EP0444078B1

EP0444078B1 - Electrical power distribution system

Info

Publication number: EP0444078B1
Application number: EP19890912643
Authority: EP
Inventors: Michael John Shand; John Michael Allen
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1988-11-15
Filing date: 1989-11-02
Publication date: 1993-09-01
Anticipated expiration: 2009-11-02
Also published as: DE68908898D1; WO1990006006A1; EP0444078A1; GB8826712D0; GB9110351D0; GB2243502A; DE68908898T2; GB2243502B

Abstract

An electrical power distribution system comprising a power point (8) connectable to a direct current power supply means and provided with sockets (42, 43 and 44) connectable to one polarity of the supply and sockets (45, 46 and 47) connectable to the other polarity of the supply. A number of power supply cables (9, 10 and 11) of different current carrying capacity are provided each of which contain two conductors and are provided with plugs (30, 41 and 48) respectively having contacts for engaging the sockets. The number of contacts connected to each conductor being dependent on the current carrying capacity of the cable. One, two or three plugs may simultaneously engage the power point (8) depending on which plugs are used. A number of different electrical supply means may be provided each of which is connected to a power point with more or less sockets per polarity of the supply depending on the electrical capacity of the supply.

Description

The present invention relates to the field of electrical supply systems for portable battery powered hand-held tools and other such items of electrical equipment which are particularly suitable for use in hazardous and inhospitable environments.
When hand held power tools are to be used in remote locations at which no mains electricity supply is available, a number of alternatives exist for supplying power to the tools. The three sources of power most commonly used are pneumatic and hydraulic power and rechargeable batteries. The use of pneumatic or hydraulic power require the provision of mobile compressors or pumps respectively which are normally very bulky, require fuel and are not easily transportable. Cordless tools incorporating rechargeable batteries are available, but these suffer from a number of disadvantages. The incorporation of the battery into the tool, usually the handle often results in the tool being clumsy to handle due to its weight and size and the resulting restriction on the battery size means that the continuous operating time between charges is severely limited. An alternative to cordless tools is to provide separate battery packs which are connected to the hand tools by cables. When the hand tools, cables and battery packs have to be transported manually however the weight of the cables can be prohibitive, particularly if the cables have a high enough current rating to take the DC current suitable for a tool with a relatively high power consumption. Furthermore if cables of an insufficient current rating are used for supplying current to a heavy duty tool the cable will be damaged.
The invention seeks to overcome the above disadvantages associated with the supply of direct current electrical power to hand held power tools.
Thus according to the invention there is provided a power distribution system comprising the features of claim 1.
By providing separate cables of different current carrying capacities the need to always carry heavy duty cables is obviated, which will result in a greatly reduced load being carried when a light or medium duty tool with its associated cable is required. By comparison, copper cables capable of safely conducting 93, 40 and 15 amps respectively weigh approximately 0.91kg, 0.275kg and 0.12kg per metre respectively and thus the weight saved by carrying a 10m light duty cable rather than a 10m heavy duty cable would be approximately 7.9kg. Furthermore the possibility of the plug being engageable with more than one pair of sockets means that the number of pairs of sockets can be used to limit the demand made on the power supply means.
The absence of the battery weight from the hand tool makes it much easier to handle and enables larger batteries with associated increased continuous operating times to be used.
A number of different socket arrangements are proposed below the advantages of which will become apparent from the description of the preferred embodiments.
Preferably at the opposite end of the cable to that at which the power distribution plug is connected a load engageable plug is connected the size of which is dependent on the current carrying capacity of the cable. In this manner a cable can be prevented from being overloaded by being connected to a load which is too large for the cable. Furthermore this feature in combination with the plug and power point interaction described above can be used to limit the demand made on the power supply means.
In order that heavy high capacity power supply means do not always have to be taken to a location where work is to be carried out a variety of power supply means of different electrical capacity may be provided. One of these electrical supply means may be a relatively light duty supply which is connected to a power point having one pair of sockets only.
The power point is advantageously provided with a switch for isolating the power point from its associated power supply means, and preferably a charge meter is also provided which indicates the extent to which the power supply has been exhausted.
In order to make the power supply means easily transportable it is preferably incorporated in a waistbelt, a back-pack, a case or a trolley.
To facilitate engagement of the power distribution plugs with the power point in the dark or when the user is wearing cumbersome gloves the external shape of each power distribution plug preferably conforms with part or all of the external shape of the power point.
The invention will now be described by way of example only with reference to the following Figures in which:-

Figure 1: is a schematic diagram of a power distribution system in accordance with the invention.
Figures 2 to 4: show the power points and compatible power distribution plugs of the preferred embodiment.
Figure 5: shows the connection between a power distribution cable and a tool.
Figures 6 to 8: show the power points and compatible power distribution plugs of an alternative embodiment.
Figure 9: shows a possible modification of the preferred embodiment.

