First on the list of power consumers is the exhaust fan, taking it in
average use. There are, however, circumstances under which its use
will be limited to as low as 70 or 75 per cent. of its contract hours
of service. As, for instance, in a dining room it may be cut out
except during meal hours, or entirely cut out on cool days. In places
of this description, however, its contract use is usually limited to
five or six months in the year, and other than electric power is, by
circumstances of first cost and inconvenience, but a feeble
competitor.
The first four applications on the accompanying list, viz., exhaust
fans, blowers, ceiling fans, and fan outfits, are all more or less
subject to the foregoing conditions, and therefore currents supplied
to motors for these purposes command the maximum price per horse
power. One important feature in the installation of ceiling fans is
the countershafting to the motor. In one recent case we had a
complaint from a customer that the half horse power motor sent him
would not drive the ceiling fans, and that the motor must be
defective, and should he return it for repairs. We immediately sent a
representative to find out the difficulty, which was found, as is
usual in such cases, in the countershafting, or rather the want of it.
The 3 in. pulley on the motor was connected to a 6 in. pulley on the
line shafting. The rated speed of the motor was 2,000 revolutions, and
had it been able to develop this speed, would have driven the line
shaft 1,000 revolutions and the fans a relative speed. To accomplish
this would probably require a motor of 3 or 4 H. P. The line shafting
driving ceiling fans usually runs about 75 revolutions. To give this
speed on the line shaft with a rated speed of 2,000 on the 3 in.
pulley of the motor would require a countershaft with a 24 in. pulley
belted to the motor. On the same countershaft should be a 5 in. pulley
belted to a 15 or 16 in. pulley on the line shaft. Fully three-fourths
of the trouble found in electric motors arises from improper shafting
and belting. The average make of 30 in. exhaust wheel, a ½ H. P. motor
should drive about 400 revolutions. Say, then, the speed of the motor
is 2,000 and the pulley 3 in., it would require a 15 in. pulley on the
fan to do the work. A 36 in. wheel requires 1 H. P. to develop the
same speed. If the motor speed is 1,800, the pulley 4 in., it would
require an 18 in. pulley on the fan to do the work. These are the most
popular sizes of exhaust wheels.
The next application on the list, open tank elevator pumps, commands
the highest price for current per H. P. in the motor of any elevator
application. The methods of operating the open tank hydraulic
elevators in question are undoubtedly familiar to you all. Instead of
the usual steam pump, a power pump of some approved design is
substituted, and connected to the motor by suitable countershafting to
give the required revolutions at the pump. The regulation of the motor
in this case should be controlled by the position of water in the
lower tank, as in the case of the steam pump. And in this connection
let me suggest the necessity of great care, both in installation and
insulation.
On all installations in basements and cellars or elsewhere where there
is the slightest tendency to dampness, raise the motor off the floor
on a suitable frame or stand and build around it on all sides of
possible approach a low platform, using glass insulators as legs or
standards to support it. So arrange this that the motor or its
connections cannot be reached except when standing on this insulated
platform, and the liability to a shock will be reduced to the
difference of potential between the terminals of the machine. To
return to the subject. Let us take for an illustration an elevator
using 120 gallons of water per trip and consuming one minute in making
its entire up trip or about two per round trip. The lower tank or
water supply is on a level with the pump. The upper tank is 70 ft.
above the pump, and in the piping to the upper tank are five elbows.
For each elbow add 2 ft. to the elevation, or an approximate total
elevation of 80 ft. × 120 gallons gives us 9,600 foot gallons. This
amount would be required every two minutes if the elevator was in
absolutely constant operation, or 4,800 foot gallons per minute × 8½
gives us 40,800 foot pounds. This we must at least double to allow for
friction in pump shafting, etc., making 81,600 foot pounds, or about
2½ H. P., say 3 required in the motor.
This class of elevator is confined almost entirely to passenger use.
Therefore the service required of the motor is much more constant and
the margin between the H. P. hours contracted for and the H. P. hours
of actual service much smaller than in any other elevator use,
excepting possibly the services in connection with pressure tank
elevators in the more popular office buildings. In this case we have a
maximum average use of 80, and instances such as the hotels, small
office buildings, etc., where the service will not exceed 60 of the
contract H. P. hours. In order, however, that the electric light
company shall derive the greatest benefit from this inconstant
service, the installation and wiring should be the best, and only the
most approved and economical apparatus employed.
