Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to various
points on the glob of 1/5 to 1/2 of the original value for areas where there
was conductance, some areas above 30 Meg ohm.

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

N Cook wrote:
Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to various
points on the glob of 1/5 to 1/2 of the original value for areas where there
was conductance, some areas above 30 Meg ohm.


Wasnt there some guy on the interweb with a formula for this a couple of
years back?

Ron(UK)

Ron(UK) wrote:
N Cook wrote:
Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor
in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to
various
points on the glob of 1/5 to 1/2 of the original value for areas where
there
was conductance, some areas above 30 Meg ohm.


Wasnt there some guy on the interweb with a formula for this a couple of
years back?

Ron(UK)

Here ya go, send him forty bucks and he`ll tell you how to do it!

Ron(UK)

N Cook wrote:

Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to various
points on the glob of 1/5 to 1/2 of the original value for areas where there
was conductance, some areas above 30 Meg ohm.

wouldnt it be easier to look at the circuit and work out what would
work in it?


NT

"N Cook" wrote in message
...
Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to
various
points on the glob of 1/5 to 1/2 of the original value for areas where
there
was conductance, some areas above 30 Meg ohm.

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




Your formula is wrong. R = Volts / Current.

It is not possible at all. To work out rhe resistance - the current is
needed and
will be unknown due to the R being faulty.

Regards

Terry wrote in message
...

"N Cook" wrote in message
...
Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in
a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions ,
let
alone colours, may or may not be still intact in resistance of any
value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ?
and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The
resultant
glob had resistance values radially from the remnant of one lead to
various
points on the glob of 1/5 to 1/2 of the original value for areas where
there
was conductance, some areas above 30 Meg ohm.

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




Your formula is wrong. R = Volts / Current.

It is not possible at all. To work out rhe resistance - the current is
needed and
will be unknown due to the R being faulty.

Regards



A bit of confusion crept in.
Ignoring any remnant resistance, one scenario is exploded to bits, I'm
starting from a table of wattages and likely to result in those sorts of
damage.
Then with some idea of the voltage involed ,getting some sort of idea of the
original resistance via V x V / R. Its only for "ball-park" purposes.
Would anyone care to put some W values to scenario 2/ and 4/ ?

--
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
...
Can anyone assist in expanding this table.
If you know the maximum voltage likely to have fell across a resistor in a
fault condition - how to get an idea of the original value , if the
schema/parts listing is unavailable. Using V x V /R

Say for a 1/3 watt metal oxide resistor
1/ Discoloured unreadable bands , body of resistor browned, intact , but
ohmage may have varied
2/ Charred to the point of not being able to discern band positions , let
alone colours, may or may not be still intact in resistance of any value.
3/ Melted and fused into a small glob
4/ Exploded apart

For 1/ I would guess about 0.5 to 1W, value likely going up or down ? and
different result due to long term or catastrophic overheating ?
3/ from one recent example , dissipation of about 10 watts. The resultant
glob had resistance values radially from the remnant of one lead to
various
points on the glob of 1/5 to 1/2 of the original value for areas where
there
was conductance, some areas above 30 Meg ohm.

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




Destructing a few 1/3 R, for the 4.7 ohm ones I chose then about 1W with
constant voltage but the remnant resistance decreased so runaway at about
2.5W.
Dropping to about 80 percent of original resistance for 1W and discoloured
bands and only browned body. For the one about 2W then black body and about
70 percent of the original resistance, held for 2 minutes but a bit more
than that and it would have accelerated to complete destruction.

So for those end results, approximate wattages
1/ , 1W
2/ , 2W
3/ , 10W
4/ , presumably 20W

Number 3/ I should have said one lead broken and the glob being retained by
one lead

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

I don't think you can come up with any useful table.

If you don't know the voltage across the resistor, or the current,
you're a bit short on the information front.

For most circuits you need to be no more than 20% off. With very
little information, you're guesses as to the voltage and current are
likely to each be off by much much more than that. Multiply one wild
guess by another and the results are not good.