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RE: [TCML] Questions on grounding
I'm sorry Bart, but I'm going to have to challenge your grounding
comment, if for no other reason than to give you and the other wise
gurus the opportunity to enlighten me if I am off base.
My own critical analysis (some time ago) of how a Tesla coil functions
led me to this conclusion:
The energy from the primary circuit of a tesla coil is not actually
transferred electrically to the secondary coil, but rather it creates a
strong magnetic field that effectively induces an oscillating electron
pumping effect in the secondary coil. I had always just assumed (because
I never really thought about it) that the electrons somehow moved from
one coil to the other.
Looking at it from this perspective, if we visualize that the electrons
are being pumped into the collector at the top of our coil via this
pumping action, then there must be an abundant source of these electrons
to draw from in order to keep the before mentioned collector filled to
capacity and have enough extra energy to create a substantial streamer.
>From this observation I tend to believe that a good earth ground is
paramount to optimum coil performance.
In addition, if we think about the coil as a capacitor charger, with the
collector being one plate of the capacitor, the earth being the other
plate, and air acting as the dielectric, it seems to me that our
streamer length is dependent upon the capacitive coupling between the
collector and everything that surrounds it. Everything that is in
contact with earth that has some amount of conductance potential. We all
know that this sort of voltage will turn most insulators into
semiconductors, and that resistance becomes a moot point with this sort
of voltage pressure, so in effect everything that is connected to the
earth becomes a part of that other capacitor plate. So again, from this
perspective, since everything connected to the earth in some fashion,
and thus is electrically attractive, wouldn't a really good ground make
it even more so, on account that the resistance between the
secondary->earth->object close to collector could be reduced by millions
of ohms that would otherwise be present if the bottom of the secondary
was not well connected to earth?
It makes sense in theory.
"If I had a world of my own, everything would be nonsense.
Nothing would be what it is, because everything would be what it isn't.
And contrary wise, what it is, it wouldn't be. And what it wouldn't be,
it would. You see?"
From: bartb [mailto:bartb@xxxxxxxxxxxxxxxx]
Sent: Monday, April 20, 2009 7:01 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Questions on grounding
Remember when I said (after the other replies) that it may or may "not"
help? That was the reason I responded in the first place is because
"grounding" is not about spark lengths, it's about component protection.
For spark length increases I mentioned the gap as did others and also
more power needed. These are still the two main adjustments you can make
to your coil to gain spark length. The gap is always #1 on the list of
things to do. Carriage bolts have been used by everyone at some point
(including myself), but there is a time when you must simply build a
smart gap that is smart for Tesla coil systems.
When considering a static gap, it's important to understand "why" a tube
is better than a solid stock of anything else. The tube has a great deal
of surface area (both inside the tube and outside the tube). This area
allows heat to be radiated away from the initial path of high current
contact of the spark as well as the build up of heat throughout the
tube. A bolt or even a cylindrical tube which is solid, only has the
outer surface to dissipate heat. The thicker the solid stock, the slower
it will rise to temp, but, even thick solid stock electrodes heat up
rather quickly and then performance begins to diminish due to the poor
ability to radiate heat away. Tubes however, have the ability to radiate
heat away when air is blown through them and across them. Thin walled
tubes are actually better for this as opposed to thick walled tubes.
Consider a 1" diameter sphere made of copper. Heat it up to 300
degreesF. Then do the same with a 1mm sphere. The 1mm sphere will heat
up to temp faster because it's mass is smaller. But, it will also cool
faster. Thin walled tubes act the same way. They heat up quick but they
also cool down quick, so they are easier to maintain a specific
temperature without a wide variation. They are more responsive to air
flow and this is a key aspect.
