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Hig Fu Spe by JOHN CLARKE O will tend to “cog”, caused by erratic firing of the Triac within ur last Motor Speed Controller, published in Febthe Drill Speed Controller, so that the motor receives interruary 2009, utilised a simple phase-control circuit mittent bursts of power. An electric motor that is cogging which works reasonably well with most universal badly is virtually useless and the only cure is to increase motors. However, there are some applications where a the speed setting – and this rather defeats the purpose if wider and smoother control range is required. you want to operate at low speed. One shortcoming of the February 2009 design is that This new SILICON CHIP Motor Speed Controller overcomes the maximum speed from the motor when under speed these drawbacks. The design does not use phase-control control is significantly reduced. So for an electric drill circuitry but uses switch-mode power supply techniques that normally runs at say 3000 rpm, the maximum speed to produce an outstanding controller for universal brushmight be reduced to around 2200 rpm. This is inevitable type motors. with a controller circuit that effectively half-wave-rectifies By the way, before we go further we should point out the 230VAC mains waveform to give a maximum output that virtually all mains-powered power tools and applivoltage of around 160V RMS. ances use universal motors. These are series wound motors The second drawback of the February 2009 design has with brushes. to do with low speed control. While the circuit does alAnd most power tools will low your drill or other appliance to run at quite do a better job if they have a low speeds, the result speed control. For example, leaves much to be Features: m electric drills should be desired. There isn’t imu max to of motor speed from near zero slowed down when using much torque avail- • Full control larger drill bits as they make able and the speed • Speed regulation under load a cleaner cut. regulation is poor. This on rati ope or mot ed ooth low-spe Similarly, it is useful to be means that if you’re • Sm to 2300W able to slow down routers, operating the drill at a • Rated for universal motors rated up jigsaws and even circular low speed and you put • Over-current protection and limiting saws when cutting some a reasonable load on materials, particularly plasit, its speed will drop • Fuse protection tics. The same applies to right away or it may e cas ast diec • Rugged earthed sanding and polishing tools stall completely. n filter and even electric whipper Worse still, the motor • Interference suppressio 36  Silicon Chip siliconchip.com.au gh Performance 230VAC 10A ull-Wave Motor eed Controller This full-range Motor Speed Controller will give smooth control from near zero to full speed on electric drills, routers, circular saws, lawn edgers, food mixers – in fact, any appliances with universal (brush-type) motors. snipers are less likely to snap their lines when slowed down. Phase control Before we continue, we should explain what we mean by phase control so we can illustrate the benefits of the new circuitry. As you know, the mains (AC) voltage closely follows a sine wave – it starts at zero, rises to a peak, falls back to zero, then does the same thing in the opposite direction. This repeats over and over – and does it 50 times each second (50Hz). A motor connected to the mains uses all of the energy it can take from each “cycle” and it runs at its maximum speed. But what if you were able to stop the motor receiving energy until, say, half way through each cycle? Obviously, with less energy available to power it the motor would not run as fast. If you were able to vary the time during each half cycle when power was applied, you would have a variable speed control. This then is the basis of “phase control” Allow power very early in the cycle and it runs fast. These waveforms illustrate the operation of a typical phase-controlled SCR. In Fig.1 (left) the SCR is triggered fairly late in the positive half-cycle, so the motor voltage is just 143V RMS and it runs at a relatively low speed. Compare this with Fig.2, right, where SCR is triggered earlier in the half-cycle and the RMS value rises to 163V. Hence the motor runs faster. siliconchip.com.au May 2009  37 This series of scope screen grabs show the voltage waveforms applied to the motor at progressively higher speed settings. Fig.3 (above) is the lowest setting with very short pulses from the IBGT delivering just 92V RMS to the motor. Fig.4 shows a significantly higher speed setting (167V RMS) with the IGBT being switched on with longer pulses. Each time the IGBT turns off it causes a significant voltage spike due to the back-EMF produced by the motor inductance. Allow power very late in the cycle and it runs slowly. The term “phase control” comes about because the timing of the trigger pulses is varied with respect to the phase of the mains sine wave. It doesn’t just work with some types of motors – it has also been the basis of