¶ Introduction
See this page on Choosing the power supply to select a suitable power supply for your Duet board(s).
Minimum and maxium input voltages for Duet mainboards.
| Minimum input voltage | Max input voltage | |
|---|---|---|
| Duet 3 Mainboard 6HC v1.01 and earlier | 11V | 32V |
| Duet 3 Mainboard 6HC v1.02 and later | 11V | 48V |
| Deut 3 Mini 5+ | 11V | 25V |
| Duet 2 WiFi/Ethernet | 11V | 25V |
| Duet 2 Maestro | 11V | 25V |
¶ Main power
Connect your power supply to the terminal block labelled POWER IN on the Duet board. 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.
If you use stranded core wire, do not tin the ends of the wire. If you do, then the heat generated by the current will cause the solder to flow and the connection will become loose.
Caution: be sure to get the polarity right!
Duet boards are not protected against reverse polarity. The positive wire from the power supply goes to the terminal marked +. Check the wiring diagram for your board if you're unsure. The polarity (+ and -) is also silk screened onto the board.
Whether or not a Duet will survive reverse polarity input depends on the power supply. The stepper driver output mosfet body diodes are forward biased, so they will conduct the current and clamp the voltage to about 2V because there are two in series. A good power supply will go into hiccup mode when it sees this near short-circuit, which means it will supply short bursts of its maximum current or a little greater, with longer intervals of no current. We have known Duets survive this, with no blown drivers and the fuse remaining intact. A less good power supply may just supply its maximum current continuously.
¶ Duet 3, Duet 2 Maestro
All Duet 3 boards (except Duet 3 Toolboard 1LC), and the Duet 2 Maestro, have a barrier strip with screw terminals to connect power supply wires, and are supplied with insulated spade crimp terminals. Use an appropriate crimping tool; we find ratchet wire crimping tools produce better crimps than the non-ratcheting type.
Duet 3 Toolboard 1LC uses a 2-pin JST VH connector for power. You will need a suitable crimping tool for the crimp pins, for example Engineer PA21 (use the 2.2mm jaw opening to crimp the bare wire and the 2.5mm on to crimp the insulation). Alternatively you can solder the wire to the crimp pin.
¶ Duet 2 WiFi and Ethernet, DueX2/5
Duet 2 Wifi and Ethernet and DueX2/5 use bootlace ferrules on the end of the power supply wires, which connect to the screw terminal on the Duet board. Use an appropriate bootlace ferrule crimping tool to crimp the wires in the bootlace ferrule. Tools are available that can crimp the ferrule into a C shape along it's length, or that crimp around the ferrule to make it into a square or hexagonal shape.
The gauge of wire should be appropriate to the current that the Duet will draw. This depends on a number of factors, however at its maximum this will be dominated by the 15A for the bed heater. The red and black ferrules provided are 1.0mm2 and 1.5mm2 respectively. This relates to 17 and 15 AWG respectively.
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.
¶ Grounding
The metal parts of your machine generally need to be connected to a common grounding point, to earth any static discharge and protect the user from electrocution from electrical faults. This includes:
- Hot end and extruder metal parts
Running filament through the extruder can cause a static electricity build up, which can arc out through the stepper motor wiring, or through the wiring to the hot end (hot end heater or temperature sensor). Any of these may cause enough of an electrical discharge to corrupt memory on the MCU (leading to a crash, often reported as a 'Hardfault' reset in M122) or even damage or destroy the electronic components on the controller board. - Stepper motor casings
These should also be grounded, especially in belt-driven printers. Motion of the belts also causes static charge to build up, which eventually arcs over to the windings, and may damage the stepper driver or MCU. If the motors are screwed to a metal frame, grounding the frame is usually sufficient.
Ideally, run the earthing wire from the power outlet (NOT the earth terminal of the PSU) to a common grounding point (e.g. a bolt on the frame), and then run that on to the earth on the PSU. Then run grounding wires from all components that require grounding to this common grounding point.
It is NOT recommended to:
- connect the frame (or common grounding point) to the PSU negative output. This can cause electrocution in case of a power supply internal fault.
- connect the PSU negative output to earth ground. This can trip the RCD or harm the power supply.
- connect the PSU negative output mains neutral. This can lead to electrocutions if the power supply has an internal fault.
¶ 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. Duet boards are able to supply 15A (fuse limited) to a heated bed.
As with the main power wiring, do not tin the wires. It is recommended to use the included insulated spade crimp terminals (Duet 3 and Duet 2 Maestro) or bootlace ferrules (Duet 2 WiFi and Ethernet, DueX2/5).
If you want to use a second supply to power the bed (still not exceeding the 15A the Duet can sink), it is possible to arrange this. Connect the bed heater and its PSU as follows:
- One bed heater wire to the BED- pin on the Duet bed heater terminal block
- Other bed heater wire to the +ve output of the bed heater PSU
- -ve output of the bed heater PSU to the -ve side of the VIN terminal block (marked GND) (the -ve input from the main power supply goes here too).
- Do not connect the bed heater PSU +ve output to the Duet.
¶ 5V 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 the original USB specification to 500mA. Keep this in mind if you are running a PanelDue, especially the 7" 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. This is the most typical way of providing the 5V supply but it means the board is only powered when VIN is present. The regulator is enabled if the INT 5V_EN jumper is fitted.
-
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.
If the main PSU supports an ATX-style PS_ON pin (power supply on when pin is connected to ground), the Duet 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 ATX power supply 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
On the web interface there is a button for toggling the external supply:
This button will only show if M80 or M81 has been sent. Put M81 somewhere in your config.g for it to show from startup. Using M81 will default the PSU off when the Duet board is powered on.
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 PSU is powered on again.