US3443192A - Arc suppression circuit for road vehicle battery charging system - Google Patents

Description

I M y 1969 R. w. NOLAN ETAL 3, 3,

ARC SUPPRESSION CIRCUIT FOR ROAD VEHICLE BATTERY CHARGING SYSTEM Filed 001;- 4. 1966 lllllllllll l.|

Ill-l IIIIIII Ill-L United States Patent 3,443,192 ARC SUPPRESSION CIRCUIT FOR ROAD VEHICLE BATTERY CHARGING SYSTEM Roger William Nolan, Redditch, and Brian Gilbert, Sutton Coldfield, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Oct. 4, 1966, Ser. No. 584,239 Claims priority, application Great Britain, Oct. 18, 1965, 44,017/ 65 Int. Cl. H023 7/04; H02h 3/20 U.S. Cl. 32061 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to battery charging systems for road vehicles, of the kind including a generator for charging the battery, and a voltage regulator for limiting the output voltage of the generator by opening a pair of contacts in series with the generator field winding whenever the output voltage of the generator exceeds a predetermined value.

In systems of this kind, opening of the contacts is commonly accompanied by arcing and sparking between the contacts. Considering a 12-volt system, as the contacts open the voltage between them rises to about 15 volts and an arc discharge passes between them, the voltage remaining substantially constant and independent of current until the arc quenches. The voltage then rises still further very rapidly and reaches a level at which a spark discharge passes between the contacts. This spark may be followed by a low voltage arc which quenches again with a further riseof voltage, followed by another spark and so on until separation is finally effected. Unless these processes are controlled, rapid erosion and burning of the contacts ensues at particularly high currents. It is well known in practice to effect such control by the use of a simple linear resistor of appropriate value connected across the contacts. If this resistor is of sufiiciently low value arcing may be virtually eliminated. If the resistor is of intermediate value, an initial arc of modified duration and intensity is permitted whilst the development of a subsequent voltage high enough to cause further arcing is prevented. It is in fact found with some practical contact materials, eg, tungsten, that a certain small amount of arcing must be permitted to occur in order to keep the contact surfaces clean and it is necessary therefore to select a value of resistor which does not suppress arcing altogether but prevents excessive discharge between the contacts. This becomes more difficult to achieve with a single value resistor as the range of field current to be handled by the contacts increases.

According to the invention, a battery charging system of the kind specified includes a voltage-sensitive resistor which has a resistance which decreases as the voltage across it increases, the resistor being connected, in the system in a position to limit the voltage developed across the pair of contacts, and the arrangement being such that as the current broken by the contacts increases, the resistance of the resistor decreases.

It will be appreciated that with the arrangement specified in the preceding paragraph, the resistance of the resistor is high where low currents are broken, and so arcing still occurs. However, where higher currents are broken by the contacts, the resistor presents a considerably lower resistance, and so excessive voltage rise and unwanted arcing is avoided.

Although the invention is applicable broadly to a battery charging system, the resistor can, as will be explained, be connected either in the generator itself or in the voltage regulator, and accordingl the invention resides in a generator and a voltage regulator for use in a battery charging system. It will further be appreciated that the invention can be incorporated in both alternator and dynamo charging systems if required.

In the accompanying drawings, FIGURE 1 is a circuit diagram illustrating one example of the invention, and FIGURE 2 is a fragmentary view illustrating a modification of part of FIGURE 1.

Referring to FIGURE 1, there is shown a generator having a live terminal 11, a field terminal 12 and an earth terminal 13, the armature 14 being connected between the terminals 11, 13 and the field winding 15 being connected between the terminals 12, 13. The generator can be a dynamo, or an alternator having a rectifier associated therewith so that direct current appears between the terminals 11, 13. The generator supplies power through a combined voltage and current regulator 16 to a battery 17 which in the example shown has its positive terminal earthed. The regulator 16 includes a first terminal 18 connected to the terminal 11, a second terminal 19 connected to the terminal 12, a third terminal 21 connected to the negative battery terminal, and a fourth terminal 22 which is earhed.

The terminal 21 is connected to the terminal 18 through a series circuit including a first pair of contacts 23 which are normally open, and first and second coils 24, 25. Moreover, the terminal 18 is connected to one end of each of third and fourth coils 26, 27, the other ends of which are interconnected and connected to the terminal 22 through a pair of resistors 28, 29 in parallel. The terminals 18, 19 are interconnected through second and third pairs of contacts 31, 32 connected in series, these contacts each being normally closed.

In operation, the contacts 23 prevent the battery 17 from discharging into the generator. When the generator starts, as soon as its voltage reaches a predetermined value the voltage developed across the coil 27 closes the contacts 23 so that current flows through the first coil to the battery. The coil 24 is wound on the same coil as the coil 27 and assists the operation thereof.

Current also flows to the field winding 15 through the second and third pairs of contacts 31, 32 in series. However, if the output voltage of the generator rises above the predetermined value, the voltage developed across the coil 26 opens the contacts 32. Similarly, if the output current rises above a predetermined value, the current flowing in the coil 25 opens the contacts 31. In either case, the generator output falls.

If the battery 17 commences to discharge into the gen erator, the winding 24 will oppose the action of the winding 27 so that the generator output voltage at which the contacts 23 open is reduced.

At the instant when either the contacts 31 or the contacts 32 open, a back is induced by virtue of the inductance of the winding 15, and this back tends to cause arcing and sparking across the contacts. As previously explained, where a low field current is broken, some arcing is useful in keeping the contacts clean, but where a higher field current is broken, the arcing can cause damage. In order to prevent such damage, a voltage-sensitive resistor 34 is connected across the contacts. The resistor 34 is a known device which has the property that its resistance increases as the voltage across it decreases. Thus, where a high field current is broken, the back will be high, and the resistor will have a low resistance. Where the field current which is broken is low, the back will be low and the value of the resistance will be high. The parameters of the device can be selected so that in the latter case the back causes arcing, which will clean the contacts without causing damage, and in the former case suflicient arcing is still allowed to cause cleaning of the contacts, the major current path being through the resistor.