incandescent lamp dimmers and even heater controls for many decades (it doesn’t work on most forms of fluorescent nor compact fluorescent bulbs). The oscilloscope waveform of Fig.1 shows the chopped waveform from a phase-controlled SCR circuit when a motor is driven at a slow speed. Fig. 2 shows the waveform from an SCR speed control at a higher setting. The motor has 163V applied to it while at the low setting (Fig.1) the motor has 143V applied. These examples show only the positive half of the mains waveform being used, as is the normal case with a phase- controlled SCR circuit. This automatically limits the amount of power which can be delivered to the motor – one half cycle is wasted. So this means that in a phasecontrol circuit the range of speed control is severely limited at the top end. For the motor to run at full speed, it would need to be fed with both the positive and negative half-cycles of the 50Hz mains waveform. Normally this is not possible with an SCR circuit (which is, effectively, a controlled diode which therefore only conducts in one direction). While it is possible with a Triac, it is difficult to achieve without a complex circuit. Another big problem with conventional phase-controlled circuits is that the trigger pulse applied to the Triac or SCR is very short and if this corresponds with the instant when the brushes hit an open-circuit portion of the commutator, no current will flow and consequently, the motor will miss out on a whole cycle of the mains waveform. This problem is more critical at low speed settings and is one of the reasons for the “cogging” behaviour referred to earlier. Incidentally, the sparks you see when you look into a universal (brush-type) motor are mostly caused by brushes passing through an open-circuit section of the commutator – a typical power drill might have a dozen or more of these which keep the motor windings separate. Speed regulation Fig.7: These waveforms show the interaction of the triangle waveform and the speed voltage. The triangle waveform at the top is compared to the speed voltage, the horizontal voltage intersecting the triangle wave. The resulting lower trace is the pulse width modulation signal from the comparator. The comparator output is fed to the gate driver IC2 and Q2 and Q3 that then drives the IGBT. 38  Silicon Chip Most phase-controlled SCR speed control circuits incorporate a form of feedback that is designed to maintain the speed of the motor under load. When the motor is loaded, the back-EMF (electromotive force) produced by the motor drops and the circuit compensates by triggering the SCR earlier in the mains cycle. This helps to drive the motor at the original speed. In practice, the back-EMF generated by most series motors when the SCR is not conducting is either very low or nonexistent. If there is any back-EMF it is produced too late after the end of each half-cycle to have a worthwhile effect on the circuit triggering in the next half-cycle. Pulse-width modulation As we mentioned, the new SILICON CHIP speed control siliconchip.com.au Similarly, Fig.5 shows an even higher speed setting with now 208V RMS being delivered to the motor by the IGBT. Motor speed would already be higher than that capable of a phase-controlled circuit and shows how good this circuit is! Fig.6: here the IGBT is virtually full-on delivering maximum voltage to the motor. However, the RMS voltage reads lower, due to the fact that the spikes which were present in the earlier waveforms are no longer there to confuse the scope. circuit uses Pulse Width Modulation (PWM) and a different feedback method for speed regulation that effectively solves the problems above associated with phase control. Fig.3 and Fig.4 shows the voltage waveforms applied to the motor at high and low speed settings. What happens is that we rectify the mains voltage and then chop it up at a switching rate of about 1.25kHz using a high-voltage IGBT (Insulated Gate Bipolar Transistor). For the high-speed setting the pulses applied to the motor is relatively wide (Fig.3) while at the low speed setting, the pulses are very narrow (Fig.4). There are 12 pulses during each half-cycle, so the motor receives a more continuous stream of current compared to when driven via phase control. As a result, the motor operates very smoothly over the whole of its speed range. For speed regulation the circuit does not rely upon back-EMF from the motor. Instead, it monitors the current through the motor and adjusts the pulse width to maintain the motor speed. If the current rises, indicating that the motor is under load, then the pulse width is widened to maintain motor speed. FUSE & FILTER F1, L1, L2 230V AC IN Block diagram Fig.8 shows the basic circuit arrangement. The 230VAC input waveform is fed through a filter and full-wave rectified. The resulting positive-going waveform is fed to one side of the motor. The other motor terminal is switched on and off via IGBT Q1. Switching of the IGBT is under the control of comparator IC1b, which compares the speed setting required (as