Re: [TCML] Toroid Problems

["Nicholas J. Goble" <ngoble@xxxxxxx>]

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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