Re: Mains conditioners and power cables

In article <4316f911$0$12922$cc9e4d1f@xxxxxxxxxxxxxxxxxxx>, Nick Gorham
<nick@xxxxxxxxxxx> wrote:
> Jim Lesurf wrote:

> >
> >>Therefore as the diodes have to provide the same energy as before (1),
> >>but over a smaller time (3) the peak current MUST be higher.
> >
> >
> > Bear in mind though, that the charging current might be limited by the
> > transformer impedance.
> >

> Tis true, but the transformer impedance will be the same as before, so
> you would expect the peak current to still be higher than with smaller
> caps.

I'm afraid that the behaviour may not be as you assume. The transformer may
be limting the current by reaching its current saturation during the
recharding periods. This means that the transformer becomes like a current
source during the recharging, and ensures the current is the same, for both
values of capacitance. If this is happening with the original caps, then it
can be expected to occur with hight value replacements.

What then happens when you fit larger caps is that the amount of voltage
ripple falls, and the time-averaged voltage changes, but the duration and
current of the recharging episodes is almost unchanged.

In fact it is a good idea in some ways to ensure saturation as this limits
the current drawn, and hence protects the diodes (and the caps to a lesser
extent) from things like a large inrush at switch-on. It also tends to
improve the spectrum of the current spectrum in use as it tends to reduce
the relative level at HF.

However, if the transformer has an impedance which is much lower than the
series resistance+inductance of the caps and diodes, you will be correct,
and larger caps will lead to shorter recharge episodes, and a shift to HF
in the current spectrum.

Slainte,

Jim

--
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