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Motor Speed Control (part 2)

Step 2.2 – Motor Speed Control (part 2 – making a simple circuit)

 

The pulse-width-modulation circuit that we want can be made in a number of ways. It is essentially the same stuff that is in a light dimmer switch, all be it beefed up a bit so it can handle higher current. One might be salvaged from some other device that has speed control: many modern vacuum cleaners have one, discarded power tools would be another possible source. Really though, this would be quite a lucky find.I chose to make my own (to better understand it and to and add some mods). It is essentially very simple and can be made using some strip board and a few cheap electronic components.Most of the stuff can be scavenged from old boards – we need the following (maplin code in brackets so you can look it up):C1 Polyester capacitor 0.1uF 250V (BX76H)
C2 Polyester capacitor 0.047uF 250V (BX74R)
C3 Polyester capacitor 0.01uF VAC
D2 MOV (Metal Oxide Varistor – commonly just referred to as a ‘varistor’) 250VAC (scavenge or e-bay – not sure what the code is)VR1 Variable resistor or POT 220k (FW06G)
R1 Min Resistor 4k7 (M4K7)
R2 Min Resistor 22k (M22K)
R3 Min Resistor 100R (M100R)D1 Diac DB3 (QL08J)
T1 Triac BTA26-600B (UK56L) (the 16A version would suffice – I was in an overkill mood)

Some strip board to put it all on.

Optional components (more on this later):

2X Rectifier J04 (BH46A) ~ £3 each (but I got very similar ones on e-bay for 99p each)
50VA Step down transformer 240V to 9V – (search out old power supplies, audio amps, hi fi’s, etc.)

The triac itself can often be salvaged from the washing machines along with the motor. I could have also ordered some spade connectors to make the ‘live’, ‘neutral’, ‘the armature’ and the ‘stator coil’ contacts, but I felt like making my own to save a few pennies (see photo). I used some standard 2mm copper wire scavenged from some old house wiring, and soldered on some cut (using a hacksaw) and flattened (hammer or vice) scrap of copper pipe.

The contacts for the control board

When it comes to actually making the circuit, there is loads of good advice on soldering on instructables, so I will not talk much about that. Enough to say that is is not a complex circuit and it should be pretty straightforwards if you read the instructions here carefully. Thanks to Westfw for the Eagle schematic ‘able (http://www.instructables.com/id/Draw-Electronic-Schematics-with-CadSoft-EAGLE/).

The speed control on strip board

This is the simple chopper circuit made on a piece of stripboard.