Disconnecting Heater and Thermistor while powered



  • Hi Guys,

    I'm working on implementing a tool change setup to my printer, tl;dr my idea depends on being able to disconnect the heater and thermistor wires while the printer is powered on. I'm sure there is more to it (maybe set heater to 0 before and reset faults after?), but I remember many stern warnings about not physically disconnecting a stepper while everything is powered so I thought it best to ask before I do anything remotely similar.

    Thanks!
    Brandon



  • Most tool changers I've seen leave the heater and thermistor with the tool. And have the other heaters and thermistors plugged into their own ports. The expansion boards have such connections for all the tools. Don't they? I would not risk burning anything on my Duet out just to do a live plug and unplug.



  • I found this on the description for the Duex 5.
    The Duex 5 has the following features:

    5 additional TMC2660 stepper motor drivers with stall notification.
    5 additional extruder heater outputs.
    5 servo outputs with 5V power and 5V signal levels, sharing control channels with the heaters. So you can use unused heater channels to drive servos.
    5 additional endstop inputs with indicator LEDs and 3.3V/5V voltage selection. These are also usable as outputs.
    5 additional controlled fan outputs, also usable for driving LEDs etc. The output voltage may be switched between 5V, 12V and VIN.
    4 uncommitted general purpose I/O pins.
    12V switching regulator, for generating a 12V supply for fans, LEDs etc. when the VIN power is higher than 12V.
    5 additional thermistor inputs.
    Support for 2 more thermocouple or PT100 daughter boards, supporting up to 4 more sensors.
    Optional 5V external power input for powering servos, fans etc.
    

    The Duex 2 has the same feature list, just with 2 channels of everything, rather than 5. Both are supplied with the 50 way connector cable between the Duet 2 Wifi and the Duex.

    So I would just use a heater and thermistor input for each tool.


  • administrators

    @efficientaf said in Disconnecting Heater and Thermistor while powered:

    Hi Guys,

    I'm working on implementing a tool change setup to my printer, tl;dr my idea depends on being able to disconnect the heater and thermistor wires while the printer is powered on. I'm sure there is more to it (maybe set heater to 0 before and reset faults after?), but I remember many stern warnings about not physically disconnecting a stepper while everything is powered so I thought it best to ask before I do anything remotely similar.

    Thanks!
    Brandon

    You should definitely turn the heater off before connecting or disconnecting it, otherwise you will get arcing across whatever contacts you use. Other than that, it should be safe. Make sure that nothing can short the contacts together if something goes wrong. For example, if the tool pickup is misaligned with the tool head, you don't want metal parts of the tool head able to short contacts on the tool pickup. So it's probably a good idea to recess the contacts on the tool pickup (the ones that connect to the Duet).

    Note, there is a patent on tool changing printers that connect/disconnect the tool heads with the controller.



  • @dc42 Thanks a bunch! I'll be sure to recess the contact points sufficiently. I'm sure I'll have more questions later about scripts and macros, but troubleshooting those shouldn't be harmful to the board so I'll try to work through them 🙂

    Is this the patent you were referring to? Admittedly I've only looked over the images, but from what I can see that's pretty interesting. It's more or less what I had in mind. I was thinking about only heater and thermistor connections of course, but have 2 sets of contacts, "dock" side for pre-heating before that tool is loaded and "carriage" side for actual printing, hence my original question. The other main difference would be that I'm going to try using a standard E3D Titan drive gear as part of the tool and pinion/stepper attached to the carriage. I'm hoping it would be sufficient to just jog the motor a little bit to get the teeth to mesh, but I can imagine that would cause wear over time. It looks like they have a crown shape for coupling the stepper to the filament drive, but I'm sure they have something with some tapers in mind already lol My printer will mostly be for my own use, so I assume I should be OK if there is some design overlap, accidental as it may be lol But I also don't know how this stuff works haha

    @vhoward I have a duex5 but I'm looking to potentially use those other drivers for different purposes like operating the tool change lock, among other things. My printer currently uses 5 drivers just for motion (2 on Z, 2 on X and 1 on Y), leaving me with only 5 for tools and other things. Since I'm not limited on heater and thermistor inputs, I am working on a setup that grants me that flexibility, but reliability still remains to be seen overall. I could still do it without using the contact based method, but that would mean more wiring for my particular printer. Note that my printer is not like the others, which is why I can't do what others do, sadly. I'd love to take E3d's setup and use it whole hog, but as I mentioned, I would be limited by the total number of tools and features I can use as a result.


  • administrators

    The patent I had in mind it this one https://patents.google.com/patent/US8926484.



  • Oh that's a bit different lol I don't think I'm capable of parsing what is going on there 🤷 Thanks again for the info David, very much appreciated!



  • @dc42 said in Disconnecting Heater and Thermistor while powered:

    The patent I had in mind it this one https://patents.google.com/patent/US8926484.

    It probably doesn't apply anyway to one offs that many people here do but the patent claims seems to this layperson to have very specific requirements and thus narrowing the protection and allowing workarounds. For example 'a portion of the actuator assembly is configured to move along an axis toward the master unit' which doesn't prohibit configurations where the lock/actuator movement is in parallel to the gantry. That restriction was added for a reason, probably due to prior art.


Log in to reply