WO2008132499A1

WO2008132499A1 - An electrical contact clip

Info

Publication number: WO2008132499A1
Application number: PCT/GB2008/050283
Authority: WO
Inventors: Nigel Scott
Original assignee: Nigel Scott
Priority date: 2007-05-01
Filing date: 2008-04-23
Publication date: 2008-11-06
Also published as: GB0708370D0

Abstract

An electrical contact clip (20) comprising an annular washer (21) having outwardly extending tabs (22) and inwardly extending deformable tongues (23) defining a central opening (24) which is slightly smaller than the outermost edges of a nut (15) to which it is to be attached, thus to provide a firm electrical contact with the nut and to prevent the clip from being readily released. Spade terminals may be used to attach leads to the tabs (22). The entire clip is preferably integrally formed from electrically conductive material such as spring steel. The clip provides ready connection of electrical cables to a battery terminal without the need for removal of the nut (15) or any other integral part of the battery.

Description

An Electrical Contact Clip

This invention concerns a clip to be attached to a first electrical conductor such as a battery terminal post and to which may be temporarily attached a second electrical conductor such as a lead of a testing instrument.

As an example of use to which the invention may be applied, standby battery systems, sometimes called stationary batteries, are used to supply electrical power in Uninterruptible Power Supplies (UPS), Telecommunication systems and many other critical situations where backup power is required.

A high percentage of these batteries are now of the Valve Regulated Lead Acid (VRLA), Sealed Lead Acid (SLA) Gel, or similar types, which are sealed in opaque containers, such that the user cannot know the state of health of the battery by traditional methods, such as testing the specific gravity or visually examining the plates.

The battery cells or monoblocs (blocs) are grouped in series, or series parallel, to achieve the necessary end terminal voltage and current to achieve their specified autonomy, or 'hold-up' time. 'Total battery', or end terminal, voltages are often in the region of several hundred volts DC.

Since testing such a battery by traditional methods is no longer possible, there is an increasing requirement for regular monitoring of individual cells in battery systems for terminal voltage, internal impedance and other parameters, over their lifetimes, perhaps up to twelve years or more, using electronic monitors. However, in order to monitor the cells, the monitoring system must establish a reliable electrical connection to individual cell terminals.

Most blocks for stand standby use are manufactured with 6mm, 8mm, 10mm or 12mm threaded terminal studs and nuts, or with upright posts through which a bolt may be fitted for connection of the load carrying cables, straps or bus bars to the battery posts, held in place by a nut.

Standard ring-tab washers, sometimes called spade terminal washers, can be used for this type of connection, which will allow permanent monitoring connections to be made to the terminals of the bloc. These washers can be of the single tab type or, for sensitive measurement of very low values, such as cell internal impedance or resistance, a device known as a Kelvin connection is used, in which the lead which draws the current used in the test is separate from the sensing lead. This avoids the resistance of the current carrying lead's connection from interfering with the sensitive measurement which is made by the sensing lead. In this case Kelvin-type washers may be used, with two spade tabs. The connectors, which connect the current and sense wires to these tabs are, for example, of a crimp terminal push-fit, or spade type.

The normal method of connecting monitoring systems to a battery for measurement purposes would be where the Kelvin-type washer is secured to the cell terminal post by the same retaining nut that is used for securing the battery load connection. The existing nut must be used in the majority of cases, as there is often not enough threaded post remaining after this is fitted to fit an additional washer and securing nut exclusively for the monitoring connection.

The problem with connecting measurement systems which are based on any standard type of washer is that, if the battery is already installed, all the battery connections must be disturbed and the securing nuts removed and replaced in order to effect the installation of the measurement connection washers. It is then important to ensure that the load carrying bus-bar nuts are re-tightened to a particular torque setting and this adds to the time involved. All this is expensive in both time and labour and in many cases can add 30% to 40% to the cost of installation of the monitoring system, representing many thousands of Euros in any but the smallest of batteries.

Using other known types of retro-fit connections which do not disturb the existing battery load carrying connections, such as crocodile clips, is not an option, since they are dependent on coil springs, which can weaken with age, thus compromising the integrity of the electrical connection, and allowing the measurement values to change over time. In addition, the security of such clips is suspect, as, should the attached leads be disturbed, the clips may 'spring' or jump off the terminal.

An additional difficulty with such connection methods is that many cell or bloc terminals are situated in a recess in the case, with a cover which is fitted over the terminal connections as a safety measure, thus there is very little room to fit permanent measurement connections, particularly those which rely on long jaws and coiled spring tension. An object of the present invention is to provide an electrical contact clip for use as described herein but which avoids problems experienced with conventional clips of the types described.

