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180-230V DC Moto Controls 180-230V DC motors rated from 1A to 10A (¼HP to 2.5HP) Controlled by four common op amp ICs with one opto-coupler and three linear regulators Zero to full speed control Safe startup procedure Emergency cut-out switch facility Automatic over-current switch-off Optional reversing switch capability PWM, Live and Power indicator LEDs Rugged diecast aluminium enclosure Current and back-EMF monitoring for speed regulation under load Initial setup adjustments can be done with a low-voltage supply M otors rated at between 180V and 230V DC are supported; they are driven by PWM-chopped rectified mains. Motor load/speed feedback is via current and back-EMF monitoring. The circuit is based on analog techniques and is designed to be robust and easily adjustable. Most of the active devices are common types of operational amplifiers (op amps). The motor speed is controlled by a rugged IGBT (insulated gate bipolar transistor). Most parts are throughhole types except for a few resistors and the opto-isolated IGBT driver. It all fits in a convenient diecast aluminium case. Having already described the overall design and how the circuit works in the first article published last month, let’s move on to building it. Construction Most of the parts are mounted on a double-sided, plated-through PCB coded 11104241 that measures Warning: Mains Voltage This Speed Controller operates directly from the 230V AC mains supply; contact with any live component is potentially lethal. Do not build it unless you are experienced working with mains voltages. 78 Silicon Chip 201×134mm, which fits in a 222 × 146 × 55mm diecast aluminium enclosure. The only off-board parts are the GPO socket for the motor, the speed potentiometer and the IEC mains input socket. Some of the PCB tracks connecting to Q1, BR1 and CON1 on both sides of the PCB are tin-plated so they can handle more current. Before installing any parts, they should be covered with a layer of solder to thicken the tracks and further reduce their resistance (shown in red in Figs.3 & 4). However, be careful to avoid getting solder in the component through-holes when doing so. Fig.3 shows the layout of the topside parts on the PCB, which you can use as a guide during assembly. Begin by fitting the surface-mounting opto-coupled Mosfet driver (IC5). You will need a soldering iron with a fine or medium tip, a magnifier and good lighting. It’s also a good idea to have a syringe of flux paste and some solder-­ wicking braid on hand. Solder IC5 to the PCB pads by first placing it with its pin 1 locating dot to the top left and the IC leads aligned with the pads. Solder a corner pin and check that the IC is still aligned correctly. Soldering the small leads will be easier if you apply a small amount of flux paste on top first. If it needs to be realigned, remelt the solder and gently nudge the IC into Australia's electronics magazine alignment. When correct, solder all the IC pins. Any solder that runs between and bridges them can be removed with solder wick. Following that, mount diodes D2-D10 and zener diodes ZD1-ZD3. Ensure each is orientated correctly and that the correct diode or zener diode is installed in each location before soldering their leads. Diodes D2 and D6-D8 are 1N4004 types, while the remainder (except for the zeners) are 1N4148 types. ZD3 has a different voltage rating from ZD1 and ZD2, so don’t get them mixed up. TVS1 can also be installed now; it is bi-directional, so it can go in either way around. Follow by soldering the SMD resistors in place. These mount on the underside of the PCB, as shown in Fig.4. They are the 10kW resistor under IC5 and the four 0.022W resistors under inductor L1. If you are building the speed controller for a motor rated at 5A or less, see Table 1 for the required number and value of these shunt resistors. Otherwise, fit all four. Install these by soldering one end first, then the other after you’ve checked that the part is aligned correctly and the first solder joint has solidified. The low-wattage (½W) throughhole axial resistors can be fitted now. siliconchip.com.au or Speed Controller Our new High-voltage DC Motor Speed Controller, revealed last month, can control motors commonly used in lathes and treadmills. It can operate such a motor from stopped up to full speed and maintains a constant speed even with a varying load. This article covers the assembly, testing and setup of the Speed Controller. They have colour-coded bands and the codes were shown in the parts list last month. However, you should also use a digital multimeter to check each resistor before soldering it, as the colour bands can be difficult to distinguish (especially brown, red and orange). The remaining ICs can now be installed, taking care to get the correct one in each place and with pin 1 in the proper location (double check that!). Sockets can be used for each of the ICs, although they can also be soldered directly to the PCB, which is likely to give better long-term reliability. The 1W and 5W resistors can be mounted next. When fitting the 5W resistors, leave a gap of around 1mm between the body and the PCB to allow air to circulate. Regulators REG1-REG3 mount horizontally with their leads bent by 90° to fit into the allocated holes in the PCB. Each Part 2 by John Clarke regulator is secured to the board using a 6mm-long M3 screw and nut before the leads are soldered. Make sure you don’t mix up the three different regulator types. Diode D1 is mounted horizontally with its leads bent by 90° so you can insert them into the