Ecnerwal wrote:

In article ,
"N Cook" wrote:

Anyone know the term for laying double traces of solder along copper traces
to increase current carrying , so I can research it ?

No, but it's a dumb idea. It's fairly easy to dump solder "accurately"
on a trace (if not covered by soldermask, hopefully that's obvious) -
just heat and feed solder, it will follow the trace, and you can build
it up quite a ways simply from surface tension. If you need more current
capacity on the trace, bend up a chunk of copper wire that actually
conducts well and solder that on. Solder is a lousy conductor, compared
to copper. The copper will hold more solder on there, but most of the
current will be carried by the copper.

I've seen something similar done intentionally and neatly inside a couple of
amplifiers.

The power trace has a number of tinned copper wire 'links' in parallel with it on
the 'top' of the pcb. Quite clever since it can be done with auto-insert
machinery.

Personally I prefer to use equipment cable to deliver power to where it's needed
rather than string it out along pcb traces.

Graham

Eeyore wrote:

"Ron(UK)" wrote:

Eeyore wrote:
"Ron(UK)" wrote:

You're never going to be able to protect against stray metal object clattering
around inside,
Quite !

and I`m sure the original designers never gave it a thought.
In which case it shouldn't have a CE sticker.

I would imagine that the stray object originated inside the amp,
probably a panel screw or captive nut never secured in the first place.

I thought the OP said something did actually fall inside ?

Maybe


How often you you pick up an item of gear and hear something loose
rolling around inside

Thankfully not too often. I do recall one time about 30 yrs ago when I withdrew a
Bulgin mains lead and the earth prong of the equipment connector came out with it
though ! They were just held in place with screws !

They were held in by the same screw that held the cable iirc

I once found the entire tip and centre core of a jackplug neatly welded
twixt power transistor and heatsink. Presumably some clown snapped off
the plug, so pushed it right through with another.

The one thing most designers fail to allow for is the stupidity of the
end user.

Ron(UK)

"Nutcase ****ing ****"


So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


** Be very wary of adding +/- DC rail fues to any power amp designed
without them.

Very likely if one or other DC fuse blows or is removed, the amp's output
will swing fully to the rail with its fuse still intact.

Recipe for fried speakers.

You have been warned.



I'm just trying to engineer a more respectable equivalent of fuses for
trace
rupture.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Eventually one DC rail ruptured as a fuse.


** BULL**** !!!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


I've now decided to do some
calculation to determine what the rupture current for that trace was.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Then as the common return almost fused and is the same dimension but in
the
even worse case then carries twice the current , halving this trace
rupture
current to use as the fuse rupture current and reduce that for current
carying capacity , by half again ?



** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



If all output trannies fused short circuit all round so loading both DC
rails the combined common return would have ruptured at whatever that
rupture current is for the trace that did burn up.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?


** That term is : ******** !!!!!!!!!!!


I'm intrigued how you lay quite accurate molten solder runs and parallel
over and with existing traces.


** YOU are intrigued with eating your own putrid faeces.


Anyway measurements:
Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then
area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major
axes of .15mm and .8mm.


** Where are the guys in white suits ???

Hope they have those tranquillisers jabs handy ...



From tables of fusing currents for copper, also tin and lead (NB in the
form
of circular wires ) for different diameters.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
thought)


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Total 18 amps so 18/4 = 4.5 amps conventional fuse rating.
Presumably the circular to sheet allowance would up this 4.5 amp figure ,
but by how much ?


** BULL**** !!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Diverse Devices, Southampton, England


** Straight from the local schizophrenia ward to YOU !!!!!!!!


Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy .............


- have we got ourselves a ****ing LIVE ONE !!



......... Phil

"Nutcase ****ing ****"


So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


** Be very wary of adding +/- DC rail fues to any power amp designed
without them.

Very likely if one or other DC fuse blows or is removed, the amp's output
will swing fully to the rail with its fuse still intact.

Recipe for fried speakers.

You have been warned.



