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200BPS rotary gaps and cap selection




On 8th April Gary Lau wrote:

> It will be interesting to run a similar simulation with the gap firing
> multiple times per half-cycle, to see which cap size draws highest power


Do you mean like this.....


"PSpice simulation to determine most effective tank capacitor size for
 maximum power transfer using ballasted radar transformer and 200 BPS
 synchronous rotary,"

The ballasted transformer was measured and then PSpice simulation was
carried out after modelling the transformer winding res. and ind. etc.

Open circuit voltage:   10Kv rms
Short circuit current:  224mA rms
Effective leakage ind:  142H (referred to HV sec.)
50Hz resonant cap:      71.3nF

For each capacitor value that was tried the firing delay of the simulated
rotary was "Manually" adjusted to give TWO EQUAL BANGS per half cycle
of the supply voltage.  This involved many, many hours of simulation
to get the optimum firing delays to the nearest 10us !  This is necessary
to avoid getting one insignificant bang and one MASSIVE bang per half
cycle.  I'm sure the massive bang would overvolt something in the real
world.

Once the best firing angle was found for each capacitor,  the firing
delay,  firing voltage,  and RMS supply current were examined.
>From these the following parameters were calculated,

Simulation results:
        C = Capacitor value in nF
        t = RSG firing delay (in ms after mains zero cross)
        V = Capacitor firing voltage
        P = Power throughput (= 200 * 0.5 * C * V * V)
        VA= Mains supply VA
        pf= Power factor (kind of like a measure of efficiency)


C [nF]  t [ms]  V [v]   P [W]   VA      pf

15      0.01    17717   471     825     0.571
20      0.04    19655   773     953     0.811
22      0.10    20049   884     1074    0.823
24      0.17    20314   990     1150    0.861
26      0.24    20570   1100    1233    0.892
28      0.35    20699   1200    1319    0.910
30      0.46    20790   1297    1405    0.923
32      0.57    20792   1383    1494    0.926   <---- Max firing volts
33      0.63    20757   1422    1534    0.927
34      0.69    20739   1462    1575    0.928   <---- Best power factor
36      0.81    20639   1533    1654    0.927
38      0.93    20484   1594    1727    0.923
40      1.05    20296   1648    1801    0.915
42      1.17    20068   1691    1864    0.907
44      1.28    19843   1732    1927    0.899
46      1.38    19524   1753    1988    0.882
48      1.49    19237   1776    2041    0.870
50      1.60    18946   1795    2090    0.859
52      1.70    18608   1801    2136    0.843
54      1.80    18271   1803    2178    0.828   <---- Maximum power thru'
56      1.89    17914   1797    2213    0.812
58      1.98    17585   1794    2248    0.798
60      2.07    17216   1778    2282    0.779
65      2.27    16354   1738    2345    0.741
70      2.45    15500   1682    2396    0.702
80      2.76    13914   1549    2467    0.628
100     3.22    11327   1283    2526    0.508

50Hz resonant cap:      71.3nF
Cap for max voltage:    32.0nF  (45% of 50Hz res cap)
Cap for best power fac: 34.0nF  (48% of 50Hz res cap)
Cap for max power:      54.0nF  (76% of 50Hz res cap)

So which cap do you choose ?

Well I did this work to try to decide what cap to use for my new coil.
I finally chose to build a total of 44nF of tank capacitors,  this
is in between the maximum efficiency and maximum power values.
However I realise that using 44nF only draws 1927 VA through my
transformer,  so I have made provision to lower the ballast inductance
if desired in order to get more power and to get closer to the maximum
power match.

Since there has been a lot of "eye-strained hours" looking at a PC
I hope this bit of research leads to big sparks for myself and others,


PS. If anyone is interested in my 200BPS sync rotary simulations I have
graphs of the above data along with PSpice schematics for other
simulations including the chaotic behaviour of static gaps.  I could
post these to a "Tesla Friendly" site.

***** US Readers BEWARE, this all refers to 50Hz UK power *****


                        Richie Burnett,

                                - Spendin' far to long at the PC
                                  in sunny Newcastle