GB2346746A - Temporary repair of a faulty alternator in a vehicle - Google Patents

Abstract

A temporary repair to a faulty alternator in a vehicle may be made by connection of a temporary regulator 10 between the alternator output 12 and the field coil connection 14, the regulator 10 pulsing the field coil excitation on and off to provide a maximum alternator output in the range of about 13.5 to 14 volts (1.5 to 2 volts above the nominal battery voltage), substantially regardless of the vehicle load requirement and the battery state. The regulator 10 may have a Zener diode D1 which becomes conductive at about 13.9 volts and switches off at about 13.7 volts. Current flows through a resistor R3 when diode D1 is conductive, so that a transistor Q2 turns on and a transistor Q2 turns off to remove the field coil excitation. The alternator output is thus regulated to about 13.8 volts. The regulator 10 may be designed such that transistor Q1 operates near to its junction breakdown temperature so that the regulator has a limited working life and can only be used as a temporary repair. A repair kit may include the regulator 10 with a heatsink (30, Figs.2,3) and a mounting bracket (20), a block of brush material of a size which can be cut down to suit any vehicle alternator, and quick setting glue to stick the brush material to the brush holder or remaining brush part in the alternator.

Description

This invention relates to the repair of alternators in vehicles.

Despite the high reliability of most vehicle components alternators are a source of problem and for a roadside repairer, such as the applicants. Thus alternator faults constitute the second largest reason for a demand for rescue and roadside repair. It is, therefore desirable to provide a way of repairing an alternator quickly and easily so that the vehicle can continue on its journey. In that connection the repair need not be permanent since, provided one can effect a temporary repair, this will enable the vehicle to complete its journey and later on, at the convenience of the driver, a permanent repair, such as a replacement of the alternator or certain of its components can be made.

There are a very large number of alternators available for different vehicles. It is, therefore, virtually impossible for a garage or for that matter a roadside repairer to carry the full range of spare parts. In practice what is likely to happen is that, if a replacement alternator or spare part is available, then the repair can be made quickly and easily. On the other hand if the alternator which has failed is not one of the more widely used models then, in the case of a roadside repair, the vehicle will have to be towed, at significant expense, to a garage.

In that connection even a garage may have to tell the motorist that the correct spare part is not in stock so that an immediate repair is not possible.

The ability to make a quick and immediate repair, even if temporary, is therefore very desirable.

The most usual type of failure in an alternator is that the regulator has failed or that the brushes are worn out or broken. Therefore currently the repairer needs to have available a new regulator and/or a new brush set for each and every model of alternator and as explained above the resulting inventory would be very large.

Therefore it is an object of the invention to provide a repair kit which will enable a roadside repairer to make an immediate and temporary repair to any alternator.

According to the invention the method of repair comprises replacing a faulty regulator with a temporary replacement which is capable to being attached to the exterior of the alternator and which is designed to pulse the excitation field of the alternator on and off to provide a maximum alternator output in the range of about 13.5 to 14 volts, and more preferably 13.7 to 13.9 volts, e. g. approximately 13.8 volts which is 1.8 volts over the nominal voltage of the battery, regardless of the vehicle load requirement.

Thus this temporary regulator is not designed to monitor the electrical load required from the alternator and adjust the excitation field as in a normal regulator for an alternator. Instead it works in a simplistic fashion to provide an output which will not harm the vehicle's electrical system but it will definitely meet the immediate vehicle needs and ensure that the battery is kept charged or recharged if required. In effect the efficiency of the vehicle's electrical system is ignored for a repair which is designed to deal with any alternator and to provide a temporary repair which enables the vehicle to complete its immediate journey.

It is desirable that such a regulator be constructed and operated in such a way that it will work as a temporary, as opposed to a permanent, replacement for the alternator. Therefore it is preferred that the regulator use components such as a power transistor operating near its operating breakdown characteristics. For example in the case of a power transistor this can be allowed to run at a temperature below but near its junction breakdown temperature. This will ensure that the regulator slowly breaks down with time and ensure that the replacement regulator can only be used on a temporary basis since the overall alternator and its regulator is not now being used in the normal fashion for which it is designed and for which the rest of the electrics of the vehicle are designed. Operating in this temporary manner according to the invention is entirely satisfactory for a relatively short period of time, e. g. 48 hours, but it is undesirable for a user to regard the temporary repair as something which can be used permanently.

