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WR overlay designation for a fusible resistor?

N

N_Cook

Jan 1, 1970
0
W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing
 
A

Arfa Daily

Jan 1, 1970
0
N_Cook said:
W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

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
 
E

Eeyore

Jan 1, 1970
0
N_Cook said:
W for Wood's metal for the fusible part ?
Googling "wood's metal" AND "fusible resistor" produces nothing

Wimpy resistor ?

Graham
 
E

Eeyore

Jan 1, 1970
0
Michael A. Terrell said:
'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
 
E

Eeyore

Jan 1, 1970
0
Michael A. Terrell said:
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
 
N

N_Cook

Jan 1, 1970
0
Eeyore said:
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.
 
R

Ross Herbert

Jan 1, 1970
0
: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.
 
A

Arfa Daily

Jan 1, 1970
0
Ross Herbert said:
: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
 
A

Arfa Daily

Jan 1, 1970
0
Eeyore said:
Wimpy resistor ?

Graham

Weak resistor ?

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

Arfa
 
N

N_Cook

Jan 1, 1970
0
Arfa Daily said:
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
 
R

Ross Herbert

Jan 1, 1970
0
:
::>
:> :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/msds-evansgroup/msds-Woods Metal.pdf
 
G

Geo

Jan 1, 1970
0
How about "CR" for a diode ? Copper (oxide) Rectifier, maybe ?

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

Geo
 
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