According to the present invention there is provided an electrical contact clip comprising a body having an opening to receive a projecting terminal post, at least one electrically conductive tab integrally formed with or permanently attached to the body, and at least one electrically conductive deformable tongue integrally formed with or permanently attached to the body and extending into the opening, thus to enable an interference fit with, and electrical connection to, a terminal post, the or each tab and the or each tongue being mutually electrically conductive.

The body may be an annular washer, the or each tab extending outwardly from a peripheral region thereof.

The body may be an annular washer, the or each tongue extending radially inwards from a peripheral region thereof into a central opening.

The or each tab may extend tangentially from the periphery of the annular washer.

A plurality of peripherally spaced tabs may extend from the body.

A plurality of circumferentially spaced tongues may extend radially inwards into the central opening, in the form a star washer.

The tongues may be inclined upwardly and inwardly relative to the plane of the washer and deformable to permit the clip to be forced onto a terminal post but to prevent ready release therefrom.

The tongues may have innermost edges disposed so as mutually to define a circular space thus to enable the clip to be forced onto a hexagonal nut attached to a terminal post in any orientation.

The or each tab may be deformably attached to or integrally formed with the body thus to enable the tab to be deformed from the plane of the body to present an upstanding surface to receive a spade connector. The clip may be a one-piece article of spring steel.

The or each tab may include a notch adapted resistively to receive an insulated cable thus to make electrical contact with the cable within its insulation.

An embodiment of the invention will now be described, by way of example of only, with reference to the accompanying drawings in which:

Figs 1 a, 1 b and 2 illustrate conventional contact clips permanently attachable to a battery terminal post with a securing nut;

Figs 3, 4 and 5 are plan views of an electrical contact clip made in accordance with the invention;

Fig 6 is a side elevation of the clip of Figs 3, 4 and 5 in the form illustrated in Fig 5;

Figs 7a and 7b illustrate how the clip of Fig 6 is attached to a terminal post of a battery having a nut thereon;

Figs 8a and 8b are side elevation and plan view respectively of the clip after attachment to the terminal post;

Fig 9 illustrates a standard spade terminal connecting a cable to the clip;

Fig 10 shows a notch in the clip and illustrates how a cable may be directly connected to the clip without the use of a spade terminal; and

Fig 1 1 illustrates current flow from the battery terminal through the clip into a pair of cables.

Although the example given here is of a clip used for measurement connections to a battery, the invention may be used to make a secure electrical connection to any nut, or protuberance, without disturbing the original or primary connection in the electrical circuit. Referring now to the drawings, Fig 1 a shows a conventional ring-tab washer 10 having a radial tab 1 1 to which may be attached a standard spade terminal 12 electrically connected to an end of a cable (not shown).

When the washer is required for connection to instrumentation for measurement of very low values such as cell internal impedance or resistance, a ring-tab washer 13 having a pair of tabs 14 may be provided for connection of a pair of cables, again via spade connectors 12. One of the cables will draw current used in the test while the other may be the sensing lead. This is standard practice and avoids the resistance of the current carrying lead's connection from interfering with the sensitive measurement taken by the sensing lead.

As will be seen in Fig 2, a ring tab washer of the type illustrated in Fig 1 a or Fig 1 b and illustrated by the reference numeral 10 in Fig 2, is usually placed beneath a nut 15 screwed onto the threaded battery post 16. The battery load connection is made by way of a washer 17 placed beneath the washer 10.

It will be seen therefore that in order to place such washers 10, 13, onto existing battery terminals for the purpose of connection of measuring instrumentation, it is necessary initially to remove the nut 15 from each terminal post and then to place the washer 10, 13 over the post before reintroducing the nut 15. It is required that such nuts be tightened to a specific torque measurement in order to ensure a firm electrical connection. This exercise involves considerable time and the use of special tools.

Referring now to Figs 3 to 1 1 , an embodiment of the the invention here disclosed is a compact, self-securing clip, specifically designed to enable an effective electrical connection to a hexagonal nut, or bolt-head or other type of electrical circuit securing device.

The clip 20 is cut from flat metal sheet, preferably spring steel.

The clip 20 comprises a body 21 in the form of an annular washer having a pair of diametrically spaced electrically conductive tabs 22 extending tangentially from the periphery of the body 21 and preferably formed integrally therewith.

A plurality of radially inwardly directed circumferentially spaced tongues 23 are integrally formed with the body 21 and present inner edges which mutually define a hexagonally shaped central opening 24 within the body. The tongues 23 are inwardly and upwardly deformed as can be seen in Fig 7a for a purpose to be described.

Fig 4 illustrates how the tabs 22 may be bent upwardly about dotted lines 22a thus to be disposed normal to the plane of the body 21 as can be seen in Figs 5, 6 and 7a.

