Not DIY because I wouldn't even consider doing much in the way of
electrics in the house but I'm hoping one of the electrical gurus out
there might be able to shed some light on this.

Basically I'm wondering if I've got a problem with the electrics or just
2 "appliances" at the same time. The other day the DVD player was only
transmitting sound via it's coax connection (to the amp). No picture
(or sound) was coming out of the scart. After much fiddling with
various connections etc I touched the case of the DVD player and could
feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway
this seemed to cure the problem and the DVD came back on. The only
thing I could think of was either it's becoming faulty or it was some
build up of static (however I didn't get a static shock).

Anyway, it's happened again. I don't think I've used the player in a
week and it's gone off. Touching it doesn't help this time but it's got
that same humming feeling.

Now this is where I start to think "hold on what's going on" because the
same thing is now happening when I put my Palm T3 (metal case not
plastic) into it's cradle. When I touch it in the cradle it's humming
and feels "sticky". When it's out of the cradle it smooth. I've had it
a year and never noticed that before.

I haven't noticed it on anything else but I'm not about to go round the
house touching everything with a metal case!

In all honesty my other half thinks I'm daft cos she can't see what I'm
going on about (beyond the fact the DVD player's gone funny).

Is it possible something's wrong with the electrics (in which case I'll
get an electrician out) or just coincidence?

Cheers

Anth

"Anthony Bowles" wrote in message
...
Not DIY because I wouldn't even consider doing much in the way of
electrics in the house but I'm hoping one of the electrical gurus out
there might be able to shed some light on this.

Basically I'm wondering if I've got a problem with the electrics or just
2 "appliances" at the same time. The other day the DVD player was only
transmitting sound via it's coax connection (to the amp). No picture
(or sound) was coming out of the scart. After much fiddling with
various connections etc I touched the case of the DVD player and could
feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway
this seemed to cure the problem and the DVD came back on. The only
thing I could think of was either it's becoming faulty or it was some
build up of static (however I didn't get a static shock).

Anyway, it's happened again. I don't think I've used the player in a
week and it's gone off. Touching it doesn't help this time but it's got
that same humming feeling.

Now this is where I start to think "hold on what's going on" because the
same thing is now happening when I put my Palm T3 (metal case not
plastic) into it's cradle. When I touch it in the cradle it's humming
and feels "sticky". When it's out of the cradle it smooth. I've had it
a year and never noticed that before.

I haven't noticed it on anything else but I'm not about to go round the
house touching everything with a metal case!

In all honesty my other half thinks I'm daft cos she can't see what I'm
going on about (beyond the fact the DVD player's gone funny).

Is it possible something's wrong with the electrics (in which case I'll
get an electrician out) or just coincidence?


Is there a full moon ?

Failing that have you just had a new carpet installed ?

Anthony Bowles wrote:

feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway

I have experienced exactly the same phenomenon. It s probably the mains
getting capacitively coupled to the case work, possibly in combination
with a poor earth (for devices that are earthed).

Is power to your property fed by overhead cables? Have you tried
plugging it into a different mains socket (and all the things that it is
connected to like the TV, amp etc?

The feeling you get is unlikely to be dangerous in itself, but may serve
as a warning that the earth at that socket position is not as good as it
could be.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Fri, 15 Oct 2004 21:02:58 +0100, Anthony Bowles wrote:

After much fiddling with
various connections etc I touched the case of the DVD player and could
feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway
this seemed to cure the problem and the DVD came back on. The only
thing I could think of was either it's becoming faulty or it was some
build up of static (however I didn't get a static shock).

This is normal for any non-earthed mains operated device with a metal case - it's capacitive
coupling of the mains through the transformer. Very low current and not harmful.

Mike Harrison wrote:

This is normal for any non-earthed mains operated device with a metal case

aye, more or less;

- it's capacitive coupling of the mains through the transformer

pickyif it's through the transformer it's scarcely capacitive, is
it/picky It is usually capacitive coupling, either through
interference-suppression capacitors in the mains input filter (but in
that case the case *should* damn well be earthed, so you won't feel any
juddering/humming/whatevering: and if you can, it could indicate a
broken earth conductor in the supply lead (bad) or at the wall socket
(worse); or, in the case of Class-II ("double insulated") kit, designed
not to need an earth connection, capacitive coupling through stray
capacitances as mains wires or switched-mode PSU wiring comes close to
the case. VCRs and TVs additionally may have small-value capacitors
which couple the mains feed to the outer core ("earth") of their aerial
connectors - for these, you can sometimes get rid of the tingle by
reversing the mains input lead if it's one of those figure-of-8 leads.

