AC Motor Controller

A project that mounts an AC motor speed controller in a box that incorporates a standard Australian power point for use with any device that uses a standard 240V plug.  This controller can be used with loads such as an incandescent light (or LED lights that are marked as compatible with a dimmer) or as a speed controller for general-purpose (ie, not induction) AC motors.


AC Motor Speed Control Module
AC Wall Socket with mounting screws
Power cord, grommet and ferrite ring
Switch, DPST 240VAC 5A
Fuse holder and fuse, 240VAC 5A
Slide terminals, ferrules, wire and cable tie.

The AC Motor Speed Controller is rated at 2000W for 110-250 volt input up to 25A.  The maximum rating would be sustainable for very short bursts only, but for things like fans and small motors it is quite suitable.   In this case it is intended for a small AC motor mounted with a grinding wheel, and the components (including fuse) are rated for a maximum 5A at 240VAC to keep performance well within the rated maximum.  Note that the minimum available output voltage should be adjusted to ensure that any attached motor is not driven at less than its stall voltage.

As this is a 240V project construction must be to a suitable standard.  Wiring must be mains rated and all terminals should be shrouded.  The connection to the socket should use crimped ferrules, to eliminate the risk of stray wires.   The mains input lead should be grommetted and firmly secured.  The case must be securely closed - this project uses the wall socket securing screws to close the case, which also means that there are no external exposed metal parts, and the securing screws are not exposed in the interior. It is particularly important that the frame supporting the potentiometer cannot contact any of the internal wiring, as that part is potentially exposed through the shaft of the pot.

The fuse used in the project is only accessible with a screwdriver, and also holds the fuse firmly in the cap so that the potentially live end of the fuse is not exposed when the cap is undone and being removed.  There are many panel-mounted fuses available that do not have this important protection even though they are mains rated. Note that some fuse holders include this protection only if they are wired with the correct polarity.



The unit incorporates a switch for the source as well as the output, so that the supply to the controller can be switched off when there is no device attached.



AC Motor Controller Assembly

The wall socket is mounted to the front surface of a 3D-printed case.  The controller and supply switch are mounted through the front face, while the fuse and input cord mounting are fitted to the back.  The halves of the case are held together by the screws that also secure the wall socket. The 240VAC earth lead is secured by cable ties to a pillar provided for that purpose.  Note that this lead must have the most slack of the 3 leads from the power cord.  A ferrite bead will help in preventing switching noise being fed back into the mains - there is room available for a bigger inductor if noise is a problem (as used in this example).


As Used


The driver has been used for a small AC motor mounted with a grinding disc, and also for a brushed 230VDC motor via a rectifier.