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Improved Speed Controller for Universal Motors

Use it to control the speed of circular saws, routers, jig saws, electrics drills and lawn edgers rated up to 1200W.

By John Clarke

This circuit is essentially a revised version of the Speed Controller published in September & November 1992. It has been a particularly popular project and readers have come up with countless applications for it.

In fact, you might think that since there are now so many battery-powered and 240VAC power tools with inbuilt speed controls that the uses for a circuit such as this would have declined. In fact, this circuit is more popular than ever and people are constantly coming up with new applications for it.

Apart from drills and circular saws, the speed control is particularly useful for controlling routers and jig saws (when cutting plastics, for example), hobby lathes (which use sewing machine motors), food mixers (where the in-built speed control has failed) and lawn edgers (where full speed operation tends to frequently break the Nylon line). The speed controller also offers much improved operation of sewing machines, in comparison to the conventional resistive pedal controller.

The new 5A Speed Controller is housed in a diecast box which is much more rugged than the previous project which used a plastic case. The diecast case also improves heat dissipation from the Triac.

The controls on the front panel comprise a full/control switch and a knob to set the speed. Power comes in via a 3-core mains lead and mains plug while the outlet is a flush-mount mains GPO (General Purpose Outlet) socket on the front panel.

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