CNC Information and Projects

The drives require low voltage direct current power. Since power from the wall receptacle is a higher voltage and alternating current, a specially made power supply is required.
There are commercial units available but many DIY builders make their own.

The transformer has to be able to handle the current that the motors require, so a little doorbell transformer, shown below with the toroid, though perhaps of the correct voltage, may not be able to deliver enough power to some systems.

Larger transformers for the popular drives, steppers and servos, cost in the $35 to $100 range.
The lower cost larger transformers, shown on the upper right, are less efficient than the toroids (donut shaped) transformers, shown below.
(The ruler with the toroid is 6 inches long; the rectangular transformer on the above right is around 4 inches wide and high.)

Toroids usually run cooler and can deliver a higher current than similarly sized laminated body transformers.

The secondary or low voltage wires from the transformer are connected to the rectifier, which is a set of diodes that allow the current to pass in only one direction, thus turning AC into DC.

A rectifier can be made from four diodes, or a bridge rectifier can be used.

The rectifier has to be sized for the power that will pass through it or it will cook.

The capacitor also has to be sized for the power, and large capacitors can cost a few tens of dollars. However, it is possible to use two half sized capacitors attached in parallel to do the same job.

The smaller capacitors cost much less, so a few dollars can be saved, even though two are used in place of one.

The math for deriving the sizes of components is in a document from Geckodrive (pdf document page 11) that is linked on this site’s Links page. The document also includes wiring diagrams.

Other options include computer power supplies, and rewinding microwave oven transformers.
Computer power supply outputs can be too low for many CNC systems, but they have been used.

Rewound microwave oven transformers work, but the process can be tedious.
The transformer's original secondary coil is removed with a hacksaw and then rewound with new wire. Each turn produces around 1 volt.

The homemade microwave oven transformer shown here works okay, but it was lot of work and potential danger for its quality.
It becomes much hotter than the toroids, and it interferes with the computer monitor when close.

Antek sells toroids at a good price. One of their $55 toroids was used in this shop to power some Gecko stepper drives, and it has proved to be a good product.  It is the smaller unit in the right photo.
The larger Antek power supply shown on the far right is used with a bench mill; it was around $200.

As shown on the Controls page, a Plitron toroid was used for the servos on this shop's 4x8 CNC table. It also is a good unit and can be custom built to specific voltages, but the price is higher.

In the Helpful Hint department.

To prevent electrical shocks, the capacitors should have a resistor across their terminals so they will discharge when the power is turned off.

In this shop a 110v 4 watt night light bulb is used for this load. The lamp serves as a pilot to show that the power supply is on, and it dims out as the capacitors discharge after the power is turned off.

These small bulbs have worked well with a variety of power supplies. They will glow in a large range of voltages.