FIGURE 1 shows the electrical connection of the resistor 34 correctly but not of course its correct physical position. The generator and the voltage regulator are supplied to vehicle manufacturer as separate components, and are interconnected in the road vehicle. In order to ensure that the resistor 34 is correctly connected, it can either be incorporated in the generator connected between the terminals 11, 12, or in the voltage regulator connected between the terminals 18, 19.

In another arrangement, the resistor 34 is bridged by a diode 35 in series with a capacitor 36, the discharge path for the capacitor 36 being provided by a resistor 37 which can be connected across the diode 35 as shown, or across the capacitor 36 as shown in dotted lines. These components can be connected physically in the same place as the resistor 34. In operation, when the contacts open, the capacitor momentarily charges via the diode, so slowing down the rate of rise of voltage across the contacts and delaying the onset of arcing, so reducing the intensity of the arc. The capacitor voltage reaches a peak value, and the capacitor then begins to discharge via the discharge resistor 37. Since the contacts quite commonly re-close While field current is still flowing, that is whilst the voltage across the contacts is still high, the diode is necessary to prevent damage as the result of discharge of the capacitor. Moreover, the inclusion of the diode permits the use of an independent resistor 37 to control the rate of discharge of the capacitor.

The time available for the capacitor to discharge depends on the frequency of operation of the contacts, which in turn depends on the generator speed and battery load. It is found that values of capacitance and resistance for the components 36, 37 can be chosen which allow the capacitor 36 to be nearly fully discharged between cycles under high field current conditions, but which leave the capacitor 36 with an appreciable voltage under low field current conditions. This differential effect may be used to prevent the capacitor from having a significant effect on arcing at low field currents, whilst of course allowing the capacitor to have some considerable effect on arcing at high field currents. Thus, the capacitor considerably assists the action of the resistor 34.

The capacitance of the diode 35 permits the flow of a transient discharge between the contacts as they close, the magnitude of which is a function of the diode design as well as the external circuit conditions. This small discharge can be controlled to give a beneficial cleaning action to the contact surfaces without detrimental erosion.

In the modification shown in FIGURE 2 the resistor 34 is connected across the winding 15. In this position the current carried by the contacts when they are closed is now increased slightly by the amount flowing through the resistor 34. If this extra current is small it may usefully improve contact conditions when the field current is low without significantly worsening conditions when the field current is high.

The capacitor circuit may also be connected across the winding 15 or it may remain in the position shown in FIGURE 1.

In both examples, a fusible link may be included in se ries with the resistor to prevent damage if the resistor should become short-circuited.

The invention has been illustrated as applied to a conventional current-voltage regulator such as is used with a dynamo charging system. However, where an alternator is used to charge the battery, the current regulating properties of the regulator are not necessary, and so a simplified regulator can be used. Moreover, the cut-out contact 23 in its associated components can be replaced by a diode.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. A battery charging system for a road vehicle, including a generator for charging the battery and a voltage regulator for limiting the output voltage of the generator by opening a pair of contacts in series with the generator field winding whenever the output voltage of the generator exceeds a predetermined value, the system further including a voltage-sensitive resistor which has a resistance which decreases as the voltage across it increases, the resistor being connected in the system in a position to limit the voltage developed across the pair of contacts, and the arrangement being such that as the current broken by the contacts increases, the resistance of the resistor decreases.

2. A battery charging system for a road vehicle, comprising in combination a generator having an earth terminal, a live terminal and a field terminal, the armature being connected between the live and earth terminals and the field winding being connected between the field and earth terminals, and a voltage regulator having a first terminal connected to the live terminal, a second terminal connected to the field terminal, a third terminal which in use is earthed through the battery, a fourth terminal which in use is earthed, a normally closed pair of contacts through which the first and second terminals are interconnected, and a coil connected in a series circuit between the first and fourth terminals, said coil opening the pair of contacts when the output voltage of the generator exceeds a predetermined value, the system further including a voltage-sensitive resistor which has a resistance which decreases as the voltage across it increases, the resistor being connected in the system in a position to limit the voltage developed across the pair of contacts, and the arrangement being such that as the current broken by the contacts increases, the resistance of the resistor decreases.

3. A system as claimed in claim 2 in which said voltage-sensitive resistor is connected across the field winding.

4. A system as claimed in claim 3 in which said voltage-sensitive resistor is connected between the field and earth terminals of the generator.

5. A system as claimed in claim 3 in which said voltage-sensitive resistor is connected between the second and fourth terminals of the voltage regulator.

6. A system as claimed in claim 2 in which said voltage-sensitive resistor is connected in a circuit across the pair of contacts.

7. A system as claimed in claim 6 in which said voltage-sensitive resistor is connected between the live and field terminals of the generator.

8. A system as claimed in claim 6 in which said voltage-sensitive resistor is connected between the first and second terminals of the voltage regulator.

9. A system as claimed in claim 2 including a diode and a capacitor connected in series across the voltagesensitive resistor, the capacitor charging through the diode when the contact opens to delay the onset of arcing, and a resistor providing a discharge path for the capacitor.

References Cited UNITED STATES PATENTS Cook et a1. 317-11 X Glover et a1. 317-11 Siwko 317-11 Slepian 3 17-1 1 JOHN F. COUCH, Primary Examiner. STANLEY WEINBERG, Assistant Examiner.

US. Cl. X.R. 317-11

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