Electrically Propelled Fire Apparatus
Now that Mr. Edison has produced a storage battery that can be recharged in three minutes sufficient to propel a vehicle sixty miles, the following from “The Fireman” of London is of especial interest to fire departments of America:
Although practically nothing new has been discovered for many years in the construction of electric accumulators or storage batteries, and although we are still waiting anxiously for Mr. Edison to invent a battery of phenomenally light weight with an equally phenomenally high rate of discharge, such improvements have been made in the construction of pasted plates and their instalation in the cells of an accumulator that the propulsion of vehicles for carrying lire apparatus by electricity has become a perfectly practicable proposition. An accumulator can now be obtained that will stand, without injury, all the shaking up on the road that can be given it, and at the same time allow of a useful capacity being provided well within the weight of a ton, without undue allowance to be made for cost of upkeep. To obtain the best results from an electric accumulator it should be frequently discharged to a partial degree ami recharged to its full capacity as soon as possible. In actual lire service this is exactly the sort of duty it would be required to perform, as if the machines were not actually required for fire duty they could always be usefully employed for short periods daily for testing tire alarms, hydrants, etc. Nearly every town of any size now lias electric current, either provided by the municipality or by a power company, available for charging accumulators, and where multiphase currents only are available a small generating set can easily be installed in the lire station for charging at a convenient voltage. An accumulator requires a certain amount of skilled supervision periodically, which can always be procured from makers like the Electric Power Storage Company, who always have a staff of skilled experts going round the country doing this class of work, and who would also, doubtless, keep the accumulators in proper order for a fixed annual charge, although there may be in many cases skilled men available on the brigade staff. As regards the number of cells necessary to make up tile accumulator, this must be determined by the design of motor used and also the voltage of the current available for charging them. Eighty-eight is the maximum number generally used, and it is inadvisable to increase this, as the additional voltage tends to increase the danger from short circuiting, especially if there is any slight leakage in between the accumulator cells. The cells should be carried in equal numbers in stoutly constructed hard wood trays, arranged in units of suitable size to exactly lit the space available for their accommodation. It would always be well to keep as a standby one of these trays fully charged, for substitution for any of the working units should they require examination or replacement of damaged plates. So much for the accumulators.
The motors are the next most important feature and it is well known that excellent electric motors specially designed for traction purposes have been on the market for some years It is found that a separate motor for each driving wheel is desirable, as by this arrangement a differential gear is dispensed with. As regards the type of motor most suitable for atl round l ire Brigade requirements, it may be stated that there are two types now generally in use, one constructed in the hubs of the wheels, either in front or rear or in all four wheels, and the other carried on the framing of the vehicle and coupled to the driving wheels by roller chains. The former hails from the Continent of Europe, where the streets of the important towns possessing electrically propelled apparatus are generally very level, well paved, and offer very little resistance to traction with a minimum amount of vibration. Apart from the question of electrical efficiency, this type of motor, although at tirst sight possessing some attractive features as regards the elimination of transmission gearing and the possibility of using a front wheel drive, has many grave defects from a point of view of durability, when used on such rough roads as are generally found in the populous districts in the North of England that would be most likely to adopt electrical appliances Any mechanism carried directly on the wheels or axles of a vehicle is “unsprung” weight, and is therefore subject to all the road shocks not taken up by the rubber tires. Where pneumatic tires are used this disadvantage is not so apparent, but tires of this type are of course out of the question for a vehicle weighing from 3 to “i tons. Hence solid tires must be used, and the vibration on the mechanism contained in the wheel hub motors when traveling at a high rate of speed on bad granite setts is quite obviously a very serious factor to be dealt with. Copper enters largely in the construction of all electric motors both in the commutators and connections, and this metal is liable to rapid deterioration, due to its crystallization under undue vibration rendering it extremely brittle. When the motors arc fixed to the framing of the vehicle itself nothing of this sort can occur, as all road shocks are taken up by the springs that connect the frame work to the axles. Moreover from the point of view of electrical efficiency