set by VR1) against a triangle waveform generator. If the speed voltage is high relative to the triangle waveform, then the MOTOR CURRENT FULL WAVE RECTIFIER K + A – D1 TRIANGLE GENERATOR IC1a COMPARATOR IC1b SPEED CONTROL MOTOR C GATE DRIVER IC2, Q2, Q3 Q1 G SNUBBER E VR1 OVERCURRENT Q4 AMPLIFIER IC3b A CURRENT SENSE R1 SAMPLE & HOLD IC4 D2 K IC3a REFERENCE OVER CURRENT COMPARATOR siliconchip.com.au Fig.8: the basic circuit arrangement of the Motor Speed Controller. The 230VAC input is full-wave rectified and fed to one side of the motor, while the other motor terminal is switched on and off via IGBT Q1. A conventional PWM circuit using IC1, IC2 & IC3, controls Q1. May 2009  39 40  Silicon Chip siliconchip.com.au N SC 33k 12 VR1 1k 8.2k – SPEED 10k LIN ~ 10 9 8 IC1b 1M A K 6 7 10k 1 22k 7 IC3: LM358 K FEEDBACK GAIN VR2 1M A 4 IC3b 100k B 6 10k 5 9 325V 15 IC2e 12 IC2b 4 IC2d IC4 4066B 4 5 A K 100nF 7 14 3 G 1nF 10k R1 D1 STTH3012W +15V ZD2 15V 1W 10 10 F C E E C SAMPLE & HOLD 100nF 100nF 10 100k 10k Q3 BC327 B B Q2 BC337 GATE DRIVE 8 IC2f 1 1M 270 0.394V 10k 14 11 CURRENT 6 AMPLIFIER 5 3 2 1nF (15.8A LIMIT) Q4 BC547 IC3a OVER-CURRENT D2 COMPARATOR 8 1N4148 E C 7 IC2c +15V MOV1 275V 0V OVER CURRENT DETECTOR 220pF 470 F 16V 4.7k 100nF 250VAC X2 PWM COMPARATOR 470 10 F 1k ZD1 15V 1W K D3 1N4004 A IC1: LM319 IC2: 4050 +15V 4.7k 5W 4.7k 5W + 10A/230V MOTOR SPEED CONTROLLER ALL COMPONENTS AND WIRING IN THIS CIRCUIT OPERATE AT MAINS POTENTIAL. DO NOT OPERATE WITH CASE OPEN – ACCIDENTAL CONTACT COULD BE FATAL! SAFETY WARNING! 100nF 4.7k L2 L1 ~ BR1 35A/600V Fig.9: the circuit uses a 50A 1200V avalanche-protected IGBT (insulated gate bipolar transistor) as the switching element to the load. It is switched at 1.2kHz so that there are about 12 on and off cycles for each half-cycle of the 50Hz 230VAC mains supply. 2009 3 IC1a 11 470k 1W TRIANGLE GENERATOR 5 4 100k 10nF 250VAC X2 CASE F1 10A 100k 18nF 100k IEC MALE INPUT CONNECTOR E A 230V AC INPUT E N G A STTH3012W C C K K A K ZD1, ZD2 A 1N4148 A 1N4004 E FGA25N120ANTDTU K E B BC327, BC337, BC547 X2 CASE E 470  1W Q1 FGA25N120 ANTDTU 47nF IGBT 250VAC A CURRENT SENSE 0.025  5W C A K 230V AC OUTPUT 3-PIN SOCKET comparator will produce wide pulses at its output. Conversely, a lower speed voltage will reduce the pulse width. This operation can be seen in the scope waveforms of Fig.7. The triangle waveform at the top is compared to the speed voltage, the horizontal voltage intersecting the triangle wave. The resulting lower trace is the pulse-widthmodulation signal from the comparator. The comparator output is fed to the gate driver (IC2 and transistors Q2 and Q3) that then drives the high voltage IGBT (Ql). Diode D1 is a fast-recovery type to conduct the motor current when Q1 is switched off. The snubber across Q1 prevents excessive voltage excursions across it. Resistor R1 monitors the current flow through the motor when Q1 is on and the resulting voltage generated is sampled using switch IC4. This sampling occurs whenever Q1 is on. Excessive current drawn by the motor is detected by siliconchip.com.au transistor Q4, used as an over-current detector to switch off the IGBT gate drive if current exceeds about 48A. IC3b amplifies the voltage from R1 and applies it to the speed pot. This operates such that an increase in motor current, as the motor is loaded and slows down, leads to an increase in the output from IC3b. This in turn increases the speed setting from VR1, resulting in an increase in the voltage applied to the motor. IC3a also monitors the voltage produced from R1 via IC4 and compares it against a reference voltage. If the voltage from R1 exceeds the reference threshold, IC3a’s output goes low and reduces the speed pot voltage via diode D2. This reduces the voltage applied to the motor and provides current limiting. Current limit is set at 15.8A. Circuit description The circuit for the Motor Speed Controller is shown in May 2009  41 Q1 FGA25N120ANTDTU D1 STTH3012W : N OITUA C ST NE N OP M O C LLA TA OLF SK CART D NA E GATL OV S NIA M TA A ZD2 15V 47nF 250VAC X2 470  1W 10 N A R1 F1 10A 100nF 250VAC X2 1nF 10nF 250VAC X2 10 F 10k Q2 470k 1W Q3 4.7k 5W 10k 4.7k 5W 100nF 22k 10 F 470 F ZD1 1M 4.7k 10k 270 10k 100k 4.7k 1k IC2 4050B 1k 220pF 100k 100nF (-) ~ 1M 100k 470 L1 L2 VR2 Q4 + IC3 LM358 18nF 100nF D3 4004 4148 29050101 D E EP S R O T O M RELL ORT N O C MOV1 ~ 100k 1nF 10k 100k N IC4 4066B 0.025 100nF 15V Fig.10: the complete component overlay for the Full-Wave Speed Controller. Be very careful not to mix up the diodes and zeners – they often look very similar. It’s also a good idea to use IC sockets, just in case! IC1 LM319 1M 33k CON1 8.2k 1RV Fig. 7. It comprises four ICs, three low current transistors, output when changing levels. several diodes, resistors and capacitors plus the high voltThe pin 7 output of IC1b drives buffers IC2c and IC2d. age IGBT, Q1. IC2c drives three paralleled buffers, IC2b, IC2e & IC2f. These IC1a is a comparator that forms the triangle waveform in turn drive emitter-followers Q2 and Q3 to provide a high