I'm just trying to engineer a more respectable equivalent of fuses for
trace
rupture.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Eventually one DC rail ruptured as a fuse.


** BULL**** !!!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


I've now decided to do some
calculation to determine what the rupture current for that trace was.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Then as the common return almost fused and is the same dimension but in
the
even worse case then carries twice the current , halving this trace
rupture
current to use as the fuse rupture current and reduce that for current
carying capacity , by half again ?



** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



If all output trannies fused short circuit all round so loading both DC
rails the combined common return would have ruptured at whatever that
rupture current is for the trace that did burn up.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?


** That term is : ******** !!!!!!!!!!!


I'm intrigued how you lay quite accurate molten solder runs and parallel
over and with existing traces.


** YOU are intrigued with eating your own putrid faeces.


Anyway measurements:
Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then
area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major
axes of .15mm and .8mm.


** Where are the guys in white suits ???

Hope they have those tranquillisers jabs handy ...



From tables of fusing currents for copper, also tin and lead (NB in the
form
of circular wires ) for different diameters.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
thought)


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Total 18 amps so 18/4 = 4.5 amps conventional fuse rating.
Presumably the circular to sheet allowance would up this 4.5 amp figure ,
but by how much ?


** BULL**** !!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Diverse Devices, Southampton, England


** Straight from the local schizophrenia ward to YOU !!!!!!!!


Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy .............


- have we got ourselves a ****ing LIVE ONE !!



......... Phil

"Nutcase ****ing ****"


So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


** Be very wary of adding +/- DC rail fues to any power amp designed
without them.

Very likely if one or other DC fuse blows or is removed, the amp's output
will swing fully to the rail with its fuse still intact.

Recipe for fried speakers.

You have been warned.



I'm just trying to engineer a more respectable equivalent of fuses for
trace
rupture.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Eventually one DC rail ruptured as a fuse.


** BULL**** !!!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


I've now decided to do some
calculation to determine what the rupture current for that trace was.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Then as the common return almost fused and is the same dimension but in
the
even worse case then carries twice the current , halving this trace
rupture
current to use as the fuse rupture current and reduce that for current
carying capacity , by half again ?



** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



If all output trannies fused short circuit all round so loading both DC
rails the combined common return would have ruptured at whatever that
rupture current is for the trace that did burn up.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?


** That term is : ******** !!!!!!!!!!!


I'm intrigued how you lay quite accurate molten solder runs and parallel
over and with existing traces.


** YOU are intrigued with eating your own putrid faeces.


Anyway measurements:
Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then
area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major
axes of .15mm and .8mm.


** Where are the guys in white suits ???

Hope they have those tranquillisers jabs handy ...



From tables of fusing currents for copper, also tin and lead (NB in the
form
of circular wires ) for different diameters.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
thought)


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Total 18 amps so 18/4 = 4.5 amps conventional fuse rating.
Presumably the circular to sheet allowance would up this 4.5 amp figure ,
but by how much ?


** BULL**** !!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Diverse Devices, Southampton, England


** Straight from the local schizophrenia ward to YOU !!!!!!!!


Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy .............


- have we got ourselves a ****ing LIVE ONE !!



......... Phil

"Nutcase ****ing ****"


So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


** Be very wary of adding +/- DC rail fues to any power amp designed
without them.

Very likely if one or other DC fuse blows or is removed, the amp's output
will swing fully to the rail with its fuse still intact.

Recipe for fried speakers.

You have been warned.



I'm just trying to engineer a more respectable equivalent of fuses for
trace
rupture.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Eventually one DC rail ruptured as a fuse.


** BULL**** !!!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


I've now decided to do some
calculation to determine what the rupture current for that trace was.


** BULL**** !!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Then as the common return almost fused and is the same dimension but in
the
even worse case then carries twice the current , halving this trace
rupture
current to use as the fuse rupture current and reduce that for current
carying capacity , by half again ?



** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



If all output trannies fused short circuit all round so loading both DC
rails the combined common return would have ruptured at whatever that
rupture current is for the trace that did burn up.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!



Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?


** That term is : ******** !!!!!!!!!!!


I'm intrigued how you lay quite accurate molten solder runs and parallel
over and with existing traces.


** YOU are intrigued with eating your own putrid faeces.


Anyway measurements:
Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then
area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major
axes of .15mm and .8mm.


** Where are the guys in white suits ???

Hope they have those tranquillisers jabs handy ...



From tables of fusing currents for copper, also tin and lead (NB in the
form
of circular wires ) for different diameters.


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
thought)


** BULL**** !!!!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Total 18 amps so 18/4 = 4.5 amps conventional fuse rating.
Presumably the circular to sheet allowance would up this 4.5 amp figure ,
but by how much ?


** BULL**** !!!!!!!!!!

You are a total ****ing nut case ASSHOLE !!!!!!!


Diverse Devices, Southampton, England


** Straight from the local schizophrenia ward to YOU !!!!!!!!


Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy .............


- have we got ourselves a ****ing LIVE ONE !!



......... Phil

" Diverse Devices, Southampton, England"

http://home.graffiti.net/diverse:graffiti.net/


** Straight from the local schizophrenia ward to YOU !!!!!!

Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy ........

- have we got ourselves a ****ing LIVE ONE !!





....... Phil

" Diverse Devices, Southampton, England"

http://home.graffiti.net/diverse:graffiti.net/


** Straight from the local schizophrenia ward to YOU !!!!!!

Usenet is the GREATEST lunatic magnet in the known universe.

Boy oh boy ........

- have we got ourselves a ****ing LIVE ONE !!





....... Phil

Ecnerwal wrote in message
...
In article ,
"N Cook" wrote:

Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?

No, but it's a dumb idea. It's fairly easy to dump solder "accurately"
on a trace (if not covered by soldermask, hopefully that's obvious) -
just heat and feed solder, it will follow the trace, and you can build
it up quite a ways simply from surface tension. If you need more current
capacity on the trace, bend up a chunk of copper wire that actually
conducts well and solder that on. Solder is a lousy conductor, compared
to copper. The copper will hold more solder on there, but most of the
current will be carried by the copper.

--
Cats, coffee, chocolate...vices to live by

I get the impression board layout designers just use what has worked before
as far as track dimensions etc and don't actually consider in great detail
catastrophic failure modes. Yes this kit does support the CE mark.
I've not been able to find design data/tables for such traces.
I may dig out a low voltage 60 amp transformer fed via a variac and
sacrifice some otherwise unaffected tracks on this board to determine what
sort of amperage to cause excessive heating and then another bit of track to
find the rupture current. Having to avoid localised failure at my test
join-points with a lot of distributed solder.

"Ron(UK)" wrote:

Eeyore wrote:
"Ron(UK)" wrote:
Eeyore wrote:
"Ron(UK)" wrote:

You're never going to be able to protect against stray metal object clattering
around inside,
Quite !

and I`m sure the original designers never gave it a thought.
In which case it shouldn't have a CE sticker.

I would imagine that the stray object originated inside the amp,
probably a panel screw or captive nut never secured in the first place.

I thought the OP said something did actually fall inside ?

Maybe


How often you you pick up an item of gear and hear something loose
rolling around inside

Thankfully not too often. I do recall one time about 30 yrs ago when I withdrew a
Bulgin mains lead and the earth prong of the equipment connector came out with it
though ! They were just held in place with screws !

They were held in by the same screw that held the cable iirc

There was another one - oh actually I think that terminal section did actually have a
male thread on it.


I once found the entire tip and centre core of a jackplug neatly welded
twixt power transistor and heatsink. Presumably some clown snapped off
the plug, so pushed it right through with another

LOL !


The one thing most designers fail to allow for is the stupidity of the
end user.

'Tis often true.

