I have this 3D printer hotplate and I'm wanting to convert it into an SMD PCB hotplate for soldering.
There are two issues I've come across.
The hot plate has a resistance of 1.3 ohms. This means that at 24V the plate would draw almost 18.5 amps! The only power supply I can think of capable of delivering 18.5 amps is either an ATX power supply or the wall, neither of which are very safe. I could run it at 12V (9.25A) which would be safer but I don't know if it would get hot enough. I also don't know if I have any relays that can switch currents that high. Should I move to MOSFETS?
The plate has a thermocouple installed but I have no idea what type it is or how to amplify the signal. This is not that big of a problem because I don't need to know the temperature but it would be nice.
For this you need to be able to know the current temperature and ramp up the temperature to the correct soldering temperature, hold the temperature for the required time and then ramp down the temperature.
How is the plate temperature controlled now?
The plate heat element may have a resistance, but doubt you have measured an impedance at your mains line frequency.
The thermocouple must be there for a purpose. How was it used?
That shouldn't be hard. I could probably do that without knowing the plate's temperature it would just be hard.
I have no idea. Probably some fancy PID system built into whatever firmware the 3D printer was running.
EDIT - In terms of power, 3D printers use huge MOSFETS to drive all the heating stuff.
I'm not sure what you mean by this.
To relay information back to the 3D printer that the hotplate was being used by. 3D printer mainboards have build-in thermocouple driving stuff though.
I mean you either do not know the difference, or you have lab equipment to measure impedance at line frequency.
But before you go too far into this project. Is the plate made of material that will not be effected by solder flux or solder or the temperatures necessary for soldering?
The first one I found on amazon: # SSR-40DA Solid State Relay DC to AC (Input 3-32V DC Output 24-380V AC) with Heat Sink, 40A
Solid State relay * Input voltage 3-32V DC, Load voltage 24-380V AC, Max load current 40 Amp
Arduino drives it directly!
I used this with a pulse width of about 1 second 0~1Second on 0~1 second off
To control this, use a PID loop with a slow integral value to ramp up to setpoint, add then increase proportion until oscillation occurs and back off, and then add some derivative to tame the loop and make it very responsive.
Come up with some code and share I'll follow to help where I can.
ZHomeSlice
The organic flux in solder paste and aluminum do not get along well, especially when the flux is heated and becomes active. Test a corner of the plate with your solder paste and heat with a propane torch until the paste melts and the solder flows. Let cool and examine the results.
So another way to tame the high current. How to source it though...
The heating curve you describe seems more complex than what I've seen. Is there a reason for that? What I am seeing online is a slow linear ramp up, a holding temperature, a linear rise to melting temp, a few seconds of hold, and then a slow cool down.
You need the organic flux the is in the solder paste you will use. IT becomes very active when heated to the temperature need to fuse the solder particles. In fact it only looses it's chemical activity after it has been heated. That is why SMT boards MUST be washed to remove any traces of the flux. Otherwise the flux will continue to react.
You could try thin sheet of stainless steel.
IF you don't care about costly ICs, then that is correct. ICs have silicon filler inside the plastic/ceramic case to move the chip heat to the connecting pins and/or the heat conductive belly pan on some ICs. When that gets too hot for too long, the case ruptures. Some ICs from Asia also have been subject to high humidity which allows moisture to penetrate the case. That will turn to steam.
I meant that the temperature doesn't need to be spot on within 1C. Like I can pretty easily run a temperature curve with basic PID and feedback and stuff, just by checking the temperature and turning on/off the plate as needed.
The most pressing issue is still the power supply. I'm starting to like the idea of using a slightly modified (aka less dangerous) ATX power supply. This would be done by packing away the excess wires and wiring the fan to be always on, as well as introducing some voltage converter stuff for powering the logic without having the handle the full power of the thing.