The next application on our list, pressure tank pumps in connection
with elevators, represents a somewhat smaller percentage of H. P.
hours of actual service in the motor as compared with the possible H.
P. hours than in the case of an open tank pump. In case of the
pressure tank the water reserve is usually limited, and the motor
therefore must be equal to the continuous operation of the elevator at
maximum load. Taking this fact into consideration, and the
circumstances of elevator use being about the same in this case as in
the case of the open tank elevator, we have a greater ratio of
difference between the possible or contract H. P. hours in the motor
and the H. P. hours of actual service, the maximum average use being
about 70 per cent. to 75 per cent. and the minimum as low as 35 per
cent. to 40 per cent., depending, of course, on the character of
building in which the elevator is employed or the character of
service. In calculating the size of motor required on an elevator of
this description, a very convenient fact to remember is that every
pound of pressure per square inch is equivalent to lifting water about
23 ft., or about 230 ft. per 100 pounds pressure, By reducing the
required pressure to a relative lift in feet, and knowing the amount
of water required by the elevator per minute, the motor calculation
becomes the same as in case of the open tank elevator, the same
allowances being made for friction, etc., as in the first case. The
regulation of the motor in this case should be accomplished by the
conditions of pressure in the pressure tank, as is the case with a
steam pump employed in this service.
The next application of importance on the list is sewing machines. In
the tests I have been able to make on this class of work I have
obtained some singular results. One item of importance is the fact
that the single thread machines, which are lightest running, consume
the most power in operating. Paradoxical as this may seem, it is
easily explained. As a rule this class of machine is used on light
work, such as shirts, ladies' underwear, etc., and operated at a
higher speed than any other class of machine. At equal speed the volts
consumed on a single thread machine as compared with a shuttle machine
is about as 2 to 3. In average commercial use, however, the positions
are reversed, and the ratio of volts consumed in the single thread as
compared with the shuttle machine is about as 5 to 3. To double the
speed on a sewing machine requires about 2½ times the power. The
difference in volts consumed on the different makes of sewing machines
is so small that we may disregard it entirely, as well as the
character of work done by the machine, for the heavier the work the
slower the speed, and more frequent and longer stops on the machine,
thus keeping the average volts per operator about constant in all
cases. This leaves the speed in stitches per minute at the sewing
machine the factor from which we must calculate the power required in
a sewing machine plant. To illustrate this I will give you the record
of two cases which are about the average. Case No. 1 is a shop in
which are 30 sewing machines connected to a 2 H. P. motor. At the time
tests were made there were but twenty operators at work, leaving ten
idle machines, the entire shafting, however, being in operation. The
class of goods manufactured in this shop is a cheap grade of cotton
and wool pants, rather heavy goods to sew. A volt meter across the
terminals of the motor gave the following readings with the current at
9 amperes: Minimum 90 volts, maximum 148 volts, average 119, which
gives us a minimum average per operator of 4.5 volts and a maximum
average of 7.4 volts, or a general average of 5.9 volts per operator.
This motor was driving the shafting for 30 machines, and as the
average operators employed the year round will not exceed 75 per cent.
of the shop capacity, it will, I think, be entirely fair to estimate
the average volts per machine rather than per operator, as the user of
the motor has contracted for power sufficient to drive his entire
plant. In this case, then, we have a minimum average of 3 volts per
machine and a maximum of 4.9 volts, or a general average of say 4
volts per machine. A 2 horse motor of 82 per cent. efficiency with 9
amperes of current will require about 200 volts to develop 2 actual H.
P. Two hundred volts therefore is what the electric light company
contract to deliver, while, in reality, they deliver only 129 volts or
60 percent., or a minimum average of 90 volts or 45 per cent. of the
power contracted for. These machines were making about 1,200 stitches
per minute--an average of 4 volts per 100 stitches.
Case No. 2 is a shop in which there are 32 machines, running about
1,200 stitches, each being supplied with an individual motor of 1/8 H.
