Analog scopes are better than digital in this case ??
In my opinion analog scopes are better than digital period - if the
wave form is important to you.
A digital scope really shines where it is handy to freeze several
traces and compare them.
Ok so you are saying its normal
A 200 volt peak would be normal.
The way it works - voltage output (spike) is a function of how fast
the magnetic field collapses, the number of turns of wire, the amount
of stored energy.
How fast the field collapses is dependant on the type of core,
conductive material in and around the core (eddy currents).
Even the inter winding capacity (small distributed capacitances due to
one wire being close to another), and dielectric characteristics of
the insulation on the wire, how close the wires are to one another.
Eddy currents are currents of electricity induced in a material when a
magnetic field is changing - they oppose the change. Some eddy
currents are present in your core material (steel rods or wires?),
your core may have a conductive bobbin - done in solenoids to increase
the eddy current effects.
In a transformer or inductor eddy current are generally treated as
wasted energy. The core material behaves like shorted turns of wire -
to get around that, the core is broken up by using thin wires or
laminations or even powdered metal bits that are insulated from one
another
You can see the effects of eddy currents by dropping a very strong
magnet between two aluminum sheets - it will fall slowly. (assuming
it stays oriented as it falls) An easier example is to just put an
aluminum baking sheet at a steep angle but something other than 90
degrees and let the magnet slide down the surface.
Same principle used in old automobile speedometers and tachometers -
rotating magnet tries to drag an aluminum disk or ring with it. The
disk is working against a spring and has a pointer on it.
They deliberately increase the eddy currents in AC solenoids so they
don't buzz. The eddy current is giving up some of its energy in the
form of a magnetic field while the AC sine wave is at zero.
Anyhow - eddy current is the largest single factor on how fast a field
collapses.
My induction coil has a core of 2" of bundled steel wires about 20"
long. Basically I duplicated something I saw in an 1800's manual on
electricity. There's 1200 turns of wire in four primary windings and
86,000 turns of wire in the four secondary bobbins. It will make a
spark three and a half inches long. It weighs about 60 pounds - not
the typical auto ignition coil.
When the electrodes are separated by a few inches the spark is a
relatively thin bright line and makes a cracking sound. when the
electrodes are only a 1/4" apart, the spark is very thick (obviously
has some vaporized electrode in it). The interesting thing is the
spark makes a hissing sound and lasts lots longer - I attribute that
to the fact that the secondary behaves like a shorted turn when it is
asked to carry more current, the shorted turn acts to slow the
discharge. (slower changing field = lower voltage, but the same
stored energy so it lasts longer)