Graham

N Cook wrote:

I get the impression board layout designers just use what has worked before
as far as track dimensions etc

There are published guidelines for temp rise vs current, copper thickness and
track width. You'll find a chart of same in IEC60065 (electrical safety) in
fact.

The board layout guy will only use the data supplied by the design engineer.
They're not psychic. Some 'design engineers' have a clue however.


and don't actually consider in great detail
catastrophic failure modes.

Good designers will design for that.


Yes this kit does support the CE mark.

So what's the damn make and model FFS ! Why are you refusing to tell us one of
the most important pieces of information ?

Graham

N Cook wrote:


I get the impression board layout designers just use what has worked before
as far as track dimensions etc and don't actually consider in great detail
catastrophic failure modes.

On a well designed circuit board, you can often see which traces are
involved with each part of the circuit. Broad traces carry the heavy
current, spidery ones are the signal path. I remember a time when some
quality gear actually had the signal path screened onto the component
side of the board, together with typical voltages etc. That was when
they actually wanted us to repair the stuff.

I dont think any designer worries too much about 'catastrophic failure'!



.. Yes this kit does support the CE mark.

You still havent shared with us the make and model


Ron(UK)

Eeyore wrote:
I do recall one time about 30 yrs ago when I withdrew a
Bulgin mains lead and the earth prong of the equipment connector came out with it
though ! They were just held in place with screws !
They were held in by the same screw that held the cable iirc

There was another one - oh actually I think that terminal section did actually have a
male thread on it.

Aye that`s right, and when they came loose, Johnny guitar would try to
tighten it by sticking a screwdriver (table knife) in the slot in the
pin and twist, neatly snapping half the pin off!

Ron(UK)

"N Cook" wrote in message
...
Ecnerwal wrote in message
...
In article ,
"N Cook" wrote:

Anyone know the term for laying double traces of solder along copper
traces
to increase current carrying , so I can research it ?

No, but it's a dumb idea. It's fairly easy to dump solder "accurately"
on a trace (if not covered by soldermask, hopefully that's obvious) -
just heat and feed solder, it will follow the trace, and you can build
it up quite a ways simply from surface tension. If you need more current
capacity on the trace, bend up a chunk of copper wire that actually
conducts well and solder that on. Solder is a lousy conductor, compared
to copper. The copper will hold more solder on there, but most of the
current will be carried by the copper.

--
Cats, coffee, chocolate...vices to live by

I get the impression board layout designers just use what has worked
before
as far as track dimensions etc and don't actually consider in great detail
catastrophic failure modes. Yes this kit does support the CE mark.
I've not been able to find design data/tables for such traces.
I may dig out a low voltage 60 amp transformer fed via a variac and
sacrifice some otherwise unaffected tracks on this board to determine what
sort of amperage to cause excessive heating and then another bit of track
to
find the rupture current. Having to avoid localised failure at my test
join-points with a lot of distributed solder.



Just interested ... Do you actually make a living out of repairing this
stuff ? If I spent as much time as you seem to, worrying about esoteric
things like how much current a track will take before it vapourises, I would
long since have ceased to earn enough money to get by on. These days, I find
that it has to be 'wheel it in, fix it, wheel it out , invoice it, next
please'. If the bit called 'fix it' takes longer than an hour, and the value
of the kit is less than 150 quid, that bit changes to 'bin it' ...

Arfa

Meat Plow wrote:

On Sat, 14 Jul 2007 22:37:37 +0100, N Cook wrote:

Eeyore wrote in message
...


N Cook wrote:

The 2 reservoir caps are 6800uF, 80V rating with presumably about 65V
on each , when all is in working order.

That's a reasonable size. They won't be causing excessive switch on
current.

Is the power transformer toroidal or EI ? That's where the big
difference
is.
Toroids will take a considerable switch-on current (it's largely due to
their
magnetic characteristics).

Graham


Toroidal , not E-I lamination transformer
I'm coming around to thinking 5 amp anti-surge in the mains fuse-holder
and a 5 amp fuse shunted in the + and - rail traces from the DC side of
the bridge rectifier before the reservoir caps, but undecided whether
quick-blow or anti-surge ones there.

