After having access to a Metcal MX5200 with the full 2 soldering pencils, the lion kingdom became aware of its limitations & advantages.  The mane problems: changing temperature required changing tips & having the right tip.  There wasn't enough room for 2 stands.  Most of the time, only the copper wool in 1 stand would be used for cleaning while the other was behind a pile of cables.  The connection to the base station was also constantly glitching out.  The smartheat/curie point system is all but obsolete, nowadays.  

It was luxurious having tips that fine.  It was much easier to pick & place surface mount parts with 2 fine tips.  It could heat ground planes effortlessly.  The base station was a very compact way to power 2 tips.  Unfortunately, it was a loaner.

The lion kingdom's previous irons were the Hakko FX-888, Weller WES51, & for the 1st 15 years, the $8 Radio Shack iron.  The Hakko FX-888 was the duck's guts in 2012, for soldering 0603's & bigger, but its mane problem was the lack of any tips for it as small as the Metcal.  The finest tips were conical.  These required turning up the heat to get the very end hot enough & risking burning up components. 

The quest for an affordable & modern alternative to the Metcal revealed this Jeri Ellsworth video showing 2 JBC stations.

Dual JBC's were obviously a sign of someone who had arrived.  That was what people were using for the newest components.  The next step was figuring out what made a JBC better & trying to clone it in a smaller, dual iron package.

 The thermal inertia of a very fine tip is too low to rely on a wide heater separation.  To make the tip finer, the heater has to be closer to the end.  The curie point was the original way of doing it, but better manufacturing has proven good enough to use active temperature control.

The lion kingdom really needs a single controller feeding 2 tips & a single stand for holding 2 tips with 1 copper cleaner.  There's no commercial solution at any price.  The idea of making your own soldering station didn't exist 7 years ago when the FX-888 arrived.  It only seems to have appeared in the last 3 years.

The Hakko FX-951 is the cheaper version of the JBC & uses T-12/T-15 tips.   It has an impossible user interface.  They have a thermocouple in series with the heater.  The thermocouple makes a voltage when the heater is off, which is proportional to the temperature difference between the copper leads & the heating element.  It's heated by 24V AC.

Cold junction compensation:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/4026

They're basically measuring the temperature where the copper connects to the thermocouple with yet another thermister & using a table that factors in the copper temperature.  The trick is a thermocouple only senses difference between the copper & the alloys while a thermister senses absolute temperature.  This is not actually used anywhere but internet comments.  Assuming the copper temperature is 72F has proven good enough.

Chinese pinout diagram:

https://www.eevblog.com/forum/reviews/hakko-t12-pinout/

It's quite clear that the internet doesn't really know what the pins do.  They all just copy the same wiring diagram from China.

Universal solder controller with typical voltages & wiring patterns for the various tips, but no functional description:

http://dangerousprototypes.com/forum/viewtopic.php?f=56&t=7218

This is incredibly overcomplicated, but it shows how recently it wasn't trivial to make your own soldering station.

Teardown:

Analog circuit for reading the thermocouple & powering the heater:

The mane problem is getting the op-amp to handle the 24V when the heater is on.   There's also a current flowing out of the op-amp input, which affects the voltage reading if a large current limiting resistor is used.  They also have an extra circuit for detecting when there's no tip.  There's no cold junction compensation.

It turned out all the components for making your own JBC clone are now readily available in China, so the idea turned into a shopping list.

Cheap 24V 360W power, plug, cables & connectors:

https://www.banggood.com/AC-110-240V-Input-To-DC-24V-17A-360W-Switching-Power-Supply-Driver-Board-p-1272112.html


Naturally, to be derated way below 360W.

https://www.banggood.com/1pcs-10A-250V-3Pin-IEC320-C14-Inlet-Module-Plug-Fuse-With-Switch-Male-Power-Socket-p-1120059.html

Manes connector & switch.

https://www.banggood.com/DANIU-2M-AWG-Soft-Silicone-Flexible-Wire-Cable-12-20-AWG-1-Meter-Red-1-Meter-Black-p-985529.html

14 gauge x 1 meter x 2 color coded wires

Need 1 for dual soldering station, 2 for regulated supplies, more for bananas.

https://www.banggood.com/20-Pair-Of-Fireproof-T-Plug-Connector-For-RC-ESC-Battery-p-1046492.html

T plugs.  The lion kingdom standardized on these for high current, 10 years ago.  The newer XT connectors will be obsolete just like the T's.

