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From: Pooh Bear on 27 Feb 2006 23:29


Terry Given wrote:

> Pooh Bear wrote:
> >
> > Reg Edwards wrote:
> >
> >
> >>Using an inductor will give better output voltage regulation versus
> >>load current.
> >
> >
> > Really ?
> >
> > How about the inductor DC resistance ?
> >
> > Graham
> >
>
> you're an audio guy Graham, go read the Langford-Smith, its all in there :)
>
> an inductor (if > 3%) will also knock the input harmonics down, a lot.

Oh, very true.

When IEC1000-3-2 came along I did some simulations using inductors to reduce
the harmonic currents.

The regulation compared to a simple capacitor input filter was utterly
miserable though ( and I assumed DC R to be near zero ! ).

Graham

From: Pooh Bear on 27 Feb 2006 23:30


Tim Williams wrote:

> "Pooh Bear" <rabbitsfriendsandrelations(a)hotmail.com> wrote in message
> news:44036787.D2DFE69E(a)hotmail.com...
> > > Using an inductor will give better output voltage regulation versus
> > > load current.
> >
> > Really ?
> >
> > How about the inductor DC resistance ?
>
> A damn lot better than an equivalent resistor, at any rate.

There is no such thing as an 'equivalent resistor'.

> I wonder how the relations work out for ripple vs. transformer regulation.
> Metric shitloads of capacitance don't make transformers happy.

Just keep the DC R low and they don't actually mind !

Graham

From: Tony Williams on 28 Feb 2006 04:13
In article <4403D1A0.701EB694(a)hotmail.com>,

> When IEC1000-3-2 came along I did some simulations using
> inductors to reduce the harmonic currents.

> The regulation compared to a simple capacitor input filter was
> utterly miserable though ( and I assumed DC R to be near zero ! ).

The regulation from no-load to full-load is
certainly worse, but the regulation from a
defined minimum-load to full-load is better.
The final dc output is always lower than the
RC filter, but the choke input filter makes
better use of the available VA.

AFAIR the harmonic currents are better, but
there is a nasty shorting effect when the
diodes switch over, (commutate), effectively
shorting the leakage inductance of the transformer.

--
Tony Williams.
From: Tony Williams on 28 Feb 2006 04:21
In article <1141099260.863806(a)ftpsrv1>,
Terry Given <my_name(a)ieee.org> wrote:

> but hey, it can be made from sheet steel - McKenzie Holland used
> to do this for big battery chargers!

I used to have a dc arc welder, powered by a 24V
lead acid battery. It had a curious (over)current
limiter in series with the supply.

It was a 'spring' of heavy gauge galvanised steel
wire, about 2" diameter, 7" long, tightly wound
so that adjacent turns touched (and had continuity).

It was claimed that under a transient overcurrent
the magnetic field between adjacent turns extended
the spring, breaking the inter-turn connections.

--
Tony Williams.
From: Pooh Bear on 28 Feb 2006 04:46


Tony Williams wrote:

> In article <4403D1A0.701EB694(a)hotmail.com>,
>
> > When IEC1000-3-2 came along I did some simulations using
> > inductors to reduce the harmonic currents.
>
> > The regulation compared to a simple capacitor input filter was
> > utterly miserable though ( and I assumed DC R to be near zero ! ).
>
> The regulation from no-load to full-load is
> certainly worse, but the regulation from a
> defined minimum-load to full-load is better.

How do you reconcile that with your first statement ?

I found the regulation to be much worse than a capacitor input filter
under any practical conditions.


> The final dc output is always lower than the
> RC filter, but the choke input filter makes
> better use of the available VA.

I simply reduce the ( typically toroidal ) transformer's DC R to avoid
any such problems. VA isn't determined by core size in reality when the
possibility of 'special winding' is there.

p.s *what* RC filter ?

Graham

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