>In a message dated 3/18/03 5:21:58 PM Eastern Standard Time,
>wmoorejr@cox.net
>writes:
>
>>
>> hat those like me,
>> >who are justing getting this news, might like to see a little serious bit
>> of
>> >explanation.
>> >
>> > Imagine placing a small inductance in series with the filament.
>>
>> ** How about the filament choke for the inductance? I know very little, but
>> I seem to remember that an inductor resists rapid current change ? **
>>
>
>
>Rich,
> Your explanation is MUCH TOO simplistic and straight forward ....I
>prefer lengthy erudite and pompous explanations such as the one which
>follows.
>
** mo' words ain't always mo' betta.
cheers, Dave
>
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>> 73,
>> Steve wd0ct
>>
>> For
>> >definiteness, let the filament hot resistance be 4 ohms and let the
>> >inductance have an X(sub)L of 1 ohms. The effect of the 1 ohm of X will
>> be
>> >to raise the total filament load by only a few percent (Z=4.1<17 degrees)
>> and
>> >the power factor will become .97 (vs 1.0) which will cause a small
>> increase
>> >in the dissipation of both primary and secondary. So far, nothing earth
>> >shaking has happened. Supposedly, the transformer primary could be tweaked
>> a
>> >few turns to keep the load voltage precise.
>> >
>> >Now suppose we get a dead-short across the filament (approx. to the cold
>> >start), and the secondary will see a load of X=1ohms and a Z of pure +j1.
>> The
>> >result will be, neglecting the R's at first, a secondary current of 4
>> times
>> >the normal running current. It is a purely reactive load (nearly) so there
>> >won't be much real power dissipation, for what that's worth. But the
>> current
>> >is safely limited to 400%, and could probably run like that for a while if
>> >needed.
>> >
>> >So with a little basic circuit strategy, the addition of some L, the
>> current
>> >limit is achieved. The next step is tricky and I am not going to go into
>> >detail here. I state without proof (it is proven in books on transformer
>> >design) that one of the effects of leakage inductance in a transformer is
>> the
>> >appearance of parasitic inductances in series with primary and
>> secondary -
>> >exactly as conjured up above. In fact, by strategically designing the
>> >transformer and core to be less than perfect, an appropriate amount of
>> >effective series inductance can be synthesized.
>> >
>> >Sometime I would like to see the detailed construction of that
>> transformer,
>> >because it is not a totally trivial job to achieve exactly the desired
>> amount
>> >of leakage. Apparantly, there are several applications in the world where
>> >this is common (e.g. neon transformers, AC welders, and oil burner
>> ignition
>> >transformers.)
>> >
>> >73
>> >Eric von Valtier K8LV
>>
>
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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