Therefore, according to another aspect of the invention there is provided a regulator assembly for an alternator comprising voltage control means which become conductive at about 13.9 volts and return to being non-conductive at about 13.7 volts, and which are to be positioned between the output from the alternator and ground, resistor means through which current passes when the breakdown means becomes conductive, so creating a voltage across that resistance, and switch means to be positioned between the alternator output and the alternator field coils which switches between"on"and"off"conditions such that when the breakdown means become conductive the switch means are switched"off"and when the breakdown means are non-conductive the switch means are switched "on", so limiting the maximum output voltage of the alternator to the region of about 13.8 volts.

Such a circuit can very simple and can very easily be connected as appropriate to a failed alternator.

The switch means can be a power transistor and as noted above, this can be designed so that its operating temperature is near to the junction breakdown temperature so as not to be long lasting.

The voltage control means is preferably a Zener diode.

Another problem which often arises with alternators is damage to its brushes. Again because of the wide variety of alternator models one needs a specific brush set to be available for each model and it is not practical for a roadside repairer to carry all possible combinations of such brushes. According to a preferred embodiment of the invention, therefore, a kit is provided which includes, not only the temporary regulator assembly but in addition a block of brush material of such a size that it can be cut down to the shape and size of any vehicle alternator brush. This means that the block needs to be some what larger than a normal brush and a typical block of brush material should preferably be approximately 10 by 20 by 100mm. A roadside vehicle repair man will have available to him a knife, rasp, hacksaw or the like, and so he can then shape this block to the required size to replace the damaged brushes in a broken alternator.

To complete his repair it will often be convenient to stick the newly shaped piece of brush material to the brush holder or the remaining brush material with a quick setting glue, which can also optionally be provided, so that it is held in place whilst the brush set is reassembled in the alternator.

According to a further aspect of the invention, therefore, there is provided a kit for effecting a temporary repair to an alternator which includes a temporary regulator assembly as described above together with a block of brush material of a size capable of being cut down and shaped to fit to act as a replacement brush, and optionally some glue to stick that shaped brush to a broken brush or the brush holder.

Such a kit can also be provided to motorists and other vehicle drivers who are undertaking a long journey, for example abroad, where it is perhaps expected that not all alternator replacement parts are likely be to readily available. If, however, a failure of the alternator does occur then the motorist can provide a local garage with the kit to enable them to effect a temporary repair or, of course, if the motorist is sufficiently skilled himself he may be able to make the repair himself which would then allow him to return home to have a proper repair of the alternator made.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of a regulator assembly according to the invention; Figure 2 is a diagram showing one possible connection of a temporary regulator according to the invention into a vehicle; and Figure 3 is a diagram similar to Figure 2 showing an alterative connection.

The regulator assembly 10 according to the invention shown in Figure 1 includes a power transistor Ql which is positioned between the alternator output 12 and the output 14 to the alternator field coil. When the power transistor Ql is"on"then the output passes directly from the output 12 to the alternator field coil output 14.

A Zener diode Dl is positioned between the output and ground 16 in series with a resistor R3. The Zener diode is one which is chosen to have a break-down voltage of about 13.8 volts so that, in effect, it becomes conductive at about 13.9 volts and switches off again at about 13.7 volts. When it becomes conductive current passes from the output 12 t-o ground through the resistor R3 but whilst it is nonconductive virtually no current passes.

When current passes through the resistor R3 a voltage drop is created across it and this voltage is applied via a load limiting resistor R2 to the base of a transistor Q2. The transistor Q2 is normally off but once the voltage applied to its base rises above ground level it becomes conductive with the result that current now flows to ground through a resistor Rl so raising the voltage level of the base of the power transistor Ql. This now switches"off"as a result.

Therefore, there is no output provided at the output 14 to the alternator field coil.