generator. It is wired as an oscillator where the 18nF cacurrent drive capability to charge and discharge the gate pacitor at pin 5 is charged and discharged via the 33kΩ of the high voltage IGBT Ql. The gate of Q1 is protected resistor connected to the output at pin 12. The triangle or from excessive drive voltage using with ZD2, a 15V zener ramp waveform across the capacitor has an amplitude of diode. The high voltage can be impressed on the gate via about 5V peak-to-peak. capacitance between the gate and collector when the IGBT Comparator IC1b compares the triangle waveform at switches off. pin 10 with the speed voltage at pin 9, as set by VR1. VR1 Several circuit features combine to ensure that the IGBT is part of a voltage divider with a 1kΩ resistor connecting can safely switch high levels of current through the moto the +15V rail and an 8.2kΩ resistor to 0V. The speed tor load. voltage from VR1 is filtered with First, there is a snubber a 10μF capacitor to prevent any network comprising a 470Ω Warning! sudden changes in level and resistor and 47nF capacitor this voltage is monitored by the connected in series across the d controller (1) The entire circuit of this motor spee inverting input (pin 9) of IC1b via IGBT’s source and drain. Seclly lethal. Do not floats at 230VAC – and is potentia a 1kΩ resistor. ond, there is the fast recovery g. doin t you are build it unless you know exactly wha The 1MΩ resistor between pin diode D1. Third, there is a IT LE WHI UIT DO NOT TOUCH ANY PART OF THE CIRC 9 and the pin 7 output provides 275VAC metal oxide varistor and do not operate IS PLUGGED INTO A MAINS OUTLET positive feedback to give a small (MOV) connected across the without its lid on. the circuit outside its metal case or amount of hysteresis in the comoutput of the bridge rectifier. parator action. This is to prevent These measures combine to ors mot ction (2) This circuit is not suitable for indu oscillation of the comparator damp any spike voltages that – see text. or shaded pole motors used in fans 42  Silicon Chip siliconchip.com.au Parts List – Full Wave Universal Motor Speed Controller 1 PC board, code 10105092, 112 x 142mm 1 metal diecast case, 171 x 121 x 55mm 1 front panel label, 168 x 118mm 1 powdered iron core, 28 x 14 x 11mm (L1,L2) 1 single switched mains power outlet 1 10A IEC mains lead 1 IEC male chassis connector with mounting holes 1 3-way PC-mount screw terminal block with 5.08mm spacing (CON1) 8 6.35mm PC-mount male spade connectors with 5.08mm pin spacing 8 6.35mm insulated female spade quick connectors with 4-6mm wire diameter entry 2 5.3mm ID insulated quick connect crimp eyelets with 4-6mm wire diameter entry 1 knob 1 16-pin DIP IC socket 2 14-pin DIP IC sockets 1 8-pin DIP IC socket 2 3AG PC-mount fuse clips 1 10A 3AG fast blow fuse (F1) 2 M4 x 10mm screws (Earth connections) 2 M4 x 15mm screws (GPO Mounting) 1 M4 x 20mm countersunk screw (BR1 mounting) 5 M4 nuts 2 M4 star washers 2 M3 x 12mm countersunk screws (for IEC Connector) 2 M3 x 15mm screws (for Q1 and D1) 4 M3 nuts 3 3/16” x 6mm screws (PC board to case) 4 stick-on rubber feet 8 100mm cable ties 2 TO-3P Silicone insulating washers 1 300mm length of blue 10A mains wire 1 300mm length of brown 10A mains wire 1 300mm length of green/yellow 10A mains wire 1 100mm length of 0.8mm tinned copper wire 1 1.1m length of 1mm enamelled copper wire 1 45mm length of black 5mm heatshrink tubing 1 45mm length of red 5mm heatshrink tubing 1 15mm length of green 5mm heatshrink tubing would otherwise occur every time the IGBT switched off. Current monitoring R1 is a used to monitor the current flow through the motor and IGBT, Q1. Transistor Q4 directly monitors the current via a voltage divider comprising two 10kΩ resistors in series. At about 48A there is about 1.2V across R1 and the base of Q4 is at 0.6V. The transistor conducts and pulls the IC1b comparator output low to disconnect drive to the IGBT. Thus Q4 provides for transient current limiting. Voltage developed across R1 is also fed through a low pass filter consisting of a 10kΩ resistor and 1nF capacitor to one side of IC4, a 4066 analog switch. This is the sample-and-hold circuit and IC4 is switched on to sample the voltage across R1 each time the IGBT is switched on. IC4’s gate signal comes from comparator IC1b and is buffered by IC2d. The sampled signal from R1 is stored using siliconchip.com.au 1 45mm length of white 3mm heatshrink tubing Semiconductors 1 LM319 dual comparator (IC1) 1 4050 hex CMOS buffers (IC2) 1 LM358 dual op amp (IC3) 1 4066 quad CMOS analog switch (lC4) 1 BC337 NPN transistor (Q2) 1 BC327 PNP transistor (Q3) 1 BC547 NPN transistor (Q4) 1 FGA25N120ANTDTU NPN 50A 1200V TO-3P IGBT (Q1) (Farnell cat 149-8965) 1 STTH3012W 30A 1200V TO-247 ultrafast recovery diode (D1) (STMicroelectronics) 1 1N4148 signal diode (D2) 1 1N4004 1A 400V diode (D3) 2 15V 1W zener diodes (ZD1,ZD2) 1 35A 600V bridge rectifier (BR1) 1 S14K275 275VAC metal oxide Varistor (MOV1) Capacitors 1 470μF 16VW PC electrolytic 2 10μF 16VW PC electrolytic 1 100nF 250VAC X2 