the higher the speed of the motor (within certain limits) the lighter it is possible to make it and the more economical it is to run. With the motor arranged on the framework of the vehicle a transmission gear is of course necessary, and this uses up a certain amount of power. A speed reduction gear of the worm and wheel type, if properly designed, takes up very little power, and roller chains to the driving wheels arewell known to give a very high mechanical efficiency. One of the largest electrical concerns in this country, which specializes in traction motors and makes both the w’heel hub and the high-speed type of machine and has no particular axe to grind definitely asserts that for solid tired vehicles the high speed motor proves itself more reliable and efficient than the wheel hub type; and looking at all the factors of the case it certainly w’ould appear that this contention is a reasonable one. As regards the controller, the simpler this and its connections are the better. There are some controllers made that give a regenerative combination, that is to say, the motors when running down hill are arranged to recharge the accumulators to a slight degree. This combination is an unnecessary one, and the amount of current saved is not worth consideration. An electric brake combination is also quite unnecessary, provided of course that good foot and hand brakes, entirely independent of one another, are provided. Five speeds forward and two reverse are more than sufficient, in fact it is found in practice that a low speed for starting and another for normal running are all that are required for work on the level and up a long hill. As regards the total distances alleged to have been run on a single charge of an accumulator, many “broad” statements have been made. A well-known accumulator enthusiast exhibits to admiring friends a certificate setting forth the fact that he ran an electrically propelled vehicle from London to Brighton on a certain date without recharging his accumulator en route. There is no doubt that he started from London full up and arrived at his destination with still a little juice left in his batteries, but nothing is said as to how many miles in between the machine was “man handled,” therefore it behoves us to accept with caution all statements as to the enormous distances that can be covered on a single charge. For ordinary town calls a mile is a fair average run, and it is extremely unlikely that three consecutive calls would occur without an opportunity for recharging even the small amount of current used on such a short distance. For country calls no responsibility should be taken with any type of motor appliance for any distance greater than ten miles, and calls from such distances are very few and far between and would always allow for the few hours necessary for recharging. An accumulator in proper working condition weighing well within a ton can be easily made to undertake a ten-mile run out and ten miles home without completely discharging the accumulator, and for all practical purposes this would be sufficient. If in isolated cases it was found necessary to make arrangements for longer runs, a larger accumulator could be provided, an in fact the distance run is only limited by the weight of accumulator carried. As regards speed, an accumulator of the above weight will drive a five-ton vehicle on a good level road at 25 miles per hour, and will go up a good long I in 15 hill at a speed of about 15 miles per hour. The above speed on a level road is as fast as a vehicle of the weight can safely be driven, and it is doubtful if a (id horsepower petrol motor could pass an electric machine in an ordinary main road with its usual traffic.
An extremely valuable combination is that of a steam fire engine and boiler carried on a similar chassis. There are many first class horse drawn steamers in use in all parts of the world, the engines and boilers of which are to all intents and purposes as good as new’. These can easily be removed from their present carriages and installed on electrcally propelled chassis, as shown in the illustration. A great number of such conversions have already been carried out on the Continent of Europe with very successful results. From the point of view of reliability alone such a combination has much to recommend it. For turntable ladders electric propulsion is extremely suitable as the current is also available for extending the ladders through a separate motor at the foot of the main ladder, and does away with a lot of complication that exists when power for the purpose has to be provided by compresed gas and a separate high-speed engine and gearing. When a town or a large works is properly installed with electric power connection in close proximity to its hydrants an electrically worked pump up to almost any capacity can be fixed on the accumulator propelled vehicle, and such a scheme is specially worthy of the attention of municipalities providing their own power and lighting current, it is, of course, quite unnecessary to point out that the whole of the apparatus described is of British origin. In certain quarters there seems to be an impression that nothing good in the way of modern fire apparatus can come from any other place than Germany, but that this is a complete fallacy can be proved by anyone that cares to pay a visit to Greenwich and have a run on an upto-date Merryweather electric appliance.