, the connection between cable members 32 and 42 is interrupted by normally open relay contact 61. The negative electrodes of the source and receiving battery are connected together directly, and usually to ground. In a conventional booster cable pair, and even in the cable pair disclosed and claimed in the above referenced parent application, the user tries to achieve a solid physical connection or engagement to the respective electrodes. However, the creation of sparks is commonplace with the associated risk of igniting fuel vapors that may be present. This is specially true in remote areas inside a boat. With the present invention, this risk is eliminated because the present improved booster cable does not close contact 61 until after sufficient time has elapsed from the time of first physical contact of the last alligator clip 50 connection to its corresponding electrode. The following paragraphs describe the operation of the preferred embodiment.

Two branches of one diode and one resistor in series are connected between the electrodes of the source and battery, respectively. Diode 90 in series with resistor 91 provide a positive (logic high) voltage at P when a positive (correct) voltage is presented to the clip 50 of cable member 32. If the source's polarity is inverted, a negative voltage would be blocked by diode 90 and point P would be grounded (logic low) .

Diode 95 and resistor 96 work in a similar fashion with the receiving battery side and Q will sit at a positive (high) voltage only when cable member 42 is connected to the positive voltage of the receiving battery. This, of course, presupposes that the battery is not completely dead. Points P and Q are connected to the inputs of AND gate 80 which will produce a logic high when both, P and Q, are connected to the proper positive electrodes through diodes 90 and 95, respectively. Gate 80 is disabled or enabled depending on whether or not its supply voltage (Vcc) is applied. Vcc is only applied to gate 80 when either one of the two positive electrodes is connected to either cable member 32 or 42.

A protection circuit is provided through back to back diodes 70 and 75. This protection circuit protects gate 80 from an inadvertent connection of either cable member 32 or 42 to the wrong polarity (negative) that would damage it. The back to back connection point is used to provide the supply voltage to gate 80.

Then, after both P and Q produce a high at the output of gate 80, capacitor 50 starts charging through resistor 55. The time constant of capacitor 50 and resistor 55 will determine how long it will take to reach a voltage V _R at point R once the output of gate 80 is pulled up to a logic high. To activate relay coil 65 which in turn would close contact 61, a minimum treshold voltage V„ is required. In the preferred

embodiment, V_ needs to be above 1.4 volts, approximately, which corresponds to the voltage drop across diode 56 and the voltage drop across the base/emitter junction NPN transistor 57. When this treshold voltage is reached, transistor 57 is turned on, activating coil 65. Of course, diode 56 and transistor 57 may be replaced with any other devices, such as inverter buffer, gate, comparator latch or equivalent that switches on when a predetermined V _R voltage is reached. In the preferred embodiment, capacitor 50 and resistor 55 are chosen so that it takes about 6 seconds to reach a V_ of 1.4 volts with batteries of 12 volts. In 6 seconds, the user has had ample time to make a solid physical connection and after this is accomplished, there is no reason for any sparks to occur.

A protection diode 120 is utilized to protect the circuitry against any back e.m.f. (electro motive force) voltage produced by relay coil 65. Coil 65 is connected to ground on one end and to the emitter of transistor 57 on the other end. When transistor 57 is switched on, the voltage provide by the electrode to which cable 32 is connected is substantially applied across relay coil 65 thereby actuating (closing) contact 61.

It is believed the foregoing description conveys the best understanding of the objects and advantages of the present invention. Different embodiments may be made of the inventive

concept of this invention. It is to be understood that all matter disclosed herein is to be interpreted merely as illustrative, and not in a limiting sense, except as set forth in the following appended claims.

VII. INDUSTRIAL APPLICABILITY

It is apparent from the previous paragraphs that an improvement of the type for such cable boosters is quite desirable for the convenience and safety of the user.