.. Very low current and not harmful.

Not harmful by itself, no, but in some cases an indication of the case
not being earthed when it should be. In the OP's case, it's *not* that
for his Palm 3, but possible for the DVD player, depending on whether it
takes a 2-wire feed from the mains or a 3-wire one...

Stefek

Anthony Bowles wrote in message ...
Not DIY because I wouldn't even consider doing much in the way of
electrics in the house but I'm hoping one of the electrical gurus out
there might be able to shed some light on this.

Basically I'm wondering if I've got a problem with the electrics or just
2 "appliances" at the same time. The other day the DVD player was only
transmitting sound via it's coax connection (to the amp). No picture
(or sound) was coming out of the scart. After much fiddling with
various connections etc I touched the case of the DVD player and could
feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway
this seemed to cure the problem and the DVD came back on. The only
thing I could think of was either it's becoming faulty or it was some
build up of static (however I didn't get a static shock).

Anyway, it's happened again. I don't think I've used the player in a
week and it's gone off. Touching it doesn't help this time but it's got
that same humming feeling.

Now this is where I start to think "hold on what's going on" because the
same thing is now happening when I put my Palm T3 (metal case not
plastic) into it's cradle. When I touch it in the cradle it's humming
and feels "sticky". When it's out of the cradle it smooth. I've had it
a year and never noticed that before.

I haven't noticed it on anything else but I'm not about to go round the
house touching everything with a metal case!

In all honesty my other half thinks I'm daft cos she can't see what I'm
going on about (beyond the fact the DVD player's gone funny).

Is it possible something's wrong with the electrics (in which case I'll
get an electrician out) or just coincidence?

Cheers

Anth

this is normal with unearthed goods. There is a small amount of
capacitance from L to case, resulting in miniscule current flow. This
causes that feeling when you stroke the metal gently. Normal and
harmless on unearthed items. If it happens on earthed goods its
another matter entirely.

NT

On Sat, 16 Oct 2004 13:52:13 +0100, Stefek Zaba wrote:

Mike Harrison wrote:

This is normal for any non-earthed mains operated device with a metal case

aye, more or less;

- it's capacitive coupling of the mains through the transformer

pickyif it's through the transformer it's scarcely capacitive, is
it/picky

Yes - transformers have capacitance between their primary and secondary windings.

Yes - transformers have capacitance between their primary and secondary windings.

A miniscule amount, mayhap: 99.999% of the energy transferred is
transferred *inductively*, though (and 99.999% of the losses are
inductive, too ;-)

Stefek Zaba wrote:

Mike Harrison wrote:

This is normal for any non-earthed mains operated device with a metal
case


aye, more or less;

- it's capacitive coupling of the mains through the transformer


pickyif it's through the transformer it's scarcely capacitive, is
it/picky It is usually capacitive coupling, either through
interference-suppression capacitors in the mains input filter (but in
that case the case *should* damn well be earthed, so you won't feel any
juddering/humming/whatevering: and if you can, it could indicate a
broken earth conductor in the supply lead (bad) or at the wall socket
(worse); or, in the case of Class-II ("double insulated") kit, designed
not to need an earth connection, capacitive coupling through stray
capacitances as mains wires or switched-mode PSU wiring comes close to
the case. VCRs and TVs additionally may have small-value capacitors
which couple the mains feed to the outer core ("earth") of their aerial
connectors - for these, you can sometimes get rid of the tingle by
reversing the mains input lead if it's one of those figure-of-8 leads.

. Very low current and not harmful.

Not harmful by itself, no, but in some cases an indication of the case
not being earthed when it should be. In the OP's case, it's *not* that
for his Palm 3, but possible for the DVD player, depending on whether it
takes a 2-wire feed from the mains or a 3-wire one...

Stefek


I missed the original post but all steel cases will vibrate at 100hz in
the presence of a mains frequency transformer due to magnetic field leakage.

Its even possible to induce quite large hum currents in them - you
should never for exaple earth circuits to more than one part of them, as
they will be at different potentials.

Mike Harrison wrote:

On Sat, 16 Oct 2004 13:52:13 +0100, Stefek Zaba wrote:


Mike Harrison wrote:


This is normal for any non-earthed mains operated device with a metal case

aye, more or less;


- it's capacitive coupling of the mains through the transformer

pickyif it's through the transformer it's scarcely capacitive, is
it/picky


Yes - transformers have capacitance between their primary and secondary windings.



neither of which is normally connected to the case.