Figs 7a illustrates how the clip formed as aforesaid can then be forced onto the nut 15 of the battery terminal to form an interference fit, the circular aperture 24 being initially slightly smaller in circumference than a circle described by the outermost edge of the nut 15 whereby the tongues 23 perform much as a star washer which once fitted to the nut 15 will grip the nut and prevent the ready removal of the clip.

Fig 7b illustrates a cylindrical tool 30 which may be used to push the clip onto the nut. Figs 8a and 8b illustrate the clip in place upon the nut and Fig 9 shows how a spade terminal 12 connected to a cable 12a may be pushed onto each of the tabs 22 to form a secure electrical connection thereto.

Fig 10 shows a notch 25 in a lower edge of the tab 22 thus to receive, directly, an insulated cable, the width of the notch being such as to cut into the insulation and to make sound electrical contact with the cable within the insulation. A heat shrink sleeve 26 may be provided for protection of the otherwise exposed cable and tab end.

Fig 1 1 shows a pair of leads 26 and 27 connected to a pair of tabs 22 for connection to electrical testing instrumentation. In this example, the lead 26 draws current from the battery terminal as illustrated by arrows 28, while the lead 27 serves to sense and measure low values such as cell internal impedance or resistance.

As shown in Fig 1 1 , when significant test current is drawn via the clip from one tab via lead 26, the perfect electrical connection made by the spring tongues 23 is sufficient to ensure that measurement of voltage response from the other tab 22 via lead 27 is not significantly affected.

Also, because the main transport interface of the impedance test current is via the seat of the securing nut 15, through the load connection to the lead post collar, the inter-cell load connection resistance is tested simultaneously with the cell internal resistance or impedance. Since a sound connection resistance should be around 20 μOhms or less, the connection resistance will not significantly affect the cell internal measurement unless there is a high resistance connection which can be detected by the use of a clip in accordance with the invention.

It will be appreciated that the inherent stiffness of the tongues 23, while preventing release of the clip, also tend to abrade the outer edges of the nut 15 during installation of the clip thus ensuring a high quality electrical connection between the clip and the nut.

It will further be appreciated that a clip of this kind may be of different shape, e.g. U- shaped and have tongues of different formation thus to provide sound electrical connection to, for example, a post or stud having other than a hexagonal shape.

The time taken to attach a clip in accordance with the invention and to connect monitoring instrumentation to it is found to be reduced by up to 95% when compared to the equivalent procedure using a standard monitoring washer connection, without a reduction in measurement quality assurance.

While, in the above example, the clip is described as providing monitoring connections to individual battery cells, it may be used in other applications where a rapid and reliable connection is required to be made to an existing electrical circuit.

Claims

1 . An electrical contact clip comprising a body having an opening to receive a projecting terminal post, at least one electrically conductive tab integrally formed with or permanently attached to the body and at least one electrically conductive deformable tongue integrally formed with or permanently attached to the body and extending into the opening thus to enable an interference fit with and electrical connection to a terminal post, the or each tab and the or each tongue being mutually electrically conductive.

2. An electrical contact clip according to claim 1 wherein the body is an annular washer, the or each tab extending outwardly from a peripheral region thereof.

3. An electrical contact clip according to claim 1 or claim 2 wherein the body is an annular washer, the or each tongue extending radially inwards from a peripheral region thereof into a central opening in the washer.

4. An electrical contact clip according to claim 2 or claim 3 wherein the or each tab extends tangentially from the periphery of the annular washer.

5. An electrical contact clip according to any preceding claim including a plurality of peripherally spaced tabs extending from the body.

6. An electrical contact clip according to any one of claims 2 to 4 including a plurality of circumferentially spaced tongues extending radially inwards into a central opening, in the form of a star washer.

7. An electrical contact clip according to any preceding claim wherein the or each tongue is inclined upwardly and inwardly relative to the plane of the body and deformable to permit the clip to be forced onto a terminal post, but to prevent ready release therefrom.

8. An electrical contact clip according to claim 6 wherein the tongues have innermost edges disposed so as mutually to define a central circular opening having a circumference selected to be slightly smaller than a circle described by the outermost edges of a hexagonal nut onto which the clip is to be installed, such as to cause the edges of the nut to be abraded by the innermost edges of the tongues.

9. An electrical contact clip according to any preceding claim wherein the or each tab is deformably attached to or integrally formed with the body thus to enable the tab to be deformed from the plane of the body to present an upstanding surface to receive a spade connector.

10. An electrical contact clip according to any preceding claim, being a one-piece article of spring steel.

1 1. An electrical contact clip according to any preceding claim wherein the or each tab includes a notch adapted resistively to receive an insulated cable thus to make electrical contact with the cable within its insulation.