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Use second extruder thermistor and ssr to control heated chamber.

Posted by DjDemonD 
Use second extruder thermistor and ssr to control heated chamber.
November 28, 2015 12:15PM
Okay I've an i3 rework, ramps 1.4 and marlin 1.02 moving to RC 1.1 soon. Currently have 1 extruder. I have just built a heated chamber which uses a mains voltage heater I am currently controlling using a dedicated control box.

I'd much rather have the printer Control this heater. So this is what I think I need to do can anyone say if this sounds right?

Change firmware to say I have 2 extruders
Attach a thermistor to the 2nd extruder thermistor pins define it in firmware etc..
Wire my ssr to the d9 mosfet output and heater to the other side of the ssr.
In slic3r or pronterface set extruder 2 temp to say 45 deg C.

Currently my firmware controllable fan is connected to d9 so can I move it to another set of pins on the board or do I need to buy a fan controller add on board I keep seeing adverisised. Do I change the fan in pins.h?

This part is the bit I am a bit confused about? How does the printer know which mosfet is associated with which function?

Edited 1 time(s). Last edit at 11/28/2015 06:06PM by DjDemonD.
Re: Use second extruder thermistor and ssr to control heated chamber.
November 29, 2015 04:27AM
you can treat the chamber as the bed without much change in the config but I guess the bed is more important than the chamber. or just use the heated bed as the chamber heater. the heat should build up relatively quickly if the chamber is sealed.

btw how did you solve the hotend cooling?
Re: Use second extruder thermistor and ssr to control heated chamber.
November 29, 2015 05:03AM
Whilst the chamber is certainly warmer with the bed on, the ambient air temperature in my workshop has been 3 deg C at times, so the bed alone is not enough to keep the chamber hot. As for hot end cooling my chamber heats easily to 40-45 deg C and there is still enough of a thermal gradient between the air in the chamber at this temperature and the heat break on my e3d, to keep the heat at the hot end and prevent it heating up the extruder body enough to cause a problem - so far.

My intention is to have a heated bed, an extruder and a mains voltage chamber heater, all controlled independently from the printer. Having done a bunch more reading I think the options are to buy a fan extender board and remap my fan to it leaving the d9 mosfet output free to be connected to an ssr which the heater is controlled by, allowing PID/PWM control of the heater. Or fit a mechanical relay to the heater and use bang bang control to run the heater. Is it possible in Marlin to have extruder 0 using PID and extruder 1 (the heater) running bang-bang?

The external controller I am currently using for the heater works just fine but I cannot remotely switch it off from the PC that hosts the printer, it does not turn off at the end of a print and I cannot remotely monitor the chamber temperature, all of which would be easy if it were controlled by the printer. I am having to do unattended printing as my printer is in an outbuilding and I do not have the time to sit watching every print. I have a smoke detector shut off system on the printer and the detector is within the chamber so should function even better as any smoke will build up to a level where it will trigger the detector faster within an enclosure than with an open printer. I have had no false triggers from normal printing fumes/particulates yet. I appreciate that by the time there is enough smoke to trigger the electrical shut off something might have ignited, but I am also working on having a dialer system that will ring me if the smoke detector triggers, so I can take action. I have cameras to remotely monitor the printer when I am away from it.

On the plus side it has enabled me to print even in this cold weather and the ABS print quality is considerably improved. It seems a real stumbling block that with the Stratasys patents on heated chambers this is something few reprappers are doing, certainly with ABS (haven't tried nylon yet but I have got a bunch of nylon to play with) its like a different machine altogether.
Re: Use second extruder thermistor and ssr to control heated chamber.
November 29, 2015 05:21AM
I once tried to use the 2nd extruder as a 2nd motor for the 1st extruder to get more power and only found a function in repetier that would allow me to control the 2nd extruder as such. Going outside of the standard functions that marlin uses will require goind deep into the programming and making these functions.

you can get a zero crossing optical SSR, that could handle the PID frequency if you manage to turn it down to bed level 7hz i think.

and for remot stuff you can certainly build a little arduino controller cercuit that is hooked into the your wifi for remote access, just not printer controlled.
Re: Use second extruder thermistor and ssr to control heated chamber.
November 29, 2015 08:54AM
A few comments:

You don't need to worry about special cooling of the hot-end in a 45C chamber. You're only going to use that temperature for printing ABS, and ABS is fine at 45C. For PLA you're going to set the temperature inside the chamber to a more normal room temperature.

If you build the enclosure using insulation panels and add a window so you can see what's going on, you won't need much added heat to get the thing up to 45C. I built a box for my original printer that way and actually had to prop the door open a little to keep it from getting too hot inside, using only the bed heater and extruder for heat. The current incarnation of my printer has 3 walls insulated and 3 clear polycarbonate walls. I started with only the floor insulated, but found through trial and error that I need to add insulation to two more walls to get the temperature to 45C inside the box. Now I'm printing in my cool basement and I may convert one more wall to insulation board because the temperature barely gets to 45C when printing.

I don't know the frequency of the PID for an extruder heater, but I don't think its going to be a problem for driving an SSR that's switching power through a resistive load like a heater. I wouldn't worry about the SSR having a zero crossing detector, either. A resistive load won't produce a big current surge when power is connected to it, even if the voltage isn't at zero when the power switches. In my printer I turned down the PID frequency for the bed heater because I use an SSR to switch power into a transformer that powers the heater. Transformers are inductive and will produce large surge currents if the switching frequency is too high and if you don't use a zero crossing SSR. Don't try to switch AC power into a switching power supply under PID (or even bang-bang) control. The switching power supply won't last long if you do.

I don't know of anyone who worries about Stratasys (or anyone else's) patents when it comes to running their printers. People have been putting enclosures on their printers from the beginning of DIY 3D printing, for reasons including noise control and safety. An enclosure keeps kids fingers away from moving or hot parts that could injure them. I would bet there are many other patents being violated by things like extruder/carriage designs, cable management, etc. that people are doing. I do not do patent searches for everything I do myself because I would end up spending all my time searching patents and none of it actually doing anything (though I occasionally do patent searches to find ideas for things to do- one of the purposes of patents...). Also, a lot of people buy Chinese kits of 3D printer parts. Some of those parts may well be manufactured using patented techniques, but how will you ever know? If you're going to live in fear of patent violations, you better just sit around and watch TV instead of making things, because sooner or later you're going to violate someone's patent on something.

If you have a problem getting the printer controller to manage the enclosure temperature for you, you can get a PID controller like this for $23 that will do the job. You'll need a thermistor or thermocouple to monitor temperature and you'll still need an SSR to switch power to the heater, but it doesn't get much simpler than this. I used one of these devices to make a temperature regulated water jacket (with a pump and a 300W aquarium heater) for a syringe type chocolate extruder and it does a fine job of regulating the temperature. It even has programmable alarm outputs for temperature too high and too low.


Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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