Naturally these figures lead to the conclusion that the higher the voltage the more economical the conveyance, and such is indeed the case. These higher voltages are, however, dangerous to human life if contact is accidentally made with them, and therefore can only be used with highly insulated wires, which cost much more than the bare wires which may be safely used at 100 to 120 volts. Great divergence of opinion exists as to the limit of safe voltage. In England, it is customary to regard all over 200 volts as approaching the dangerous limit. In America, tensions of 400 volts are constantly used on naked wires in towns. The opposite table of power-conveying capacity of cables, with cost per 1,760 yards' run, will afford the necessary information for a selection of what is suited to given distances. The cost is liable to fluctuation with the price of copper. PARTICULARS OF ELECTRO-MOTORS. Motors. Electro-motors are practically dynamos reversed, that is their construction is exactly the same, but COPPER CABLES CONVEYING ELECTRIC FORCE AT DIFFERENT PRESSURES OR VOLTS. 100 200 300 400 500 600 700 800 1,000 Volts. Volts. Volts. Volts. Volts. Volts. Volts. Volts. Volts. Volts. 500 Volts. 1,000 Places. Ground. Volts. 7 20 .036 .0072 7.2 .841 1.69 7 18 .048 .0128 12.8 1.38 2.77 4.16 5.55 6.9 8.2 9.6 II 13 7 17 .056 .0174 17.4 2 4 6 8 ΙΟ 12 14 16 20 7 16 .064 .0229 22.9 2.69 5.38 8.08 10.77 13.5 17.3 18.8 21.5 26 £20 10 £76 10 £79 £83 £105 $102.50 $382.50 $395 $415 525 7 15 .072 .0289 28.9 3.28 6.56 9.84 13.12 16.4 19.6 22.9 26.2 £26 £92 £94 10 £126 32 $130 $460 $472.50 $505 $630 £33 £107 £118 £143 $165 $535 $550 $519 $715 £51 33.7 39.4 45 56 £137 £140 10 £152 £182 $255 $685 $702.10 $760 $910 51.6 44 58.7 73 £64 £173 £178 £193 10 £229 $320 $865 $890 $967.50 $1,145 £218 £238 £281 $395 $1,060 $1,090 $1,190 $1,405 £105 £258 £263 £281 £331 91.5 114 $525 $1,290 $1.315 $1,405 $1,655 30.16 45.24 60.32 75.4 96.4 105.5 120.6 £136 £336 £341 £360 £428 150 $680 $1.680 $1,705 $1,800 $2,140 19 12 .104 .1647 164.7 19.37 38.75 52.18 77.5 96.8 116.2 135.6 154.9 193 £181 £414 £422 £466 £532 $905 $2,070 $2,110 $2,330 $2,660 they rotate by the reception of current. The current is conveyed to them by cables or simple wires. The sections. of these wires varies with the power carried, and naturally, the larger they are the less loss of power occurs from internal resistance. About 22 per cent. is thus lost per 100 yards of distance at a tension of 100 volts in cables of good proportions and of a moderate first cost. Loss further occurs in the motor due to leakage and to the force necessary for its own rotation. This is surprisingly small, and in many tests has proved as little as 10 per cent. TABLE OF THE CONVERSION INTO ELECTRICITY OF EFFECTIVE HORSEPOWERS OF AN ENGINE, WHEEL, OR OTHER MOTIVE Power, the DEVELOPED ELECTRICITY DRIVING A MOTOR. Ι The basis of the foregoing table is the fact that I effective horse-power put through a dynamo, a wire, and a motor, brings out .624 of an effective horse-power. This is equal to an efficiency of the whole of 62.4 per cent., which is quite a safe figure to work on, as some such systems when tested have yielded over 70 per cent. efficiency of the indicated horse-power. COST OF SETS OF ACCUMULATOR CELLS TO SUIT VARIOUS TENSIONS. (With approximate 60-Watt lamps easily maintained by them.) The Settlement of the Number and Details of Accumulators. The standard accumulators to be relied upon for general purposes of lighting and of driving motors, are those known as the L type. These are made in 5 standard sizes, known by the number of plates they contain, 7, 11, 15, 23, or 31. Naturally their capability for reception of current, and consequent amount of output, are in a similarly increasing ratio, their maxima being 13, 22, 33, 50, and 66 for 10 hours in each case. The pressure of the current being made up by coupling accumulators one on to the other in succession, each may be taken at 2 volts, with a few additional cells to maintain the pressure as the discharging takes place. We must thus have, either a set of 26 to get 50 volts, We thus find that any of these sets give us the following maximum work for 10 hours in electrical and in effective horse-powers for a motor of .80 efficiency. |