P. capacity, and the class of goods manufactured being men's summer
clothing, such as white duck vests, flannel coats and vests, etc., the
duck from which these vests are made being about as hard work on a
sewing machine as can be found. In this shop were 24 operators at
work. The maximum volts in this case were 116 and the minimum 40, or
general average of but 78 volts, or about 2½ volts per machine with 4
more operators than in the first case, in which we had an average of
119 volts. This shop has been paying the electric light company $32
per month for more than a year, which is the price the company charge
for current for a 4 H. P. motor which approximates 400 volts, the
company contracts to deliver. This gives us a minimum average use of
but 10 per cent. and a maximum of 29 per cent. with a general average
of 19½ per cent. In other words, the company is saving in this shop
the price of a 1/8 H. P. motor each month, besides making a profit on
the volts actually delivered. On a contract for three years the
electric light company would be money in pocket if they would present
the customer with 30 small motors, charging him $1 per month per motor
for current, rather than let him buy a 2 H. P. motor to operate the
same machines with the necessary shafting at a charge of $18 per month
for current. Taking this average in case No. 2 of 2½ volts per
machine, from a 50 light machine, we could run not less than 900
sewing machines, or about 18 to the arc lamp. At $1 per month per
machine an income of $900 per month would be derived from a 50 light
machine without any lamp expenses, such as carbons, repairs on lamps,
globes, etc. On the average, in case No. 1, of 4 volts per machine, we
could operate but about 562, say 600 machines. Divided up in shops of
30 machines and a 2 H. P. motor to each shop, we would have 20 two H.
P. motors. At a charge of $18 per month each, we would have an earning
capacity of but $360 per month from the same 50 light machine.
This is but one page from the thus far unwritten history of the much
maligned small motor. Still the question is frequently asked, "Can we
sell current for $1 per month for a small motor driving a sewing
machine and make a profit?" As a matter of fact, 50 cents per month
for small motors driving sewing machines yields a better profit to the
company supplying the current than $10 per month per H. P. in large
motors to drive the same machines, besides the immense advantage which
the small motors possess of keeping the circuit in much better
balance, the fluctuations due to the stopping and starting of large
motors being at times a serious matter. One electric light company,
making rather a specialty of these small machines, rent the motor and
supply the current for $1.25 per month per sewing machine, and report
that at this price the motor pays them a better percentage of profit
than their lamps. This company have some 200 small motors on their
circuits.
A more striking illustration of the advantages to the electric light
company in the subdivision of power into the smallest possible units
it would be hard to find. There is a difference in efficiency of from
15 to 20 per cent. in these two sizes of motors, but this difference
is fully lost to the large motor in driving the shafting, and the
small motor still has the advantage of being out of circuit entirely
when the machine it is driving is stopped. There is scarcely a
manufacturing industry which does not possess its busy and dull
seasons. This means that in no industry will over 75 per cent. of the
machines or machinery employed be in average operation. The entire
shafting in the shops must be kept in operation the entire year, often
for less than 50 per cent. of the machinery. Subdivide these same
shops into as many small units as possible, and the current necessary
to operate the shafting for this idle machinery will be saved, besides
the saving from frequent stops while the machinery is in active use.
To return again to the list, the next two applications, picture frame
manufacturers and moulding manufacturers, are very similar. Their busy
seasons, as a rule, are in the spring and fall, and also follow
closely any activity in house building. In the case of the larger
manufacturers in this line, a maximum average of 75 per cent. will
possibly be reached, but probably never exceeded. In the case,
however, of the picture dealer who has a small shop in which he makes
picture frames and mouldings to order the actual service of the motor
will fall as low as 25 per cent. or 30 per cent. of its contract
hours, one case in our experience the actual service having reached
this low average. A fair general average in this class of works would
be about 60 per cent.
The next application, nickel and silver platers and buffers, are good
contract customers as a rule; one case in our experience showing but
an average use of 20 per cent. of the contract horse power hours.
This, however, is probably an exceptional case, and, as near as we can
estimate on this class of work, the actual motor service will not
exceed in any case 60 per cent. of the contract hours; a fair average
being probably 45 or 50 per cent.
The next two applications, printing presses on news and job work, are
probably met with more frequently than any other. On exclusively news
work, the instances where the motor is in service more than 3 or 4
hours is rare. It is, however, usual in news offices to find two or
more job presses. If the newspaper printed happens to be a morning
paper, the hours of news work are usually between 12 midnight and 4
o'clock in the morning, the job work being done through the day. I
have in mind a case of this description. In the shop is one cylinder
press and three job presses connected to a 2 H. P. motor. This motor
is on an incandescent circuit of 110 volts. To develop its rated power
at 110 volts would require about 16 amperes in the motor. An ampere
motor in series with the motor while running off the morning paper
with only the cylinder press in operation stood at 12 amperes. For 3
hours this load was practically constant, when it was thrown off
entirely. This gave on the night service but 30 per cent. of the
contract hours. This motor required 5 amperes to drive the shafting,
and but 8 amperes or one H. P. to drive the three job presses with the
cylinder press off. Here then is but a 50 per cent. use if the presses
be used constantly; there are, however, many days when they are
comparatively idle, 30 to 40 per cent., therefore, is a very safe
estimate of the maximum use of this motor on the day circuit, or, had
the motor been a 1 H. P., which would have been sufficient to drive
the job presses, the use would be 60 to 80 per cent. of the contract
hours, probably not above 60 per cent. All printing offices will
probably come within this range, unless the motor be larger than is
necessary to do the work.
