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Page 26
The advantages of storage battery street cars for city traffic are
self-evident, so that I need not trouble you with further details in
this respect, but I would beg those who take an interest in the
progress of the electric locomotive to give this subject all the
consideration it deserves, and I would assure them that the system
which I have advocated in this brief but very incomplete sketch is
worthy of an extended trial, and ready for the purposes set forth.
There is no reason why those connected with electric lighting
interests in the various cities and towns should not give the matter
their special attention, as they are the best informed on electrical
engineering and already have a local control of the supply of current
needed for charging.
In the car which we use in Philadelphia there are actually 80 cells,
because there are considerable gradients to go over. Each cell weighs
40 pounds and the average horse power of each battery is six.
Sometimes we only use two horse power and sometimes, going up grades
of 5 per cent., we use as much as 12 horse power, but the average rate
is 6 electrical horse power. With reference to the weight of
passengers on the cars, we have never carried more than 50 passengers
on that car, because it is impossible to put more than 50 men into it.
There are seats for 24, and the rest have to stand on the platforms or
in the aisle.
The changing of the batteries takes three minutes with proper
appliances. One set of cells is drawn out by means of a small winch
and a freshly charged set is put in. It takes the same time to charge
the battery as it does to discharge it in the working of the cars, so
one reserve set would be sufficient to keep the car continually
moving.
The loss of energy from standing about is probably nothing. If a
battery were to stand charged for three months in a dry case, the loss
of energy might be in three months 10 per cent. I purposely had a set
of cells standing for two years charged and never used them. After two
years there was still a small amount of energy left. So as regards
the loss of energy in a battery standing idle, it is practically
nothing, because no one would think of charging a battery and letting
it stand for three months or a year.
I have had them stand three or four months and I could hardly
appreciate the loss going on, provided always that the cells are
standing on a dry floor. If the exterior of the box be moist, or if it
stands on a moist floor, there will naturally be a surface leakage
going on: but where there is no surface leakage the mere local action
between the oxides and metallic lead will not discharge the battery
for a very considerable time.
I have made experiments in London with a loaded car pulled by two
horses. I put a dynamometer between the attachment of the horse and
the car, so as to ascertain exactly the amount of pull, measured in
pounds multiplied by the distance traversed in a minute. You will be
surprised to know that two horses, when doing their easiest work,
drawing a loaded car on a perfectly level road, exert from two to
three horse power. I have mentioned a car in Philadelphia where we use
between two and twelve horse power. A horse is capable of exerting
eight horse power for a few minutes, and when a car is being driven up
grades, such as I see in Boston, for instance, pulling a load of
passengers up these grades, the horses must be exerting from 12 to 16
horse power, mechanical horse power. That is the reason that street
car horses cannot run more than three or four hours out of the
twenty-four. If they were to run longer, they would be dead in a few
weeks. If they run two hours a day, they will last three or four
years.
The life of the cells must be expressed upon the principle of ampere
hours or the amount of energy given off by them. Street car service
requires that the cells work their hardest for fifteen or sixteen
hours a day. The life of the cells has to be divided; first, into the
life of the box which contains the plates. This box, if appropriately
constructed of the best materials, will last many years, because there
is no actual wear on it. The life of the negative plates will be very
considerable, because no chemical action is going on in the negative
plate. The negative plate consists almost entirely of spongy lead, and
the hydrogen is mechanically occluded in that spongy lead. Therefore
the depreciation of the battery is almost entirely due to the
oxidation of the positive plates. If we were to make a lead battery of
plates � inch thick, it would last many years; but for street car
work that would be far too heavy. Therefore we make the positive
plates a little more than one-eighth of an inch thick. I find that the
plates get sufficiently brittle to almost fall to pieces after the car
has run fifteen hours a day for six months. The plates then have to be
renewed. But this renewal does not mean the throwing away of the
plates. The weight is the same as before, because no consumption of
material takes place. We take out peroxide of lead instead of red
lead. That peroxide, if converted, produces 70 per cent. of metallic
lead, so that there is a loss of 30 per cent. in value. Then comes the
question of the manufacture of these positive plates, which, I
believe, at the present day are rather expensive. But I believe the
time will come when battery plates will be manufactured like shoe
nails, and the process of renewing the positive plates will be a very
cheap one.
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