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Full Wave Universal Motor Speed Controller Want exceptionally smooth speed control over the entire range for your power tool? You want our new Universal Motor Speed Controller. It is ideal for use with mains-powered electric drills, lawn edgers, whipper snippers, circular saws, routers or any other appliance with universal (ie, brush-type) motors, rated up to 10A. By JOHN CLARKE O ur latest Full Wave Universal Motor Speed ControlWe have also added the ability to switch the soft-start fealer is an upgrade on the one we published in March ture off, also via an external switch. Soft start is useful when 2018. That one worked very well, but we identified the speed controller is set at a certain speed and the motor several upgrades and improved features that could be made is switched on and off at the appliance. When the appliance to the design. is switched on, the motor speed is slowly and automatically One of the main drawbacks of the previous design was brought up to the set speed. Without it, power to the motor that the feedback gain control was located inside the Con- is suddenly applied, and the motor can kick back. troller’s housing. That control set the amount of compensaSoft start is essential when using the Controller with a tion for maintaining motor speed under load. high-powered router or circular saw. For smaller appliancOnce set, the Controles, and when the moler was only suitable tor is switched on and for the appliance being off often, you might This Speed Controller operates directly from the 230V AC mains used, since the feedback find that it limits how supply and contact with any live component is potentially lethal. control would require fast you can work, as Do not build it unless you know what you are doing. changing for different you wait for the motor DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS motors. to come up to speed. PLUGGED INTO A MAINS OUTLET and never operate it This control is now exThat would be the outside its Earthed metal case or without the lid attached. ternally adjustable via a case when used with This circuit is not suitable for use with induction motors and must control knob, making it a whipper snipper and only be used with universal ‘brush type’ (series-wound) motors or easy to use the Control- shaded pole (fan) motors with nameplate ratings up to 10A. For more some hand drills. So ler across a range of difwe made it so you can information, see the section titled “What motors can be controlled”. Power tools with inbuilt fans must not be operated at low speeds for ferent power tools and easily switch the soft extended periods; otherwise, they could overheat. other devices. start feature off. While WARNING! 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au we were making those changes, we took the opportunity to improve its ability to maintain motor speed under load, especially at low speed settings and for low-power appliances. The Full Wave Universal Motor Speed Controller can be used with mains supplies over the range of 220250V AC at 50Hz or 60Hz. This means that it can be used in many different countries, although it is not suitable for use with 100-120V AC mains supplies. The Controller is mounted in a relatively low-profile diecast aluminium case with mains plug and socket leads attached to one end, through cable glands. A panel fuse is also provided on the same end of the case. The speed control and feedback gain potentiometers, and soft start switch, are mounted on the lid. Features * For universal and shaded-pole motors rated up to 10A * Runs from 220-250V AC at 50Hz or 60Hz * Full-wave motor speed control * Full speed range (from nearly zero to close to 100%) * Current feedback for maintaining speed under load * Feedback gain adjustment * Optional soft start from zero speed and at power-up * Optimised control for inductive loads such as motors Why do you need speed control? Most power tools will do a better job if they have speed control. For example, electric drills should be slowed down when using larger drill bits as they make a cleaner cut. Similarly, it is useful to be able to slow down routers, jigsaws and even circular saws when cutting some materials, particularly plastics, as many will melt rather than be cut if the speed is too high. The same comments apply to sanding and polishing tools, and even electric lawn trimmers; they are less likely to snap their lines when slowed down. What motors can be controlled? This Controller suits the vast majority of power tools and appliances. These generally use universal motors which are series-wound motors with brushes. They’re called universal motors because they can operate on both AC and DC. You