class MKT polyester 4 100nF 63V MKT polyester 1 47nF 250VAC X2 class MKT polyester 1 18nF 63V MKT polyester 1 10nF 250VAC X2 class MKT polyester 2 1nF 63V MKT polyester 1 220pF ceramic Resistors (0.25W, 1%) 2 1MΩ 1 470kΩ 1W 5 100kΩ 1 33kΩ 1 22kΩ 5 10kΩ 1 8.2kΩ 2 4.7kΩ 2 4.7kΩ 5W 2 1kΩ 1 470Ω 1W 1 470Ω 1 270Ω 1 10Ω 1 low ohm shunt resistor 0.025Ω, 1%, 5W (OAR5 – R025F1) (TT Electronics) 1 10kΩ 25mm linear potentiometer (VR1) 1 1MΩ horizontal trimpot (VR2) (Code 105) the 100nF capacitor and discharged over a 100ms period with a 1MΩ resistor. The sampled voltage from IC4 is fed to two op amps, IC3a & IC3b. IC3b amplifies the voltage by about 100 when VR1 is set to maximum and 3.2 when set to minimum. IC3b acts to vary the DC level fed to comparator IC1b from VR1 and thereby compensates for speed variations in the motor. IC3a acts as a comparator, comparing the sampled voltage from R1 with a 394mV reference voltage at its pin 3. If the current through R1 rises above 15.76A, the voltage across the resistor equals the 394mV reference and the output of IC3a goes low and pulls pin 9 of IC1b low via diode D2 and a 470Ω resistor. This has the effect of greatly reducing the motor drive voltage and so it limits the current. Power for the circuit is derived directly from the 230VAC mains. Fuse F1 protects against shorts while the 10nF capacitor in conjunction with L1 & L2 prevents switching May 2009  43 INSULATING PAD Fig.11: the complete wiring diagram of the Motor Speed Controller. Follow this wiring exactly – including the earthing detail. It is very important that the case and lid be separately earthed, as shown here. Note also that all parts of the circuit, including the terminals of VR1, float at 230VAC. Inset at right is the mounting arrangement for both D1 and Q1, which mount on the inside of the case with insulating washers. Their legs must be kinked outwards slightly so they sit flush on the case wall. M3 NUT Q1 (IGBT) & DIODE D1 KINK IN LEGS PC BOARD 15mm x M3 SCREW CASE INSULATING WASHERS Q1 FGA25N120ANTD D1 STTH3012W CASE EARTHING: M4 x 10mm SCREW WITH EYELET CONNECTOR, LOCKWASHER & NUT ! N OITUA C ST NE N OP M O C LLA SK CART DRA O B CP D NA LAIT NET OP S NIA M TA TA OLF 15V A N A M3 SCREW & NUT IEC MAINS INPUT SOCKET N 19050101 D E EP S R O T O M RELL ORT N O C + 4148 CABLE TIE CABLE TIES L1 M3 SCREW & NUT CABLE TIE CABLE TIE L2 CAUTION! ALL COMPONENTS AND PC BOARD TRACKS FLOAT AT MAINS VOLTAGE (-) CON1 ~ ~ 1RV L1: 12 TURNS – ~ ~ + BR1 (MOUNTED ON SIDE OF CASE) CABLE TIES LID EARTHING: M4 x 10mm SCREW WITH EYELET CONNECTOR, LOCKWASHER & NUT CABLE TIES VR1 HEATSHRINK SLEEVING (LID OF CASE) L1 & L2 BOTH WOUND USING 1mm ENAMELLED COPPER WIRE ON 28 x 14 x 11mm IRON POWDERED TOROID 44  Silicon Chip A L2: 12 TURNS Fig.12 (inset left): winding details for the input filter choke. Note that L1 and L2 are wound so that their flux cancels in the toroid core. OUTLET MOUNTING BOLTS AND NUTS (M3 x 10mm) E 3-PIN OUTLET N siliconchip.com.au A close-up photo of the input (IEC socket) wiring, fuse, choke and bridge rectifier. All mains leads are terminated in quick-connect terminals. Similarly, a close-up of the IGBT (right) and fast recovery diode (left). These devices do not require an insulating bush but definitely do need an insulating washer, as seen here. artefacts from the IGBT and motor being radiated back to the mains wiring. BR1 is a bridge rectifier with a 600V 35A rating. The bridge provides the circuit with the positive full-wave rectified mains voltage and this is lightly filtered using a 100nF 250VAC capacitor. Power for the low voltage circuitry is derived via two series 4.7kΩ 5W resistors, diode D3 and the 15V zener diode ZD1. A 470uF capacitor across the 15V zener smooths the DC while diode D3 prevents the capacitor from discharging when the mains voltage falls to below 15V every half cycle. The result is a regulated 15V supply. quite hot to the touch. When inserting diode D2 and D3 and zener diodes ZD1 and ZD2, take care with their orientation and be sure to place each type in its correct place. D1 is installed later. We used IC sockets for the ICs. Be sure to install these the correct way around with the notch facing the direction shown on the overlay. Transistors Q2-Q4 can now be inserted, again taking care to place each in its correct position. Capacitors can be installed next. The accompanying capacitor table shows the various codes that are used to indicate the capacitance values of the polyester capacitors. The electrolytic capacitors must be oriented with the correct polarity. L1 & L2 are windings wound on a single powdered iron toroidal core as shown in Fig.12. Each winding is wound using 12 turns of 1mm enamelled copper wire with the shown direction. While the exact number of turns is not critical, it is important that both windings have the same number of turns and that they are wound in the directions as shown. The wire ends can be soldered to the PC board after they have been stripped of insulation using some fine abrasive paper, or a sharp hobby knife. After