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I was hoping for some new material ...** Fuck off - you illiterate, bloody imbecile.
I was hoping for some new material but OK I'll settle for reruns"klem kedidelhopper"
** Fuck off - you illiterate, bloody imbecile.
Thanks, Phil."spamtrap1888"
I'm wondering though if a secondary is supposed to deliver say 20
volts with a 120V primary and it's hit with 240 then that secondary
will produce 40 volts out.
** Totally wrong !!!!!
Try it yourself and see what REALLY happens.
I'm confused. I would have thought that, at least for the first
instant, the turns ratio means there would be 40 VAC on the output,
until the primary's turns start shorting together as the enamel
combusts because of heating caused by the excessive input current.
** Nope.
Magnetic saturation is an instantaneous phenomenon.
The cores of most small transformers operate well into saturation, even at
rated voltage - so doubling the incoming primary voltage causes complete
core saturation and the primary side current flow is limited only by the
resistance. The RMS current goes up by 5 or 10 times the normal level.
Crucially, the secondary voltage rises only slightly due to a large voltage
drop being caused by the primary's resistance.
A correctly rated fuse will blow immediately and the event is all over.
With the PSU in question, the AC fuse was missing - but very likely had
been replaced with a larger one at some stage.
Well yes, it is a quite rapid action, but does not occur till the"spamtrap1888"
I'm wondering though if a secondary is supposed to deliver say 20
volts with a 120V primary and it's hit with 240 then that secondary
will produce 40 volts out.
** Totally wrong !!!!!
Try it yourself and see what REALLY happens.
I'm confused. I would have thought that, at least for the first
instant, the turns ratio means there would be 40 VAC on the output,
until the primary's turns start shorting together as the enamel
combusts because of heating caused by the excessive input current.
** Nope.
Magnetic saturation is an instantaneous phenomenon.
** Strangely enough, the peak saturation currents occurs near to each ACMagnetic saturation is an instantaneous phenomenon.
Well yes, it is a quite rapid action, but does not occur till the
current in the primary is sufficiently high. Saturation does not
occur over the whole input wave, and drops and reverses as the sine
wave input reverses. So during the non saturated period, the input
and output voltages are proportional to turns ratio.
Yes phil, that is interesting, and why I referred to current, as the"Peter"
"Phil Allison"
Magnetic saturation is an instantaneous phenomenon.
Well yes, it is a quite rapid action, but does not occur till the
current in the primary is sufficiently high. Saturation does not
occur over the whole input wave, and drops and reverses as the sine
wave input reverses. So during the non saturated period, the input
and output voltages are proportional to turns ratio.
** Strangely enough, the peak saturation currents occurs near to each AC
supply voltage zero crossing.
With a small transformer and double the rated AC input voltage, the (off
load) current wave is very peaky in shape and rises to about 15 times the
usual RMS value.
Shorted turns in the primary results in a few seconds, the resistance drops
suddenly and blows a fuse even 10 times the correct size.
The PSU in question contained only electros, resistors and zeners - all
operating well within their ratings in normal circumstances, so well able to
take a brief increase in voltage.
... Phil