cannot control the speed of any universal motor which already has an electronic speed control built in, whether part of the trigger mechanism or with a separate speed dial. That does not include tools such as electric drills which have a two-position mechanical speed switch. In that case, you can use our speed controller with the mechanical switch set to fast or slow. The slow selection usually drives the motor with a half-wave voltage. Scope1: the output waveform (Active voltage, in cyan) at a higher speed setting with a resistive load (a light bulb). You can see that the output voltage matches the input voltage most of the time, so the attached load will receive almost full power and, if a motor, will run at high speed. siliconchip.com.au Induction motors (except shaded-pole types, which are often found in fans and such) must not be used with this speed controller. How do you make sure that your power tool or appliance is a universal motor and not an induction motor? One clue is that most universal motors are quite noisy compared to induction motors. However, this is only a guide, and it’s certainly not foolproof. In many power tools, you can see that the motor has brushes and a commutator (usually through the cooling vents) and you can see sparks from the brushes during operation. That indicates that the motor is a universal type. But if you can’t see the brushes, you can also get a clue from the nameplate or the instruction booklet. Most induction motors used in domestic appliances will be 2-pole or 4-pole types which operate at a fixed speed, typically 2850 RPM for a 2-pole unit or 1440 RPM for a 4-pole unit. The speed will be on the nameplate. Bench grinders typically use two-pole induction motors. If you do need to control the speed of this type of motor, use the 1.5kW Induction Motor Controller published in April and May 2012 (siliconchip.com.au/Series/25) with important modifications in the December 2012 issue. Phase control The AC mains voltage closely follows a sinewave. It starts at 0V, rises to a peak, falls back to 0V, then does the same Scope2: by triggering the Triac later in each mains halfcycle, the output voltage (cyan) is zero most of the time, and the load power is greatly reduced. This will cause an attached motor to spin quite slowly, as the average applied voltage will be low. Australia’s electronics magazine April 2021  37 Specifications * Power: 230V AC sinewave up to 10A * Operating frequency: any fixed frequency between 40Hz and 70Hz * Soft start rate: two seconds from start to full speed * Triac gate drive: 68mA * Triac gate pulses, phase angle <90°: 40µs gate pulses repeated at 200µs intervals thing in the opposite direction. This repeats 50 times per second for 50Hz mains, or 60 times per second for 60Hz mains. A motor connected to the mains makes full use of the energy from each cycle so that it runs at its maximum speed. So if supplied only a portion of this sinewave to the motor, with less energy available to power it, the motor would not run so fast. Varying the time during each half-cycle when voltage is applied to the motor gives speed control. This is the basis of phase control: start feeding power very early in the cycle, and the motor runs fast; delay power until much later in the cycle, and it runs more slowly. The term ‘phase control’ comes about because the timing of the trigger pulses is varied with respect to the phase of the mains sinewave. Several devices can be used to switch the mains voltage; here, we are using a Triac. That device can be used to switch both the positive and negative voltage excursions of the mains waveform. The oscilloscope traces show phase control varying the power to an incandescent light bulb, as this shows phase control in its pure form, without the extra hash caused by driving a motor. Scope1 shows the chopped waveform from the phase control circuit when the incandescent light bulb is driven at high brightness. This is equivalent to driving a motor at a fast speed. Here, the Triac is triggered 2.5ms after the zero-crossing (the point where the mains waveform passes through 0V). The voltage applied to the load is the cyan trace, and measures 200V RMS. That is less than the 219V RMS mains waveform shown by the yellow trace. Scope2 shows the waveform from the phase controller driving a light bulb at a lower setting, with the Triac triggered later in the cycle. The voltage applied to the load is now much less at 87.9V RMS. Scope3 shows the waveform when driving a motor. The lower blue trace is the voltage applied to the motor, with the input mains shown on the top (yellow) trace. Note the extra hash on the lower trace due to the motor being an inductive load. Speed control For a motor to have good