Tweet

---

October, 1951

---

Efficient lamps, equipped with either acid or alkaline batteries, are available. Present practice is to use a twin-cell acid battery to give a nominal voltage of 4, or alternatively a three-cell alkaline battery with a nominal voltage of 3.75. Typical discharge curves for such batteries are shown in Fig. 10 for discharge rates of 0.8 A. for acid battery, and 1.0 A. for the alkaline battery, which are the relative operating conditions. End of shift M.S.C.P., after 9 hours continuous burning, in either case is approximately the same, being in the region of 1.5, but whereas the acid lamp employs a 4 V. 0.8 A. bulb, the alkaline lamp uses a 3.5 V. 1.0 A. bulb, the initial output of which is in the region of 40 lumens. The total light output of the alkaline lamp will therefore be, in all probability, a little higher than that of the acid lamp, reckoned over the whole shift, although they end the shift more or less on level terms, so far as M.S.C.P. is concerned. In other words, the acid lamp gives a more constant light, but probably a lower average light, than the alkaline lamp.

The Oldham Wheat battery has achieved marked success since its introduction in Great Britain a little over 15 years ago, and it is only fair to say that the introduction of this cap lamp, which showed a complete breakaway from tradition in the design of such lamps, represents a marked advance in the evolution of portable mine lamps which is comparable to those of the mid-nineteenth century in the development of flame safety lamps. The extent of this advance in acid-type cap-lamp design can be judged by the fact that it is only within recent years that it has been possible for its alkaline competitors to make an effective challenge in the cap-lamp field.

The general construction of the Oldham Wheat battery, which is illustrated in Fig. 11, is well known. Its main features are the provision of tubular positive plates, in which the active material is retained within slotted rubber tubes, and flat negative plates of lattice grid construction, separated by absorbent "Sponac" separators which take up 85 per cent. of the total acid in the cells. There is thus only a small volume of free electrolyte in the battery, the specific gravity of the electrolyte being kept between 1.28 and 1.30 when the cells are fully charged. Two cells in series supply current at 4 volts either to a 0.55 A. bulb in the smaller size lamp or to a 0.8 A. bulb in the larger type now generally in use.

Another lead-acid type cap lamp is the Youle lamp which incorporates an Exide battery, illustrated in Fig. 13. This battery is contained in an ebonite moulding with a central partition, has two cells to give a total of 4 volts, and supplies current for a 0.8 A. bulb. Tubular positive and flat-pasted negative plates are assembled in a composite construction. The positive tubes are rectangular in cross section so that a flat face is given to the plate as a whole. A glass-wool separator is interposed between the positive armour and an absorbent "Lignex" separator, the whole construction being given the designation of "Triclad." Spillage of electrolyte is obviated by adopting a non-spill chamber and a special venting system.

Typical of the steel-cased alkaline batteries are the Nife Type N.C. 113 C., and the Ceag Type A.7. The latter battery has a stainless-steel case holding three cells to give a total of 12 ampere-hours capacity. It has the advantage of long life and durability, and from five to seven years life can be expected under normal conditions without the necessity for the renewal of plates. These embody the tubular positive method of construction, with flat negative plates. All are assembled in steel containers and enclosed in a rubber bag, the purpose of which is to give complete insulation and a certain amount of cushioning to the cells. The battery has a double lid, which enables the cable connections to be isolated from the main body of the battery, and a side entry cable is fitted. (See Fig. 14.)

A further advance in the development of alkaline cap lamps is shown in the use of a four cell battery on the Wolf Alkaline Cap Lamp, No. 442. The cells are of the well known Wolf nickel-cadmium construction, using pure nickel foil and nickel frames to form the finished plate. The case is of acid-resisting plastic with either an outer casing or an outer frame of stainless steel. The headpiece, of light weight design, has a plastic body, and is fitted with an anodised aluminium reflector. The armour plate glass is secured by a brass ring fitted with a hooded screw locking device.

The capacity of the four-cell alkaline battery is 10.5 ampere hours, with a nominal voltage of 5.2. It supplies current to a 48 volt 0.8 amp. Krypton-filled bulb of 46 lumens output at the rated volts. The lamp gives approximately 3.8 initial mean spherical candle power, falling to 22 M.S.C.P. after nine hours burning. (Fig. 15.)

