Wattage,= Volts*Amps
Voltage is Amplitude or the size of the electromagnetic wave, Amperage is electron flow. The higher the Amplitude (Voltage) the more drive behind the Electrons (Amperage). Both Voltage and Amperage together make Wattage, and one watt is one Joule.

One Joule = one Watt
Resistance and Ohms law is used to calculate electron flow E=I*R using Voltage (Amplitude) and Amperage (Current flow) values, the equation is linear, meaning it works any way, front to back, or back to front.


Say we have a 300W power supply, it's rated at 10V and 30Amp (300-Watt), and we have a spindle motor that's rated at 300W, if we connect the spindle motor to that supply it will use the full 30Amp and 10V, however if we connect a power supply rated at 20V 30A, the speed of the motor will increase and the motor will use less amperage. (This happends with motors only, not all devices or hardware functions this way.)

Moving stepper motors.

Say you want to connect three steppers to your milling machine, if the motor is rated at 2.5A the potential draw will be 2.5A x 3, making it important to supply the recommended Amperage or more than the recommended Amperage, for example if two motors are rated at 12V 2.5A the potential overall wattage needed will be 60-Watt.

Ohms: Also known as resistance can be determined using Ohms law, you can also determine other things using the same equation "E=IxR", where "E" = Voltage, "I" = Amperage and "R" = Ohms or Resistance.

Given that data, selecting a power supply for anything should be pretty easy.
The next question that comes into play is "how do I obtain a power supply that works for most applications for cheap?"

The answer, ATX.
The ATX power supply used in Computer Towers will work wonders for any application and they are inexpensive, you can convert them to work as bench-top supplies for anything your experimenting with and they cost less than $45. USD.
The power needed to run a mill or lathe depends on the motors used.
If the application calls for the use of stepper motors, the power must be DC opposed to AC. The Voltage and amperage required depends on the stepper motor size.
Most DB25 and COM style breakout board, driver board style setups require two power supplies, however USB style Micros only require power to the drivers, the logic power is supplied from the pc threw the USB port.
Some DIY projects only require ATX power supplies, the kind found in old computer chasis, these supplies provide different voltages, generally you see two voltage values, 12V and 5V. These supplies are the best for a person building a CNC for the first time, they have IC's that prevent damage from occuring, the ATX supply will provide you with 120 Watts of power or more for under $40.00, and in some cases the ATX supply will provide over 500 Watts of power. For a pinout
The supply must provide the correct voltage, if the voltage is too high the stepper motor and driver will get warm or produce smoke, generally this is not agood sign. If too little voltage is supplied brown-outs  will occur and things just simply won't work properly.
Amperage can be much much higher than the item requires, for example if you have a 3-amp stepper motor the power supply can be 300-amp with no issues. Wattage is the overall power povided or consumed, and voltage is the force behind it.
Back to main page

Wikipedia Power supply

Wikipedia Computer Power Supply (ATX)



Most common Electronics required for:

A CNC Milling Machine:

  • Power Supply

o    Amperage and Voltage Multiplied together give you Wattage.

o    Wattage is the overall unit of measurement for electricity.

o    When choosing a power supply make sure to choose something with the Recommended Voltage and High Amperage.

o    Always use caution, do not wire things with power ON.

o    Always double check that Anode and Cathode are connected properly.

  • Stepper Motors

o    Three motors most common for sale or in devices at home, are the "Bipolar", "Unipolar", and "Hybrid" Stepper.

o    Steppers work by charging individual coils.

o    Stepper Motors may have anywhere from 4 - 8 wires, just because a motor has 4 or more wires does not make it a stepper.

  • Break-out board/ Driver-board(s). Note: (Maybe on one PCB).

o    Common "All in one" PCB's can be found online and use TB6560 Integrated Circuits

  • Computer/ PLC

o    The CNC milling machine can be programmed to run from a "Programmable Logic Controller" like the "RepRap" 3D printer.

o    Machines that use the common TB6560 IC noted above will also connect using a DB25 parallel port

  • Spindle Motor

o    Generally a DC motor with a High Wattage.

o    Higher Voltage with a DC motor equates to higher RPM and less torque, it also means less amperage draw

o    Low Voltage supplied to a DC motor will result in lower RPM and more torque if Amperage is available


  • Power Supply

o    Same as the milling machine

o    Some people use ATX (Computer) power supplies because of the high wattage and three output voltages. (12v, 5v, 3.5v).

  • Stepper Motors

o    Same as the milling machine

  • Break-out board/ Driver-board(s). Note: (Maybe all on one PCB).

o    Same as the milling machine

  • Computer/ PLC

o    Same as the milling machine

  • Spindle Motor

o    Lathe spindles for CNC should have "encoder" disks attached

o    Encoders are used for DRO (Digital Readout) and cutting threads.

o    Some of the best spindles are AC motors known as "Servo-Motors", although the motor is controlled using a DC power-supply they're actually AC motors.

o    Treadmill Motors are great for Do-It-Yourself CNC lathe spindles.

3D Printer:

  • Motors


  • Power


  • Motion Control


  • Other