low-speed performance, the Controller needs to compensate for any drop in motor speed as the load increases. Many phase-based speed controllers rely upon the fact that a motor can be used as a generator when it is spinning with no power applied. When the motor is loaded and the motor speed slows, the back-EMF (electromotive force) produced by the motor drops, and the circuit compensates by providing more of the mains voltage cycle to the motor, 38 Silicon Chip Scope3: the same speed setting as shown in Scope2, but this time with a motor attached. The inductance of the motor windings causes the Triac to switch off after the zero-crossing due to the output current phase shift from its reactance. triggering the Triac earlier in the mains cycle. But in practice, the-back EMF generated by most series motors while the Triac is not conducting is either very low or non-existent. This is partly because there is no field current, and the generation of voltage is only due to remnant magnetism in the motor core. If there is any back-EMF produced, it is too late after the end of each half-cycle to have a worthwhile effect on the circuit triggering in the next half-cycle. So we use a different method for speed regulation, by monitoring the current through the motor. When a motor is unloaded, it draws a certain amount of current to keep itself running. When the motor is loaded, the motor speed drops and the current draw increases. The motor controller senses this, and compensates for this speed drop by increasing the voltage to the motor. This might sound like positive feedback, where the detection of more current drawn will increase the voltage and so allow the motor to draw more current. It’s true that this can happen if the amount of compensation is too high, which is why we include a feedback control knob, to adjust the compensation gain. With the right setting, the speed regulation is very impressive, but too much feedback will have the motor increasing in speed with increased load instead of maintaining the set speed. Controlling a Triac with an inductive load One major problem when using a Triac for full-wave control of a motor is the way a Triac switches off and the nature of the motor load. A Triac is usually switched on by applying a current to its gate. If the current flowing between the Triac’s main terminals is greater than its holding current, the Triac will remain switched on for the remainder of the mains cycle. A Triac will only switch off when the gate is not being driven and the Triac current drops below its holding current. As a motor is not a purely resistive load, but instead has a significant inductance, the motor current lags the voltage. That means that a Triac driving a motor will not nec- Australia’s electronics magazine siliconchip.com.au Scope4: the first stage of the precision full-wave rectifier works as a half-wave rectifier with an output voltage half that of the input. Both signals (original and clipped/ attenuated) are fed into the second stage and combined to produce the output shown in Scope5. Scope5: the final output waveform of the precision full-wave rectifier is in cyan. It is identical to the yellow trace, except that the negative portions have become positive voltages, so that it can be fed to a single-ended ADC for measurement. essarily switch off at the zero-crossing; motor current can continue to flow until sometime after. Our circuit uses a microcontroller to produce the required gate pulses to correctly drive an inductive load like a motor using a Triac. It feeds a series of gate pulses to the Triac to provide for the full range of phase control. time the Triac turns off. The snubber network acts to damp transients and reduce their amplitude. The DC supply for the microcontroller is derived directly from the 230V AC mains supply via a 470nF 275VAC X2 rated capacitor in series with a 1kΩ 5W resistor. The capacitor’s impedance limits the average current drawn from the mains, while the 1kΩ resistor limits the surge current when power is first applied. When the Neutral line is positive with respect to Active, current flows via the 470nF capacitor, diode D1 and 47Ω resistor to the 1000μF capacitor to charge it up. On negative half-cycles, the current through the 470nF capacitor is reversed and flows through diode D2, discharging the capacitor back into the mains. Zener diode ZD1 limits the voltage across the 1000µF capacitor to 5.1V. This is the supply for microcontroller IC1, op amps IC2a and IC2b, and for the gate current of Triac Q1. IC1’s 5.1V supply is bypassed with a 100nF capacitor while IC2 is bypassed with 100uF. Switch S1 allows the soft-start feature to be enabled or disabled. This switch controls the input level of the GP3 input (pin 