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Gordie Orange

Wed Aug 31 2016, 06:16PM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

My wife bought me a Velleman hand held scope and a function generator but im struggling to work out what to do (sorry to all the seasoned pros facepalming right now)

I followed the instructions here http://www.hvtesla.com/tuning.html but all i seem to be getting is noise and no visible peaks when i sweep through the frequency.

Im guessing i haven't set the scope up properly but n

idea where to look for destructions.

Any help for an enthusiastic newbie greatly welcome

Sulaiman

Wed Aug 31 2016, 08:33PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The tuned circuit formed by the primary capacitor and inductor ;

the inductor will be a near short circuit from dc to just below the resonant frequency
the capacitor will be a near short circuit at frequencies above the resonsnt frequency

only at or very near resonance will there be a signal,
the amplitude of the signal across the primary would be the same as from the signal generator
if there were no losses, in practice, look for a smaller signal.
The resonant peak can be very narrow (high 'Q' tuned circuit) and can be easily missed,
sweep the frequency painfully slowly :)

First just feed the sig-gen straight into the 'scope and practice getting a stable display at different frequencies and amplitudes.

alan sailer

Wed Aug 31 2016, 10:07PM

Registered Member #59110 Joined: Mon Apr 11 2016, 04:35PM
Location: Camarillo, California
Posts: 74

Learning how to use a o,scope is not an especially intuitive thing. So take your time.

As Sulaiman said try first to just get a signal from your function generator into the scope. Skip the coil for now. If you can't get a good stable sine wave display on the scope directly from the signal generator then you need to work on that.

Triggering the scope is always the most difficult part of using one. I am not familiar with the Velleman scope, however most scopes have several triggering modes and a method of setting the trigger point. Messing with these controls is what you need to work with.

If you have a signal generator/scope set-up that can reliably show a sine wave and are able to sweep the sine wave in frequency then you can move to the tesla coil. I only did the test you are trying to run once and I found the test on the secondary easier to run. As Suliman says the resonance can be very narrow so you do need to change the frequency carefully. If your signal generator doesn't have fine frequency control it is possible that you can tune right through the resonance.

Finally, although this way of tuning a coil looks like it is popular, I didn't find it very helpful. Your results may be different.

Cheers.

Gordie Orange

Thu Sept 01 2016, 06:08AM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

Thanks for the advice,
I had a play and got a stable sine wave while connected directly to the scope and messed about with frequency and amplitude on the signal generator

Sulaiman

Thu Sept 01 2016, 12:46PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I've only built a few small TC but I like to measure my coils at sig-gen levels,
most of the key concetps such as simple resonant circuits, coupled resonant circuits, skin-effect, proximity effect, proximity/arc length de-tuning ....
much easier then measuring a running TC
some things can only be tuned at full power,
but a good understanding of tuning, and what makes a 'good TC can be obtained without frayed nerves :)

with a sig-gen and a 'scope you can investigate
capacitors and inductors both have capacitances, inductances and resistances
the ballance of these properties determine its performance as a component in a circuit.

I think that N.Tesla would have eaten his underpants to have a 'scope and sig-gen.

P.S. once the sig-gen and 'scope are easy to use
(where I work, dozens of engineers with decades of 'scope usage each, NONE of us have familiarised ourselves with all of the features of the 'company scopes')
to sweep for the resonant frequency, increase the sensitivity of the 'scope untill you see noise
as you approach resonance reduce the gain on the 'scope.

P.P.S. before you ask, many members have written about high voltage probes,
research before asking ;)

Gordie Orange

Thu Sept 01 2016, 06:20PM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

Little squeal of joy, slowly swept the signal and found a big rise at 265Khz on the secondary, will try the primary when my daughter is asleep.

Sulaiman

Thu Sept 01 2016, 06:26PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

just a quick one;

put a hand a few cm from the topload and see how far the resonant frequency drops (needs practice)
easier, tune to resonance, watch the 'scope as you move your hands around.

add say 12" of wire to the topload to simulate a spark,
notice the slightly reduced resonant frequency
due to increased capacitance.

P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed the secondary)
is enough to light a neon lamp :)

Gordie Orange

Thu Sept 01 2016, 06:42PM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

Sulaiman wrote ...

P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed to secondary)
is enough to light a neon lamp :)

Sorry you've lost me

Sulaiman

Thu Sept 01 2016, 06:52PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

if you connect the -/outer/Gnd side of your sig-gen to physical or mains earth,
then connect the +/inner/live sig-gen to the bottom of your TC secondary
the voltage at the top of the secondary is high enough to cause a small neon bulb to glow
one side of neon to earth (your hand will do)
the other side to the top of the secondary.
don't forget, 'earthy' objects near the top cause a drop in resonant frequency.

just a way to 'play', lighting a neon from a sig-gen.

Gordie Orange

Thu Sept 01 2016, 09:26PM

Registered Member #55076 Joined: Sat May 23 2015, 08:26AM
Location:
Posts: 20

ooooh, I'll give that a go.
Thanks for taking the time to explain it

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