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Main power

Connect the terminal block labelled POWER IN to your power supply (minimum 11V, maximum 25V). Make sure the wires you use are of adequate gauge to carry the current to supply the bed heater, extruder heater, stepper motors and electronics.

Caution: be sure to get the polarity right! The board is not protected against reverse polarity. The positive wire from the power supply goes to the terminal marked + which is the one nearest the stepper motor connector side of the board.

If you use stranded core wire, do not tin the ends of the wire, because if you do then the heat generated by the current will cause the solder to flow and the connection will become loose. Preferably, use bootlace ferrules on the end of the wires, as supplied with the Duet 2 Wifi and Ethernet.

Important! Re-tighten the terminal block screws after doing the first few prints, and check that they are still tight occasionally after that. The heat generated by the high current carried by the power wires can cause them to creep and make the connection less tight, especially if you used stranded core wire and no ferrules.

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Bed heater power

The Duet boards are designed to power the heated bed (or the solid-state relay controlling it) from the same power supply as they power everything else. The Duet 2 is able to supply 18A to a heated bed. If you still want to use a second supply to power the bed (still not exceeding the 18A the Duet can sink), it is possible to arrange this; see Wiring and hardware differences from RAMPS etc for details.

Standby power

The Duet operates on two power circuits: a 5V circuit that powers the CPU, WiFi, and web interface, (mostly through a 3.3V LDO) and a 12/24V circuit that powers the motors and heaters.

5V Options

5V power can be supplied in three ways:

  • From USB ( whether or not an external power supply is attached). This is normally used for initial setup but is not required for normal operation. Note that USB current is limited by older to 500mA. Keep this in mind if you are running a PanelDue, especially the 7Inch version which requires more current than this. Some more modern USB ports and USB hubs will supply more than 500mA.
  • From the 12/24V supply through the internal switching regulator. The regulator is enabled if the INT 5V_EN jumper is fitted, as shown here:
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  • Alternatively the board can obtain 5V power from an external 5V supply (for example, the +5VSB rail on an ATX power supply) if you fit the EXT 5V_EN jumper:
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If the main PSU supports an ATX-style PS_ON pin (power supply on when pin is connected to ground), the Duet 2 can enable and disable the main power as needed. Obviously this will not work if the only source of 5V is the 12/24V circuit you are switching; you must either supply USB power or use the 5V in pin from a supply that is not shut down when the 12/24V supply is. On an which provides this function.

If you are using an external relay to control mains power to the PSU, you can wire either the +5v or +3.3v (depending on what your relay requires) outputs from the duet in to the positive terminal of the relay, and wire the ground terminal of the relay to the PS_ON output on the duet. If you are using a mechanical relay and it does not include a flyback diode of some sort, you will need to wire one in parallel with the relay signal.

Controlling the external power supply

If you are using the PS_ON pin to turn on and off an external 12/24V supply it can be toggled using the M80 and M81 gcodes:

M80 ; Turns on the ATX power supply

M81 ; Turns off the ATX power supply

Note If the M80 command is inserted into the config.g file and +5V VSB ( standby) power is connected, you can not switch off the board by

doing a reset, as after reset the config.g is read and the board powered on again.

On the web interface there is a button for toggling the external supply:

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To display this button select the check box in the user interface settings area.

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Please note the 5v pin next to the PS_ON is an input and as it is has a diode in series with it will not output 5v. If you need 5v to power a relay of some sort you need to use the expansion connector pin 1 or the 5v pin on the vfan jumper.

Simon Khoury - Reply

Note that X-BOX power source also has +5VSB and +12V (switchable by the PS_ON pin) and is a very good candidate for a controlled power source, specially if you have an AC bed and don’t need more than the 11A on the 12V rail. But beware that the PS_ON pin on this PSU is inverted in relation to the ATX one (on the ATX it is LOW=on and HIGH=off, and on the X-BOX one it is HIGH=on and LOW=off). I still have no idea if the duet supports this inverted logic.

Andre Ruiz - Reply

“If you are using a mechanical relay and it does not include a flyback diode of some sort, you will need to wire one in parallel with the relay signal.”

Can someone please confirm what this means? To where should I connect each of the ends (anode and cathode) of the diode? Thanks in advance!

André Zibaia da Conceição - Reply

Does this only work on ATX PSU’s? I have a regular non atx one.

John Fajardo - Reply

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