Weller soldering iron sensor

[Chuck]

The sensor in my Weller temperature controlled soldering iron has apparently
died ( sensor measures open circuit, display shows EEE instead of iron
temperature). The replacement part from the manufacturer costs almost as
much as a new iron. Does anyone know what the nature of this sensor is:
thermistor, thermocouple or ? It might be worth trying to modify or repair
the old one.

thanks for your thoughts...

--Chuck

 

[Jack]

It's a bimetal switch

 

[BOB URZ]

It's a bimetal switch

Not in the models with variable temp. The WTCPX series maybe.
Try finding a compatible pencil on Ebay. The temp sensor is in the
pencil. What series is it? Maybe a bad or broken wire in the pencil.
Take resistance readings on the pencil terminals.

Bob

 

[Chuck]

The sensor element (Weller part # EC229A) is in a black plastic housing, at
the end of a thin metal probe which extends up through the heating element
to contact the soldering tip. Two terminals on the housing are soldered to
leads from the 5 conductor cord (two wires to sensor, two to heater,
ground). The sensor is open circuit, measured at the solder terminals. The
wires to the control unit check ok - fractional ohm series resistance, no
shorts. The solder terminals on the sensor make me suspect a thermistor
rather than a thermocouple. Does anybody have any firm information ??

--Chuck

 

[Jim Adney]

It's a bimetal switch

The type of switch varies depending on the Weller model. I'm not aware
of any that actually use a bimetal switch.

The WTCPx models use a magnet and a bit of iron allow which has its
Curie point at the set temp. When the Curie temp is exceeded the
magnet is no longer attracted to the alloy piece and the magnet is
pulled back by a spring. This motion opens a mechanical switch. These
irons will only regulate at the temp labeled on the back of the tip.

Weller also makes irons with some kind of electronic sensors, I think
it is a resistor which changes resistance with temp, These can be
adjusted to regulate at any temp you like.

I don't think the OP told us which kind of iron he had.

-

 

[Guest]

No hard info on what's in there but I have fixed my iron (same symptom)
about twice over a period of about 5 years and it's been in the cable both
times FWIW.
Todd

 

[(remove)sound(remve)]

That was my understanding as well. Perhaps the OP (if he has this type of
station) merely needs a new tip; or needs to clean or replace the mechanical
switch....

jak

Well, if it has a digital display it NOT a WTCPX series that uses a
switch and slug method of temp control. I would take the pencil apart
and measure the resistance at both the heater and temp sensor directly.

Bob

 

[jakdedert]

The type of switch varies depending on the Weller model. I'm not aware
of any that actually use a bimetal switch.

The WTCPx models use a magnet and a bit of iron allow which has its
Curie point at the set temp. When the Curie temp is exceeded the
magnet is no longer attracted to the alloy piece and the magnet is
pulled back by a spring. This motion opens a mechanical switch. These
irons will only regulate at the temp labeled on the back of the tip.

That was my understanding as well. Perhaps the OP (if he has this type of
station) merely needs a new tip; or needs to clean or replace the mechanical
switch....

jak

 

[Andy Cuffe]

The sensor element (Weller part # EC229A) is in a black plastic housing, at
the end of a thin metal probe which extends up through the heating element
to contact the soldering tip. Two terminals on the housing are soldered to
leads from the 5 conductor cord (two wires to sensor, two to heater,
ground). The sensor is open circuit, measured at the solder terminals. The
wires to the control unit check ok - fractional ohm series resistance, no
shorts. The solder terminals on the sensor make me suspect a thermistor
rather than a thermocouple. Does anybody have any firm information ??

--Chuck

This doesn't answer your question, but if it's similar to the sensor on
the WCC-100, although the wires aren't color coded, the polarity of the
sensor does matter. After replacing the heating element I connected it
backwards and it failed to control the temperature.