No discussion on the relative merits of alkaline and acid batteries would be complete without mention of that problem, which has caused so much trouble in the past and which, indeed, is still with us, the problem of battery spillage. This results in burns or damage to skin and clothing. Either acid or alkali are equally undesirable in this respect, but if anything the acid battery has the advantage that, generally speaking, its contained fluid is a little less potent than the alkali, at least, so far as its effect on the skin is concerned. Not only that, but it may be that the rubber container is not so liable as is a metallic battery case to produce condensation of moisture upon it, to become contaminated by any droplets of battery fluid lodging in crevices or other similar places on the surface of the battery case, with consequent ill effect. The recent adoption of a moulded plastic container for some types of alkaline battery may help to counteract this. Recent designs of alkaline battery have also been made as smooth as possible on the outside so as to minimise this possibility.

One such battery is that fitted on the Concordia C.L.A. cap lamp. This is constructed with an outer casing of a plastic material called alkathene. This material is inert to the action of the alkaline electrolyte of the nickel cadmium accumulator and also has suitable insulating properties and high mechanical strength. The cells are completely sealed, except for the vents, by an injection moulding, the upper surface of the cells being left smooth, to facilitate cleaning and to prevent the lodging of any free electrolyte. The high insulating properties, together with the considerably improved mechanical strength as compared with ebonite, make alkathene a suitable and improved material for use as the plate separators. A further feature is that the method of construction enables ribs to be included on the inner walls of the cells in the moulding process, to hold the plate groups in position rigidly and without fear of displacement or vibration. The terminals and vent sockets, inserted during the sealing process, form an integral part of the battery structure, and the cable connections and fuse are housed in a separate chamber in the detachable upper lid of the battery. This lamp is shown in Fig. 16.

The Venner accumulator

The introduction of the silver-zinc alkaline accumulator, which is manufactured in Great Britain by Venner Accumulators Ltd., may herald a new revolutionary advance in mine lamp design. These cells, first invented by Professor Andre and developed in France during the war, have many outstanding features. Their electrodes are enclosed in an absorbent material which also holds the electrolyte, very little free liquid being present. The plates contain no paste and are not liable to buckle or collapse in service. No separators are required and the cells are not adversely affected by prolonged charge or discharge.

The most notable characteristics of the Venner cell are those of comparative size and weight, when compared with other types in general use. As a general comparison they are less than half the size and less than one third the weight of conventional type batteries of the same capacity.

As yet the operating characteristics of the Venner accumulator are not favourable to its successful application in mine lamps, but progress and development is continually being made, and it may be that the lightweight silver-zinc accumulator will make an important contribution in the field of mine lighting.

Protection against spillage

Protection against battery spillage is achieved in two general ways, by improvement in battery design, and by improvement in lamproom routine, particularly in the operation of topping up. Close attention is being given by the manufacturers of alkaline batteries to the design of improved vent stoppers. Some batteries embody "gassing chambers" at the top of the cells, in which any frothing of the electrolyte can be accommodated. Others, such as the Ceag Type A.7, also incorporate a sponge rubber pad to seal the battery completely when closed. This feature is clearly visible in Fig. 18.

Spillage of battery fluid is very often the result, not so much of misuse underground, but of faulty lamproom maintenance. The operation of topping up has been made the subject of much investigation in order to try to ensure that batteries cannot be overtopped in the lamproom.

While, as has already been mentioned, spillage of battery acid may not be so unpleasant in its effects as that of alkali, nevertheless it is undesirable, and moreover, if permitted it would result in loss of electrolyte and consequent deterioration of the battery. As shown in Fig. 20, the Oldham battery is therefore designed so that topping up can be done by means of a gun, through a vent in the side of the case. A lamp, which is attached to the gun, shines into the vent and assists the attendant to see when sufficient distilled water has been added.