Both hyperbaric and TCBOR cylinder spark gaps use tubes. Tubes do very
well. Tubes on a flat slab are not wonderful simply due to how the air
is forced across the tubes. Ideally, you want cool air from the outside
to be drawn in across both the outer and inner surfaces equally for all
the tubes (that's hard to do on a slab). The TCBOR gap allows this very
feature if built correctly. The hyperbaric gap also pushes air inside
and outside the tubes. The hyperbaric gap has the added advantage that
there are only 2 tubes. This is both a mechanical and electrical
Although air might help your carriage bolts (barely), a new gap and
doubling the power is what will help your coil perform to the potential
it is capable of. You can certainly skip around this and look at other
avenues, but none of those avenues will lead you to greater spark
> Hello. I am somewhat disappointed at the moment. Tonight I got to fire
> up the coil now that the secondary and nst are grounded to earth and I
> have a boxer fan blowing on the gap. I am only getting 12" sparks to
> ground using my 14 turn prin/1400 second with 12kv/30ma nst, .0125uf
> mmc and 4"x17" toriod. The Q of the circuit must be pretty low as
> moving the tap from 14 to 15 turns make almost no difference.
> Adjusting the gap wider apart makes a little difference but going too
> wide and I start getting flash over somewhere near the nst and some
> spark jumps from the pri to sec. As I said before, the pri is too
> close to the sec form, almost flush up against it. If I try to move
> the pri up (right now it is at least 1" below the secondary) I get
> spark shorts between the two.
> So I plan to increase the pri diameter and then raise the pri coil and
> see if that helps. I am still thinking about getting a blower fan for
> the gap.
> Joe C.
> ----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Friday, April 17, 2009 10:18 PM
> Subject: Re: [TCML] Questions on grounding
>> Hi Joe,
>> I don't think your over-coupled, but it would be normal to start the
>> primary turn 1.25" from the secondary outer diameter (due to the 12kV
>> supply and your coil) , then raise the primary to 1.5" above the
>> bottom secondary turn as measured from the center of the primary.
>> This will put coupling at 0.13 for your particular coil. Looks to be
>> about 13.9 turns on the tap if that is done.
>> For coupling, well, don't ask for a calc. Use Javatc or other program
>> for something like that.
>> Take care,
>> jocatch wrote:
>>> Hello Christopher (and everyone else who responded),
>>> I haven't had time yet to fire up the coil at night since I grounded
>>> the secondary and nst case to earth ground. Will do tomorrow night.
>>> I also relocated my spark gap so I can blow air on it. Right now I
>>> am still using the cartridge bolts but I got a 120v 100 cfm boxer
>>> fan about 2" away blowing air on it. If it improves the output, I'll
>>> look for a blower fan that really cranks and see if that works.
>>> Of course I need to be more exact in my breakout measurements so I
>>> am going to mount a grounded wire on a pole and set on a tripod so I
>>> can accurate measure the spark length to gauge improvements.
>>> I am also thinking I may be over coupled. The inside of the primary
>>> is almost flush up against the secondary form. The primary is about
>>> 1" lower than the bottom of the secondary coil. If I try to raise
>>> the primary so it is even with the secondary winding, I get sparks.
>>> So I may rewind the primary out another inch or two.
>>> Thanks for everyone's input so far.
>>> ----- Original Message ----- From: "Christopher Karr"
>>> To: "Tesla Pupman List" <tesla@xxxxxxxxxx>
>>> Sent: Wednesday, April 15, 2009 3:50 PM
>>> Subject: RE: [TCML] Questions on grounding
>>> Hello Joe,
>>> The reason that a fan on the spark gap helps improve output of a
>>> Tesla coil is that it helps to extinguish the arc and blow out the
>>> ions. When the ions are all gone, the gap takes a higher voltage to
>>> make it break down, which means that there's more 'bang energy',
>>> resulting in more energy transferred to the secondary coil and that
>>> means larger streamers on the output.
>>>> From: jocatch@xxxxxxxxxxx
>>>> To: tesla@xxxxxxxxxx
>>>> Subject: Re: [TCML] Questions on grounding
>>>> Date: Wed, 15 Apr 2009 14:01:07 -0400
>>>> Hello to everyone who has responded so far. Thank you!
>>>> Today I went and got a 4' ground rod and banged it into the ground
>>>> and ran a wire to the secondary coil and nst case. I used a 4' rod
>>>> because my ground here has lots of rocks and I have never been able
>>>> to go more than about 4'
>>>> with ground rods. As you can see from my photos that the coil is on
>>>> my rear deck, there is no concrete floor. The wire from the coil to
>>>> the rod is less than 20' long. Tonight after dark I will power it
>>>> up and see if it helped. I will also connect the ground wire to the
>>>> end of a pole and see how long of a spark I can get.
