Type of ceramic wirewound resistor?

[N_Cook]

I have one in front of me labelled
UTM 210-9 25435,3 watt probably Russian and can find no info
Like the standard pillar white/grey ceramic resistors but instead of the
wire returning down the flute of the ceramic there is a sprung join set in
the flute with bismuth solder or something. Anyone know a generic name for
this type of thermal cut out resistor or a maker name ?
Other than the opening temperature must be greater than the sustained power
rating temp of the resistor and lower than standard solder, anyone know what
sort of safety cut out temperature?

 

[Baron]

N_Cook Inscribed thus:

I have one in front of me labelled
UTM 210-9 25435,3 watt probably Russian and can find no info
Like the standard pillar white/grey ceramic resistors but instead of
the wire returning down the flute of the ceramic there is a sprung
join set in the flute with bismuth solder or something. Anyone know a
generic name for this type of thermal cut out resistor or a maker name
? Other than the opening temperature must be greater than the
sustained power rating temp of the resistor and lower than standard
solder, anyone know what sort of safety cut out temperature?

Woods metal is used to secure the spring ! So about 70C.

 

[N_Cook]

N_Cook Inscribed thus:


Woods metal is used to secure the spring ! So about 70C.

Must be higher than that, as a rule of thumb or finger I've come across
plenty of in service droppers that are too hot to touch more than fleetingly
which means 70 C or above. Unfortunately my variable soldering iron cannot
go down that low to try this one in front of me. Looks like a lump of metal
with thermometer in it, heated on the stove to check this one

 

[Baron]

N_Cook Inscribed thus:

Must be higher than that, as a rule of thumb or finger I've come
across plenty of in service droppers that are too hot to touch more
than fleetingly which means 70 C or above. Unfortunately my variable
soldering iron cannot go down that low to try this one in front of me.
Looks like a lump of metal with thermometer in it, heated on the stove
to check this one

I've got some resistors with thermal breaks attached kicking about
somewhere. If I recall they were used in some TV sets. If I can lay
my hands on them I'll have a look and see what values they are. I do
recall being warned not to solder them closed, but to replace them with
new ones.

 

[N_Cook]

N_Cook Inscribed thus:


Woods metal is used to secure the spring ! So about 70C.

70 degrees C is the standard ambient temp maximum for the specified power
rating of a resistor , not its in service maximum temperature.

 

[Geo]

I have one in front of me labelled
UTM 210-9 25435,3 watt probably Russian and can find no info
Like the standard pillar white/grey ceramic resistors but instead of the
wire returning down the flute of the ceramic there is a sprung join set in
the flute with bismuth solder or something. Anyone know a generic name for
this type of thermal cut out resistor or a maker name ?
Other than the opening temperature must be greater than the sustained power
rating temp of the resistor and lower than standard solder, anyone know what
sort of safety cut out temperature?

Used to be quite common in TV sets (fusible resistor).
Have a look at the top left diagram on page 4 of this which shows
mechanical drawing:-
http://www.vishay.com/docs/21008/kk.pdf

Geo

 

[N_Cook]

Used to be quite common in TV sets (fusible resistor).
Have a look at the top left diagram on page 4 of this which shows
mechanical drawing:-
http://www.vishay.com/docs/21008/kk.pdf

Geo

if page 41 and in thermally cutout view , sprung open, then yes that type.
I'll have another look tomorrow in that pdf but I could not see the melt
temperature.

Only approximate this. Some flux over the join of this one in front of me
and then using the temp read function of my soldering iron before switching
off before reaching set point. Approx 130 deg C no cutout , 160 deg cuts out

 

[Baron]

Geo Inscribed thus:

Used to be quite common in TV sets (fusible resistor).
Have a look at the top left diagram on page 4 of this which shows
mechanical drawing:-
http://www.vishay.com/docs/21008/kk.pdf

Geo

Yes ! Those are the ones I remember. Looking at the power curves
suggests that they could get extremely hot, however the top graph
suggests 70C. The body temperature could get to be far more than that
depending upon how long and how good the heat conduction to that joint
is.