The circuit operates, therefore, such that during each output cycle from the alternator, the voltage, as it rises from 0 to about 13.9 volts, passes through the power transistor Q2 direct to the output 14. At the point of about 13.9 volts the Zener diode Dl breaks down and becomes conductive with the result that transistor Ql becomes non-conductive. Therefore the output to the field coil is now"off"which switches the alternator"off". Once the output 12 reduces below about 13.7 volts again, then the Zener diode Dl becomes nonconductive with the result that the power transistor Ql then becomes conductive and so an output is again provided to the alternator field coils.

In this way the voltage output from the alternator is stabilised at about 13.8 volts regardless of the vehicle load requirements and regardless of the battery state. This output, however, will do no harm and will provide a steady output which is sufficient to keep the battery in good condition or charge it should it be run down and to provide electrical power for running the vehicle.

Figure 2 shows one way in which the temporary regulator circuit 10 may be mounted in a vehicle.

According to the embodiment shown in Figure 2 the circuit 10 has three output leads, red, blue and black. These correspond to outputs 12 and 14 and ground 16. The blue wire constitutes the output 14 and is connected to the alternator field coil via the IND input to the alternator. The red wire 12 is connected to the positive terminal of the battery.

Finally the black wire constitutes the ground 14 and is connected to the vehicle chassis. As can be seen the circuit is mounted on a clip 20 which can readily be connected to a convenient point on the alternator as by the adjusting nut and bolt 22 for positioning the alternator to tighten the fan belt.

The circuit 10 is also provided with heat dissipating fins 30 to dissipate the heat produced in the power transistor Ql. However, as noted above, the overall circuit and its heat dissipation properties are arranged such that the power transistor operates at a temperature near it junction breakdown temperature so that the overall circuit cannot be regarded as a permanent repair and is likely to break down after a period of time. A minimum period of at least 48 hours is the designed limit, however, and that should be sufficient for a motorist to return home.

Finally the circuit shown is Figure 3 differs from that shown in Figure 2 in that the input for the regulator is now connected via the red wire to the alternator failure warning indicator warning lamp fitted in the host vehicle. The regulator output 14 is attached via the blue wire to the IND or independent input on the host alternator and the ground black wire is connected to the host vehicle.

In this arrangement it is important to ensure that the output brush of the alternator field coil, is shorted to ground either through the fault in the original alternator or by the addition of a temporary earth from the brush to chassis ground.

Claims (7)

1. CLAIMS 1. A method of repairing a faulty alternator comprising replacing faulty regulator with the temporary replacement which is capable of being attached to the exterior of the alternator and which is designed to pulse the excitation field of the alternator"on"and"off"to provide a maximum alternator output in the range of about 13.5 to 14 volts which is about 1.5 to 2 volts over the nominal voltage of the battery, regardless of the vehicle load requirement.
2. 2. A method of repairing a faulty alternator, substantially as herein described with reference to the accompanying drawings.
3. 3. A regulator assembly for an alternator comprising voltage control means which become conductive at about 13.9 volts and return to being non-conductive at about 13.7 volts, and which are to be positioned between the output from the alternator and ground, resistor means through which current passes when the breakdown means becomes conductive, so creating a voltage across that resistance, and switch means to be positioned between the alternator output and the alternator field coils which switches between"on"and"off"conditions such that when the breakdown means become conductive the switch means are switched"off"and when the breakdown means are non-conductive the switch means are switched "on", so limiting the maximum output voltage of the alternator to the region of about 13.8 volts.
4. 4. An assembly as claimed in Claim 3 in which the switch means are a power transistor designed to operate so that the operating temperature is means to its junction breakdown temperature.
5. 5. An assembly as claimed in Claims 3 or Claim 4 in which the voltage control means is an Zener diode.
6. 6. A regulator assembly for an alternator, substantially as herein described with reference to the accompanying drawings.
7. 7. A kit for effecting a temporary repair to an alternator which includes a temporary regulator assembly as claimed in any preceding claim above together with a block of brush material of a size capable of being cut down and shaped to fit to act as a replacement brush, and optionally some glue to stick that shaped brush to a broken brush or the brush holder.