4). When S1 is open, the GP3 input is held high at 5.1V via a 47kΩ resistor, so soft start is disabled. When switch S1 is closed, GP3 is pulled low, and the program runs the soft-start routine. S1 pulls GP3 low via a 100Ω resistor, which is included to protect the input from current transients that could cause latch-up in the IC. The 100nF capacitor provides a low impedance to transients, preventing incorrect detection of the GP3 input when S1 is open due to transients or interference. VR1 is the speed potentiometer, and it is connected across the 5.1V supply. IC1 converts the voltage from VR1’s wiper into a digital value using its internal analog-to-digital converter (ADC). The 100kΩ resistor from the wiper to ground holds the AN1 input at 0V, setting the motor speed to zero should VR1’s wiper go open-circuit. Potentiometer VR2 is connected similarly. Its wiper voltage sets the feedback gain to maintain motor speed under load. It is also converted to a digital value within IC1. The capacitors at the wiper of VR1 and VR2 provide a low source impedance to IC1’s ADC, and to filter out supply ripple. Circuit description The Speed Controller circuit is shown in Fig.1. Its key components are Triac Q1 and PIC12F617 microcontroller IC1. IC1 monitors the speed potentiometer, VR1, at its analog input AN1 (pin 6) and the feedback gain potentiometer, VR2, at AN0 (pin 7). It also monitors the motor current at analog input AN3 (pin 3), with that signal originating at current transformer T1 and passing through a full-wave rectifier based around IC2. The mains voltage waveform is monitored for zero crossings at pin 5, via a 330kΩ resistor. In response to all those parameters, IC1 produces a series of pulses at its digital output GP5 (pin 2), and these drive the base of NPN transistor Q2 which, in turn, sinks current from the gate of Triac Q1. The Triac gate current flows via the 47Ω resistor connected between the 5.1V supply and the Triac’s A1 terminal, then out through the gate and to circuit ground via Q1 (ie, the gate current is negative). This method of connection places the 47Ω resistor between the 230V AC mains supply and the 5.1V supply which runs the PIC microcontroller. This avoids Triac switching noise getting into the 5.1V supply, which can cause the microcontroller to latch-up. Snubber The snubber network comprises two 220Ω 1W resistors in series and a 220nF 275V AC X2-rated capacitor connected between the A1 and A2 terminals of the Triac. This network prevents rapid changes in voltage from being applied to Triac Q1, which would otherwise cause it to turn on (due to dV/dt switching) when it is supposed to be off. These rapid changes in voltage can occur when power is first applied, or can come from voltage transients generated by the inductance of the motor being controlled each siliconchip.com.au Australia’s electronics magazine April 2021  39 Both VR1 and VR2 are connected to IC1 via screw connectors. CON2 provides the common +5V and 0V connections for VR1 and VR2, while VR1’s wiper also connects to CON2. CON3 provides the wiper connection for VR2, with switch S1 utilising the remaining two connections in CON3. Mains synchronisation The timing of the Triac’s trigger pulses is critical to its correct operation. IC1 monitors the mains voltage at its pin 5, with the 330kΩ resistor connecting to Neutral plus a 4.7nF low-pass filter capacitor. An interrupt routine is triggered in IC1 whenever the voltage at pin 5 changes from a high to a low level or vice versa. The interrupt tells IC1 that the mains voltage has just passed through 0V, so it can synchronise its gate triggering with the mains waveform. The phase lag introduced by the 4.7nF capacitor is compensated for within IC1’s software, as is the asymmetry of the triggering due to the 5V difference between low and high levels. Current feedback T1 is a current transformer comprising a ferrite toroid with a two-turn primary winding in series with the Triac. The secondary winding has 1000 turns, and it is loaded with a 510Ω resistor. With this loading, the transformer produces 800mV per amp of load current at the secondary output. This is proportional to the current through the motor being controlled. Its output signal is applied to a precision full-wave rectifier comprising IC2a and IC2b. This configuration is unusual in that it does not use any diodes. Most precision rectifiers with diodes require a negative supply for the op amps. While we could have incorporated a negative supply, it would increase the circuit complexity and cost. The full-wave rectifier operation relies on op amps that have specific characteristics. The first is that the op amp output has to swing fully to the negative supply rail (ie, all the way down to 0V). Also, this 0V output must be maintained when the input to the op amp drops below 0V. The LMC6482 op amp (IC2a and IC2b in the circuit) has these characteristics, as well as a low supply current. 