GB2090001A - Device for testing fuses and bulbs - Google Patents

Abstract

A device comprising a circuit (10) for the testing of fuses and bulbs with a simple voltaic cell battery (11). The bulb (12) is deactivated when a conducting fuse is placed across terminals (15 and 16) and optionally a light emitting diode 21 is activated when a bulb is placed across terminals (19 and 20). <IMAGE>

Description

SPECIFICATION Device for testing fuses This invention relates to a device for determining whether a fuse will conduct electricity.

The use of fuses which protect electrical circuits from surges of current is widespread. A fuse comprises a wire having a low melting point such that it melts when a current exceeding a threshold value passes along the wire. In some cases one can determine whether a fuse wire has melted (that is to say a circuit has fused) by inspecting the fuse wire but in many fuses the wire is concealed from view.

According to a first aspect of the invention, there is provided a device for testing a fuse comprising a circuit which includes terminals for connecting across a fuse, a battery and a light source, the circuit being adapted to change the condition of the light source when a fuse is connected across the terminals.

The device provides a simple means of determining whether a fuse will conduct electricity which is less prone to error than known techniques.

in the preferred embodiment, the light source and the battery are in series, and the terminals are in parallel with the light source. There is preferably a switch which is in series with the light source.

The light source may be an incandescent filament bulb with a lens for directing a beam of light.

In use, the bulb is energised to emit light by closing the switch unless a fuse is connected across the terminals. Where fuses are in a dark environment, the light may be used and the beam directed to enable examination of the fuses to take place. When a conducting fuse is momentarily placed across the terminals, the bulb will be shorted out momentarily.

Preferably the device comprises a light emitting diode and further terminals for connecting across an extraneous bulb wherein the diode and further terminals are in series with the battery so that the diode is energised when a conducting bulb is placed across the terminals.

Thus the device also provides a ready means for testing bulbs.

The invention will now be described by way of example, with reference to the accompanying drawings, wherein: FIGURE 1 is a diagram of an electric circuit of a device for testing fuses and bulbs; FIGURE 2 is a perspective view of the device; and FIGURE 3 shows an end view of the device with parts cut away.

The circuit 10 of Figure 1 includes a battery, a light source and a circuit switch. The battery 11 comprises two voltaic cells which suitably develops a total electro-motive force of 3 volts.

The light source is an incandescent filament bulb 12 of relatively a low power requirement which is less than 1 5 watts. The circuit switch 1 3 is in series with the bulb.

The bulb 12 and switch 13 of the circuit 10 are in parallel with fuse testing terminals 1 5 and 1 6. A current flows from terminal 1 5 to terminal 1 6 when a conducting element such as a fuse is connected across the terminals. In the case of a cartridge type fuse a cap of the fuse is rested on each terminal. An additional terminal 17 is connected in series to terminal 1 5 and may be used instead of or as well as that terminal.

When switch 1 3 of the circuit 10 is closed, a current may pass through the bulb 12. The bulb is thereby energised so that it lights up. However, when a fuse is connected across the fuse testing terminals 1 5 and 16, a path of lower resistance is opened for the current. In accordance with Ohms law the greater part of the current will therefore flow across the fuse testing terminals so that there is insufficient current to energise the bulb. The light emitted by the bulb will considerably diminish or become non-existent. It may be noted that terminal 1 7 is used in particular where extraneous bulbs of low wattage, for example bulbs of the type used to adorn Christmas trees, are to be tested. A base of the bulb is placed on terminal 17 and the outer casing on terminal 16.

A further set of terminals, bulb testing terminals 19 and 20, are shown in Figure 1 as being in parallel, both with the fuse testing terminals 1 5 and 1 6 and bulb 12. The bulb testing terminals of the circuit 10, are in series with a light emitting diode 21. The diode is of a common form which emits radiation spontaneously in the visible region for a forward biassing current. These diodes can emit a light as bright as incandescent bulbs for a much lower power requirement. A suitable power consumption rate for the diode is 32 mW. A resistor 22 is in series with the bulb testing terminals, diode and battery 11 and may be omitted from the circuit when a single 1 .5V cell is used for the battery. The resistor is required in circuits where the electromotive force of the battery is greater then the maximum power consumption of the diode.

When a conducting bulb to be tested is connected across the terminals 1 9 and 20 (that is to say each of the terminals 1 9 and 20 are in contact with one of the terminals of the bulb), a path is opened for current from the battery 11, irrespective of the condition of the switch 1 3.

