6 replies to this topic

[fruitfulsteve]

Does anyone know where i could get one of those things you used to be able to get to vary the speed of a drill ? (before the acceleration trigger became popular)

[helix]

I'm using the innards of foot pedal from a sewing machine to control the speed of a small elecric motor that I'm making into a wee ball mill (motor with brushes as opposed to an induction motor). It seems to work ok but I havent had it running for any length of time yet so I'm not sure how the motor will perform long term -as its probably not rated for continual operation but I'm going to see how it goes.

james

[BrightStar]

There's a Velleman kit here that might do the trick:

http://www.rapidonli...a...&kw=70-4176

These controllers are essentially glorified dimmer switches, but use either dc or pulse train 'hard firing' of the triac to overcome the inductance of the motor. They're generally designed for universal motors rather than induction motors.

[Arthur Brown]

An electric drill with integral varispeed can be used by making a holder box with a long machine screw pressing onto the trigger.

The old drill speed controllers were simple phase angle controllers - lamp dimmers! They are hard to get past the current radiated electronic interference regulations, hence them vanishing from the market.

A simple but over rated lamp dimmer as found in B&Q or an electrical shop may function, but may cause interference, You NEED to find one that is capable of powering the maximum that the drill can draw. Most drills are for intermittent use only, any motor running at low speed will over heat as the integral cooling may depend on the speed of the motor.

[BrightStar]

The old drill speed controllers were simple phase angle controllers - lamp dimmers!

Yes, in essence.

As far as I know, a lamp dimmer generally has a small capacitor that charges from the ac line voltage via a potentiometer, following the waveform. A diac from this small capacitor 'breaks over' at 35 volts or so after a variable delay, triggering the gate of the triac. The triac then conducts for the remainder of the half cycle and the whole process repeats 10ms later...

To make a motor speed controller, this doesn't always work!

The single pulse as the triac is triggered will be met with the inductance of the motor and any interference supressors in the series loop. This inductance hinders the rise of current and can prevent the triac from latching on, with unpredictable results. This is where the 'hard firing' circuit comes in - either by supplying multiple pulses to the gate (optimal for large motor loads) or just a dc trigger.

Although I don't have the schematic, the Velleman circuit seems to have the necessary characteristics - a transformer to power the 'hard firing' of the triac and a decent toroidal supressor to prevent interference, so it might work reasonably well.

Edited by BrightStar, 12 June 2009 - 06:15 PM.

[fruitfulsteve]

Having read the spec on the one from Rapid online 5amps should be enough so i'm gonna order one and give it a try. Watch this space as i'm hopefully going to be posting some pics later and all will become clear!!

[fruitfulsteve]

Has anybody seem one of these? I acquired it from a local junk shop, very handy looking thing made by Selecta. The drill speed controller is to slow it down to use it as a star roller (perhaps). I don't think you can buy these any more but apparently you can get lots of different attachments for it. If anyone sees one at a car boot sale it's worth acquiring, it seems to work as a low pressure press, drills angled compound mitre angles in tubes (flightless rockets?) plus obvioulsy works as a bench drill. The drill that came with it is a bit shabby but I intend to change that. This is it;



http://img23.imagesh...p?g=0005wiu.jpg