Simple variable temperature soldering station idea without thermistor.

Hello I have found this one https://laserpointerforums.com/f42/...n-regulator-etching-tutorial-part1-45008.html
It controls the temperature of the iron without a thermistor, by observing the heater's resistance, as far as I can understand.

What are it's advantages and disadvantages compared to observing the tip temperature using a thermistor?

Advantages: No additional high temperature sensor device needed, no additional connection wires.
Disadvantage: Probably less percentage resistance change with temperature than from a thermistor, more accurate amplification necessary.

It makes the heater and barrel of the iron, narrower and simpler. The down side is you need the electronics. I still like the Weller system of the curie point thermostat.
Frank

chuckey said:

It makes the heater and barrel of the iron, narrower and simpler. The down side is you need the electronics. I still like the Weller system of the curie point thermostat.
Frank

Click to expand...

One downside I see is that since the feedback is taken from the heater, no actual tip temperatire is monitored. So if the tip cools down due to soldering, how do the electronics know that?
Maybe the tip is cooling down the heater?

The tip will cool a lot more than the heater because there is thermal resistance between them.
What will hold the tip very tightly to the heater? Oh, will the heater be built into the tip and the replacement will cost a fortune?

Consider that most of the available heat energy is stored in the mass of the tip not the heating element. Think of it as a reservoir for the heat you want to use and the element as a trickle of heat to replenish it. Given a few seconds the trickle of heat will replenish the store in the tip. The element itself is relatively isolated from the soldering point, both in terms of heat coupling and the time it takes for a change in tip temperature to reach it. The element in most soldering irons is a coil around or inside the barrel so there is likely to be a temperatue difference between a cooled down tip and the end of the coil nearest the handle. As the temperature of the tip cools quickly, the end of the heater will cool slowly (dropping resistance) and the temperature drop will tend to incease the current in the other end of the heater increasing it's resistance. It means the overall resistance is a poor indicator of instantaneous tip temperature.

Curie point control is very effective but mechanicaly difficult to make. Thermistors and other resistance based methods will always has a slow response and be some way from the soldering point. I've never tried it but perhaps a method of detecting IR would work, looking at the radiated temperature, maybe looking down the center of the shaft with the detector in the handle. A modified PIR sensor perhaps.

Brian.

One practical method for a low cost home brew temperature controlled iron that I have seen, is to drill a very small hole into the base of the tip, and insert a thermocouple.
Then just use that to cycle the mains power on and off with a solid state relay.

Its hardly worth building your own temperature controller, something like this perhaps :
**broken link removed**

Here is the construction article for drilling a hole above the tip and using a thermocouple. It has plans for complete temperature control plus display.

https://pcbheaven.com/projectpages/Homemade_Soldering_Station/?p=0&topic=worklog