Bare controller for the FX-951:

https://www.banggood.com/STC-T12-Digital-Soldering-Iron-Station-Temperature-Controller-DIY-Kits-for-HAKKO-T12-Soldering-Iron-p-1146578.html

Includes only 3ft of cable & a wide tip.  You need a 4ft cable.  It uses motion of the handle to go into sleep mode, which actually might be better than the stock FX-951.  

Considering making the dual stand out of steel wire & wood.  Enclosures would be tupperware or coroplastic.


The Finest tip:

https://www.banggood.com/T12-ILS-Replace-Solder-Iron-Tips-Soldering-Tips-For-HAKKO-942950951952202203204206-Soldering-p-1064393.html

Assorted tips for drag soldering & larger parts:

https://www.banggood.com/5pcs-T12-BC2T12-IT12-BT12-KT12-24-Solder-Iron-Tips-Soldering-Tips-p-1071677.html

Cleaner:

https://www.banggood.com/DANIU-1-Pcs-Heavy-Duty-Soldering-Solder-Iron-Tip-Cleaner-Steel-Wire-With-Stand-Set-NEW-p-1182609.html

Power switches, longer cable.


https://www.banggood.com/5Pcs-SPST-2Pin-Heavy-Duty-15A-250V-ONOFF-Rocker-Toggle-Switch-Waterproof-Boot-p-1130622.html

Enough for 2 soldering irons, 2 regulated supplies, 1 as a front switch for the manes voltage.

https://www.banggood.com/Five-Core-Silicone-Wire-for-T12-HAKKO-936-937-907-Soldering-Station-Handle-Line-p-1153992.html

The soldering iron cable.

Regulated supplies & bananas:

Once you invested in 24V, it might as well supply something else. 

https://www.banggood.com/RD-DPS5005-50V-5A-Communication-Function-Constant-Voltage-Current-Step-down-Power-Supply-Module-p-1161704.html

The tiny display & membrane buttons are a bummer.  Really don't know why it devotes its limited display to calculating wattage.


Better buttons for the power supplies:

https://www.banggood.com/Wendao-R13-507-125V-3A-16mm-No-Lock-Self-reset-Switch-Push-Button-OFFON-10pcs-p-1060608.html

Bananas:

https://www.banggood.com/DANIU-P3008-10Pcs-4mm-Copper-Banana-Plug-Jack-Speaker-Amplifier-Test-Probes-Connector-p-1109354.html

https://www.banggood.com/DANIU-10-Pairs-4mm-Terminal-Banana-Plug-Socket-Jack-Connectors-Instrument-Light-Tools-Black-and-Red-p-1046083.html

More stuff:


https://www.banggood.com/Excellway-20pcs-2-Pins-JST-Male-Connector-Plug-Cable-Wire-Line-110mm-22AWG-p-1277856.html

https://www.banggood.com/Excellway-20pcs-2-Pins-JST-Female-Connector-Plug-Cable-Wire-Line-110mm-22AWG-p-1277825.html

Tact buttons:

https://www.banggood.com/20Pcs-6x6x12mm-Momentary-4pin-Push-Button-Micro-Tactile-Tact-Switch-w-Cap-p-1205166.html

Always using these in the day job.

The mane problem is lack of space.  Lions rarely solder nowadays.  Raspberry pi has replaced most dedicated boards.  The big solder marathons were in the days of through hole microcontrollers, where it was a miracle to get a chip to print hello world, a lot of reworking was done, & a lot was being learned.  The biggest soldering task is replacing the TOSLINK on the ultimate amplifier with USB which can be captured.  There might be a need for something which can measure the duration of long delays down to the microsecond, but that might evolve into a super oscilloscope of some kind.