Machine shops doing principally lathe work as a matter of course use a
larger percentage of their contracted power than shops doing lathe and
bench work with the same hands. In no case will the service of the
motor exceed 65 or 70 per cent. of its contract use, for machine
shops, like sewing machine shops, will never average over 75 per cent.
of the shop capacity for operators the year round. The average,
especially in the case of a shop doing much bench work, will fall as
low as 40 per cent.
The driving of laundry machinery, which is our next application,
usually proves a profitable contract, according to reports. This fact
arises from the intermittent use of the machinery. The heaviest
service on motor will probably be found during the early part of each
week, with a general falling off in work during the summer months,
while the patrons of the laundry are away at the sea-shore or in the
mountains. In this application, therefore, a 75 per cent. service
would probably be an exception, with, probably, many instances where
the service would fall below 50 per cent.
The next application, model and pattern makers, are small users of
power, as their occupation requires a large proportion of hand work.
50 per cent. service in the motor will be found a fair average maximum
use, with instances as low as 20 or 25 per cent.
The next application, direct power or belt elevators, is another
application frequently met. The average service in the motor is also
much smaller than in any other elevator application. Let us suppose a
case of the familiar grip connected to the ordinary hand hoist, with a
lifting capacity of 2,000 pounds. In this case the motor is in use
only going up, and the usual brake is used in coming down. Connected
to this elevator, in the loft of the building, we have a 5 H. P. motor
wired to a cut-out on the ground floor. We will call the lift 45 feet
and the time consumed per trip 1 minute. We will allow 60 full trips
of the elevator at full load, at 2,000 lb. per trip, each day. This
would approximate 10 car loads of merchandise handled by the elevator,
which is certainly above the average. This motor, we will say, is on a
ten hour day circuit. Its possible horse power hours, therefore, would
be 5 H. P. for 10 hours, or 50 H. P. hours per day. 60 trips of 1
minute each gives us exactly 1 hour's service of the full 5 H. P. or 5
H. P. hours. To drive the shafting only while the elevator is coming
down or idle would require about 150 volts or 1½ H. P., and if this
was in constant operation the balance of the day, 9 hours, its total
use on shafting would be 13½ H. P. hours, which, added to the 5 H. P.
hours, gives us a grand total of 18½ H. P. hours, or 37 per cent. of
the contract hours. If, however, the user of the motor avails himself
of the cut-out box, and cuts the current out when the motor is not in
use, the average use would drop to 20 or 25 per cent., instead of 37
per cent. In the case of a direct power passenger elevator, the use
might possibly run up to 60 per cent., but this would be exceptional.
Coffee mills will average from 40 to 60 per cent. of their contract
hours, manufacturing jewelers about the same, while retail jewelers
will run as low as 25 per cent. Ice cream freezers will not average
over 25 per cent., but as the contract season in this case is usually
short, they should be rated at least a 50 per cent. basis, except
possibly in cases where the customer pays the cost of installation and
wiring, which is usual in these cases.
A dentist is one of the smallest of power users, so small, in fact,
that if every one in a city were connected with a circuit, the load
from this cause would never be felt. We will, however, put them down
at from 10 to 20 per cent.
The optician uses a motor to turn his grind stones, and its use in
this case will average from 20 to 30 per cent.
The last application on the list--church organs--uses only from 10 to
20 per cent. of the contract service.
These are, of course, but few of the very many applications of the
electric motor, and if, as I trust, the possible subsequent discussion
of this general plan may establish a basis for rating motor
applications, not only will the objects of this paper be obtained, but
a question of considerable annoyance now existing between the motor
man and the electric light or power company will be solved.
In conclusion, Mr. Chairman, I beg to suggest that the supply and
rates of charge for electric power have become of sufficient
importance to this association to be represented by a permanent
committee, whose duty it should be to obtain from the different
members of the association, as far as possible, their experience in
the supply of power in such manner and form as shall be deemed by the
committee best suited to the wants of this association.
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