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Re: [TCML] Toroid Problems
Nicholas -
What is the actual total length of your primary wiring, and if included in your "primary coil" calculations, what is your "new" primary resonant frequency? We were assuming that when you installed your toroid, your secondary frequency was dropping below your primary frequency. However, it is possible that your primary frequency is significantly lower than you originally calculated. Please provide updated primary data.
When I suggested "pulling an arc" from each bushing of your NST, I mean just determine the longest continuous arc that can be created between each bushing and the NST case (or your RF ground, which should include your NST case). You may be able to do this by adjusting the oblong doorknobs you are using in your safety gap. Each side of the NST secondary winding should be able to generate essentially the same arc length.
Regards,
Herr Zapp
"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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