Every hardware hacker need good soldering tool. My idea was to build own but with very specific qualities. On one side not so expensive, on second side high quality and also small with precise control and features. I found some projects where is used Weller soldering tips designed for WMRP soldering iron with standard 3.5mm jack and inside the tip is also thermocouple for sensing temperature. These tips are not so cheap but the quality is really great, especially for fine soldering. Hardware design is based on similar projects but with many modifications and improvements. Also my request was to make the hardware small as possible to fit into handle and capable to supply from hobbyist LiPO battery.Buy one on tindiy: https://www.tindie.com/products/vlk/rt-soldering-pen/
very compact - will fit into handle
display show status, preset and tip temperature, power, supply voltage, drop, ...
sensing supply voltage and tip current
precise regulation with PID (PSD controller with some modifications)
supply voltage is from 5V to 18V (best is 10-13V)
designed to supply from LIPO battery 2S (7.4V max is about 18W) or 3S (11.1V max is more than 40W)
calculating consumed Wh
heat-up in 5sec from 25 to 400°C (with 40W limit)
Idle current about 8mA
What is planed:
battery monitor (warn when battery need charge)
configuration editor for some constants from PSD controller, power limit, ....
Weller this year introduced new series of RT tips with nice slogan "No compromise".
There are three types:
RTM - RT Micro - they are same like previous line RT, but with new naming
RTP - RT Pico - these tips are smaller, shorter for more precise soldering
RTU - RT Ultra - these tips are in opposite bigger and designed for higher power (till 150 Watts)
All the tips have same pinout and in general are compatible,
RTM and RTP (also previous RT) have resistance of heating element 2 Ohm and they are designed for 12 V (current is 6 A) but maximum average heating power is 40 Watts - this power is controlled and limited by PWM.
RTU has resistance of heating element 3.5 Ohm, this mean, to reach 150Watts is necessary to use higher voltage - at least 24V, but the current will be still similar - what is good for the JACK connector.
But actual design of RT soldering pen has limitation for power at 18 V and current to RT, RTM and RTP will be at 18 V: 9 Amps - the pen it should withstand it, because average pulse power is limited by SW to 40 W) question is what can withstand the JACK connector.
The main question is how to use this with RTU tips they need 24 V. so, absolute maximum rating of HW 1.0* is 25V for supply voltage (limiting element is input capacitor) after replacing input cap next limit will be 30V (maximum voltage of MOSFET switches)
*Absolute maximum rating for previous HW v0.3 is 20V - this is limited by 20V MOSFET switch.
For RTU if the supply will be 24V then output power can be near to 150 Watts, but this need also modifications in SW to allow higher output power. Yes, this is planed and new release will available be soon.
Another problem with new tips is that each kind RT/RTM, RTP and RTU has different dimensions of the cylinder on JACK side and is necessary to count with this for case design. (old RT and new RTM have same dimensions of the cylinder) this is also reason why Weller sell for each kind different tip holder.
If I talking about tips there is one more question: What it mean if in name is "MS", it mean that tip meets Military Specifications. But there is no more informations. In general the main different is that shield of the tip is electrically isolated from the connector, standard tips have shield connected to ground.