Fix the amp, put the fuses of your choice in and put it through its paces.
You'll probably want to run some music through it at high volume
preferably some Hip Hop barf. See which fuses blow and which don't.

There are uses for sine, square, multiple sine, and complex waveforms in
testing. I suggest using each for what it will make esily visible in the
performance.
--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â*
--Schiller

Tim Shoppa wrote:

CJT wrote:
Tim Shoppa wrote:

N Cook wrote:

400 watt RMS amp for use on 240 V mains.
Destructed due to metal dropping in and shorting the amp .
The only fuse is on the mains rated at 8 amp, maker's design rating,
which shows no sag , discolour or anything like that, ie untouched.
Shorted power trannies, burnt low power trannies and even a piece of
3mm trace from the main bridge rectifier burnt through and that had 2
runs of added solder over the track for current carrying, the other
polarity trace overheated but not ruptured
I'm thinking of bridging that gap with a fuse and another on the other
rail after cutting it.
The mains transformer is rated at 2x 47V,5 amp.
So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


The power supply to your amp probably has massively oversize filter
capacitors.

Average current draw at 400W out might be only two amps, but because
of the rectifier-filter construction it doesn't draw that two amps
continuously. It draws it in very brief gulps 120 times a second.
Typical conduction angle might be 20 percent in a well designed
supply; with massively oversize filter caps it could be as small as 5
percent. Massively oversized filter caps have been all the rage in
consumer audio for too many decades now.

The size of fuse you have to put in depends not on simple average
current (2 amps) but the root-mean-square (RMS) current (which could
indeed be 8 amps at full load).

That shouldn't be terribly hard to calculate, assuming a conduction
angle of your choice. So how about adding some support for the
assertion?

10% conduction angle gives peak current of 20A, RMS current of 6.3A,
not too unreasonable to choose an 8A fuse in that case.

6.25% conduction angle gives 8A RMS, but that'd blow the fuse way too
often.

It takes big capacitors and toroidal transformers with really stiff
windings but many folks are building audio power supplies that way. I
personally don't like razor-thin conduction angles like 10% but that's
the style of other folks, not me!

Tim.
I don't feel like whipping up bulk supply simulation right now, please run
yours and tell me the ripple voltages at 10% conduction and 6.25 %
conduction.
--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â*
--Schiller

Eeyore wrote in message
...


N Cook wrote:

I get the impression board layout designers just use what has worked
before
as far as track dimensions etc

There are published guidelines for temp rise vs current, copper thickness
and
track width. You'll find a chart of same in IEC60065 (electrical safety)
in
fact.

The board layout guy will only use the data supplied by the design
engineer.
They're not psychic. Some 'design engineers' have a clue however.


and don't actually consider in great detail
catastrophic failure modes.

Good designers will design for that.


Yes this kit does support the CE mark.

So what's the damn make and model FFS ! Why are you refusing to tell us
one of
the most important pieces of information ?

Graham


I was having a play with track width calculator
http://www.pcbco.com.au/tracecalc.html
and assuming it is still sort of valid
at very high temps.
Putting the melting point of copper of 1080 deg C then for 3.5mm strip of
presumably 1 oz copper then the rupture current would be about 48 amps
which seems reasonable. I knew it must be higher than 12 amps as that
calculation was for round wire. By 1080 deg C we can forget about the solder
run beefings.
I think I'll leave my 60 amp transformer on the shelf - I'm happy with 48
amps

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

N Cook wrote in message
...
Eeyore wrote in message
...


N Cook wrote:

I get the impression board layout designers just use what has worked
before
as far as track dimensions etc

There are published guidelines for temp rise vs current, copper
thickness
and
track width. You'll find a chart of same in IEC60065 (electrical safety)
in
fact.

The board layout guy will only use the data supplied by the design
engineer.
They're not psychic. Some 'design engineers' have a clue however.


and don't actually consider in great detail
catastrophic failure modes.

Good designers will design for that.


Yes this kit does support the CE mark.

So what's the damn make and model FFS ! Why are you refusing to tell us
one of
the most important pieces of information ?

Graham


I was having a play with track width calculator
http://www.pcbco.com.au/tracecalc.html
and assuming it is still sort of valid
at very high temps.
Putting the melting point of copper of 1080 deg C then for 3.5mm strip of
presumably 1 oz copper then the rupture current would be about 48 amps
which seems reasonable. I knew it must be higher than 12 amps as that
calculation was for round wire. By 1080 deg C we can forget about the
solder
run beefings.
I think I'll leave my 60 amp transformer on the shelf - I'm happy with 48
amps

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




I think, assuming they survive ordinary power-ups a few times, I'll settle
on a mains side 4 amp anti-surge , with a 5 amp A/S ready to hand spare and
2 off 10 amp quick-blow in the DC lines.

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

joseph2k wrote:
Tim Shoppa wrote:

CJT wrote:
Tim Shoppa wrote:

N Cook wrote:

400 watt RMS amp for use on 240 V mains.
Destructed due to metal dropping in and shorting the amp .
The only fuse is on the mains rated at 8 amp, maker's design rating,
which shows no sag , discolour or anything like that, ie untouched.
Shorted power trannies, burnt low power trannies and even a piece of
3mm trace from the main bridge rectifier burnt through and that had 2
runs of added solder over the track for current carrying, the other
polarity trace overheated but not ruptured
I'm thinking of bridging that gap with a fuse and another on the other
rail after cutting it.
The mains transformer is rated at 2x 47V,5 amp.
So drop the 8A fuse (for 2 KWatt !) to what value ? and the 2 added
fuses of what rating ?


The power supply to your amp probably has massively oversize filter
capacitors.

Average current draw at 400W out might be only two amps, but because
of the rectifier-filter construction it doesn't draw that two amps
continuously. It draws it in very brief gulps 120 times a second.
Typical conduction angle might be 20 percent in a well designed
supply; with massively oversize filter caps it could be as small as 5
percent. Massively oversized filter caps have been all the rage in
consumer audio for too many decades now.

The size of fuse you have to put in depends not on simple average
current (2 amps) but the root-mean-square (RMS) current (which could
indeed be 8 amps at full load).

That shouldn't be terribly hard to calculate, assuming a conduction
angle of your choice. So how about adding some support for the
assertion?

10% conduction angle gives peak current of 20A, RMS current of 6.3A,
not too unreasonable to choose an 8A fuse in that case.

6.25% conduction angle gives 8A RMS, but that'd blow the fuse way too
often.

It takes big capacitors and toroidal transformers with really stiff
windings but many folks are building audio power supplies that way. I
personally don't like razor-thin conduction angles like 10% but that's
the style of other folks, not me!

Tim.
I don't feel like whipping up bulk supply simulation right now, please run
yours and tell me the ripple voltages at 10% conduction and 6.25 %
conduction.

I refuse to run such a simulation: this is the sort of stuff that was
discussed in two pages of a 1930's-era electronics textbook in the
beginning of a chapter on power supplies. Math is what a high-school
student was expected to know. You might as well ask me to run a
simulation to prove that 1 volt across 1kohm gives 1mA :-).

I'll give you the result: at 10% conduction angle, ripple is 5%. (If
you have a pocket calculator, the voltage at the bottom of the ripple
is Vpeak*cos(.1*pi).) At 6.25% conduction angle, the ripple is 2%.

Other handy results: 15% conduction angle, ripple is 11%. 20%
conduction angle gives ripple of 19%.

If you look a little later in the 70-year old electronics texts, they
get into I2R and other losses in transformers and making the proper
economic choice in sizing transformers and capcitors. They also get
into my favorite filtering method, choke-input! (A method at least
mentioned in the better of the more modern textbooks).

Tim.