mike wrote:

I have an Ungar 9911 soldering iron handpiece
without the controller. Looks new.

I thought it would be trivial to build a temperature
controller.
I can make it hot. There is some PTC going on
as the current goes down as the iron heats up.

I expected some feedback.
The only other connector pins that have some
connectivity measure 497 ohms independently of
temperature. Can't use that for temperature monitoring.

Google has failed me.
Anybody know how these work?


** It is possible to use the rise in the resistance of the heater element as a temp sensor - but not so simple in a unit that claims to use zero crossing switching for power control.

My Hakko FX888 ( 24V, 70W) has a heater that measures 3ohms at room temp rising to 9 ohms at soldering temp. A feedback winding on the heater unit measures 47 ohms at room temp rising to 140 ohms at soldering temp - this is what control the tip temp.

..... Phil