Roger Holmes wrote:
The theory said to change the resonant frequency of my keypunch's
ferro-resonant power regulator from 60Hz to 50Hz I should up the 15uF
capacitor to 21.6 uF. Well I tried 21.5, and the voltage went up by
ONE volt. Hmm, scratch head, at least it went in the right direction.
Search around for AC capacitors and find one in a defunct large
electric lawnmower. Its 30uF, I think about replacing the 15 with it
but if an extra 6.5uF only gained one volt, and I need 6 then it
seemed reasonable to combine it and try 45 uF. That gives me 46volts,
only 2 volts short. I throw in the 6.5uF too and I get 47 volts. I try
I had a niggling concern about this when the suggestion to change the C was
first profferred.
I don't have a thorough enough understanding of the ferro-resonant principle
to categorically say what the problem is but I can half-think of a few
possible issues:
- Because the ferroresonance principle involves the inductor working
in the core saturation region, the standard resonance equation with
which you calculated the new C may not be applicable. (I see you got
the square of f proportion.)
- If the changed LC relationship changes the circulating current
in the LC circuit then the core magnetic field will also be affected,
which would upset the rest of the transformer design targets.
- Changing the C changes the resonant frequency in an LC circuit,
as you desire to accomplish. However, the Q factor of the resonant
circuit is dependant upon the ratio of L/C, so you have also changed
the Q factor. I'm less sure if this would matter, as the circuit
is operating at a well-fixed frequency.
My remaining concern might be that even with the new C bringing the V up,
the regulation function of the supply may have been lost if the transformer
is no longer functioning in the regions it was designed to.