On 06/26/17 02:04, Xtrchessreal wrote:
While researching ignitors on gas arc tube lamps I read about how the magnetic field collapses when the circuit is basically opened as the AC input signal falls to zero and it causes a spike in the secondary as high as 2500-3000 Volt range for 150w to 400w lamps. I know the spike in a ballast is designed for the lamp to start. I should say the lamp is designed to take advantage of the spike.
SO:
A spike must happen to a tube push pull amp as well though perhaps not that high in voltage, I don't know.
the best way to describe this is:
if you create a 5th harmonic while opening or closing the circuit to a
transformer, the current "rotates backwards" with respect to phase
rotation. Additionally, if you were to close (or open) a transformer
primary circuit at the peak voltage, you would theoretically have zero
(real) current if the load were purely inductive. And, if you opened or
closed the circuit at zero crossing, you would have maximum (reactive)
current.
This being due to reactive current 90 degrees lagging voltage.
I saw people discuss 'inrush current' once before, who then mercilously
FLAMED me, just for suggesting that experiments be done to show what the
peak amperage REALLY is (claims of 1000 amps, and so forth, pure
bull****). And that name 'inrush current' offers a poor description of
what is REALLY happening.
If you close the switch at "just the right point", or open the switch at
"just the right point", you might get unlucky and max out the current.
Zero crossing is considered one of the worst points, but 5th harmonic
(36 degrees) would be _THE_ worst.
I did some real calculations (which I don't think I ever posted, because
I was sick of the ASSHOLES that only wanted to make their own dicks look
bigger than mine) and determined that the biggest surge current would be
due to creating a 5th harmonic waveform. So if you were to close (or
open) the switch at the magic 36 degree point in the sine wave, assuming
no hysteresis on the core, and certain conditions for toroidal
transformers, you'd max out current, at an even higher level (as a
spike, not continuous) than you might expect based on the resistance of
the windings and impedence of the load, etc..
This is because phase rotation of the 5th harmonic OPPOSES the phase
rotation of the 1st harmonic. It's worse than a direct short, as you're
literally OPPOSING the current flow. This is known to burn up motors
and wiring etc. in power circuits with sufficient 5th harmonic in the
power circuit. 5th harmonic is bad. VERY bad.
https://www.allaboutcircuits.com/tex...ase-sequences/
Now the term 'inrush current' is (unfortunately) in use in the
electrical power generation industry. It's misleading as to what it
actually means. There's no "inrush" really. They just call it that.
https://en.wikipedia.org/wiki/Inrush_current -- misleading name
The wikipedia article also explains some of the issues with toroidal
transformers, which are moderately interesting - I'd just use a series
slow-blow fuse of an appropriate size, which would have a small series
resistance in the circuit, and would mitigate a lot of the problem.
Also, any 'spike' is basically in the primary of the transformer and (as
I understand it) does NOT induce problems in the secondary circuit(s).
In any case, energizing or de-energizing a transformer can cause issues
with the primary windings and the mains power you plug into. but the
secondary(s) shouldn't see any effects. Not in any significance, anyway.