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Re: larger than resonant (fwd)
Original poster: List moderator <mod1@xxxxxxxxxx>
---------- Forwarded message ----------
Date: Sun, 3 Jun 2007 08:03:27 -0400
From: Dave <dgoodfellow@xxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: larger than resonant (fwd)
Scott,
I can't imagine great performance from a 300 turn secondary. My coils
really took off when I went to 30 gauge wire, winding with about 1200 turns.
This also required more primary turns, the benefit of which should not be
underestimated. I have also used smaller than resonant capacitors with
success. STR has the advantage of a faster firing rate, which I find
produces a more pleasing sound when the coil is running. Using more turns on
the primary reduces spark gap losses, according to John Freau. Years ago, I
thought I was doing well to get a foot of spark from a 15/30 nst. That was
with a 6" coil with 800 turns on it and an 8" sphere topload. Now, if I
build a coil with a 4" x 18" secondary (1200 turns) a 13" toroid, a primary
with 20 turns on it, and a .0075uf capacitor on a 15/30 nst, I will
typically get just short of 3 feet of sparks, with the gap opened only 7/32"
. The sparks are emitted in a nice smooth continuous tone, not a raspy
rat-a-tat-tat that can be produced by a cap that is a little too large for
the transformer. As some of the other responders to this email have
suggested, you should look at the whole picture, that is, every component in
your coil, rather than hoping for improvements in performance by optimizing
your capacitance value.
Good luck,
Dave
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, June 01, 2007 11:39 PM
Subject: Re: larger than resonant (fwd)
Original poster: List moderator <mod1@xxxxxxxxxx>
---------- Forwarded message ----------
Date: Fri, 01 Jun 2007 23:40:53 -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: larger than resonant (fwd)
So, what would be best if using a sync spark gap, on a MOT powered 6-in
coil, LTR or STR? I still am unsure as to the exact amount of current going
through my MOTs, but I think 200-250 mA is a good estimate, at around 8 kV.
I currently use 75 nf, which I believe to be close to "resonant" sized,
which may be a bad thing according to what I am hearing. Also, I have a
small coil, a three incher that will ONLY run in tune with a small 2.9 nf
capacitor, I have tried lots of other values, but it always stops working at
higher or lower values, regardless of where you tap the primary. It is 10
kV at 92 mA. It has a 3-in secondary wound 12 inches with 20AWG (300 some
turns, which is low, but it is what I had at the time). Any more thoughts
would be appreciated.
Scott Bogard.
>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: larger than resonant (fwd)
>Date: Fri, 1 Jun 2007 20:43:02 -0600 (MDT)
>
>Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Fri, 01 Jun 2007 19:20:25 -0700
>From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: larger than resonant (fwd)
>
>Hi Scott,
>
>Smaller transformers like NST's will almost always run LTR. Larger
>transformers like PT's and PIG's will often run STR. Gary mentioned bang
>size. This is a big deal for both NST sized transformers and large pigs.
>If you were to run STR with an NST, the cap would be small and the bang
>energy would also be small. Your better off from a spark length
>standpoint to run LTR with one of these smaller transformers. The reason
>has to do with a transformers ability to charge the cap which is based
>on the cap value and the current available from the transformer. That is
>the reason why we only go "so far" with LTR sizes. Thus, each
>transformer rating has it's own LTR value.
>
>Larger transformers like pigs, if run LTR, would have an incredible bang
>energy that could be devastating (and expensive). There is some limit to
>transformed energy for every coil before the coil turns into a blaze of
>glory, but one we almost have to blow it up before we actually find that
>limit. In most cases, large transformers are better off running STR to
>keep the bang energy within a coils abilities.
>
>In both cases, the spark gap, when running without a failure, will limit
>the breakdown voltage. If a static gap, it's a constant limit that
>usually decreases with time due to heat buildup, but for a rotary gap,
>the timing of electrode alignment and the current available to charge
>the cap is the limit for voltage. It is possible to run very high bps,
>but the balance between current and capacitance must be met. If either
>is not designed well for the bps ran, sparks can diminish, but if done
>right, spark lengths can be very good. I personally like a 300 to 340
>bps myself when I run my variable rsg. If I were to change capacitance
>or transformer for the same coil, there would be a different bps range
>where the coil runs best.
>
>Take care,
>Bart
>
>
>
>Tesla list wrote:
>
> >Original poster: List moderator <mod1@xxxxxxxxxx>
> >
> >
> >
> >---------- Forwarded message ----------
> >Date: Fri, 01 Jun 2007 05:54:39 -0400
> >From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
> >To: tesla@xxxxxxxxxx
> >Subject: larger than resonant
> >
> >Hey everybody,
> > Can somebody explain to me the advantage to using a "resonant" or
> >"larger than resonant" tank capacitance? I seen coils get huge sparks
>using
> >LTR and also very small tank capacitors, so what is the point? Thanks.
> >Scott Bogard.
> >
> >_________________________________________________________________
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