soldering, secure the toroid to the PC board with two plastic cable ties. These wrap around the core and through holes in the PC board. (It is important not to secure the toroid with lengths of wire; these could make a shorted turn around the toroid). Fuse F1 is mounted in fuse clips that are installed into the PC board as shown. Clip the fuse into the clips first (lugs Construction The Motor Speed Controller is constructed on a PC board coded 10105092 and measuring 112 x 142mm. It is housed in a diecast case measuring 171 x 121 x 55mm. The PC board has cut-outs to match the shape of the case. Begin construction by checking the PC board. There should not be any shorts or breaks between tracks. If there are any problems, repair these as necessary. Similarly, if the cutouts in the sides of the PC board have not been shaped, they should be cut and filed before any components are assembled. A large semicircular cutout is required on both the long sides of the board. Also you will need to round off the corners of the board. Make sure the PC board fits into the case before starting assembly. Following the overlay diagram shown in Fig.10, begin by inserting and solde ring in the wire links and then the resistors, using the accompanying table for Resistor Colour Codes the colour codes. The two 5W resistors should be inserted so that they stand a No. Value 4-Band Code(1%) 5-Band Code (1%) millimetre above the PC board to allow 2 1MΩ brown black green brown brown black black yellow brown cooling. When the Drill Speed Control1 470kΩ yellow violet yellow brown yellow violet black orange brown ler is operating, each resistor will be 5 100kΩ brown black yellow brown brown black black orange brown dissipating about 2.7W so would run 1 33kΩ orange orange orange brown orange orange black red brown 1 22kΩ red red orange brown red red black red brown Capacitor Codes 5 10kΩ brown black orange brown brown black black red brown Value μF IEC EIA value code code 1 8.2kΩ grey red red brown grey red black brown brown 100nF 0.1μF 100n 104 2 4.7kΩ yellow violet red brown yellow violet black brown brown 47nF .047μF 47n 473 2 1kΩ brown black red brown brown black black brown brown 18nF .018μF 18n 183 2 470Ω yellow violet brown brown yellow violet black black brown 10nF .01μF 10n 103 1 270Ω red violet brown brown red violet black black brown 1nF .001μF 1n0 102 1 10Ω brown black black brown brown black black gold brown 220pF NA 220p 221 1 1 1 1 1 1 1 1 1 1 1 1 siliconchip.com.au May 2009  45 What Motors Can Be Controlled? We’ve noted elsewhere in this article that the vast majority of power tools and appliances use so-called universal motors. These are series wound motors with brushes. But how do you make sure that your power tool or appliance is a universal motor and not an induction motor? As we also said before, induction motors must not be used with this speed controller. One clue is that most universal motors are quite noisy compared to induction motors. However, this is only a guide – it’s certainly not foolproof. In many power tools you can easily identify that the motor has brushes and a commutator – you see sparking from the brushes and that settles the matter. But if you can’t see the brushes, you can also get a clue from the nameplate or the instruction booklet. OK, so how do you identify an induction motor? Most induction to the outer ends of the fuse) then insert them into the PC board and solder in position – this hopefully ensures that you don’t solder them in the wrong way around. Solder in the eight 6.4mm PC-mount spade connectors to the PC board for the mains wiring connections, along with the 3-way screw terminal connector for the potentiometer connecting wires. D1 and Q1 are the last components to be soldered to the PC board. Solder them in so their metal flanges are towards the edge of the PC board and their full-length leads extending about lmm below the PC board. motors used in domestic appliances will be 2-pole or 4-pole and always operate at a fixed speed which is typically 2850 rpm for a 2-pole or 1440 rpm for a 4-pole unit. The speed will be on the nameplate. Bench grinders typically use 2-pole induction motors. Note that this speed controller must NOT be used with power tools, etc, which already have a speed controller built into the trigger. One final point: if you are using this controller with a high power tool such as a large circular saw or 2HP router, it will not give the same kick when starting. Because of the current limiting, the motor will take a few seconds to come up to full speed. Normally though, if you want to use the appliance at full speed, it is better not to use the Speed Controller at all. All that is left are bridge BR1, diode D1 and IGBT Q1, all of which mount on the inside walls of the case when the PC board is in place. Mounting the hardware First of all, mark out the hole position for the IEC connector and earth screw in the end wall of the case. The IEC connector mounts in the horizontal centre, about 6mm down from the top. As you can see in our photographs, about 1mm