Referring to Figure 1 there is provided a suite of 24 volt rechargeable nickel cadmium power supplies of varying electrical capacities which comprises:-

(a) A waistbelt mounted power supply 1 consisting of a rainproof plastic belt containing four batteries connected in parallel to a control box 2. The power supply is rated at 15Ah, and is designated as a light duty supply relative to the other power supplies.
(b) A rucksack mounted power supply which is provided with a control box 4, rated at 15Ah and is designated as a medium duty power supply relative to the other power supplies.
(c) A portable case power supply 5 which is provided with a control box 6, rated at 30Ah and is also designated as a medium duty power supply relative to the other power supplies.
(d) A trolley mounted power supply 7 which is provided with a control box 8 rated at 100Ah and is designated as a heavy duty power supply relative to the other power supplies.

The suite of power supplies is provided with a selection of light, medium and heavy duty cables 9, 10 and 11, which contain conductors having sectional areas of 1.5mm², 4mm² and 16mm² respectively, which may be made up from bundles of wires. The three types of cables are provided with plugs (30, 41, and 48 respectively) at one end for conection to one or more power supplies as described below, and a load engageable plug 13 at the opposite end for connection to a hand tool with an appropriate power rating. The light duty cables 9 can carry up to 15A, have 1.5mm² conductors and are suitable for connection to tools which take up to 350W to operate such as jigsaws, orbital sanders, disc sanders, power files and 10mm diameter drills. The medium duty cables 10 can carry up to 40A, have 4mm² conductors and are suitable for connection to tools which take upwards of 350W but less than 950W such as power scrapers, disc grinders and hammer drills. The heavy duty cable 11 can carry up to 93A, has 16mm² conductors and is suitable for connection to tools which take upwards of 950W but less than 2200W such as large disc grinders, demolition hammers, circular saws and demolition breakers. Each tool is provided with a recessed twin pin socket 12 as shown in Figure 5, which is provided with flat 14 configured to mate with a corresponding flat 15 on the load engageable plug 13 in order to prevent incorrect insertion of the supplementary plug into the recessed twin pin socket. Small, medium and large recessed twin pin sockets 12 are used for tools falling into the low, medium and high relative power consumption categories referred to above and the load engageable plugs 13 are appropriately graded in size in order to ensure that cables 9, 10 and 11 can not be overloaded by connection to a tool with a current demand that is too high.
Figures 2, 3 and 4 illustrate three control boxes 2, 4 and 8 for attachment to the power supplies 1, 3 and 5, and 7 respectively. The control boxes are provided with power points 19, 20 and 21 respectively, on/off switches 22, 23 and 24 respectively for isolating the power point from the supply and charge indicators 25, 26 and 27 respectively which show the extent to which the charge in the power supply has been used.
Control box 2 (Figure 2) is attached to the light duty supply 1 and is provided with a light duty power point 19 having two sockets 28 and 29 each being connected to a different polarity of the light duty supply and having square and round cross sectional shapes respectively. Each light duty cable 9 contains two conductors each of which is connected to a contact 31 or 32 in a light duty plug 30.
The contacts 31 and 32 have identical cross sectional shape and spacing to the sockets 28 and 29 respectively, and are dimensioned so as to allow only the light duty plug 30 to be engaged with the light duty power point 19 in one orientation.
The medium duty supply 3 is provided with a control box 4 (Figure 3), which is identical to control box 6 on medium duty supply 5. The control box 4 is provided with a medium duty power point 20 having two sockets 33 and 34 connected to one polarity of the medium duty supply and two sockets 35 and 36 connected to the other polarity of the medium duty supply. The shape, size and spacing of socket pairs 33, 35 and 34, 36 is identical to those of socket pair 28, 29 of the light duty power point 19 which means that two light duty plugs 30 can be simultaneously inserted into the medium duty power point 20. Each medium duty cable 10 contains two conductors one of which is connected to two contacts 39 and 40, and the other of which is connected to two contacts 37 and 38 of a medium duty plug 41, the contacts being configured so that they are engageable in the sockets of the medium duty power point in one orientation only.
Similarly the heavy duty supply 7 is provided with a control box 8 (Figure 4) with a heavy duty power point 21 having three sockets 42, 43 and 44 connected to one polarity of the heavy duty supply and three contacts 45, 46 and 47 connected to the other polarity of the supply. The shape, size and spacing of the socket pairs 42, 45 and 43, 46 and 44, 47 are identical to those of socket pair 28, 29 of the light duty power point 19 which means that three high duty plugs 30 can be simultaneously engaged in the heavy duty power point 21. Alternatively the heavy duty socket 21 is engageable by a light duty plug 30 in combination with a medium duty plug 41. Each heavy duty cable 11 is provided with a heavy duty plug 48 and contains two conductors each of which is connected to three contacts 49, 50, 51 or 52, 53, 54 the contacts being configured so that they are engageable in the sockets of the heavy duty power point 8 in one orientation only.
By limiting the load to which a cable can be connected and limiting the cables which can be connected to a certain power supply it is possible to ensure that: (a) the cables are never over loaded and consequently heat damaged, and (b) a power supply is never damaged by being discharged too rapidly.
Figures 6 to 8 show an alternative plug and power point system that can be used instead of the plugs and power points shown in Figures 2 to 4. The main differences from the system described are given below.
The three contacts 55, 56, and 57 of the heavy duty plug 61 which are connected to the same conductor are graded in size and are spaced from the contacts 58, 59 and 60 connected to the other conductor by varying distances. The size shape and spacing of the contacts 63, 64, 65 and 66 of the medium duty plug 62 are equivalent to those of contacts 55, 56, 58 and 59 of the heavy duty plug, and contacts 68 and 69 of the light duty plug are identical in size shape and spacing to contacts 63 and 65 of the medium duty plug and contacts 55 and 58 of the heavy duty plug.
The power points 70, 71 and 72 connected to the heavy medium and light electrical supplies (1, 3 and 5, and 7) respectively are provided with sockets configured to receive the heavy, medium and light duty plugs respectively. Alternatively the heavy duty power point 70 may be engaged by a medium duty plug 62 or a light duty plug 67 in its smaller sockets, and a medium duty power point 71 may be engaged by a light duty plug 67 in its smaller sockets.
While this system gives less flexibility in that only one plug can be engaged in any one power point at one time, wastage of contact material can be eliminated as the contacts of the light duty plug need only to be able to carry the light duty current (15 amps in the example above) rather than 1/3 of the heavy duty current (31 amps in the example above).
The external configuration of the plugs 61,62 and 67 is tapered and designed to be an exact match with the appropriate power point or section of a power point with which the plug engages. This feature considerably facilitates engagement of the plug in the power point which is particularly useful when the operation is being performed in the dark and/or with cumbersome gloves on. While the tapered design is only shown with reference to the second embodiment described it could also be applied to the embodiment shown in Figures 2, 3 and 4. Alternatively the plugs and power points of the preferred embodiment (Figures 2 to 4) could be curved at one end as shown in Figure 9, which would also ease correct insertion of the plugs into the power points.

