Electronics > Projects, Designs, and Technical Stuff
What is the resistance of the Hakko FX-888D thermistor/heater at higher temps?
WarFreak131:
I'm making my own PID controller for a soldering iron using an Arduino, and as a first step, I'm going to try to control the iron that comes with the Hakko FX-888D station. I was able to get a cheap knockoff for $11.
The manual says that the thermistor resistance at room temperature will be between 43 and 58 Ohms, but there's no mention of what the resistance is at higher temperatures. I am going to hook it up with another resistor in series and hook it up to 5V and then measure the voltage across the therimstor. Since the Arduino can only read a max of 5V with a 5mV resolution, I need to know what other resistor to choose to get me a nice range of voltage values across the normal temperature range of 300C to 450C.
With regards to the heating element, does it exhibit the same rise in resistance? Typically how much current is passed through the element?
Thank you in advance.
thm_w:
Should give some ideas:
https://arduinoplusplus.wordpress.com/2016/08/15/diy-soldering-station-with-hakko-fx-888-iron/
http://dangerousprototypes.com/forum/index.php?topic=1921.0
https://www.eevblog.com/forum/reviews/genuine-vs-fake-hakko-936-ceramic-heater-a1321/
You may consider a T12 clone as well.
floobydust:
The FX-888 station uses A1560 heating element which has a separate temperature sensor, a wire-wound RTD inside. Around 43-58R at room temp but not platinum wire, but nickel-iron I think. Use the math from a ~50R RTD alpha 0.00527 and you can make a resistance table matching the thread below. I think it's the same sensor as the 936:
https://www.eevblog.com/forum/reviews/genuine-vs-fake-hakko-936-ceramic-heater-a1321/25/
A heating element can also act as a temperature sensor - its resistance increasing with temperature.
Hakko used this property for their 470-472 desoldering stations but later gave up and went to a dedicated thermocouple instead. I think it (NiCr heater wire) was too non-linear and without a MCU to correct, the analog controller could not do it accuratge enough.
A1560 is rated 26V 65W 3 ohms. Doesn't jive, I doubt it gets 8.6A.
WarFreak131:
--- Quote from: thm_w on September 01, 2020, 09:44:36 pm ---Should give some ideas:
https://arduinoplusplus.wordpress.com/2016/08/15/diy-soldering-station-with-hakko-fx-888-iron/
http://dangerousprototypes.com/forum/index.php?topic=1921.0
https://www.eevblog.com/forum/reviews/genuine-vs-fake-hakko-936-ceramic-heater-a1321/
You may consider a T12 clone as well.
--- End quote ---
Thank you, I will review these. For now, I want to stick with non-thermocouple variants. That requires a whole separate implementation of in amps that I'm just not ready for yet.
--- Quote from: floobydust on September 02, 2020, 12:45:45 am ---The FX-888 station uses A1560 heating element which has a separate temperature sensor, a wire-wound RTD inside. Around 43-58R at room temp but not platinum wire, but nickel-iron I think. Use the math from a ~50R RTD alpha 0.00527 and you can make a resistance table matching the thread below. I think it's the same sensor as the 936:
https://www.eevblog.com/forum/reviews/genuine-vs-fake-hakko-936-ceramic-heater-a1321/25/
A heating element can also act as a temperature sensor - its resistance increasing with temperature.
Hakko used this property for their 470-472 desoldering stations but later gave up and went to a dedicated thermocouple instead. I think it (NiCr heater wire) was too non-linear and without a MCU to correct, the analog controller could not do it accuratge enough.
A1560 is rated 26V 65W 3 ohms. Doesn't jive, I doubt it gets 8.6A.
--- End quote ---
I was planning on using a SEPIC/buck/boost to get the right output current. I don't feel comfortable having wall voltages in the circuit, so I was going to try to power this from a 36 W (24 VDC 1.5 A) DC power supply. But I may have to go back to the drawing board if it takes over 8 amps. But is it possible to get it up to the right temperature, albeit perhaps with a smaller thermal reservoir?
floobydust:
The Hakko 936/FX-888 heater spec seems weird 2.5-3.5R. I measure 3.3R on my FX-8801 which would only need ~16V for 65W but the power transformer is 24VAC. T12's are typically 8R and at 24VDC that's 72W.
You don't need the textbook full power. People run T12's from laptop bricks at 19VDC (45W) and at 12VDC (18W) it's still usable. But a 12VDC 7Ah gel-cell/car cig lighter with a cheap boost-converter i.e. XL6009 module is also used for a portable solution. KSGER offers a five cell 18650 lithium battery power supply too.
Hakko "Everything you need to know about watts"
"Power doesn't do it. Temperature control does. All you need is enough power to keep the tip hot. Anything more than that is a waste."
Navigation
[0] Message Index
[#] Next page
Go to full version