>>>> Regarding my spark gap, I always go for the easiest, simplest
>>>> solution as I am not that mechanically inclined. I do have some 12v
>>>> computer fans I was thinking about placing near the gap to see if
>>>> it helps. But I wanted to try the grounding, tuning and adjusting
>>>> the gap width before adding a fan.
>>>> Besides, I have no place right now to add the fan on the base; I
>>>> will have to move the gap to somewhere where there is more room.
>>>> Regarding a 'sucker'
>>>> gap, I am not sure what that is, I will have to research that.
>>>> ----- Original Message ----- From: "Lau, Gary" <Gary.Lau@xxxxxx>
>>>> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
>>>> Sent: Wednesday, April 15, 2009 10:36 AM
>>>> Subject: RE: [TCML] Questions on grounding
>>>> Hi Joe,
>>>> When you say that "Right now, nothing is grounded to earth or
>>>> electrical ground", this is REALLY bad! The secondary base needs a
>>>> ground connection.
>>>> If there is not a good, direct ground connection, the RF current
>>>> will travel through your hot & neutral wires and wreak havoc with
>>>> household appliances.
>>>> I agree with Bart's reply - that the secondary base is typically
>>>> connected to the NST case, and that this case connection should go
>>>> to a dedicated RF ground, not the mains ground. For low powered
>>>> coils, the mains ground is often used, but the definition of "low"
>>>> is subjective.
>>>> Regarding the sparks discharging all around the toroid, this may be
>>>> due to having a ragged surface on the toroid, so smoothing it out
>>>> may help. If the toroid is simply too small for the power level
>>>> you're running at, no amount of surface prep is going to help, but
>>>> yours appears to be reasonable in size.
>>>> Looking at your web site, I think the weak link in your coil is the
>>>> 2 carriage bolt spark gap. It needs forced air flow directly
>>>> through the arc (more than just a gentle breeze from a fan), and
>>>> should be designed to arc not at just a single point as yours will.
>>>> I recommend using a sucker gap, as it's easy to build and works
>>>> very well.
>>>> Regards, Gary Lau
>>>> MA, USA
>>>>> -----Original Message-----
>>>>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx]
>>>>> On Behalf Of jocatch
>>>>> Sent: Tuesday, April 14, 2009 9:35 AM
>>>>> To: tesla@xxxxxxxxxx
>>>>> Subject: [TCML] Questions on grounding
>>>>> Hello. I have built my first coil using standard parts and
>>>>> dimensions and have fired it up and so far I am producing sparks
>>>>> but only about 12" long. I am using a 12KV nst with .0125uf mmf,
>>>>> 13 turns of copper tubing as primary and 20" of #28 magnet wire on
>>>>> a 4" form with aluminum cloths dryer ducting for the toroid
>>>>> My questions concerning grounding. I have read alot about
>>>>> discharge spark length but not much regarding how to measure it.
>>>>> Above I said 12"
>>>>> discharge spark
>>>>> that was to a key ring held at the end of a boom stick handle.
>>>>> Should the
>>>>> object that I am drawing the spark to be grounded? To earth
>>>>> ground? Right now nothing is grounded to earth or electrical
>>>>> ground. The bottom side of the secondary coil is connected to the
>>>>> metal case of the nst. Should the secondary coil and nst be
>>>>> grounded to earth ground?
>>>>> Lastly, the aluminum toroid is discharging all around its
>>>>> circumference. I know the fewer discharge points on the top load,
>>>>> the bigger the discharge length will be. If I tape the toroid with
>>>>> aluminum tape to produce a smoother surface, will it help?
>>>>> I have a web page showing photos of my first tesla coil before I
>>>>> recently updated it to copper tubing and new toriod. The web page
>>>>> shows the old primary wire coil and old topload. I will post new
>>>>> pictures of the update soon.
>>>>> Thanks for your help.
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