Are you sure you're running a single MOT coil on a single static gap?
That's not supposed to be possible due to quenching issues... Mind posting
a few pictures? I might try to make one as well :)
What capacitors are you using? Not the microwave capacitor, I hope (those
can blow up).
On Wed, Dec 25, 2013 at 6:00 PM, Will <postmanw@xxxxxxxxx> wrote:
> Thank you Dave,
> I will look into getting a second MOT and a better capacitor bank
> for the primary circuit, I have re wired the primary now so that the spark
> gap (which is a static single spark gap) is in parallel with the output of
> my first MOT. The primary coil and capacitor bank are in series with the
> output of the MOT.
> I will look into building a rotary spark gap later on rated for ~4kv
> as hopefully by then I will have 2 MOTs for a power supply. I will also
> look into finding another MOT to ballast the primary circuit. Thank you for
> your help, I have noticed an improvement already and now have ~14 inch
> sparks.
>
> On 2013-12-23, at 22:40, David Speck <Dave@xxxxxxxxxxxxxxxx> wrote:
>
> > Will,
> >
> > If you are getting 12" sparks with a single MOT for a power transformer,
> I'd say that you are really doing very well. The general consensus on the
> list is that MOTs are difficult for TC use because their voltage is so low
> that it's hard to get a gap to fire without very finicky adjustments.
> >
> > You didn't mention what kind of gap you use (static single or static
> multiple gap, or rotary (synch or asynch)) and what you are using for a
> primary cap.
> >
> > If you are using a static gap, just blowing a lot of air from a beefy
> fan or shop vacuum on it will improve your quenching and make your sparks
> longer.
> >
> > I think you misspoke -- if the primary capacitor was in parallel with
> the spark gap, all of the energy in the cap would be wasted in the gap, and
> little would end up in the secondary.
> >
> > These days, the consensus seems to be that the power transformer
> secondary and the gap are in parallel, feeding the cap and the primary coil
> which are wired in series. However, that will require good ballasting of
> the MOT so that it will have some degree of current limiting while the gap
> is firing. While the gap is firing, the transformer current must be
> limited by the ballast, as the firing gap is pretty much a short circuit.
> >
> > A circuit breaker is definitely not equivalent to a ballast. A ballast
> limits the current through the transformer on a cycle by cycle basis. A
> breaker just shuts the system down if an instantaneous overcurrent
> situation happens. There's a big difference between a throttle and a kill
> switch.
> >
> > You didn't mention the length of the secondary. Current thinking says
> it should be between 4 and 5 times the secondary diameter.
> >
> > Might want to look up JavaTC, a comprehensive online calculator that can
> optimize all sorts of TC parameters.
> >
> > Just adding a second MOT in series with the one you already have would
> double your primary voltage, and give yo more spark. Of course, that will
> require a better rated primary cap.
> >
> > Just be aware that unlike NSTs, contact with a MOT output can easily be
> lethal. NSTs bite hard, but MOTs play for keeps. You don't get second
> chances when working with MOT circuits.
> >
> > Varnishing the secondary will help keep the wire in place. If the wire
> slips down, you will get a shorted turn which will significantly reduce
> your performance.
> >
> > Dave
> >
> > On 12/23/2013 10:09 PM, Will wrote:
> >>> Hello,
> >>>
> >>> My name is Will, I am 14 and have a fair bit of experience with
> tesla coils for my age (I have built several smaller coils with current
> limited Neon sigh transformers with no GFCI's on them).
> >>> My science teacher wanted me to construct a rather large SGTC for
> him. So far I have constructed a basic coil (the capacitors are in parallel
> with the spark gap, and the spark gap is in series with the secondary and
> the transformer.) It has ~3500 turns of 28 gauge magnet wire on 6 inch
> white PVC for the secondary. The torroid is comprised of a metal dryer duct
> pipe curled into a circle and measures about 18 inches in diameter.
> >>> The primary has 8 turns of copper tubing. The coil is powered by a
> 2100v Microwave oven transformer. The capacitor bank has a total
> capacitance of 1uF at 2100v.
> >>> Please note that the transformer is not ballasted, instead I simply
> ran it through a 15A breaker switch. I know that this is not exactly the
> same as a ballast but it keeps the coil from tripping other circuits in my
> house.
> >>> The secondary is not varnished (I am not sure if this effects
> overall performance of the coil, but thought I would mention it anyway.)
> >>>
> >>> I have not tuned or measured either of the coils frequencies, but
> would like to. Guidance on this would be appreciated. The coil throws out
> ~12 inch arks at the moment, and generally there are no problems with the
> coil. I would like to tweak it's performance as much as I can. Suggestions
> for improvements would be appreciated .
> >
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