One 'sanity' question for the list:
My coil is using an RF ground only. The NST ground (ie, case) is not
connected to the mains ground; nothing is connected to the mains ground at
all. This is by design because I do not want any possible over-voltage to
feed back into the mains supply and possibly damage other equipment.
The only two ground connections are 1) The bottom of the secondary coil to
RF ground and 2) The NST protection filter to RF ground. Both meet at a
common grounding point before the wire which leads to the actual earth
connection.
Can I get someone to validate this setup is normal and not somehow going to
destroy my equipment?
Thank you :)
Joshua Thomas
On Sun, Nov 21, 2021 at 2:05 PM Joshua Thomas <joshuafthomas@xxxxxxxxx>
wrote:
> Hello unnamed person :)
>
> Thank you for your feedback. I'm unfamiliar with winding my own chokes.
> That is, I'm unclear on how to design my own chokes for a particular
> specification, and I lack an LCR meter to determine I have enough
> inductance. If I use my existing 500ohm/100W resistors to form a RL lowpass
> filter, I will need two chokes of approximately 0.25mH each.
>
> > The real key to not burning out your NST is proper tuning.
>
> Yes, I'm not quite sure what other tuning I need. Changing the tap
> position has not made an appreciable difference. I have tried a smaller
> topload; a 1" torroid vs a 4" torroid, and did get increased spark length,
> but not significantly. (Obviously I had to change the tap point).
>
> > I always meter off the ground connection of secondary with a shunt
> resistor.
>
> What type of resistor do you use? I would really like to not destroy an
> oscilloscope! Do you require differential probes for this?
>
> Thanks again.
>
> Joshua Thomas
>
>
> On Sun, Nov 21, 2021 at 7:59 AM <pupman.com@xxxxxxxxxxxxxxxxxxx> wrote:
>
>> Hi,
>>
>> I just use large air cored chokes and a spark gap. It's simple, and
>> impossible to burn out. There's no need for some rube goldberg setup. HV
>> capacitors are expensive and like fuses can only be abused once. The last
>> set I made was probably on 2" PVC with 6" of #28 windings or something
>> similar to that. Protection spark gaps should be pointy and just on the
>> verge of firing. If they arc at full line voltage and no load, even
>> better. You don't get full nameplate voltage on a NST at full load
>> anyways, so don't expect that with a coil running. It's a not that
>> different from how you should never run a microwave oven empty. They must
>> have a load to prevent arcing.
>>
>> The solid state ignition transformer sounds fun. I ran my coils off DC,
>> rectified from NSTs or even unshunted transformers.
>>
>> The real key to not burning out your NST is proper tuning. I could tell
>> from the video you posted a week or so ago that the coil was still not
>> tuned correctly, or other adjustments are still needed. The sound of the
>> spark gap and how the arcs looked was the key. You should be able to get
>> streamers that grow in length and do not not look like DC arcs from a
>> power pack or electrostatic generator. Even for a coil the size of yours
>> the tuning will change due to the proximity of objects nearby, even your
>> arm or a ground lead. For maximum fun, tune the coil to you and the
>> ground
>> wand you draw arcs off.
>>
>> If you can look at the waveform for the coil with an oscilloscope, that
>> helps too. I always meter off the ground connection of secondary with a
>> shunt resistor. It's the safest place to obtain a low voltage with
>> respect
>> to ground for taking measurements or attaching instrumentation.
>>
>> Congrats of the first light!
>>
>>
>> On Sat, 20 Nov 2021, Joshua Thomas wrote:
>>
>> > Hello all,
>> >
>> > I've been struggling to build a lowpass ("Terry") filter to protect my
>> NST
>> > from RF feedback. The first one suffered arc-overs because
>> > the capacitor leads were too close together, and the second one had the
>> > capacitors fail - apparently only 9kV per rail wasn't enough. It's a
>> 12kV
>> > NST so I assumed 18kV > 12kVx(sqrt 2) and therefore would be sufficient.
>> > Apparently not.
>> >
>> > What suggestions are available for those who have made a NST filter that
>> > was successful? Particular capacitor types/brands would be welcome, as
>> well
>> > as how the physical layout was accomplished. I use two 500ohm/100W
>> > wire-wound resistors for the R half of the RC filter.
>> >
>> > On a different topic I got a used OBIT for $35, but it appears to be a
>> > solid-state one running pulsed DC. The model is Allanson 2275-628G.
>> 17.5kV
>> > "peak", 45mA, at 20khz. I mainly bought this for curiosity to see how it
>> > might perform on a coil. I'm a little suspicious of the voltage and
>> > amperage, as the total VA rating is only 87.5VA - which is a fraction of
>> > the 560VA that would be expected from 12.5kV RMS (17.5kV peak) at a full
>> > 45mA!
>> >
>> > What experiences has anyone had with one of these?
>> >
>> > Cheers,
>> > Joshua Thomas
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > --
>> > Joshua Thomas
>> >
>> > My new email address is: joshuafthomas@xxxxxxxxx
>> > Please update your information if you have not already done so.
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>> >
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>
>
> --
> Joshua Thomas
>
> My new email address is: joshuafthomas@xxxxxxxxx
> Please update your information if you have not already done so.
>
--
Joshua Thomas
My new email address is: joshuafthomas@xxxxxxxxx
Please update your information if you have not already done so.