Claims

A power distribution system comprising a power point (21) having at least two pairs of socket (42, 43, 44, 45, 46, 47), the sockets of each pair being connectable to opposite polarities of a direct current power supply means, at least two power distribution cables (9, 10; 11) each containing two conductors and each provided with a power distribution plug (30, 41; 48) which is engageable with the power point to electrically connect the cable associated therewith to the sockets, whereby
the at least two power distribution cables are of different current carrying capacity relative to each other, each plug is engageable with at least one pair of sockets and the plug connected to the cable (10; 11) of higher or highest current carrying capacity is simultaneously engageable with more pairs of sockets than the plug connected to the cable (9; 10) of lower or lowest current carrying capacity.
A power distribution system as claimed in claim 1 characterised in that the sockets are set in a plug-engageable face of the power point and lines taken between the sockets of each pair of sockets are mutually parallel.
A power distribution system as claimed in claim 2 characterised in that the distance across the plug-engageable face between the sockets (63, 65) of one socket pair is different from the distance between the sockets of another (64, 66) socket pair.
A power distribution system as claimed in claim 2 or claim 3 characterised in that the sockets (63, 65) of one socket pair are differnt in size from those (64, 66) of another socket pair.
A power distribution system as claimed in any one of claims 1 to 3 characterised in that the shape and size of any two sockets (42, 43, 45, 46) each connectable to the same polarity of the power supply means is identical.
A power distribution system as claimed in claim 5 characterised in that the shape of the sockets (42, 43) connectable to one polarity of the power supply are different from the shape of the sockets (45, 46) connectable to the other polarity of the power supply means.
A power distribution system as claimed in any one of claims 1 to 6 characterised in that a first and a second and a third power distrbution cable (9, 10, 11) are provided.
A power distribution system as claimed in claim 7 characterised in that all three cables have differrent current carrying capacities and the first second and third (9, 10, 11) have power distribution plugs (30, 41, 48) which are simultaneously engageable with one, two and three socket pairs respectively.
A power distribution system as claimed in any preceding claim characterised in that the power (21) point no more than three socket pairs.
A power distribution system as claimed in any preceding claim characterised in that at the opposite end of the cable to that at which the power distribution plug is connected a load engageable plug (13) is connected the size of which is dependent on the current carrying capacity of the cable.
A multiple power distribution system comprising the power distribution system of claim 1 further characterised by the inclusion of a second power point which second power point is connectable to a second direct current power supply means.
A multiple power distribution system comprising the power distribution system of claim 1 further characterised by the inclusion of a second power point having one pair of sockets, each socket of which is connectable to opposite polarities of a second direct current power supply means.
A power distribution system as claimed in any preceding claim characterised in that the one or more power points (21) are each provided with a switch (24) for isolating the power point from its associated supply.
A power distribution system as claimed in any preceding claim characterised in that the system is provided with a charge meter (27) for indicating the extent to which the power supply has been exhausted.
A power distribution system as claimed in any preceding claim characterised in that the power means is mounted on a portable waist-belt (1), a portable back-pack (3), a portable case (5) or a trolley (7).
A power distribution system as claimed in any preceding claim characterised in that the external shape of each power distribution plug conforms with part or all of the external shape of the power point.