of the top of the end-wall channel is left when the hole is made. Another view of the completed motor speed controller, very close to same size. The front panel artwork is printed overleaf, or it can be downloaded from siliconchip.com.au. 46  Silicon Chip siliconchip.com.au The IEC hole is made by drilling a series of small holes around the perimeter of the desired shape, knocking out the piece and filing to shape. Insert the PC board into the case and mark the mounting hole positions for diode D1, IGBT Q1 and bridge rectifier BR1. Note that the leads for D1 and Q1 must be kinked outward slightly so that the metal flange of each device is parallel to and in contact with the side of the case. Drill out the holes for these three components Holes are also required in the lid for the GPO, VR1 and the earth terminal. All holes must be deburred on the inside of the cas e with a countersinking tool or larger drill to round off the sharp edge of the hole and in the case of D1 and Ql, prevent punch-through of the insulating washers. Attach the PC board to the case with the 3/16” screws. Note that we do not use a screw in the corner where BR1 mounts. BR1 effectively holds the PC board in place here. Secure D1 and Q1 to the case with a screw, nut and insulating washer. The arrangement for this is shown in the inset in Fig.11. After mounting D1 and Q1, check that the metal tabs of the devices are isolated from the case by measuring the resistance with a multimeter. The meter should show a very high resistance measurement between the case and any of the diode and IGBT leads. The complete wiring diagram is shown in Fig.11. The earthing details of the case are most important since the IGBT, fast recovery diode D1 and potentiometer, VR1, are all at mains potential yet are attached to the case. If the insulating washers or the insulation of the potentiometer were to break down, the case would be live (ie, at 230VAC) if it was not properly earthed. For the same reason, the case lid must also be separately earthed, also as shown in Fig.11. The bridge rectifier (BR1) is secured to the case with a 4mm screw and nut. It does not require an insulating washer between its body and the case. All mains wiring must be done using 10A mains-rated (ie 250V) wire. Wiring for the potentiometer must also be mains rated but it does not need to be 10A rated. The IEC connector must be wired using the correct wire colours with brown for the Active, blue for the Neutral and green/ yellow striped wire for the Earth. Use quick-connectors for the mains wiring connection to the PC board connectors. Wires to the IEC connector need to be insulated with Troubleshooting the Motor Speed Controller If the speed controller does not work when you apply power, it’s time to do some troubleshooting. First, a reminder: all of the circuit is connected to the 230V AC mains supply and is potentially lethal. This includes the tabs of Dl and Ql, the terminals of potentiometer VRl – in fact, all other parts. Do not touch any part of the circuit when it is plugged into a mains outlet. Always remove the plug from the mains outlet before touching or working on any part of the circuit. If the live circuit must be worked on, it must be operated via a 1:1 mains isolation transformer. We’re only saying that because it is safer but we’d still prefer you didn’t do it. Before going any further, give you PC board another thorough check (using a magnifying glass?). Kit suppliers tell us that at least 99% of problems are due to wrong or swapped components, right components in the wrong way around and, of course, the “biggie”: poor soldering (or even completely missed solder joints). If you are 110% sure your Speed Controller isn’t suffering from any of these maladies, it’s time to get more technical! Fortunately, there is a safe way to check most of the circuit and that is to operate it from a low voltage (12V) DC supply. Naturally, before you remove the lid you would have already disconnected the 230V mains lead (don’t just turn it off, unplug it!). The supply is connected with the positive connecting to the anode of diode D3 and the negative connecting to the anode of ZD1 (the anodes are the ends opposite the striped end on the diode body). Before you connect the supply, measure it to make sure it is not exceeding 14V – if it does, you’re liable to blow up the 15V zener diode. With power applied, a multimeter connected with the negative lead to the negative supply can be used to test voltages. Firstly, check that there is 11.4V on pin 1 of IC2 and pin 11 of IC1. IC3 should have 11.4V on pin 8. Similarly pin 14 of IC4 should also have 11.4V. Voltage on the wiper of VR1 should be adjustable from siliconchip.com.au 4.86V to 10.79V or similar by rotating the potentiometer to its full extremes. The same voltage range should be seen at pin 9 of IC1a. Pin 7 of IC3a should be close to 0V. Pin 1 of IC3b should be at about 9V or more. With the meter still set to read DC volts, the triangle wave can be measured and should provide approximately a half supply reading, in