Flyback diode with water pump?



  • My system is 24v DuetWifi (early model).

    I intend to run a 120mm 24v 0.3A fan and a 12v 0.4A brushless DC water pump (via a buck converter) from a PWM fan channel (no intention to PWM just use as an on/off switch).

    Two questions

    1. the fan output should be able to handle 0.8A total load?
    2. should I consider a flyback diode? The brushless motor will be connected via the buck converter that should offer some protection yes? I intend to use the buck converter in its normal straight-through configuration not to use the fan output negative for pwm, as I am not going to run it at less than 100% pwm.


  • Newer model duet wifis have flyback diodes integrated on the fan outputs (rev 1.02 and later).

    Each fan output is rated for 1.5A continuous so 800mA will not be an issue.

    https://duet3d.com/wiki/Connecting_and_configuring_fans



  • and brushless motors shouldn't need a flyback diode anyway but the fan may if it is a brushed one



  • Cheers guys, as usual, I asked here as it was the right thing to do, but in the end, just hooked it up and gave it a whirl. Seems fine. Although I haven't added the water yet (the bit that always makes me a bit nervous) so the load on the pump is zero at present.

    Another question I fitted a pt100 via daughter board for my hotend and that works great but can I now use thermistor 0 for another dummy tool to monitor the heatsink temp in this case. I can't see any easy way to do this as thermistors are not essentially independent of heaters they are linked to them. So if I have replaced thermistor 0 with pt100 then is thermistor 0 now defunct?

    I can use thermistor 3,4,5 on the expansion connector as I am using one of these already, but maybe its time to consider uncoupling heaters from thermistor channels and just having a configuration matrix where heaters, thermistors (or other temp sensors), fans can be associated freely (or in the case of using multiple thermistors to monitor various temps, not linked to anything at all).



  • sure you can just map the thermistor channel to a virtual heater as Ian has done to monitor things like driver temp and such.

    doug

    Water is nothing to be scared of as long as you make sure nothing can leak used in my PC's for years



  • Yeah I've used it in PC's plenty but the print head of my delta moves around a lot more, and a lot faster than any parts in my PC. 🙂 I'll look into Ian's method.


  • administrators

    If you want to use a buck converter do drive your fan/pump, DO NOT connect its input to a fan output. The constant charging of the input capacitor without a current limiter may eventually wreck the fan mosfet, and PWM won;t work well. Instead, connect the buck converter input to VIN, and connect the fan/pump + wire to the buck converter output and the - wire to the FAN- pin on your chosen fan output.


  • administrators

    @DjDemonD:

    Another question I fitted a pt100 via daughter board for my hotend and that works great but can I now use thermistor 0 for another dummy tool to monitor the heatsink temp in this case. I can't see any easy way to do this as thermistors are not essentially independent of heaters they are linked to them. So if I have replaced thermistor 0 with pt100 then is thermistor 0 now defunct?

    I can use thermistor 3,4,5 on the expansion connector as I am using one of these already, but maybe its time to consider uncoupling heaters from thermistor channels and just having a configuration matrix where heaters, thermistors (or other temp sensors), fans can be associated freely (or in the case of using multiple thermistors to monitor various temps, not linked to anything at all).

    As doug says, you can do this already - that's what "virtual heaters" are for. But I am indeed considering uncoupling sensors from heaters. This would require config.g changes for anyone using PT100s, thermocouples etc. because you would need to replace this:

    M305 P1 X200 F50 ; use RTD channel 200 to control heater 1, set its rejection frequency to 50Hz
    M307 H1 A… C... D... ; set heater 1 model

    by this:

    M305 P200 F50 ; enable RTD channel 200, set its rejection frequency to 50Hz
    M307 H1 S200 A... C... D... ; set heater 1 model and assign sensor channel 200 to it



  • Yes managed to get it working, so using X1 in M305 has remapped this thermistor to a virtual heater that I can monitor.

    Water cooling working 🙂


    A few snagging issues:
    -I need to tighten the water block onto the heatsink, which has been filed flat on one side, generous thermal transfer paste applied and then attached with twisted wire. I plan to tap the fins and attach it with m2 screws at some point.
    -One water joint had a tiny drip, due to a not-great moulding leaving a nasty sharp seam on one of the barbed fittings.
    -My LEDs are now off, on the smarteffector, as I no longer have a hotend fan running on it. Can I connect the hotend heater wires to the smart effector in parallel to the hotend fan input, to get the LED's on? I know they might strobe under PWM, but I think that might actually look quite good. 🙂


  • administrators

    Why not connect the smart effector hotend fan wires to one of the always-on fan connectors?

    Or, if your buck converter is reducing the voltage from 24V to 12V for the water pump, connect the hotend fan wires in parallel with the pump and set the jumper on the smart effector to the 12V setting. The jumper only affects the supply to the illumination LEDs.



  • Thanks, yes I could do either of these, the reason why I have not so far is that I repurposed the hotend fan wires and used them for the thermistor I fitted into the heatsink. I've used all the cores on my 2 network cables.



  • So I hot-wired it, ran a parallel connection from heater screw terminals to the hotend fan port. Now my LED's go on/off with my hotend heater, which isn't annoying and at a glance I can see if it is on or off. Quite stroby when it using PWM, but not too distracting.


 

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