Fig. 21 illustrates the method of topping up the Youle lead-acid lamp battery. The watering holes for the twin cells being below the normal working level of the electrolyte, a shaped funnel is used to ensure that the correct quantity of distilled water is applied. The vent stopper is removed, and the funnel is applied, so that with the battery standing in an upright position water poured into the funnel will drain into the cells. No more water can be added than is required to fill the funnel to the brim, any excess water running to waste. When this condition is reached the water level in the funnel and the level of the electrolyte in the battery is the same, the electrolyte level being then just a little below normal. The correct level of electrolyte is attained by placing the battery on its side, when the water in the funnel drains into the cells. The funnel is then removed and the plug replaced.

A simple type of funnel is used when dealing with a small number of batteries. This has two outlet holes, one for each cell, and a thick gasket of soft rubber seals the joint between the funnel and the battery case, provision being made for the passage of displaced air through channels cut in the threaded portion of the funnel.

A watering machine is used when dealing with a large number of batteries. The equipment, which is mounted on a trolley, has a glass bottle reservoir for the distilled water. The battery to be serviced is laid flat on its back on the table of the trolley and the vent plug removed. A carrier, which normally rests in a horizontal position, is arranged to take the battery, suitably located by stops on the carrier, so that a filler head on the watering apparatus is directly opposite the filling holes of the battery, a gasket being fitted to seal the joint between filler head and battery. Movement of the carrier to an upright position then opens a valve and permits water to run into the battery. Attainment of the correct electrolyte level in the battery is indicated by the overflow of distilled water over a weir. This is the signal to return the carrier to a horizontal position and thus close the water supply valve. The battery is then removed from the carrier, the vent socket wiped dry, and the plug replaced. Fig. 22 shows the apparatus. Some of the alkaline-lamp systems also make use of a topping-up gun, though of different design. The Concordia topping-up gear is mounted on a trolley, as shown in Fig. 23, and can be moved easily about the lamproom on castors. The top of the trolley forms a table to hold about 20 cap lamp batteries, the tubular back pedestal of the trolley serving as a pump for the electrolyte stored inside it. This tube is closed with a flexible-rubber diaphragm, normally maintained in an extended position, by a spring connected to the frame of the trolley and operating against a foot pedal. Depression of the foot pedal operates a lever system against the spring and depresses the diaphragm of the pump. This causes electrolyte to flow from the outlet pipe at the bottom of the pump cylinder, and this electrolyte flows from a suitably shaped nozzle or gun at the end of a flexible pipe, and so into the battery. As the foot lever returns to its normal position, under the action of the spring, the diaphragm is again extended and exerts a suction effect on the topping-up gun, to suck excess electrolyte out of the battery. The battery therefore cannot be topped up to a level higher than the depth of intrusion of the gun. Overtopping is prevented, and there is no waste.

These advances in the methods of servicing batteries in the lamproom, together with those improvements in battery design already noted, give ample evidence of the close attention being given to the problem of battery spillage by the manufacturers, who are now able to offer batteries which should give little trouble in this respect, provided that their recommended lamproom routine is closely followed and also that no abuse of batteries takes place either on the surface or in the mine.

Lamp performance

The performance of any lamp when new is largely determined by the characteristics of the battery. As soon as it is put into service, however, other factors come into operation, the most important of these being the efficiency of the maintenance in the lamproom. The lighting regulations require not less than half of a sample number of lamps to give a lighting performance equal to 60 per cent. of the approval figure, when tested at any time. A close control of lamproom operations is necessitated in order to ensure that this regulation is complied with. This control, which involves systematic photometric observations has been a feature of many good lamprooms for some years past, but now its application will become more general. The lamproom check on mean spherical candle Power is the key to effective maintenance, and when used in con junction with systematic records of all important data relative to the batteries and the bulbs which are in use, it gives a positive means of ensuring that all the lamps in an installation are in good order. Instead of waiting for lamp failures to be reported to the lamproom staff, the progressive performance of each lamp can be observed in service, and any deterioration can be detected and corrected before the point of failure is approached. The failure of a lamp underground should then become exceedingly rare.

CORRECTION NOTE. The bezel-ring fastening for the Ceag A7 cap lamp featured on page 368 of our September issue should have been described as a screwed notched Dural bezel ring held in place by a locking lever secured to the moulding. We regret the discrepancy and apologise for any confusion that may have been caused.

(To be continued)

Drawings and Photographs accompanying the article