this case about 5V. If your meter can read a AC volts at 1kHz, then the meter can be set to read ACV. The reading will be around 1.5ACV. Similarly, when the multimeter is set to read DC volts the pulse width drive can be checked. On the output of IC1a at pin 7, the DC volts should be adjustable from 0V to close to 11V when VR1 is altered from minimum to maximum. The same voltage range should be available at the pin 4, pin 12 and pin 15 output of IC2. A slightly lower voltage range will be available on the gate of Q1. If the gate voltage remains at 0V, then suspect a damaged IGBT, a shorted ZD2 or open circuit 10Ω resistor. Measuring the resistance between IGBT pins is a simple way to check it. If there is a short circuit between collector and emitter, or if the gate is shorted to the emitter, then the IGBT is faulty. Diode (D1) operation can be checked using the diode test on your multimeter. In any case there should not be a short circuit measured between anode and cathode. Be sure to remove the 12V supply and replace the lid before reconnecting to the mains. Incidentally, do not try to monitor the waveforms with an oscilloscope unless you know exactly what you are doing. Ideally it needs with a scope with true differential inputs or a mains isolation transformer. The waveforms in Fig.7 can only be measured using a low-voltage DC supply, as detailed above. You must not connect the earth terminal of a scope probe to any part of the circuit. If you do, you are likely to cause severe damage to the circuit and possibly to the scope as well! May 2009  47 heatshrink tubing covering all exposed metal. For the earthing, solder two earth wires from the IEC connector with one terminating to the earth eyelet and the other running to the power outlet earth terminal. Another green/yellow earth wire runs between the earth connection on the power outlet and the earth eyelet on the lid. The earth eyelets are secured with M4 screws, a star washer and nut. Wire up the potentiometer, again using 250VAC rated wire. The reason for voltage rating this is to ensure that in the worst-case scenario and a mains-voltage-carrying wire lets go inside the case (eg, it unsolders due to heat), a bare end contact with one of the pot wires will not allow mains to “punch through” lesser-rated wire insulation. Finally, hold the wiring in place using cable ties as shown – also to minimize the possibility of loose wires contacting something they shouldn’t. Note that the Active and Neutral wires running to the GPO socket should not be allowed to lie near to the potentiometer wiring. Instead have these wires lie on the Q1 side of R1 when the lid is closed. Failure to observe this wiring arrangement may cause the controller to power the motor with sudden bursts of speed. This is to minimise the possibility of the high voltage switching signal on the Neutral wire being induced into the potentiometer wiring. Testing Before you power up the circuit, insert the ICs into their respective sockets, taking care with their orientation. Set SILICON CHIP trimpot VR2 to its mid-position – this setting should give good performance with most motors. Now, check all of your wiring very carefully against the overlay and wiring diagram. Also check that the case and lid are connected to the earth pin of the power socket. If you are satisfied that all is as it should be, screw the lid onto the case. Do not be tempted to operate the Drill Speed Controller without the lid in place AND screwed in position – it’s not worth the risk. The easiest way to test the circuit operation is to connect a load such as an electric drill. Apply power and check that you can vary the drill speed with VR1. Some motors may require adjustment of VR2 for best speed regulation, which must be done on a trial-and-error basis. Disconnect power from the mains wall outlet (or unplug the IEC connector) before removing the lid, adjust VR2 very slightly and replace the lid. In practice, if VR2 is adjusted too far clockwise, the motor will tend to be overcompensated when loaded and will actually speed up. It may even hunt back and forth between a fast and slow speed. If this happens, readjust VR2 anticlockwise for best results. If you are using a drill for example, at fairly low speed, the motor should not slow down by much as you put a reasonable load on it. At the risk of sounding repetitive, remove the plug from the mains outlet before making any changes to VR2 and replace the lid before reconnecting power. SC POWER OUTLET MOUNTING HOLES www.siliconchip.com.au 4mm 230V INPUT 4mm CUTOUT FOR POWER OUTLET (60 x 40mm) GREY: POWER OUTLET POSITION 230V 10A FULL WAVE MOTOR SPEED CONTROLLER Fig.13 : same-size artwork for the front panel. A photocopy of this can also be used as a drilling/cutting template. 48  Silicon Chip 10mm x SPEED For universal (brush-type) (brush-type) motors up to 10A/2300W nameplate rating 3 Do NOT use on induction or shaded-pole motors x: 3mm pot locating hole drilled from lid underside – does not need to go all the way through lid. siliconchip.com.au