Re: Sync 200BPS improvement, (long post !)
Subject: Re: Sync 200BPS improvement, (long post !)
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Fri, 23 Jul 1999 10:40:52 -0600
In-Reply-To: <Pine.GSO.3.95-960729.990722204941.5449A-100000-at-aidan.ncl.a c.uk>
This is very interesting and you should definitely try it. I have found
that simulations are great for figuring out these fun things out and they
tend to end up working perfectly as the simulation shows. They certainly
are wonderful for LTR coils...
You can easily have to rotor machined to hold all kinds of gap positions
and only use the holes you want at the moment. As long as the holes are
symmetrical so the rotor is balanced, I would go ahead and do all the hole
variations while it is at the shop.
I have never looked into such variable gaps much but sounds like you are
really onto something here!
At 08:52 PM 7/22/99 +0100, you wrote:
>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!
> \ / \ /
> \____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.
> - Richie,
> - 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 ?