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Re: [TCML] Toroid Problems
The NST may have been good when you bought it, but you could have overvolted
it already. attach a wire to each terminal and see if they both arc to the
case of the NST, but be sure that you are insulated from said wire and
case. If one end produces a feebler arc or none at all then you have a
problem.
On Wed, Aug 6, 2008 at 3:53 PM, Nicholas J. Goble <ngoble@xxxxxxx> wrote:
> Thanks for the replies, comments are made throughout the message.
>
>
> Quarkster wrote:
>
>
> >Nicholas -
> >
> > A few areas of concern are revealed by your photos:
> >
> > 1. It looks like your tank wiring to the MMC and spark gap is
> extremely small gage stranded wire (#16 AWG?). All the interconnects
> between primary coil, spark gap, and tank capacitor need to be fairly
> heavy gage (I recommend no smaller than #12 AWG for a small NST powered
> coil). The peak current in the tank circuit can be hundreds of amps
> when the spark gap fires and the tank capacitor dumps all of its
> energy, and #16 AWG is not adequate.
>
> If wire makes a big difference, that might be my problem. I've read so
> much speculation over what wire to use for connections, I didn't think
> it was that big of a deal. I'll definitely get some #12 AWG.
>
> > 2. All the wiring in the tank circuit needs to as short and direct as
> possible. You didn't post any photos of the overall coil and all the
> interconnects, but I suspect that your primary wiring may be longer
> than necessary. It appears that you have carefully calculated the
> inductance and resonant frequency of both primary and secondary coils,
> but I bet you did NOT include the length of the additional tank circuit
> wiring in your primary coil calculations. Measure the total length of
> your primary wiring, include this in the length of the primary coil,
> and re-calculate primary inductance and resonant frequency. It may be
> much lower than you thought. You may need to relocate the spark gap and
> the MMC to keep the primary wiring as short and direct as possible.
>
> I've been looking on craigslist for a free cabinet or end table that I
> could use to house my coil. Right now, I've been just setting
> everything up on my driveway. A cabinet would make it easier to make
> shorter connections and would make setup a whole lot quicker.
>
> > 3. I suspect that your solder joints where the primary wiring is
> connected to the copper tubes of your spark gaps are really "cold
> joints", and are not electrically sound. You simply cannot directly
> solder small gage wire to a large copper pipe with a small soldering
> iron. If you wiggle and pull on these joints, I suspect that the wires
> will just fall off. You either need to use a torch to get the copper
> pipe hot enough to "tin" it, and solder the wire while the pipe is hot,
> or connect your new, larger-gage wiring to the pipes using crimped ring
> terminals with screws & nuts.
>
> Wow, you've hit the nail on the head with everything so far. It was
> extremely frustrating, trying to solder to the copper pipe. Thanks for
> the tip. I think there's a kitchen torch for creme brulee in my
> kitchen; I'll try using that to heat up the pipe. If not, use ring
> terminals.
>
> > 4. Again, have you verified that the NST is good, and that you can
> pull arcs of EQUAL LENGTH from each bushing to the NST case?
>
> I'm pretty sure that my NST is good. The guy who gave it to me said he
> tested it, but I know I can't take his word. On my safety gap though,
> it seems the spacing is the same for each electrode. What do you mean
> by "pulling arcs from each bushing to the NST case?
>
> > 5. Have you verified the resistance value of EACH ONE your bleeder
> resistors? In the past, several people have had problems with using the
> wrong resistor value (1 meg instead of 10 meg), or had one or two
> resistors of the wrong value. Wrong resistor values will burn up a
> large percentage of the meager 30ma NST output current.
>
> I bought 10 Meg 1/2 Watt axial carbon film resistors and wired them in
> parallel to each cap.
>
> > 6. What type of bleeder resistors are you using in your MMC? Are they
> 1/4 watt, or 1/2 watt resistors? Are they rated for the voltage they
> are actually being subjected to in your MMC? Standard 1/4 watt
> carbon-composition and metal-film resistors are typically rated for
> only 250 volts, and 1/2 watt resistors are rated for 350 volts. In your
> MMC, assuming you are using all twelve capacitors and running only 120
> VAC input, your transformer's peak output voltage is about 12,750
> volts. Each resistor will then have over 1KV across it. Check them
> carefully for any sign of arc-over, or discoloration from overheating.
> Vishay offers a line of special high voltage resistors (VR-37 series),
> and the 1/2 watt series is rated for 3500 volts. They only cost a few
> cents more per resistor than the standard 350 volts resistors, and I
> have never had one fail, even at considerably higher than 3500 volts.
> If there is any question about your resistors breaking down, a quick
> (temporary) fix is
> > just to connect two or three resistors in series across each cap. The
> time constant to discharge the caps will increase, but it should reduce
> any arc-over problems and won't adversely affect coil performance.
>
> I bought my resistors from the following site. I haven't seen any
> arch-over's or discoloration from overheating yet though.
> http://www.metallectric.com/Tesla_coil_components.html
>
> > Regards,
> > Herr Zapp
> >
> >
>
> Thanks
>
> Nicholas Goble
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