Nikola Tesla Books
Books written by or about Nikola Tesla
From this and $! { p_{1}^{2} \, = \, {10^{9} \over 29} } $! and p1=6000 volts approx. (26 H.P. expenditure, 1600 breaks per sec.)
With this e.m.f. assume 4 ohms res. of arc, the initial current would be 1500 amp. through the primary. From these assumptions the loss in the primary may be computed.
Colorado Springs
June 22, 1899
Wire for the new secondary ordered from Habirshaw No. 10 B.&S. rubber covered; all in all about 11,000 feet needed (more nearly 10,500 feet). This will do for 80 turns of an average length of 131 feet each.
No. 10 am. gauge 5.26 mm. square or $! {5.26 \over 645} $! sq.inch
100 feet will have: $! {5.26 \over 645} $! x 1200 = 9.8 cu.inches.
The weight of this, taking 5.13 ounces per cu.inch will be
$! {5.13 \over 16} $! x 9.8 = 3.14 lbs.
Accordingly, 11,000 feet will weigh 345.4 lbs. This will give still less copper in the secondary than there is in the two primary turns. With secondary wire double we shall have 40 turns and with four wires (for quick vibration) 20 turns. The weight of copper should be equal and some of the No. 10 cord may be used on the first low turns.
Some arrangements were tried aiming chiefly at prolonging the vibration in the primary after each break. One of these was as illustrated in the diagram below:
The condenser C1 was placed in shunt to the primary P. Since there was no spark gap in this circuit and the magnifying factor was very large, the resistance being minute, the vibration continued much longer after each break as would be the case with the ordinary connection. A very curious feature was the sharpness of tuning. This seems to be due to the fact that there are two circuits or two separate vibrations which must accord exactly. The sparks were strong on terminals of the secondary always when C = aC1, a being a whole number (no fraction), and particularly when a = 2 or 4.
This arrangement was carried out in New York on one of the later type oscillators and similar results were observed.
43
June 21
Returning once more to the problem of the conversion of mains power into HF power Tesla calculates the energy in each charging cycle of the condenser (see comments for June 20th). Taking it that all the energy in the charge condenser will at some instant be found in the condenser of the secondary circuit, he in fact works out the peak voltage on the secondary condenser. The energy equation for lossless coupled circuits has the general form
$!{1 \over 2}$! CpU2p = $!{1 \over 2}$! CsU2s
where p refers to the primary, s to the secondary circuit, U is peak voltage. It should be noted that Oberbeck's theory(29) yields the same ratio between the voltage on the primary condenser just before discharge begins and the peak voltage on the secondary condenser.
June 21
Returning back again to the question of power transfer from a supply network to high frequency power, he calculates the energy per capacitor charge impulse (please see comment of June 20). Considering that all energy of the charged capacitor in one instance exists in the capacitor in the secondary circuit, Tesla actually finds the maximum value of voltage on secondary capacitor. For linked circuits without losses the energy equation is:
$!{1 \over 2}$! CpU2p = $!{1 \over 2}$! CsU2s
Where the values with index 'p' pertain to the primary circuit and those of index 's' to the secondary circuit. The maximum values of voltage are designated by 'U'. It has to be mentioned that according to Oberbeck theory (please see Appendix: Tesla's Oscillator) the same ratio of capacitor voltage in the primary before the start of the discharge and the maximum voltage on secondary circuit capacitor is obtained as well.
June 22
The circuit with two condensers, one being charged from the power supply and the second via a spark from the first represents a modification of Tesla's classic oscillator*. Theory shows that protraction of the oscillation in the primary circuit lowers the efficiency of the oscillator because energy pulses back and forth between the primary and secondary. However, in this circuit protraction of the spark does not have the same effect because while it lasts the primary capacitance is C + C1, but when it stops the capacitance is only C1. Why the sparks in the secondary were stronger with C = aC1, a a whole number, is hard to say without a more exhaustive analysis.
The note at the end of the entry indicates his satisfaction with the results and that he felt it necessary to continue research in the same direction.
June 22
The circuit with two capacitors, of which one is fed from the network, and the other via a spark from the first one, represents the variation of Tesla's classic oscillator*. According to theory the prolonging of the oscillation in the primary circuit reduces the oscillator efficiency due to energy transfer from the primary to secondary and vice versa. On the shown circuit the prolonging of the spark duration does not have the same effect, because during spark existence in primary circuit there is capacitance C + C1, and after spark interruption only C1 remains. Why the sparks in the secondary are more powerful when C = aC1, where 'a' is a whole number, cannot be determined without in-depth analysis.
As proof of better oscillator operation, Tesla accepts longer sparks at the secondary terminals. Sometimes he mentioned other spark characteristics but he assumed that oscillator operates the best when the spark is longest.
According to the schematics shown Tesla experimented with those circuits already earlier in New York. The schematic below with special oscillating circuit represents a system with three linked oscillating circuits, and therefore the oscillation spectrum is more complex. Tesla's remark that the device operates better in such a layout when the number of arcing device interruptions is low (when in the classic schematic with two oscillating circuits the oscillator operation in two oscillating conditions is more emphasized), indicates a possibility of one new approach to oscillator with suitable spectrum even with a relatively good link between exciting and operating circuit.
From time to time Tesla puts special remarks at the end of the notes. On this place, obviously satisfied with achieved results he underlines that research has to be continued in the same direction.
* Several drawings which are given on page 15 are reproduced from original slide found in archives of Nikola Tesla Museum in Belgrade. Four transmitter variations are seen on them which Tesla probably intended to protect by patent.