40 Silicon Chip We have labelled several points in the circuit and shown the expected waveforms to help explain how this section works. The signal from the transformer secondary appears at point A. This signal swings above and below 0V as shown. The signal flows along two paths from here. One is through the 20kΩ resistor to point D, and the other through the two series-connected 100kΩ resistors to 0V. IC2b is connected as a unity gain buffer. The op amp’s internal diode will clamp any voltage at the non-inverting input (pin 5) below -0.3V. Its output (pin 7) will be at 0V whenever its input is 0V or less. The operation of this part of the circuit is best explained by describing the signal flow for the negative and positive excursions of the waveform separately. Negative portion When the voltage at point A is negative, the voltage at point B is clamped to -0.3V by the internal protection diode at the pin 5 input of IC2b. The output of IC2b at pin 7 (point C) is therefore at 0V, and so is the non-inverting input to IC2a. As a result, IC2a acts as an inverting amplifier with a gain of -1. This is set by the input 20kΩ resistor and the 20kΩ feedback resistor from the pin 1 output to the inverting input at pin 2. So IC2a will produce a positive voltage at its output pin 1, proportional to the negative voltage at point A. To understand how this works, consider that the op amp operates to keep the voltages at its inputs equal. As the non-inverting input is held at 0V, with equal value resistors in the feedback path forming a 1:1 divider, the output voltage (E) must have equal magnitude and opposite polarity compared to the input voltage (A) for the inverting input voltage (D) to be at 0V. So for example, when point A is at -1V, point E will be +1V, so point D will be at 0V, equal to C. Note that the 10kΩ resistor at point D does not have any effect in this case, since pin 2 is at 0V, and therefore there is no voltage across that resistor. It has a function only during positive signal excursions. Positive portion For positive voltages at point A, the voltage at point B will be half the voltage of point A due to the 100kΩ/100kΩ Australia’s electronics magazine resistive divider. Point C and the non-inverting input to IC2a will also be half the applied voltage at A, as IC2b is acting as a buffer. Remember that usually, the inverting input voltage will be the same as the non-inverting input. The op amp will ensure this by adjusting its output so it can maintain that voltage via the feedback resistor. The only way that can happen for IC2a in this case is when the op amp output at point E is the same as the signal input at point A. In that case, the same voltage is applied to both 20kΩ resistors and they are essentially in parallel, forming an equivalent 10kΩ resistor to point D. This forms a 1:1 divider with the 10kΩ resistor from point D to ground, halving the voltage at this point compared to points A & E. So to conclude. IC2a provides the same positive voltage at its output E as the input at A during positive excursions. During negative excursions, IC2a instead inverts the voltage. So siliconchip.com.au Fig.1: the Motor Speed Controller uses current sense transformer T1 and op amps IC2a & IC2b (operating as a full-wave precision rectifier) to sense the motor current. IC1 adjusts the gate pulses from its pin 2 output to the gate of Triac Q1 to maintain a more-or-less constant motor speed under load the output of IC2a is positive for both negative and positive inputs at point A. Thus, we have a full-wave rectifier. Its output is low-pass filtered using a 4.7kΩ resistor and 10µF capacitor for a smooth DC output that’s then applied to the AN3 analog input of IC1, ready to be digitised. Scope4 shows a sinewave signal at point A (in yellow) and the lower blue trace shows waveform C, the half-amplitude positive waveform output. When waveform A goes below 0V, waveform C stays at 0V. Scope5 shows the same sinewave signal at A in yellow, and the fullwave rectified output at E in the lower blue trace. Construction Most components for the Full Wave Universal Motor Speed Controller are mounted on a double-sided, plated-through PCB (printed circuit board) coded 10102211 and measuring 103 x 81mm. This is mounted inside a diesiliconchip.com.au cast box measuring 119 x 94 x 34mm. Follow the PCB overlay diagram, Fig.2. Begin by installing the resistors except for the 5W type. The resistor colour codes are shown in a table, but you should also double-check each resistor using a digital