Re: Remote Power Supply Connection

"Ian Thompson-Bell" <ruffrecords@[EMAIL PROTECTED]
> wrote in message 
news:g0rmo0$27co$1@[EMAIL PROTECTED]
> Trevor Wilson wrote:
>
> -- Trevor Wilson www.rageaudio.com.au "Ian Thompson-Bell" 
> <ruffrecords@[EMAIL PROTECTED]
> wrote in message 
> news:g0ovq7$dq3$1@[EMAIL PROTECTED]
> > > flipper wrote:
> >> >> On Sun, 18 May 2008 07:36:56 +1000, "Trevor Wilson"
> >> >> <trevor@[EMAIL PROTECTED]
> wrote:
> >> >>
> >>> >>> "Ian Thompson-Bell" <ruffrecords@[EMAIL PROTECTED]
> wrote in message
> >>> >>> news:g0mu6g$2vgp$1@[EMAIL PROTECTED]
> >>>> >>>> Trevor Wilson wrote:
> >>>>> >>>>> **Asked and answered. Use AC. Do not use DC.
> >>>>> >>>>>
> >>>> >>>> In practice that is perhaps not such a good idea as it
> sounds. It means
> >>>> >>>> the rectifiers will be at the end of a fairly long piece of
> cable. The
> >>>> >>>> large rate of changes of current caused by rectifiers
> (especially the
> >>>> >>>> semiconductor type) combined with the series inductance of
> the cable is
> >>>> >>>> a recipe for noise, interference and possibly stability 
> >>>> >>>> problems.
> >>> >>> **I fail to see how. In practice rectifiers are already at the
> end of
> >>> >>> very long cables and are supplied by devices with prodigious
> inductance.
> > >
> > > Not true. The rectifiers are quite close to their transformer in
> normal
> > > cir***stances. Any noise they create has to be transferred back
> through
> > > the transformer and is therefore severely attenuated before it
> meets the
> > > mains cable which is what I think you you are referring to a 'very
> long
> > > cables'. With the method you propose the rectifier currents flow
> directly
> > > in the 'very long cable'
>
> **And reducing rectifier noise artefacts is an easy, cheap and
convenient
> solution. FAR easier than attempting to deal with high Voltage DC
> connections.
>
>
> I agree when the rectifiers are close to the transformer supplying them 
> but not when they are separated from it my a couple of metres of cable.

**And again, it is not difficult, nor expensive to deal with such issues.
A 
handful of capacitors will effectively deal with any problems.


>
> > >
> >>> >>>In any case, there are measures that can be taken to reduce the
> problems
> >>> >>>associated with noise from diodes. There are even (easy)
> measures which
> >>> >>>can be taken to reduce the inductance of those connecting
> cables. What I
> >>> >>>am very concerned about is the extreme ignorance displayed about
> the
> >>> >>>dangers associated with DC arcs and connectors. This, as opposed
> to your
> >>> >>>hypothetical, is a very real possibility. Read this:
> >>> >>>
> >>> >>> http://www.arcadvisor.com/faq/dc_direct_current_arc.html
> >>> >>>
> > >
> > > This clearly shows that at low currents (e.g HT currents) and high
> > > voltages (e.g.HT voltages) dc arcing is very unlikely to occur.
>
> **Remind me: How much energy is able to be stored by large (unstated 
> values)
> capacitors?
>
> 0.5*C*V^2
>
> In a 100uF capacitor at 300V that's a mere 4.5 joules. Not worth
worrying 
> about.

**Points:

* 4.5 joules is a substantial amount of energy. My small rotary hammer
drill 
is rated at 2.5 joules per strike and can pulverise bricks. 4.5 joules can

seriously damage connectors.
* I've worked on valve power amps which employ MUCH larger capacitors than

100uF. More like 2,000uF. (Just a reminder: The amp under discussion was a

power amp and B+ figures under discussion have ranged up 700 Volts) That 
makes it more like 490 joules. And that is a figure well worth worrying 
about.

-- 
Trevor Wilson
www.rageaudio.com.au