Duet Wifi 2 - DC air pump / berd air

  • Hello,

    I want to wire 1~3 DC pumps to the same channel/port. These pumps are similar as the ones used on the Berd Air systems.

    I have read online about wiring DC air pumps and they mainly talk about PWM frequency and MOSFET limit / motor resistance. I still do not fully understand these topics and would really appreciate some advice.

    • I have the Duet Wifi 2 V1.04.
    • The pump is rated at 12V and lowest resistance measured is 4.5Ohms.
    • I have a few types of DC-DC regulators, flyback diodes, pcb relays, and other basic electronics.
    • I use only 1 extruder heater port.
    • My heated bed is SSR 120VAC heater. If we somehow assign a new port for SSR, my bed heater port will be open to use.
    • I do not have any expansion boards. I do have a breakout board which I use for my external X Y stepper drivers.

    I want to wire 1~3 DC pumps in series. More than one pump greatly reduces the noise produced. Based on my testing, 2 pumps in series at 14V provides a good amount of air and low noise. If wiring multiple pumps in series pose an issue, just 1 is fine too.

    Based on the information of my setup above, may I have a guide on how to set up, wire/connect , and program my duet so the board can work with my pumps?

    If I wanted to replace my hot end "always on" fan with a pump too, what would I need to do?

    Thanks for stopping by!

  • Which version of the firmware are you intending to use? RRF3 makes it easier to remap the bed output for instance.

    You're looking at about 2.5A nominal current for each pump at 12V, or 1.5A with two in series at 14V. So two in parallel at 14V would exceed the 5A rating of a extruder output, but a single pump at 14V would be about 3A and okay for the spare extruder - however I guess it all depends on how much air you need.

    Extruders and bed heater outputs aren't protected against inductive loads, so you need to add diodes to those. (Fan outputs are protected, but limited with the 1A fuse)

    I'd probably opt for an external mosfet to drive the pumps just to increase the isolation to the Duet, which you would probably need for to replace the hotend fan anyway - unless by "always on" you mean always on and would wire it straight to the supply?

    You're using a 14v supply or is that a typo? Not sure how long the pumps would last with the increased voltage, if kept cool i suppose it would be okay.

  • Thank you for your advice.

    Sorry, I am unfamiliar with what you mean by RRF3. Is that the web service that creates all my config.g, etc.g files? Or are you talking about my version 2.04RC1?

    I tried to update to 3.1.1 today
    Here is my board information:

    Board: Duet WiFi 1.02 or later (duetwifi102)
    Firmware: RepRapFirmware for Duet 2 WiFi/Ethernet 2.04RC1 (2019-07-14b1)
    Duet WiFi Server Version: 1.23

    Am I the most up to date?

    I used a variable DC supply to externally test my pumps. I felt a 14V with 2 pumps wired in series performed very well. My Vin for the Duet board is around 24V.
    I only plan to wire my pumps in series, not parallel.

    Can I wire 2 pumps in series to my extruder? It seems like it will work because they wont go pass 5A. 2 motors will have a lowest possible of a total of 9ohms. 24V/9ohms = 2.67A which is less than the maximum rated 5A. Did I calculate it correctly? If they are in series, where should I place my flyback diodes, will I need more than 1?

    I really like your idea to use an external mosfet. I cant find any information on how to do this for DC air pumps. I am simply not experienced enough to figure this out myself.
    In order to make progress, Is it safe for me to just use the second E heater port? What types of issues would it cause if I did not use an external mosfet?

    Continuing with using duet extruder heater port, how do I change my E1 into a fan port?
    After I correctly map my heater port into a fan port, the last thing I would do is to set my PWM frequency to 25,000Hz?

  • @likevvii said in Duet Wifi 2 - DC air pump / berd air:

    what you mean by RRF3

    what would version 3.x of the RepRapFirmware, you're currently on 2.04RC1. The last version of 2.x is 2.05.1, then the next step is 3.x.

    @likevvii said in Duet Wifi 2 - DC air pump / berd air:

    Is it safe for me to just use the second E heater port?

    with the addittion of the diode, yes.

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