Mains voltage bulbs of the form to be tested generally consume power at a rate greater than 40 watts and have a resistance which is several hundreds of ohms. Whereas the greatest resistance to a current will be due to the bulb placed in contact with the terminals, a sufficient potential difference will be developed across the light emitting diode 21 for the diode to be energised.

The diode has a nominal operating voltage in the region of 1 .5V. The diode thus provides an indication as to whether the bulb to be tested is conducting or not when insufficient power is consumed by the bulb for the bulb itself to light up. Bulbs intended to operate at 240V and bulbs intended to operate at only 1 .5V can be tested in this way.

The device may include a pair of floating leads (not shown in the drawings), connected across the bulb 12. The other ends of each lead are adapted for connecting across the terminals of an external power source, so that various supplies may be used to power the device. For example, the leads may be connected across the terminals of a car battery where a suitable resistance is included in the circuit.

Figure 2 shows a base board 24 which forms a base for the circuit 10. Some of the elements of the circuit 10 are visible on the board, and those .to which access is not required, most of the wiring for example, are concealed within the board. The terminals 15, 1 6, 17, 1 9 and 20 consist of rectilinear lengths of wire on raised rib 33 of the board. Terminal 15 of the fuse testing terminals is of greater length than and in line with terminal 16, providing for a range of fuse plugs which may be connected across the terminals. Additional terminal 1 7 is connected in series with terminal 1 5 and to one side of that terminal. Termihal 1 7 protrudes in a loop from the base board.The pair of bulb testing terminals 1 9 and 20 are on the side of the raised rib of the board. Test leads 31 and 32 are connected in the board to terminals 1 5 and 20 respectively. Each provides a flexible terminal for testing fuses and bulbs respectively.

The bulb 12 on the board 24 includes a lens 26 for directing a beam of light. The beam may be directed by manipulation of the board. The switch 1 3 is of a simple push-button form. The battery 11 is partly concealed within the board and maintained in contact with terminals of the circuit 10 buy a spring.

A cord 25 for suspending the board 24 extends through a hole in the board adjacent to one end thereof. The surface and interior of the board is a useful and convenient place for attaching items of an electrical repair kit, the illustrated example showing fuses 29 and fuse wire 30. A screw driver, for example, may be attached within the board, underneath the raised rib 33. Access to space underneath the board is via the end opposite the cord 25.

A lid 34 is shown in Figure 3 for fitting over the base board 24. The lid comprises apertures which provide access to the switch 1 3 and bulb 12.

Reflecting surfaces 35 and 36 increase the amount of light imparted by the device when the device is being used as a torch.

Claims (14)

1. A device for testing a fuse comprising a circuit which includes terminals for connecting across a fuse, a battery and a light source, the circuit being adapted to change the condition of the light source when a conducting fuse is connected across the terminals.

2. A device according to Claim 1 wherein the light source and the battery are in series, and the terminals are in parallel with the light source

3. A device according to Claim 2 which includes a switch in series with the light source so that the light source is energised when the switch is closed and is then de-energised when a conducting fuse is connected across the terminals.

4. A device according to any preceding claim wherein the light source is an incandescent filament bulb with a lens for directing a beam of light.

5. A device according to any preceding claim which comprises a base board on which the terminals are fixed.

6. A device according to Claim 5 which comprises a detachable lid fitted on the base board, which lid includes an aperture through which light emitted by the light source may pass.

7. A device according to Claim 5 or Claim 6 as appendantto Claim 5 wherein the base board is provided with a cord for suspending the device.

8. A device according to any preceding claim wherein the terminals are elongate and co-linear, and one terminal is longer than the other.

9. A device according to any preceding claim which comprises one additional terminal in series with one of the said terminals.

1 0. A device according to Claim 9 as appendant to Claim 8 wherein the additional terminal is in series with the longer terminal.

11. A device according to any preceding claim which comprises a light emitting diode and further terminals for connecting across an extraneous bulb wherein the diode and further terminals are in series with the battery so that the diode is energised when a bulb is placed across the terminals.

12. A device according to Claim 11 wherein the circuit switch and the light source are in parallel with the bulb terminals and the light emitting diode.

13. A device according to Claim 1 wherein the light source is a light emitting diode.

14. A device substantially as herein described with reference to and as shown in the accompanying drawing.

1 5. A device comprising any novel feature or novel combination of features described herein.