multimeter. Following this, fit the diodes, which must be orientated as shown. There are two different diode types: 1N4004 for D1 and D2, and zener diode ZD1 is a 5.1V 1W type (1N4733). IC1 is mounted on an 8-pin DIL socket so install this socket now, taking care to orientate it correctly, with the notch facing towards the top of the PCB. Leave IC1 out for the time being, though; we’ll fit it later on. IC2 can be installed on a socket or directly on the PCB. Additionally, Q2 can be installed now. Place the capacitors next. The MKT and polypropylene types are usually printed with a code indicating their value. These are all shown in the parts list. Australia’s electronics magazine By contrast, electrolytic capacitors are almost always marked with their value in μF, along with their polarity. Typically, the negative lead is marked with a stripe. They must be inserted with the polarity shown. The screw terminals are next. The 3-way terminal blocks for CON2 and CON3 are installed with the lead entries facing each other, while CON1 does not have a specific orientation. Then fit the 5W resistor about 1mm above the PCB for improved cooling. Finally (for now), install current transformer T1. It does not matter which way it is orientated. Triac Q1 will be fitted later. Cut the underside pigtail leads from all components short to prevent contact with the base of the case. Drilling the case Fig.4 shows a template/guide for drilling the case. The lid requires 9.5mm diameter holes for potentiometers VR1 and VR2, a 19mm x 10mm April 2021  41 SILICON CHIP Fig.2: most of the components are mounted on the top of the board, with the main exception being Triac Q1. It mounts on the inside of the case, under the PCB. Once you have finished the wiring, check it carefully against this diagram. The Earth screws and lugs must all make good contact, and use cable ties to bundle up the control wires as shown. rectangular cutout for switch S1 and a 4mm hole for the Earth screw. The PCB is mounted in the base of the case using 6.3mm-long M3 tapped spacers, which require mounting holes. Use the PCB as a template, and note that the CON1 screw terminal end sits further away from the end of the box compared to the other end. This allows space for the cable gland nuts. With the PCB in place, mark out the hole positions, remove it and drill them to 3mm. Attach the 6.3mm-long spacers to the PCB using short machine screws, then bend the Triac leads up by 90° 4mm from its body. Insert the leads into the PCB from the underside (see Fig.2). Secure the PCB to the case with screws from the underside and mark the Triac mounting hole position on the base of the case. Remove the PCB again and drill this to 4mm. Clean away any metal swarf and slightly chamfer the hole edges, then reattach the PCB and adjust the Triac lead height, so the metal tab sits flush onto the flat surface. Secure the Triac tab to the case with an M4 screw and nut. The metal tab is internally isolated from the leads, 42 Silicon Chip so it does not require any further insulation between its tab and the case. Solder the Triac leads on the top of the PCB and trim them close. Now remove the screws to gain access to the underside of the PCB and solder the Triac leads from the underside of the PCB as well. Now is a good time to attach rubber feet to the base of the case. Panel preparation As well as drilling the holes in the lid mentioned above, you need to partially drill a 4mm hole on the inside for the pot location pin that prevents Close-up, same-size photo of the Speed Controller PCB. Because it is a mainspowered and mains-controlling device, your construction must be exemplary. Don’t attempt this project if you’re not experienced with mains devices. Australia’s electronics magazine siliconchip.com.au the pot body from rotating. Drill it so that it almost reaches the outside of the lid, but doesn’t go all the way through. If you use a countersunk-head Earth screw and countersink its hole appropriately, it can be mounted under the panel label for a neater appearance. Otherwise, you’ll need to cut a hole in the panel label (with a sharp hobby knife) when the label is stuck on. The panel label file can be downloaded from our website and printed. To produce a front panel label, you have several options. For a more robust label, print as a mirror image onto clear overhead projector film (using film suitable for your type of printer). Attach the label, printed side down, to the lid with a light-coloured or clear silicone sealant. Alternatively, you can print onto a synthetic “Dataflex” sticky label that is suitable for inkjet printers, or a “Datapol” sticky label for laser printers. Then affix the label using the sticky back adhesive. There’s more information