Hi Brian and Gary,
19 ohms variac input DC resistance? That sure doesn't sound right to me. If this were the case, your variac would be more like a (resistive) rheostat instead of an (inductive) variable transformer, not to mention a ~750 watt heater! I would check the resistance range of your DMM with a resistor of a known value to verify its accuracy. Like I said before, until the core magnetizes and produces the counter EMF to the 60 hz AC input, the only resistance of the input of a variac should be that of the copper conductor wire of the variac coil itself, which should be only a small fraction of an ohm. Be that as it may, I believe a circuit breaker reacts quicker to momentary over current conditions than does a typical slow-blow fuse, so the momentary inrush over current may be able to trip a 15 amp breaker before "having enough time" to melt an 8 amp rated fuse, especially if its the typical slow-blow type of fuse. However, I would think that a 10 amp rated
variac should be equipped with something like a 12 amp rated fuse?
It would seem to me that the described "Hairpin circuit" is nothing more that a standard SG Tesla coil circuit with which the primary/secondary coil is replaced with pretty much a buss bar, which would be a dead short to low freq AC or DC, but would still offer significant inductive reactance to the mutliple 10's or 100's of kHz produced by a resonant LC spark gap circuit to produce some measurable (though not very practical) output. But, as far as all of the free energy stuff that many of these sites go into, you have to filter through them and discard the "free energy" nonsense into the "BS file". ;^~
Also, Gary, what type of NTC thermistor would be suitable for inrush current protection for powering up a variac? I did a quick eBay search and many of them were rated 10K or even 100K and <1 amp and/or part of temperature sensors. I did come across these Chinese jobber pieces:
http://www.ebay.com/itm/151092289740?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
of the disc type construction. Would one (or two paralleled) of these be a decent match for the input to a 22 amp rated variac?
David Rieben
On Thursday, January 1, 2015 10:27 PM, Brian Hall <brianh4242@xxxxxxxxxxx> wrote:
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=PT271&dq=tesla+two+stout+copper+bars&source=bl&ots=lGiP_6SItj&sig=pH7gpfrtcPWONpSJWLxuf44Jxh8&hl=en&sa=X&ei=OQSmVMHkCYeYNrGBhAg&ved=0CCwQ6AEwAQ#v=onepage&q=tesla%20two%20stout%20copper%20bars&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.htm 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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