 

[N_Cook]

Used to be quite common in TV sets (fusible resistor).
Have a look at the top left diagram on page 4 of this which shows
mechanical drawing:-
http://www.vishay.com/docs/21008/kk.pdf

Geo

The KKE Si derating curve maxes out at 150 deg C , so that must be the
fusing temp, agrees with this one

 

[N_Cook]

Back in the day when I was a TV engineer, they were very common, and known
as 'spring-off resistors'. Often used to be used in the feed to the HOP
stage, and would spring open when the HOP valve failed. They were usually
re-soldered with what we knew just as 'high melting point solder'. I've no
idea what actual temperature the stuff was, just that it was issued to us, a
few feet at a time, for re-soldering these devices. The Adcola irons that we
used (about 50 watts, as I recall ??) struggled a bit with it, but were
ultimately capable of making the joint quite nicely.

Arfa

Are you saying it was somehow solder that needed a lot of heat rather than a
lot of temperature?

 

[N_Cook]

Dunno really. No. I think I mean that it needed a lot of temperature. The
Adcola, with its solid copper bit, certainly produced enough heat at the
tip to handle a small job like resoldering that spring, but it did have a
little difficulty taking the solder to a 'full flow' consistency, so
probably didn't have quite the temperature required. Remember that this was
nearly 40 years ago, when a TV engineer's soldering iron was little more
than an electric poker ...

The solder was just designated "HMP" for high melting point, and as I
recall, was a little greyer looking on the reel than 'standard' solder.

Arfa

So a more sophisticated version of the aluminium foil and nail for a fuse
replacement ?

 

[N_Cook]

No, I would say not. I worked for Rediffusion, and they were one of the best
'technical' rental companies in the business. Their training and attention
to detail, was second to none, and they used these resistors in their own TV
set designs, so if that's what they said was the right way to handle
remaking one of these devices after it had sprung off, then you can be
pretty sure that it was right. There was never any question of the resistor
having to be replaced because it had sprung open ...

Arfa

I must be missing something here , what is the point of the spring off
disconnect?

 

[Baron]

N_Cook Inscribed thus:

I must be missing something here , what is the point of the spring off
disconnect?

Its a circuit protection device...

 

[N_Cook]

It opens the resistor, and removes power from the overload condition that
it's there to protect against ...

Arfa

But not if you "weld" it shut with high melting point solder

 

[N_Cook]

What are you saying exactly ? That 'high melting point' solder was not what
was originally used to hold it shut by the manufacturers ? Are you
suggesting that a company the size of Rediffusion, who designed their own TV
sets making use of these devices, then went on to encourage their (extremely
well trained and well thought of in the trade) engineers, to execute some
kind of bodge repair on ones that had opened ?

No, of course they didn't. If that material is what central stores supplied
to the branches for remaking the spring connection, then I think you can be
pretty sure that it was appropriate for the job. Presumably, as you found it
necessary to ask what one of these resistors was in the first place, you
have no experience of them, contemporary with the time that they were
commonly in use ?

Arfa



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Perhaps N-Cook was thinking of the similar over temperature cutouts
used to protect transformers such as used in Philips Tape recorders
that used a very low temperature 'solder' to hold the spring
connection together.
This type of 'fusable link' has been used for well over 100 years and
uses very carefully formulated alloy as the sensor to operate at
remarkably precise temperatures. The fire sprinkler head is one of the
earliest mass produced applications of this technique.

Neil S.

+++++


Someone upthread mentiond a currently available type of them
http://www.vishay.com/docs/21008/kk.pdf
page 41 top left has a spring open view of the sprung type
and top right of p42 has the derating plot showing the maximum operating
temperature of 150 degrees for the spring type , compared to 350 degrees for
the non-safety, plain vanilla ones