Hypothetical toroidal transformer problem

[N Cook]

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Gareth Magennis]

"N Cook" <diverse8@gazeta.pl> wrote in message
news:g8mgss$4f1$1@inews.gazeta.pl...

Unless anyone has experienced it. What would happen if that thick
aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band
amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

I imagine that if the aluminium sheet is earthed via the chassis there would
be some smoke due to a single shorted turn.




Gareth.

 

[Dave Platt]

In article <atcfzvasbuvgflfgrzfygqhx.k60rj90.pminews@ouse>,
Rodney Pont <pmmspamscop@infohitsystems.ltd.uk> wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

SPLATTTTT (maybe) Fizzzzzz (possibly) POP as the fuse blows.

All of the above assuming that it is a toroidal transformer and that
aluminium foil is connected to the chassis

How? The OP says the coach bolt is holding the transformer to the
chassis. Everything is at the same potential, presumably earth.

You'd end up with a new metallic pathway (chassis, up through the
bolt, into the aluminum sheet, and then to the chassis again) which
forms a loop going through the center of the toroid.

In effect, you would have added an unwanted one-turn secondary winding
to the transformer, and then shorted it... just as if you had looped
an isolated wire through the center and then soldered its ends
together.

You'll end up with a *lot* of current flowing in this one-turn
secondary winding, and (as a result) through the primary... just as
you would have if you had short-circuited one of the "real" secondary
windings.

It'll be a good question whether the mains fuse/breaker will blow fast
enough to keep the sheet from arc-welding itself to the top of the
bolt. In any case, it'll probably be reasonably spectacular.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[N Cook]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:48AF4B51.2B2E3DC3@hotmail.com...

N Cook wrote:

Unless anyone has experienced it. What would happen if that thick
aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band
amp
carcass , drooped down and touched the top of the coachbolt that holds
the
mains transformer to the chassis ?

So what DID happen ?

Graham

I've no idea , its a thought experiment. Could not find the current carrying
capacity of a 3/8 inch steel bolt, assuming the worst case would be
something like one turn of a 3/8 inch steel ring.

I see where too many owners pull these amps out of their housings and then
not know how to use an old vinyl record sleeve or couple of steel rules or
similar to reintroduce amp to casing.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[DaveD]

N Cook wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

SPLATTTTT (maybe) Fizzzzzz (possibly) POP as the fuse blows.

All of the above assuming that it is a toroidal transformer and that
aluminium foil is connected to the chassis

 

[Rodney Pont]

On Sat, 23 Aug 2008 03:02:24 +1200, DaveD wrote:

N Cook wrote:
Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

SPLATTTTT (maybe) Fizzzzzz (possibly) POP as the fuse blows.

All of the above assuming that it is a toroidal transformer and that
aluminium foil is connected to the chassis

How? The OP says the coach bolt is holding the transformer to the
chassis. Everything is at the same potential, presumably earth.

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk

 

[Ancient_Hacker]

On Aug 22, 9:02 am, "N Cook" <diver...@gazeta.pl> wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

Depends on the resistance of the total loop. Bolts are usually steel,
and steel is rather high in resistance.

In your typical transformer, with say three turns per volt, you now
have something like 300 millivolts AC
running into anything from 0.1 to 1 ohms. Taking the worst case,
E^2 / R is about 1 watt. That will cause a little local warming but
not much else.

 

[Eeyore]

N Cook wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

Well, if it closed a circuit one hell of a current would flow through a single
shorted turn and the magic smoke might come out (depends on if the designer
knows how to fuse equipment properly).

Graham

 

[Eeyore]

Ancient_Hacker wrote:

On Aug 22, 9:02 am, "N Cook" <diver...@gazeta.pl> wrote:
Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

Depends on the resistance of the total loop. Bolts are usually steel,
and steel is rather high in resistance.

Not the ones that go through toroids !

In your typical transformer, with say three turns per volt, you now
have something like 300 millivolts AC

In a power amp ? Much more volts/turn than that. At least a volt from memory
(typically).

Graham

 

[Eeyore]

Rodney Pont wrote:

Hmm, I hadn't thought about the field.

Never forget the field !

I suppose a lot would depend on
how good a contact the aluminium sheet that had fallen made with the
rest of the chassis.

True. Bad luck would probably ensure a good contact.

Graham

 

[Eeyore]

N Cook wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

So what DID happen ?

Graham

 

[Rodney Pont]

On Fri, 22 Aug 2008 11:18:26 -0700, Dave Platt wrote:

Unless anyone has experienced it. What would happen if that thick aluminium
sheet, nominally stuck as screening, to the chipboard interior of a band amp
carcass , drooped down and touched the top of the coachbolt that holds the
mains transformer to the chassis ?

SPLATTTTT (maybe) Fizzzzzz (possibly) POP as the fuse blows.

All of the above assuming that it is a toroidal transformer and that
aluminium foil is connected to the chassis

How? The OP says the coach bolt is holding the transformer to the
chassis. Everything is at the same potential, presumably earth.

You'd end up with a new metallic pathway (chassis, up through the
bolt, into the aluminum sheet, and then to the chassis again) which
forms a loop going through the center of the toroid.

In effect, you would have added an unwanted one-turn secondary winding
to the transformer, and then shorted it... just as if you had looped
an isolated wire through the center and then soldered its ends
together.

You'll end up with a *lot* of current flowing in this one-turn
secondary winding, and (as a result) through the primary... just as
you would have if you had short-circuited one of the "real" secondary
windings.

It'll be a good question whether the mains fuse/breaker will blow fast
enough to keep the sheet from arc-welding itself to the top of the
bolt. In any case, it'll probably be reasonably spectacular.

Hmm, I hadn't thought about the field. I suppose a lot would depend on
how good a contact the aluminium sheet that had fallen made with the
rest of the chassis.
--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk