WR overlay designation for a fusible resistor?
 

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

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

WR overlay designation for a fusible resistor?
 

"N_Cook" wrote in message
...
W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

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



Who can tell ? Why "Q" for a transistor ? Why "U" for an IC ? Why "VDD" ?
Why "VSS" ? I bet if you think for a while, there's loads of these that
don't 'appear' to make any sense, but must have to the o.e.d. I don't think
that there is anything particularly special about fusible resistors in terms
of the materials used to make the resistive element. As far as I know, they
are still carbon or metal film, with a completely non-flammable coating. I
think it is probably the internal connections that are 'necked' or something
to make them deliberately vulnerable to excess current, or heat in the
substrate, generated by excess dissipation.

Arfa

WR overlay designation for a fusible resistor?
 

N_Cook wrote:

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

Wimpy resistor ?

Graham

WR overlay designation for a fusible resistor?
 

Arfa Daily wrote:

Who can tell ? Why "Q" for a transistor ?


'T' was already used for 'Transformer'.


Why "U" for an IC ?


'I' was already used for 'Indicator'.


Why "VDD" ?


Voltage, 'Drain' (for cmos).



Why "VSS" ?


Voltage, 'Source' (for cmos).


I bet if you think for a while, there's loads of these that
don't 'appear' to make any sense, but must have to the o.e.d. I don't think
that there is anything particularly special about fusible resistors in terms
of the materials used to make the resistive element. As far as I know, they
are still carbon or metal film, with a completely non-flammable coating. I
think it is probably the internal connections that are 'necked' or something
to make them deliberately vulnerable to excess current, or heat in the
substrate, generated by excess dissipation.

Arfa


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your account: http://www.usenettools.net/ISP.htm

WR overlay designation for a fusible resistor?
 

"Michael A. Terrell" wrote:

Arfa Daily wrote:

Who can tell ? Why "Q" for a transistor ?

'T' was already used for 'Transformer'.

Why "U" for an IC ?

'I' was already used for 'Indicator'.

By whom ?

In the UK we legend ICs as 'IC3' for example ! Too obvious ?

Now tell me a transistor is a 'Q' in the USA ! We use 'TR'.


Graham

WR overlay designation for a fusible resistor?
 

N_Cook wrote:

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing


It shouldn't. You don't want molten metal loose inside equipment.
Older fusible resistors were nichrome wire in a fiberglass, asbestos or
sand housing. A few manufacturers used carbon resistors, but running
them right at the rated current caused them to age, and the resistance
to rise, which caused false trips. The original Motorola 'Quasar, Works
in a drawer' TV chassis did this on the audio output transformer. You
had to use the specified brand and wattage resistor for repairs, because
of variations between brands. Metal film has replaced nichrome wire in
modern equipment. You wand the failed fuse to vaporize the conductor,
not melt it and let it still make contact, or worse, create plasma which
will carry a lot higher current than the fuse did.


--
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Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

WR overlay designation for a fusible resistor?
 

Michael A. Terrell wrote:
N_Cook wrote:
W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing


It shouldn't. You don't want molten metal loose inside equipment.
Older fusible resistors were nichrome wire in a fiberglass, asbestos or
sand housing. A few manufacturers used carbon resistors, but running
them right at the rated current caused them to age, and the resistance
to rise, which caused false trips. The original Motorola 'Quasar, Works
in a drawer' TV chassis did this on the audio output transformer. You
had to use the specified brand and wattage resistor for repairs, because
of variations between brands. Metal film has replaced nichrome wire in
modern equipment. You wand the failed fuse to vaporize the conductor,
not melt it and let it still make contact, or worse, create plasma which
will carry a lot higher current than the fuse did.



Woods metal fusible links are used in such things as night storage
heaters. Possibly woods metal is used in microtemps but I doubt very
much if there`s any woods metal in fusible resistors.


Ron(UK)

WR overlay designation for a fusible resistor?
 

"Michael A. Terrell" wrote:

N_Cook wrote:

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

It shouldn't. You don't want molten metal loose inside equipment.
Older fusible resistors were nichrome wire in a fiberglass, asbestos or
sand housing. A few manufacturers used carbon resistors, but running
them right at the rated current caused them to age, and the resistance
to rise, which caused false trips. The original Motorola 'Quasar, Works
in a drawer' TV chassis did this on the audio output transformer. You
had to use the specified brand and wattage resistor for repairs, because
of variations between brands. Metal film has replaced nichrome wire in
modern equipment. You wand the failed fuse to vaporize the conductor,
not melt it and let it still make contact, or worse, create plasma which
will carry a lot higher current than the fuse did.

Yes, modern 'fusible resistors' are typically made using metal film over a
ceramic former and covered with a 'cement' coating. All of which is
non-combustible and flameproof..

In comparison, carbon film covered with laquer is very combustible.

Graham

WR overlay designation for a fusible resistor?
 

Eeyore wrote in message
...


"Michael A. Terrell" wrote:

N_Cook wrote:

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

It shouldn't. You don't want molten metal loose inside equipment.
Older fusible resistors were nichrome wire in a fiberglass, asbestos or
sand housing. A few manufacturers used carbon resistors, but running
them right at the rated current caused them to age, and the resistance
to rise, which caused false trips. The original Motorola 'Quasar, Works
in a drawer' TV chassis did this on the audio output transformer. You
had to use the specified brand and wattage resistor for repairs, because
of variations between brands. Metal film has replaced nichrome wire in
modern equipment. You wand the failed fuse to vaporize the conductor,
not melt it and let it still make contact, or worse, create plasma which
will carry a lot higher current than the fuse did.

Yes, modern 'fusible resistors' are typically made using metal film over a
ceramic former and covered with a 'cement' coating. All of which is
non-combustible and flameproof..

In comparison, carbon film covered with laquer is very combustible.

Graham


Fusible resistors are what it says on the tin - a resistor and a fuse.
The MO or metal bit and then the fusible bit, so avoiding the possibility of
seriously high temperatures building up in a fault condition, rather than
just non-combustibility.
I've only ever scraped one apart, long ago , out of curiosity, and there was
a definite fusible part that I remember as a metalic? blob rather than a
necking.
Unfortunately I did not know of Wood's metal, then, and didn't try heating
it up.
I'll try scraping back a 2.2 ohm one, tomorrow.

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

WR overlay designation for a fusible resistor?
 

On Wed, 23 Apr 2008 07:49:17 +0100, "N_Cook" wrote:

:W for Wood's metal for the fusible part ?
:Googling "wood's metal" AND "fusible resistor" produces nothing


Can't say I have ever heard of Wood's Metal being used for fusible resistors in
electrical or electronic equipment. I seem to remember that a major use for
Wood's Metal was as the fusible element in thermal break-circuit fire detectors
used back in the 30's - 50's. They were superseded by much better detectors.

WR overlay designation for a fusible resistor?
 

"Ross Herbert" wrote in message
...
On Wed, 23 Apr 2008 07:49:17 +0100, "N_Cook" wrote:

:W for Wood's metal for the fusible part ?
:Googling "wood's metal" AND "fusible resistor" produces nothing


Can't say I have ever heard of Wood's Metal being used for fusible
resistors in
electrical or electronic equipment. I seem to remember that a major use
for
Wood's Metal was as the fusible element in thermal break-circuit fire
detectors
used back in the 30's - 50's. They were superseded by much better
detectors.

There certainly used to be a pellet of Wood's in the 'daisy' fire
sprinklers. I don't know of that is still the case. It's a simple, reliable,
and more to the point 'on-the-spot' and unpowered system. The lid of my
pressure cooker still has a Wood's metal pressure pressure relief valve,
which coincidentally, I replaced just last week.

Arfa

WR overlay designation for a fusible resistor?
 

"Eeyore" wrote in message
...


N_Cook wrote:

W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

Wimpy resistor ?

Graham


Weak resistor ?

How about "CR" for a diode ? Copper (oxide) Rectifier, maybe ?

Arfa

WR overlay designation for a fusible resistor?
 

Arfa Daily wrote in message
...

"Ross Herbert" wrote in message
...
On Wed, 23 Apr 2008 07:49:17 +0100, "N_Cook" wrote:

:W for Wood's metal for the fusible part ?
:Googling "wood's metal" AND "fusible resistor" produces nothing


Can't say I have ever heard of Wood's Metal being used for fusible
resistors in
electrical or electronic equipment. I seem to remember that a major use
for
Wood's Metal was as the fusible element in thermal break-circuit fire
detectors
used back in the 30's - 50's. They were superseded by much better
detectors.

There certainly used to be a pellet of Wood's in the 'daisy' fire
sprinklers. I don't know of that is still the case. It's a simple,
reliable,
and more to the point 'on-the-spot' and unpowered system. The lid of my
pressure cooker still has a Wood's metal pressure pressure relief valve,
which coincidentally, I replaced just last week.

Arfa



I scraped off one of a batch of 2.2 ohm 1/3W , called fusible resistors and
heated with hot air gun to 180 deg C with no fusing anywhere.
MO over ceramic construction with spiral cut into the oxide starting and
ending 1/10 way in, so highest risistance in the axial central area between
the 2 cuts in that area , so any excess current failure would be in that
section.
So little more than a standard MO resistor , but not having the continuous
spiral. The scraped off coating seemed no more than slightly olive coloured
varnish

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

WR overlay designation for a fusible resistor?
 

On Thu, 24 Apr 2008 07:47:54 GMT, "Arfa Daily" wrote:

:
:"Ross Herbert" wrote in message
.. .
: On Wed, 23 Apr 2008 07:49:17 +0100, "N_Cook" wrote:
:
: :W for Wood's metal for the fusible part ?
: :Googling "wood's metal" AND "fusible resistor" produces nothing
:
:
: Can't say I have ever heard of Wood's Metal being used for fusible
: resistors in
: electrical or electronic equipment. I seem to remember that a major use
: for
: Wood's Metal was as the fusible element in thermal break-circuit fire
: detectors
: used back in the 30's - 50's. They were superseded by much better
: detectors.
:
:There certainly used to be a pellet of Wood's in the 'daisy' fire
:sprinklers. I don't know of that is still the case. It's a simple, reliable,
:and more to the point 'on-the-spot' and unpowered system. The lid of my
:pressure cooker still has a Wood's metal pressure pressure relief valve,
:which coincidentally, I replaced just last week.
:
:Arfa
:


All of the sprinkler systems I have looked at in the past 50 years or so use the
glass bulb which breaks due to expansion thus allowing the plug sealing the
outlet orifice to pop out under water pressure.

You are correct regarding the pressure safety valve on a pressure cooker. It
does have a slug of low melting point alloy but not sure if this is classified
as Wood's Metal, although it would probably be very similar. Wood's Metal
appears to have set proportions of bismuth (50%), lead (25%), tin (12.5%) and
cadmium (12.5%) designed to melt at approx 150 deg F.

http://evans.mse.berkeley.edu/~dan/m...ds%20Metal.pdf

WR overlay designation for a fusible resistor?
 

On Thu, 24 Apr 2008 08:02:20 GMT, "Arfa Daily" wrote:


How about "CR" for a diode ? Copper (oxide) Rectifier, maybe ?

Crystal Rectifier (as in your original crystal set). Followed by point contact
diodes.

Geo