Unless the case is earthed it is EXTREMELY bad practice to even use an
RFI filter connected to the case.

However it is done, and the net result is a case at 110vAC with respect
to neutral. albeit at fairly low potential.

I suspect they assume it will be connected to some other properly
grounded kit.

Stefek Zaba wrote:


Yes - transformers have capacitance between their primary and
secondary windings.

A miniscule amount, mayhap: 99.999% of the energy transferred is
transferred *inductively*, though (and 99.999% of the losses are
inductive, too ;-)

There is enough capacitative couling for better trasnformers to be wound
with an (earthed) screen winding between primary and secondary layers
to reduce the transfer of energy to approximately zero.

The Natural Philosopher wrote:

There is enough capacitative couling for better trasnformers to be wound
with an (earthed) screen winding between primary and secondary layers
to reduce the transfer of energy to approximately zero.

Thanks for that nugget - you learn something every day here on Usenet!

Stefek Zaba wrote:

[...] though (and 99.999% of the losses are inductive, too ;-)

A nonsensical statement, Sir. 100% of losses are resistive :-). Pure
inductance, whether of the self or the mutual flavour, can only store
(and retrieve) energy. If losses you want, resistance you need.

Losses in transformers come in three sorts, (i) I^2 * R loss in the
windings (cooper loss), (ii) eddy current loss in the core - which is
just another sort of I^2 * R loss, and (iii) hysteresis loss in the
core, proportional to the area of the B-H loop being traversed and the
frequency, and representable by an equivalent shunt resistance.

Imperfect magnetic coupling between the windings will cause an
additional voltage drop, compared with ideal 100% coupling, but this is
not a dissipative loss. In equivalent circuit terms it appears as the
voltage drop across an inductance - the leakage inductance.

In small transformers of the type likely to be found in domestic
equipment the impedance of the transformer is dominated by the winding
resistances; leakage reactance is negligible. Most of the loss is
copper loss (except off-load).

--
Andy

Andy Wade wrote:
Stefek Zaba wrote:

[...] though (and 99.999% of the losses are inductive, too ;-)


A nonsensical statement, Sir. 100% of losses are resistive :-). Pure
inductance, whether of the self or the mutual flavour, can only store
(and retrieve) energy. If losses you want, resistance you need.

Argh! Uncle! Uncle! I give up!

You and the NatPhis are both right to take me to task on the sloppy
stuff I wrote. What I was kinda trying to get across is that the energy
transfer and energy losses are all to do with electromagnetism, rather'n
capacitive effects. And I was more or less wrong on both counts (tail
between legs) - there is an (unwanted) capacitive component to the
transfer, and as you detail the underlying mechanism for the energy loss
(inefficiency, giving rise to heating) is resistive - with actual
"ordinary" resistance dominating in small domestic transformers, while
the eddy currents (which I was thinking, loosely, about) are more
accurately considered as resistive.

We now return you to your normal broadcasts...

Stefek

Stefek Zaba wrote:

Andy Wade wrote:

Stefek Zaba wrote:

[...] though (and 99.999% of the losses are inductive, too ;-)



A nonsensical statement, Sir. 100% of losses are resistive :-). Pure
inductance, whether of the self or the mutual flavour, can only store
(and retrieve) energy. If losses you want, resistance you need.

Argh! Uncle! Uncle! I give up!

Actually the iron losses whilst they may appear as resistive in an
idealised model, are not strictly resistive in nature...

You and the NatPhis are both right to take me to task on the sloppy
stuff I wrote. What I was kinda trying to get across is that the energy
transfer and energy losses are all to do with electromagnetism, rather'n
capacitive effects. And I was more or less wrong on both counts (tail
between legs) - there is an (unwanted) capacitive component to the
transfer, and as you detail the underlying mechanism for the energy loss
(inefficiency, giving rise to heating) is resistive - with actual
"ordinary" resistance dominating in small domestic transformers, while
the eddy currents (which I was thinking, loosely, about) are more
accurately considered as resistive.

We now return you to your normal broadcasts...

hmm.


Stefek

"Anthony Bowles" wrote in message
...
Not DIY because I wouldn't even consider doing much in the way of
electrics in the house but I'm hoping one of the electrical gurus out
there might be able to shed some light on this.