online about Dataflex labels at siliconchip. com.au/link/aabw and Datapol at siliconchip.com.au/link/aabx, plus hints on making labels at siliconchip. com.au/Help/FrontPanels Wiring Cut the 10A extension lead into two, to provide one lead with a plug and another with a socket. Where you cut the lead depends on how long you want each section to be. You might prefer a long plug cord and short socket lead, so the appliance is located near the Controller, or the lead can be cut into two equal lengths. Before cutting, make sure you have sufficient length to strip back the insulation as detailed in the next two paragraphs. Make sure the two leads are fed through the correct gland and wired, as shown in the wiring diagram, Fig.2. For the socket (output) lead, you need a 100mm length of Earth wire Fig.3: Triac Q1 mounts on the base of the case, using it as a heatsink. A hole in the PCB gives access to hold the nut while you tighten the screw. siliconchip.com.au Parts list – Full Wave Motor Speed Controller 1 double-sided PCB coded 10102211, 103 x 81mm 1 diecast box, 119 x 94 x 34mm [Jaycar HB5067] 2 linear 50k 24mm potentiometers (VR1,VR2) 2 plastic knobs to suit VR1 & VR2 1 SPST mini rocker switch (S1) [Jaycar SK0984 or Altronics S3210] 1 Talema AX-1000 10A current transformer (T1) [RS Components 775-4928] 1 M205 10A safety panel-mount fuse holder (F1) [Altronics S5992] 1 M205 10A fast-blow fuse 1 4-way PCB-mount screw terminal (CON1) [Jaycar HM-3162] 2 3-way PCB-mount screw terminals, 5.08mm pitch (CON2,CON3) 2 GP9 cable glands for 4-8mm diameter cable 1 8-pin DIL IC socket (for IC1) 1 2m-long 10A mains extension cord 3 chassis lugs with 4mm eyelets 4 6.3mm-long M3 tapped Nylon spacers 3 M4 x 10mm panhead or countersunk machine screws (for mounting Q1; Earthing) 2 4mm inner diameter star washers 3 M4 nuts 8 M3 x 5mm panhead or countersunk machine screws 4 stick-on rubber feet 1 20mm length of 12mm diameter heatshrink tubing 1 80mm length of 3mm diameter heatshrink tubing 1 600mm length of 7.5A mains-rated wire (for VR1, VR2 & S1) 4 100mm-long cable ties Semiconductors 1 PIC12F617-I/P 8-bit microcontroller programmed with 1010221A.hex, DIP-8 (IC1) 1 LMC6482AIN dual CMOS op amp, DIP-8 (IC2) 1 BTA41-600B 40A 600V insulated tab Triac, TOP3 (Q1) 1 BC337 500mA NPN transistor, TO-92 (Q2) 1 5.1V 1W (1N4733) zener diode (ZD1) 2 1N4004 400V 1A diodes (D1,D2) Capacitors 1 1000µF 16V PC electrolytic 1 100µF 16V PC electrolytic 1 10µF 16V PC electrolytic 1 2.2µF 16V (or higher) PC electrolytic 1 470nF 275VAC X2-class metallised polypropylene 1 220nF 275VAC X2-class metallised polypropylene 3 100nF 63/100V MKT polyester 1 4.7nF 63/100V MKT polyester (value printed on body) (value printed on body) (code 103 or 100n) (code 470 or 4n7) Resistors (all 0.25W, 1% unless otherwise stated) 1 330k 5% 1W carbon film (code orange orange black orange brown) 3 100k (code black brown black orange brown) 1 47k (code yellow purple black red brown) 2 20k (code red black black red brown) 1 10k (code brown black black red brown) 1 4.7k (code yellow purple black brown brown) 1 1k 10% 5W wire wound (no code - value printed on body) 1 510 (code green brown black black brown) 1 470 (code yellow purple black black brown) 2 220 5% 1W carbon film (code red red black black brown) 1 100 (code brown black black black brown) 2 47 (code yellow purple black gold brown) Miscellaneous Super Glue (cyanoacrylate), thermal paste, solder Australia’s electronics magazine April 2021  43 Fig.4: drill the three holes in the lid as shown here, plus the rectangular cut-out. It is most easily made by drilling a series of small holes inside the outline, knocking the central piece out, then carefully filing the edges flat and to shape until the switch snaps in. The three large holes in the box end are for the two cable glands and fuseholder,with a small one (4mm) in the box side for the Earth screw. (green/yellow stripe) for the connection between the chassis and lid, so strip back the outer insulating sheath by about 200mm. Cut the Active (brown) and Neutral (blue) wires to about 50mm long and keep the offcuts. The spare 150mm brown wire can be used later, to connect from the fuse to CON1 via the transformer, T1. This requires two turns of the Active wire looped through the transformer hole. The 100mm Earth wire (green/yellow stripe) which is routed around the edge of the PCB, and twists together with the Earth wire from the plug (input) lead, to be crimped into one of the Earth lugs. Strip the plug lead outer sheath insulation back to expose 100mm of wire. All three wires pass through the cable gland and connect it as shown in 44 Silicon Chip Fig.2. Cut the Neutral wire to 50mm and strip back the insulation before connecting it to