Sync 200BPS improvement, (long post !)
Hi John, Reinhard, all,
Just thought I would inform the list about a simple improvement which
I discovered with the 200BPS sync gap idea. It improves power factor, and
total power throughput and also seems to get round the problem which
Reinhard had with his particularly stiff neon supply. (7.5kv -at- >700mA!)
Today I was doing drawings for a machinist to follow while making my
200 BPS sync rotary gap. I started thinking about electrode spacing
and how I would divide the disk up into equal quarters for the
electrodes. I then had a brainwave.
Equal gaps between electrodes allows equal time between presentations
for the cap to recharge. This would work great with a DC supply,
where the charging current is constant, but how many of us use DC ?
The charging current waveform is very non linear !, and we naturally
make allowances for this by setting the phase to get 2 equal bangs per
cycle when running at 200BPS. I now realise that this is not optimal,
and it got me thinking about when John Freau mentioned unevenly spaced
If the every other electrode on the rotating disk is moved clockwise
slightly, this gives alternate charging times of slightly less
than 5ms and then slightly more than 5ms. Simulation shows that this
seems to be better suited to the non-linear charging in an AC system.
Evenly spaced 200BPS sync rotor New idea 200BPS sync
rotor (for 3000RPM) rotor (for 3000RPM)
/ o \ / o \
/ \ / \
! ! !o !
!o o o! ! o !
! ! ! o!
\ / \ /
I did many simulations using MSim PSpice and found that if the time
between presentations was set to be 4.25ms and 5.75ms, and the phase
was adjusted to equal the bang sizes, then more power was sucked from
the transformer and the power factor increased considerably.
Supply o/c volts = 9540 VAC (Values were measured from my
Supply s/c amps = 224 mA actual ballasted supply.)
Supply VA = 2137 VA
Tank cap = 47 nF (MMC)
Using evenly spaced electrodes:-
Gap firing volts = 19.0 kv
Power throughput = 1690 W
Supply VA drawn = 1887 VA
Power factor = 0.896
Using unevenly spaced electrodes:- (spacing ratio 4.25ms/5.75ms)
Gap firing volts = 21.1 kv
Power throughput = 2097 W
Supply VA drawn = 2216 VA
Power factor = 0.946
This improvement seems worth the effort of offsetting every other
electrode. In my case every other electrode would need moving about
6mm. I am seriously considering doing this with the new gap design.
I did simulations with more and less offsetting of the electrodes, but
4.25ms/5.75ms seemed to look best. More offset led to higher firing
voltages still but also made the cap voltage ring higher and higher in
between electrode presentations. I think this gap makes good use of the
inductive kick effect to drive the firing voltage higher.
Although it is accepted that 100BPS can give bigger sparks, I still
like 200BPS sync because of its smaller capacitor size, and its better
ability to keep the voltage under control over time. It makes a cool
sound and although the sparks are a bit shorter they look a little
Time to try the idea out on a real coil, and see if reality matches the
Comments, (and any reasons not to offset electrodes)
welcome as always.
- In sunny Newcastle.
PS. I tried sims for many uneven spaced electrodes at high BPS, and
got poor power factor. Seems to agree with your findings John ?