Homebrew Hakko FX-591

[Ferroto]

So about a year ago I was looking at the Hakko FX-591 but didn't have well over 200 bucks to drop on a new station. Since the magic happens in the tip anyways, I decided to pick up a Hakko FX-591 handle and stand for about $40 bucks instead and homebrew the station.

This project was inspired by a similar project by Marco Reps. However unlike the JBC iron used in his video Hakko decided to put the thermocouple in series with the induction heating element which means the 24v AC signal that goes across the heating element would also go across the MAX 6675. So my solution was to use a DPDT relay instead of a TRIAC. The soldering iron goes to the two common pins and the normally closed contacts go to the MAX 6675 and the normally open contacts goes to the 24VAC making it impossible for the 24VAC signal to end up connected to the MAX 6675. A 5V zener diode is used to clamp the voltage spikes from the heating element to between 5V and -.06V and that 2n3904 driving the relay hasn't fried it's self yet 

BEHOLD MY TERRIBLE MS PAINT SKILLS.

Code: [Select]

#include <max6675.h>
#define DO 11
#define CS 12
#define CLK 13
#define relay 2
float temperature;
float setTemp = 200;
int count = 10000;  //10 seconds

MAX6675 thermocouple(CLK, CS, DO);

void setup()
{
  Serial.begin(9600);
  pinMode(relay, OUTPUT);
  digitalWrite(relay, LOW);
}

void loop()
{
  delay(500);  //chill out delay for MAX6675
  temperature = thermocouple.readCelsius();
  Serial.print(temperature);
  Serial.print(",");
  Serial.println(setTemp);
  if (temperature == setTemp){} //if we're good do nothing
  if (temperature < setTemp)       //if not do something
  {
    Serial.println("less than");
    digitalWrite(relay, HIGH);
    if (temperature > setTemp - 10){delay(1000);}  //if we're within 10 degrees of the set temperature leave the iron on for 1 second
    else {delay(10000);} //if we're a long ways off leave the iron on for 10 seconds
    digitalWrite(relay, LOW);
  }
}


The mess

[fireworks]

  That's interesting.
  Do you have a video where you use it to solder something ?
  Also, what's the heating time from room temperature to 350C ?

[Ferroto]

Srry for the potato camera I don't own a proper video camera. It takes awhile because I don't have a 24V transformer yet and I'm currently running it off of a 16.8v transformer (the side of the handle says it needs 24vac). It currently takes about a minute to reach 350 deg C but that should change once I can secure a 24v transformer.
https://www.youtube.com/watch?v=mb_uiHEQ4Ls

[wraper]

I will sound harsh, but all of this is true. Sorry, but both your circuit and control algorithm is a piece of junk. I wouldn't touch with a barge-pole something clicking all of the time and with slow, loose and dumb control algoritm. Big delay before reacting to temperature drop or overshoot and no proportional heating control according to actual temperature drop. 10s of heating while not touching some massive solder joint will result in huge temperature overshoot. It might be somewhat fine with bulky tip/heater which has slow reaction to heating and heat sinking but with cartridge type tip/heater this is unacceptable.

As the result, you'll be far better with $30 FX-951 knockoff (BAKON 950D), even if using knockoff cartridges. And can be improved by using genuine cartridges and handle.

[Ferroto]

As the result, you'll be far better with $30 FX-951 knockoff (BAKON 950D), even if using knockoff cartridges. And can be improved by using genuine cartridges and handle.

Thanks I'll have to give that a try.