A quick note - when you are using your DMM to measure your Variac, you are
measuring the direct current resistance of its windings and ___NOT___ its
inductive reactance at 60HZ.
There is a very big difference between these two...
http://www.electronics-tutorials.ws/inductor/ac-inductors.htmlhttp://en.wikipedia.org/wiki/Electrical_reactance
Also, I looked at the transformacomm website and the circuit that the guy
built uses carbon arc electrodes for his "Tesla Circuit"
Absolutely the wrong thing to use - you want an arc that will disrupt or
quench as soon as possible -- this is why so many coilers use rotary or
air-blown gaps.
Carbon electrodes will just keep the arc going and present a huge
short-circuit across whatever it is that you are trying to do.
Dave
> -----Original Message-----
> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Brian Hall
> Sent: Thursday, January 01, 2015 18:46
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Hairpin circuit triggered circuit breaker
> without the spark gap firing
>
> Thanks Dave and Gary,
> I checked my variac and it is rated for 10 amps, and as it
> turns out I only have an 8 amp fuse in it which still works.
> When I put a DMM across the variac dialed to 0 I got 19 ohms
> resistance. I do have some ceramic incandescent bulb holders
> that I might try putting inline with a bulb between the
> variac and wall, or just plugging in further away from the
> breaker box, as you suggest. Even a 50' extension cord I have
> on a spool might do the trick. Thanks for the tip on this 60
> cycle and core saturation timing issue.
>
> I did try to find a website that showed this 'hairpin'
> circuit that was NOT spouting free energy B.S. all I wanted
> to show was the illustration of the circuit, but
> unfortunately many of the google image top results for that
> diagram link to sites that immediately blast 'free energy'
> nonsense at you right away. After several minutes of
> searching I picked that one for the sake of time. and did not
> scroll down enough to see its other claims. My apologies for that.
>
>
> Tesla referred to the experiment as one with two stout copper
> bars in his lectures.I refined my search and came up with a
> google books reference, this one with the diagram starting a
> brief section about impedance phenomena: as you know turning
> lights on with Tesla coils is fun, and this circuit is
> another means by which he turned lights on.
> https://books.google.com/books?id=PmrsAgAAQBAJ&pg=PT271&lpg=PT
> 271&dq=tesla+two+stout+copper+bars&source=bl&ots=lGiP_6SItj&si
> g=pH7gpfrtcPWONpSJWLxuf44Jxh8&hl=en&sa=X&ei=OQSmVMHkCYeYNrGBhA
> g&ved=0CCwQ6AEwAQ#v=onepage&q=tesla%20two%20stout%20copper%20b
> ars&f=false
>
> ----------------------------------
>
> Brian Hall
>
>
>
>
> > Date: Thu, 1 Jan 2015 16:27:58 -0500
> > From: glau1024@xxxxxxxxx
> > To: tesla@xxxxxxxxxx
> > Subject: Re: [TCML] Hairpin circuit triggered circuit
> breaker without the spark gap firing
> >
> > Dave is absolutely correct - My 15A Variac would often trip
> the breaker
> > when switched on, even when dialed down to 0%, if it was
> plugged into a
> > receptacle in the basement near the breaker box. When I
> plugged it into a
> > more distant receptacle, the additional wiring resistance
> limited the surge
> > current and didn't trip. The solution was to add Negative
> Temperature
> > Coefficient (NTC) thermistor in line with the input of the
> Variac. These
> > devices have a resistance of some fraction of an Ohm at
> room temperature,
> > passing enough current to magnetize the Variac core and
> generate heat in
> > the NTC device to cause it to lower its resistance to a
> much lower (and
> > negligible loss-wise) resistance, so a high-temperature/low
> resistance
> > equilibrium is reached.
