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Re: LTR caps
Hi Reinhard:
>Hey, you beat me at that power level ;o)) !! At 900VA, my maximum spark
>was 51-53".
I don't know about 900VA. Lately I've been tripping my 20A breaker after
just 1 minute runs. The 14 gauge wires going to my variac are getting
warm in that time span. I suspect that with the larger caps, my NST is
pulling way more than faceplate VA from the wall. Some of that is going
to the vacuum motor, but with the dimmer, it can't be that much.
>However, you have encountered something very similar to what
>I did: You almost doubled your input Joules (from 2.7J to 4.95J), yet
>the spark length only increased by a mere 7" (of course 58" IS great, NO
>question about it).
I'm not sure there's any known reason to expect larger sparks. While the
bang size has almost doubled, the BPS has surely gone down (I've not
measured this, but it stands to reason as this is a static gap). It's
Joules times BPS (=Watts) that is the predictor of spark length.
>This is pretty much the same thing that happend to
>me. Obviously you retuned the coil. Did you try running a larger topload
>on the LTR setup? I can=B4t try this, yet, on my coil, because I ran out
>of toroid material (and $$ for this month ;o}).
No, same two-toroid setup as I always use.
>Did your coil give you
>(aka like mine) 58" arcs plus a few "non grounded rod" interested
>streamers? With my present toroid, I get 2-4 streamers of about 8-10"
>length that will emit from the toroid, even though I have a 57 incher
>connecting to a grounded rod (suggesting to me the toroid is way
>too small). And, as you suggested, my non-cooled static gap probably
>can=B4t handle the ~600A primary current properly any more. I always
>thought the Joules (And of course the transformers capability to
>recharge it "fully") were THE major factors in spark length. Yet, your
>and my own experience seems to show this isn=B4t the full truth.
My technique for measuring sparks is to set a nail on the toroid and
aim the arc at a foundation wall, the anticipated distance from the tip
of the nail. If and when the distance is met, the arc becomes much
brighter. So, with the nail, I only get one streamer.
>Didn=B4t
>you do some MSims a while ago, that told you 22nF would also be
>about right for your RSG? I would love to see the spark length
>increase you will get from static vs. rotary gap.
Well, kind of, but that was for a synchronous gap at 120BPS. My
simulations for static gaps predicted that the power throughput with a
static gap and a 20nF cap would be poor. Embarassing. I'll have to go
back to that.
>> One further thing of interest here. The reason I migrated from the
>>FRS cap to an MMC was that the FRS cap became warm. With
>>the two in parallel, that is no longer the case. This isn't too
>>surprising due to the no doubt lower BPS occuring with the larger
>>cap, but it does show that the FRS caps can be made to work
>>reliably.
>Another possibility that springs to mind is the current. While you
>increased the total primary current, you have now divided it up
>between "2" caps (MMC and FRS). Of course, if you "exactly"
>doubled the current, this theory doesn=B4t hold true, but if the
>primary current is NOT twice the old primary current (i.e. less
>than 2x), then each cap will see less current, than when they
>are run alone.
You're quite right about the current splitting. i'm not sure what the
new current is but it's surely very roughly half (per cap) as before.
That coupled with the lower BPS may result in something like 1/4 of the
heating per cap as before.
Regards, Gary