the terminal block. Now mount the fuse holder in the hole you made earlier and prepare to solder the Active (brown) wire to it, as shown. But before doing that, slide 10mm diameter heatshrink tubing over the Active (brown) wire. After soldering that wire, slide the tubing up and over the fuse holder to cover the fuseholder side terminal and shrink it. Similarly, use 3mm diameter heatshrink tubing to cover the fuse holder end terminal after soldering that wire. Now twist the ends of the input Earth (green/yellow stripe) wire and the output Earth wire together and crimp both into one of the eyelet lugs. Cut VR1 and VR2’s shafts to 12mm long from the front of the pot bodies and file the edges smooth. Then atAustralia’s electronics magazine tach the three 100mm lengths of 7.5A mains-rated wire to the three terminals of VR1, plus a fourth 100mm wire to the middle terminal of VR2. Use short lengths of the same wire to connect the two ends of VR2’s track to the same terminals on VR1. Cover all six terminals with 3mm heatshrink tubing. Next, connect the free ends of these wires to CON2 and CON3, making sure to do so as shown in Fig.2. You will also need to wire up switch S1 now in a similar manner. It is simply wired to the two remaining terminals in either order. Now secure all these wires to the PCB using a cable tie that feeds through the holes provided in the PCB. Attach VR1, VR2 and S1 to the lid of the case, noting that the potentiometers must be located as shown (ie, with their leads emerging away from the edge of the siliconchip.com.au children or other curious people. Attach the lid, ensuring the wiring is routed so that it fits around the higher components on the PCB. Use the four screws supplied with the case; don’t be tempted to run the speed controller without the lid in place! Testing This “opened out” photo matches the PCB/wiring diagram on P42. Of course, we made sure that the Controller was not plugged into mains power before removing the lid! case). This is so that they will fit between the two mains-rated capacitors on the PCB. Add cable ties around the wire bundles closer to VR1, VR2 and S2 as well. Fit the knobs now; you might need to lift out the knob caps with a hobby knife and re-orientate them so that the pointers match the rotation marks on the lid panel. That 100mm length of Earth wire you cut off from the output lead can now be crimped into two eyelet lugs, which are screwed to the underside of the box lid and the Earth screw on the side of the case using M4 screws, star washers and nuts. Ensure that the nuts are fully tightened. pins on both the mains plug and socket. Check this with a multimeter set to read low ohms. You should get readings below 1Ω between all Earth points. The cable glands need to be tightened to hold the mains cords in place. Because these are easily undone, apply a drop of Super Glue to the thread of the glands before tightening. That way, the glands cannot be undone by SILICON CHIP www.siliconchip.com.au 10A Fuse GAIN Final assembly Apply a smear of thermal paste to the underside of the Triac tab before installing the PCB inside the case. As mentioned, the tab of the Triac is insulated, so it can contact the case. The last components to insert are IC1 (taking care it is orientated correctly), the 10A fuse into its holder and the cover for the barrier terminals (CON1). This is simply pressed on to cover the screw terminals. Finally, rotate VR2 fully anticlockwise to initially disable feedback. Now check your construction carefully. Verify that the Earth wires (green/yellow striped) connect together the case, to the lid and the Earth siliconchip.com.au Connect up a universal motor appliance (eg, a mains-powered electric drill) to the Controller, apply power and check that the motor can be controlled when adjusting the speed potentiometer. VR2 may need adjustment to avoid speed changes when under load. Rotate it clockwise if the speed drops off too markedly under load, and anticlockwise if the motor speeds up under load. Check that the soft-start feature works when enabled by switching the power off, letting the tool spin down, then switching it on again to verify that it ramps up smoothly with S1 in the sc correct position. For universal motors rated up to 10A, 50/60Hz 230V AC. Not suitable for induction motors. SOFT START OFF ON . . . . . . . .. . . . . . .. . . . . . . . . . . SPEED Full Wave 10A Motor Speed Controller Fig.5: full-size “front panel” artwork which can be copied or downloaded and printed (from siliconchip.com.au). This is glued to the top of the diecast box – and it can also be used as a template to drill the three panel holes and cutout for the soft start switch. Australia’s electronics magazine April 2021  45