> >
> > I must say however that the web site you cited spouts
> nonsense. I've never
> > heard of a "hairpin circuit", but when somebody tells you
> "it goes against
> > everything that we have been taught about electrical
> energy", be very
> > suspicious. Everything about Tesla coil operation is
> compatible with the
> > math and physics that we embrace, and anyone who says
> otherwise needs to do
> > more than post a YouTube video.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > On Thu, Jan 1, 2015 at 8:43 AM, David Rieben
> <drieben@xxxxxxx> wrote:
> >
> > > Brian,
> > >
> > > You didn't mention the size of your variac, but my guess
> would be that
> > > this incident had nothing to do with your Hairpin
> circuit, but was much
> > > more likely due to heavy inrush currents from powering up
> your variac at
> > > just the right (or wrong) time along the 60 hz sine wave
> of your mains
> > > electrical service. Until the core of a variac (or any
> other inductive
> > > load, like a transformer or a motor) is magnetized to the point of
> > > developing the appropriate CEMF due to inductive
> reactance, the very low DC
> > > ohmic resistance of the copper wire coils inside the
> variac are essentially
> > > a dead short and it can take a few milliseconds for the
> core to magnetize
> > > and the inductive reactance to "kick in". I often trip my
> 20 amp service
> > > breaker on initial power up of a 20 amp or larger rated
> 120/140 volt
> > > variac, regardless of what the variac dial is set at or
> whether there is a
> > > load connected to the variac or not. From my experience,
> this doesn't seem
> > > to be an issue with
> > > smaller variacs, say < 15 amps rating, probably because
> the smaller
> > > guage wire in the coil has sufficiently more DC ohmic
> resistance to prevent
> > > the inrush currents from momentarily rising to sufficient
> levels to trip
> > > the service breaker. You can verify the very low DC ohmic
> resistance by
> > > simply placing leads of a DMM, set in resistance mode,
> across the input to
> > > your variac, as the resistance will read < 1 ohm, which
> would translate to
> > > hundreds of momentary amps if the variac is energized at
> or near the peak
> > > of the input sine wave of the mains supply. To remedy
> this problem, you
> > > could add a resistive load (like a 100 watt light bulb)
> in series with the
> > > input to the variac at power up, then sidestep the light
> bulb resistor with
> > > a straight conductor after initial power up. I've just
> been too lazy to
> > > build a setup with a relay or contactor to do this
> automatically ;^)
> > >
> > > Also, as a side note, a 15 amp breaker sounds more like a
> lighting circuit
> > > than an outlet circuit, as outlet circuits are usually on
> 20 amp breakers,
> > > at least in most electrical code jurisdictions of the US.
> But a 15 amp
> > > breaker, as opposed to a 20 amp breaker, would only
> worsen this problem.
> > >
> > > David
> > >
> > >
> > > On Wednesday, December 31, 2014 3:28 PM, Brian Hall <
> > > brianh4242@xxxxxxxxxxx> wrote:
> > >
> > >
> > >
> > > After drawing a few arcs from my simple desktop SGTC, I
> hooked up the
> > > traditional hairpin circuit (as seen at the top of this page
> > >
> http://www.transformacomm.com/en/tech/tesla-hairpin-circuit.ht
> m but with
> > > just a short copper bar across the top, there were no
> bulbs to light)
> > > Basically I added another cap in parallel, removed my
> primary coil and
> > > then where the primary coil connections would be, I
> connected a 1/2" O.D.
> > > 2' long copper tube to each side. To connect the tubes
> at a right angle I
> > > used two 90 degree elbows and an 8" length 'stub out'
> copper tube, also at
> > > 1/2" O.D., at the other end of the 2' long tubes, for
> essentially a long
> > > inverted U shape. They were just press fit, no soldering
> of any kind.
> > > The spark gap was set to trigger at about 80 volts on my
> variac, which I
> > > used to control power to my 10kv 23ma OBIT. The two caps
> were each 10kv at
> > > .01 microfarads.
> > >
> > > Now the freaky part - the variac is both unplugged and
> switched off for
> > > safety in rewiring from coils to bars, along with of
> course being at 0
> > > volts, and the instant I plug it in... I noticed a light
> go out on the far
> > > side of the basement - of course I have not yet mentally
> connected the
> > > dots. The spark gap which worked minutes earlier has not
> a single spark
> > > fired as it had when I was using this primary part of the
> circuit for my
> > > SGTC, which I also tried with the two 10kv caps in
> parallell. Still with
> > > nothing happening, I switch on the variac and turn it up,
> and no sparks
> > > were in the spark gap when there ought to be -
> something's off. I turned
> > > down the variac and switched it off, unplugged it, and
> was quite puzzled
> > > and went to turn on the overhead light - to find it
> didn't work. The 15
> > > amp circuit breaker had been tripped!
> > > After resetting the breaker, everything else still works
> thankfully - what
> > > on earth could have happened that my variac, even it it
> was switched on,
> > > was at 0 volts and still that triggered the 15 amp
> breaker? One thought
> > > is that instead of going through the spark gap, the
> current just went
> > > through the caps and copper bar (even with 0 or less than 10 volts
> > > applied?) and back fed through the transformer and variac
> into the wall,
> > > triggering the breaker instantly - but if that was the
> case, then swapping
> > > out the bars for my primary coil (which is exactly hot it
> was earlier)
> > > would have done the same thing, right?
> > > What do you think happened? I am hesitant to repeat the
> conditions
> > > because my furnace may be on the same circuit, and it is
> going to be very
> > > cold the next few days. I disconnected the caps and just
> used the variac
> > > and transformer to arc across the spark gap, that part
> still works fine.
> > > 15+ amps going through all that in what was probably less
> than 1/2 second
> > > would be... very strange?
> > > ---------------------------------- Brian Hall
> > >
> > >
> > >
> > >
> > >
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