A power supply

Be careful, mains voltage is dangerous

Without power, your board can not do much. The board uses power to operate the control logic and to move stepper motors, and power heating elements, fans, and others.

How to choose a power supply unit (PSU): two power supplies are required, 5.0V and 'bulk' power (VBB).

5.0V supply

  • Voltage (V) : The 5.0V supply should be regulated to 5% tolerance (4.75V to 5.25V). This supply provides power for the control logic circuitry, and should be a good quality regulated power supply (which is inexpensive).
    • Using a cheap buck regulator from a higher voltage is not recommended, as ever exceeding 5.5V on this supply may instantly and permanently damage the control logic on your Smoothieboard.
  • Current (A): The 5.0V supply should be rated to supply at 1A continuous current (or more). Typical load is roughly 0.5A.

VBB supply

  • Voltage (V) : VBB can be from 12 to 24V. While most of the components on the Smoothieboard are rated up to 32V, it is not recommended or supported to use that high of a voltage. 12V PSUs are more common, and generally cheaper. However, the higher the voltage, the higher performance you can get from your stepper motors. This is the reason some designers use 24V PSUs. However, be careful that with a 24V PSU, you will need 24V fans, and will need to reduce the PWM setting for your heating elements or (preferred, and safer) use 24V heating elements.
  • Current (A): The total current required is the current for each stepper motor, plus the current for every peripheral on your machine Smoothieboard will control. This depends on your machine type.
    • On a typical 3D printer, you can safely consider 10A to be sufficient for the heated bed, and 10A or a bit less for the rest of the loads.
    • Go for a 17 to 20A PSU if you have a heated bed.
    • 7A to 10 is probably enough if you do not have a heated bed (or if you are setting up a CNC mill or a laser cutter).
    • If you bought your machine as a kit, a PSU with appropriate current is most probably provided (or one is recommended).
    • If building your machine yourself by self-sourcing, the documentation for the machine model will also most probably recommend a current rating. A power supply that is able to supply more current than is needed is not a problem. Having not enough current to drive your hot-end, heater bed, or motors is a problem.
  • Some off-brand power supplies can have ratings that exceed their actual power capability (motive: writing a bigger number increases the selling price), may not be UL or CE rated (if it starts a fire, insurance may not cover the loss), or may be perfectly fine. A low selling price means cost was squeezed out of the design somehow; best to understand how.
  • Power supplies are not 100% efficient, and generate heat. Heat shortens electronics life. If they contain a cooling fan, make sure the inlet(s) and outlet(s) air flow is unrestricted. Arrange the inlet to be protected from dropped items and bits of filament; preferably off the floor or desk to not suck in dust.

General Notes

  • Multiple-output power supplies are available. In some cases, a minimum load must be applied to the primary output before the secondary output will be regulated to within tolerances. For example, a dual 5.0V and 12V supply might regulate the 5.0V well at no-load conditions, but the 12V output may be low until power is drawn from the 5.0V supply.

EMI Filtering

  • Electromagnetic Interference (EMI) : Digital logic and power circuitry (such as stepper motor drivers) switches currents and voltages on and off very rapidly. This produces EMI proportional to the voltage, current and rate of switching. EMI can be radiated (as radio waves) and / or conducted through the power line cord or other connections. EMI can interfere with (produce noise in or prevent proper operation of) other equipment, including sensors and motion encoder modules. To reduce these effects, an EMI filter module may be added to help reduce the conducted emissions.
    • An EMI filter module may not strictly be needed, however it is often simpler to take protective measures from the start rather than e.g. searching for the cause of strange, intermittent behavior or coming back to failed 3D prints for months – and then put in an EMI filter module.

Fuses / Circuit Breakers:

A typical US AC wall outlet provides 110V to 120V and is protected by a fuse or circuit breaker with a 15A or 20A rating. As (for example) a motor load such as a refrigerator or saw briefly draws a much higher starting current, in order to avoid 'nuisance trips' a 20A rating does not instantly remove power when that load is exceeded.

A VBB power supply rated (for example) 12V at 10A can provide up to 12V x 10A = 120W (Watts) of DC power. Power supplies are not 100% efficient, thus it will require 5% to 30% more than 120W of input power to produce 120W of output power. It is usually safe to assume at least 70% efficiency at full load (higher for more modern supplies), so the power supply will only need perhaps 1.5A at 120VAC input. A 1A, 5V supply will require much less than 1A at 120VAC input.

While the equipment can only use perhaps 2.5A, the AC wall outlet will provide at least 15A to 20A continuously without tripping the circuit breaker or blowing the fuse. It would be possible (though rare) for a fault condition that drew for example 10A at 120V = 1200W to occur, which would be a fire hazard, without tripping the breaker. If you wish to address this possibility, adding an additional fuse and/or circuit breaker with (for example) a 3A rating in line with the AC 'hot' wire will ensure that if there is a lot of excess power being drawn due to a circuit failure, then this fuse will blow or circuit breaker trip, and power will be removed. Too low a fuse or circuit breaker rating will result in 'nuisance' trips.


Make sure you use a Regulated Power Supply, make sure you connect the ground wire for the mains to the power supply, and if it has a fan, make sure it has sufficient space around it to let air flow and cool it appropriately.

To wire the power supply unit to mains (wall AC power), make sure you connect the right colored wires to the right connectors on the PSU. The 3 connectors are “live”, “neutral” and “ground”. Color changes from cable to cable.
You can find charts for your specific country/cable on the internet, but the following colors are the most common:

Standard Load/live color Neutral color Earth color
US Black White Green
Europe Brown Light blue Yellow/Green

Once the wires connected to the PSU, make sure none of your computers is doing something important (like a system upgrade). In case something goes wrong, plug the PSU into a power strip with an on/off button. Then turn that button ON. If your house loses power, you did something wrong. If an LED illuminates on the PSU, everything is fine: unplug the PSU and continue.

If you are new to wiring, please check our how to wire guide.

Don't die

NEVER manipulate mains (220/110V) power wires while they are plugged into the wall plug. Unpleasantness and/or death are common consequences of not respecting this rule.

Ground your printer's frame by connecting it to the Earth terminal on your power supply. In the (unlikely) event that a power supply wire comes undone and touches the printer's frame, this will prevent you from getting an unpleasant and/or deadly shock.

Now that the PSU is getting mains power, your PSU is converting it into 12V or 24V DC (Direct Current) power. You need to connect wires from it to the Smoothieboard to provide power.

The most important thing for DC is to respect polarity : + goes to +, - goes to -. On the PSU, + terminals are indicated as +, V+, 12V+ or 24V+. Ground (-) terminals are indicated as -, V-, COM or GND.

On the Smoothieboard they are indicated simply as + and -.

By convention, black (sometimes brown) wires are used for ground, and red (sometimes orange, white or yellow) wires are used for power connections.

You may want to turn on the power supplies and test the output voltages before connecting them to the Smoothieboard (and turn them back off before connecting).

Once the wires are correctly connected, you can turn the PSU ON. If everything was done correctly, the red LED (marked VBB) on the Smoothieboard will light up brightly.

Be careful

If the VBB LED does not light up, immediately turn the PSU off.

Check polarity, and check all the connections are strong and properly done.

When you turn the PSU on, make sure you are ready to immediately turn it back off.

Now that the board has power, you can use that power to move things!

Emergency stop

It is recommended you setup an emergency stop button on your machine, so that in case of a problem, you can easily and quickly turn the machine off. For information on how to do this, please read EmergencyStop.