PWM possible for AC Aquarium pump?

  • As I enter the final go at finishing my wiring, I'm wondering whether the AC motor of my parts cooling aquarium pump can possibly be controlled by the board's PWM functions? My understanding from Googling is no, at least not easily, but just thought I'd run it by you guys in case I'm missing something. Thank you.

  • PWM as in varying the speed of the pump? No, not easily, you'd need a circuit in between to convert PWM to variable freq.

  • Right, ideally that's what I'd be after. And your suggestion is in line with my understanding from searching online.
    Is such a circuit available anywhere (affordably) off-the-shelf?

  • I think you are looking for is called an inverter in industrial control. You may be able to find one contolled by a servo signal. It's similar to brushless motor controllers but they tend to generate three phases of square wave rather than one sine. Many inverters will generate three phases.

  • More specifically your looking for an AC to DC to AC single phase inverter.

  • Ah brilliant, thank you for the link! These have been among the solutions which I've come across, but I've been uncertain as to just what I was really looking for. I'm frankly over my head with everything here, but I'm now feeling that an understanding may soon fall into place. Thanks for the direction.

  • Looking at it it may be easier and cheaper to swap to a dc or brushless powered pump. The solar micro inverters could take dc and convert to AC, but the frequency range tends to be limited to close to 50Hz. These are also limited to around a minimum of 48VDC minimum input and would require some fudging to get control of the output.

    Not all AC motors react well to variable frequency either.

    If you are looking for thermal rather than noise control have you considered a servo controlled diverter valve? May be far safer as you'd need to be very confident in the safety of any system you implement.

  • The safety of AC here is certainly a real concern, and I'd have to be enormously confident in the solution should one be found before I'd implement it. I did at first look at DC pumps as being more clearly suitable, but the idea was quickly discarded as they were all horrendously loud. Focusing on AC pumps and comparing half a dozen likely candidates I did manage to end up with one which is easily as powerful as would likely ever be needed while being considerably more silent than any 40mm fan I had on hand. So yes, the noise factor is an important consideration for me.

    The pump I'm currently planning to use does have a variable frequency control built in, but as it stands it's quite ineffective. Testing to ensure that the motor does indeed respond properly to the appropriate circuit would, as you point out, of course need to be done first.

  • I'd looked a few times at the DC air pumps for part cooling but ditched them in favour of more work onbthe radials as they are so noisey!

    I'm guessing you'd struggle to get both the correct torque and speed that you need from a stepper?

  • I'm fairly certain that you're right about that, though I've not looked into it closely ... might be worth further investigation, I'd sure love to be surprised by a solution in that direction!

  • Drills do have plenty of torque but maybe this is doable?

    Edit: with a stepper / geared stepper, not drill.

  • Wow, I like the way you're thinking! 😁
    At first glance this has me rather excited ... quite possibly

    I suppose the question to be answered is whether this would create adequate air pressure.

  • Sorry, thought you were thinking about water cooling. That pump wouldn't like running dry.

    Edit: my comments on the air pump were coincidental comments just refering to the noise of dc pumps.

    Edit 2: you clearly said parts cooling too! Meh, back to trying to sleep...

  • Ha! My initial reaction confirms that I'm not thinking clearly anymore either ... got a bit ahead of myself.

  • My guess is that it would fail on the noise front compared to what I've found, but the servo flow valve idea has been my backup concept ... in which case I'll need assistance from the group in figuring out the means of regulating it via PWM I suppose. Or SOME means of variable actuation via the Duet -- not something I've thought through yet.*

    Just for fun I've now turned on the aquarium pump right next to me at my desk, and I can easily forget that it's running.

    • I'm assuming that the servo would need to be controlled by the Duet's fan control, is this true? Would be nice to have not just on/off but variability for bridging and such.

  • I'm watching this with interest as both the noise and reliability of the brushed DC air pumps did concern me. My current two-pronged radial solution is a chunky beast at best.

  • Industrial solution for noisey compresor being put the noisey bit somewhere else! 😄

  • Yes, even the low low hum of my pump would presumably be placed in a sound box ... might as well!

    I'd be interested in reading of your current solution, clearly you're a very clever chap! 👨‍🎓

  • Most aquarium pumps are solenoid vibrators, not motors. I think decreasing frequency will make them very hot or burn them.
    The DC pumps for medical devices (used by Berd-Air) are not noisy if under powered. I have a 24V one used on 12V mounted on a rigid leg on the extrusion and the loudest sound is the hiss from the outlet.
    There are spring mounts on thingiverse that will make it totally silent even at 24V but I didn't bother.

  • Thanks very much @sigxcpu! Seems I'd read that they were quite loud so I hadn't investigated further, but I'll be sure to check their pump out. I'm guessing that "under powered" is still plenty.

    I did discover that the exhaust can indeed be the noisiest bit, by fiddling around with tight airflow routes I was able to get the sound muffled to the point of near-inaudibility.

  • Search for 555 pump on aliexpress. That is the motor/pump combo I am talking about.
    I am not using 3mm OD tube because that restricts airflow too much. Mine is 4mm OD/3MM ID.
    Depending on the nozzle (squash the tube at the end) size, shape and position, you need to reduce the cooling from 100% (yes, even at 12V) because the plastic will cool down too quickly and it will reduce inter-layer adhesion. It is THAT powerful.
    I have made an ABS job but selected PET-G in slicer by mistake. I usually print PET-G with 100% cooling, noticed it likes it like that. Didn't stop but forced 0 cooling from DWC. At some 2-3cm above the bed, with my UI set at 1 second update, that near second of 100% cooling resulted in an instant inter-layer crack 🙂
    One more overlooked advantage of the cooling pumps: near instant output. I've never had/seen a fan based solution that cools when it is really needed, except maybe for big bridge layers. This thing ouputs even for short overhangs (slic3r PE enables bridge cooling when it detects overhangs).

  • Sounds like good news! And thanks for the search tip.

    I've not yet actually experienced air-pump cooling in use, but the theory sounds good and I love getting rid of fans ... if things go as planned not one of them will be on the machine. That's why I'm so concerned about eliminating any noise I can -- running the printer now in air-print mode, everything is eerily silent.

  • @sigxcpu, this one look okay?

    Also, for a given output which is likely to be quieter ... 12V or 24V? In any case, as mentioned earlier, don't mind building a sound box for it.

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