Basically I'm wondering if I've got a problem with the electrics or just
2 "appliances" at the same time. The other day the DVD player was only
transmitting sound via it's coax connection (to the amp). No picture
(or sound) was coming out of the scart. After much fiddling with
various connections etc I touched the case of the DVD player and could
feel a humming through my finger tips. If ran my fingers across the
case they didn't so much as "glide" across it as "juddered". Anyway
this seemed to cure the problem and the DVD came back on. The only
thing I could think of was either it's becoming faulty or it was some
build up of static (however I didn't get a static shock).

Anyway, it's happened again. I don't think I've used the player in a
week and it's gone off. Touching it doesn't help this time but it's got
that same humming feeling.

Now this is where I start to think "hold on what's going on" because the
same thing is now happening when I put my Palm T3 (metal case not
plastic) into it's cradle. When I touch it in the cradle it's humming
and feels "sticky". When it's out of the cradle it smooth. I've had it
a year and never noticed that before.

I haven't noticed it on anything else but I'm not about to go round the
house touching everything with a metal case!

In all honesty my other half thinks I'm daft cos she can't see what I'm
going on about (beyond the fact the DVD player's gone funny).

Is it possible something's wrong with the electrics (in which case I'll
get an electrician out) or just coincidence?

Cheers

Anth

Hiya Anth.
Get a neon screwdriver, check the cases involved if it lights then contact a
qualified electrician.
A newsgroup's great for tips on the odd diy project, but this one's possibly
very dangerous.
best left to peole who know what they're talking about. (imo)

jim.

On Mon, 18 Oct 2004 01:36:56 GMT, "jim." wrote:

Get a neon screwdriver, check the cases involved if it lights then contact a
qualified electrician.

A neon screwdriver is considered to be potentially very dangerous (as
in lethal) to those in the profession.

Andrew

In article ,
jim. wrote:
Get a neon screwdriver, check the cases involved if it lights then
contact a qualified electrician. A newsgroup's great for tips on the odd
diy project, but this one's possibly very dangerous. best left to peole
who know what they're talking about. (imo)

A neon screwdriver will by its nature show a positive result on some
things which are perfectly safe.

--
*OK, who stopped payment on my reality check?

Dave Plowman London SW
To e-mail, change noise into sound.

Get a neon screwdriver, check the cases involved if it lights then contact
a
qualified electrician.

If I had a neon screwdriver, it would be in the bin. Terrible things, full
of false positives and false negatives.

Christian.

"Christian McArdle" wrote in message
. net...
Get a neon screwdriver, check the cases involved if it lights then
contact
a
qualified electrician.

If I had a neon screwdriver, it would be in the bin. Terrible things, full
of false positives and false negatives.



You're just too picky! All tools should be used within their limitations. A
neon screwdriver is a useful screwdriver that has the added benefit of being
able to tell which of two wires is live. I can live with false positives and
I wouldn't trust my safety to a negative - I'm getting to old to flick live
wires with my finger to check them ). Mind you, I think we've already had
this conversation.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

"Andy Wade" wrote in message
...
Stefek Zaba wrote:

[...] though (and 99.999% of the losses are inductive, too ;-)

A nonsensical statement, Sir. 100% of losses are resistive :-). Pure
inductance, whether of the self or the mutual flavour, can only store
(and retrieve) energy. If losses you want, resistance you need.

Losses in transformers come in three sorts, (i) I^2 * R loss in the
windings (cooper loss), (ii) eddy current loss in the core - which is
just another sort of I^2 * R loss, and (iii) hysteresis loss in the
core, proportional to the area of the B-H loop being traversed and the
frequency, and representable by an equivalent shunt resistance.

Imperfect magnetic coupling between the windings will cause an
additional voltage drop, compared with ideal 100% coupling, but this is
not a dissipative loss. In equivalent circuit terms it appears as the
voltage drop across an inductance - the leakage inductance.

In small transformers of the type likely to be found in domestic
equipment the impedance of the transformer is dominated by the winding
resistances; leakage reactance is negligible. Most of the loss is
copper loss (except off-load).

I think you've been seeing too many good transformers. The cheap ****e
coming in from China nowadays has most loss due to saturation of the core -
your (ii) and (iii) above. Worse still it varies wildly from batch to
batch.

G&M wrote:

I think you've been seeing too many good transformers. The cheap ****e
coming in from China nowadays has most loss due to saturation of the core -
your (ii) and (iii) above.

Not really, because the iron losses will flatten out as you reach
saturation. When the core is being driven into saturation the main
source of increased loss is copper loss in the primary, due to the
magnetising current shooting up.

Worse still it varies wildly from batch to batch.

Find yourself a better manufacturer. Nor everything cheap from China is
crap.

--
Andy