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Re: [TCML] RE: Need assistance in diagnosing poor performance
Steve,
The problem is , its not as easy as you many think. For example, if you tune
at low power, when you crank up to high power, the sparks add to the topload
of the coil (act as a larger toroid) and lower your frequency. So even if
you tune 100% correctly, the sparks will change whatever you set the
frequency at anyway. With my coil 250watts I was at something like tap 4,
and at 500W I had to retune to like tap 7, just on the basis that the longer
sparks lowered the frequency of the secondary and then caused me to tap out
a few tunes.
In actual fact the problem becomes pretty complex. If the sparks are short ,
say 10", then the frequency could be 100khz, then as the sparks grow in
length the frequency could go down to 80khz, so then your primary is
detuned. As it goes off tune, energy will drop and you are back to the
100khz 10" sparks again... tuning becomes a general "suck it and see" kind
of affair. The coil is going in and out of tune constantly and tuning
manually is the only way to find the best overall tap.
It complicates things further if you are using a none-sync spark gap. Where
the AC voltage varies and this also will effect the bang size and then the
spark length, which again effects coil tuning. If you play around for long
enough, you could have a coil which will "cough and splutter" then blast out
100" spark as it hits the top of the AC cycle and hits the ideal tuned
frequency.
Its why I think sync gaps are much better overall, it makes life easier I
think overall aswell. Its enough that the sparks can de-tune the coil,
without adding in another factor of varying input energy.. Its getting back
to onto RSG spark gap types, one vs. the other.. and that's a topic in
itself.
I like to keep things as simple as possible. A constant bang size is a good
start, at least in theory once the coil is turned at full power, then the
coil will always deliver full power and always be in tune. Though sparks do
vary in length all the time and so does the tuning. You could retune your
coil just from environmental effects.. the list is endless..
Sorry it does not help with your problem as such..... Though I hope it gives
you a little bit more insight to tuning coils..
Chris
----- Original Message -----
From: "Stephen J. Hobley" <shobley@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, July 30, 2008 3:18 PM
Subject: RE: [TCML] RE: Need assistance in diagnosing poor performance
More info
- noted - I'll document the whole assembly tonight and put up a web page so
you can take a look.
But in the meantime if there's any general tips that apply to all coils - I
would welcome them.
Chris - Great tip about the fluorescent tube BTW - nice way to detect if we
are on a harmonic other than the root.
Tuner -
This brings up a great point, and one that has been asked at least once on
the tuner design page.
This is the procedure that I use - I leave primary and secondary in place
and connect the tuner in between the secondary base and ground. Turning the
knob gives me a very definite lowest brightest point on the LED, way
brighter than any of the others - I leave the knob set at that position.
Then I remove the secondary coil, short out the spark gap and connect the
tuner across the tank cap. I then take my primary tap and move it around the
primary coil until I get the dimmest response from the led. This was at turn
11, and not between turns 8-9 as Teslamap said it should be.
At this point I have assumed that the primary is resonating at the same
frequency as the secondary. Can someone confirm if this is correct?
Steve
Stephen Hobley Photography
www.stephenhobley.com
317 201 4281
The Laser Harp Project - www.stephenhobley.com/build
________________________________
From: tesla-bounces@xxxxxxxxxx on behalf of Lau, Gary
Sent: Wed 7/30/2008 9:30 AM
To: Tesla Coil Mailing List
Subject: [TCML] RE: Need assistance in diagnosing poor performance
We can't give you additional input until you give US additional input. We
can't see your coil, remember? ;-) Pictures and specs are needed,
particularly of the gap. Yes, 3" is clearly below par.
As stated earlier, the 555 tuner is useful for a rough tuning, but the final
tuning must be determined experimentally - i.e. which tap yields the longest
sparks.
I'm not sure I follow how you used the tuner. The tuner is used to
determine the resonant frequency of the primary and secondary circuits,
individually. It's up to you to get them to resonate at the same frequency.
Regards, Gary Lau
MA, USA
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Stephen J. Hobley
Sent: Tuesday, July 29, 2008 7:54 PM
To: Tesla Coil Mailing List
Subject: [TCML] Need assistance in diagnosing poor performance
We're still not getting the performance we would expect out of the Tesla
coil we built.
It might have been the humidity that killed it tonight, as performance
was the worst yet - spark length was only 3" using the safety wand.
Where should I start in looking for problems? I've built the 555 timer
based tuner and re-tapped the primary at coil 11, as this gave the
dimmest indication, as per the instructions.
Apart from that, I'm a bit stumped.
I've seen evidence that this coil can give much better performance -
Alan sent me some recent pictures of a US military coiler over in Iraq,
getting at least 25" arcs out of his coil - exact same specs.
Maybe the desert air helps...
Any help is greatly appreciated.
Steve
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