PCB holes. Secure it with an M3 screw, washer and nut before soldering. The capacitors can now be installed. There are four types used. The 630V-rated 47nF capacitors operate at rectified mains voltage, so make sure the correct types are used in the upperleft corner of the PCB. The other types are ceramic, MKT polyester and electrolytic. The 100nF and 1μF ceramic capacitors are placed near IC5. The electrolytic capacitors need to be orientated correctly since they are polarised. The longer lead indicates the positive side, while the negative stripe down one side of the capacitor indicates the negative side. One 100μF (just above IC3) and 10uF capacitor (above D4) is rated at 25V, so ensure it is located correctly, or it will be damaged when power is applied. For the MKT and ceramic capacitors, the 10nF capacitor is likely to be marked 103, the 100nF capacitors marked 104, the 220nF capacitor marked 224, and the 1μF capacitor marked 105. Solder in the three PCB-mounting spade connectors (CON5-CON7), then bridge rectifiers BR1 and BR2, ensuring correct orientation. BR1’s positive lead is spaced further from the others, so it will only fit in one way. Mount it so there is about 1mm of lead length below the PCB for soldering. For BR2, the longer lead is positive. The AC and + terminals will also be marked on the package. LED1-LED5 can be fitted now. Be sure they are correctly orientated with the longer lead placed into the anode (A) hole in each case. The power LED, Table 1 – shunt resistor values depending on motor rating HP ¼ ½ ¾ 1 1¼ 1½ 1¾ 2 2¼ 2½ kW 0.18 0.36 0.54 0.72 0.9 1.08 1.26 1.44 1.62 1.8 A 1 2 3 4 5 6 7 8 9 10 2S* 3 3 3 4 4 4 4 4 913W 764W 645W 0.022W W shunts 2S* VR2 value (R1) 4.95kW 2.25kW 1.95kW 1.36kW 1.47kW 1.36kW 1.1kW IC1b gain 12.5 siliconchip.com.au 6.25 5.55 4.16 3.33 4.16 3.57 Australia's electronics magazine 3.125 2.77 2.5 * S = in series. Alternatively, you can use two 0.05W resistors in series and set R1 to 1.93kW (¼HP) for a gain of 5.5 or 752W (½HP) for a gain of 2.75 August 2024  79 Fig.3: most components mount on the top side of the PCB. T1 and L1 are heavy, so both are secured to the PCB using cable ties. The large relay, RLY3, is attached to the board using screws and nuts, and will later be wired to CON1 and CON3. This diagram and Fig.4 are both shown at 90% of actual size. The red areas are where extra solder is added. LED2, is green while the remainder are red. LED1 and LED3 can be mounted vertically with 5mm of the leads projecting above the top PCB surface. LED2, LED4 and LED5 display the Power, Reset and Run status on the front lid via fibre-optic light transporters. Before soldering each LED, clip the LED bezel end piece for the fibre optic connection onto the LED, then solder it in place with the clip touching the PCB surface. CON1 to CON3 can be fitted now. CON1 can be installed either way around, but CON2 and CON3 must be orientated correctly. That is most easily done by plugging the screw terminal plug into each socket before mounting it to the PCB. For the 3-way terminal, CON2, the wire entry faces toward diode D5. For the 2-way terminal, CON3, the wire entry faces away from diodes D7 and D3. The next step is to install the relays. RLY1 and RLY2 directly mount onto the PCB, while RLY3 is held to it using M3 screws, washers and nuts, with 80 Silicon Chip each screw inserted from the underside of the PCB. The washers go under the nuts on top of the relay’s mounting feet. T1 can now be mounted onto the PCB. Its pins hold it in place, but we use a large cable tie to ensure it cannot move and break the transformer pins if it is dropped. There are slots in the PCB to accommodate the cable tie, to wrap around the transformer body and under the PCB after soldering it in place. Winding inductor L1 L1 is made using two powdered iron cores side-by-side. Use epoxy resin to glue the two cores together. Once the glue has set, wind on seven turns of 1.25mm-diameter enamelled copper wire. The winding direction is not important. The finished winding and core are mounted on the PCB with a cable tie securing the toroid to the PCB. This tie is fed through the slots in the PCB to wrap around through the centre hole of the core and under the PCB. Australia's electronics magazine Trim the wires to sufficient lengths to solder to the PCB pads, then strip the insulation off the ends of the enamelled wire. It’s generally best to do that with a sharp hobby knife (be careful not to cut your fingers!) or emery paper. Depending on the enamel used, you may be able to burn it off by holding a blob of molten solder over the wire ends. Make sure the enamel is entirely removed so you can make a good solder joint, then solder the wire ends to the pads for L1. Q1 can be installed now. Stand it above the PCB so there is about 1mm of lead projecting below the PCB to allow soldering. Because the PCB tracks near the IGBT are thin, the exposed, tinned PCB tracks at the emitter and collector should be built up with solder to lower the resistance. Final assembly The PCB is secured inside the enclosure base using M3.5 screws into the integral standoffs in the base. However, before attaching the PCB, the IEC siliconchip.com.au Fig.4: if all four 0.022W shunt resistors are soldered to the board, as shown here, the Controller will suit motors rated at 6-10A (1.5HP+, 1.08kW+). For lower-powered motors, fewer resistors are fitted, as per Table 1. For ¼HP and ½HP motors, make sure the two resistors are in series, not parallel. If three resistors are required, any three can be fitted. connector cutout will need to be made in the side of the enclosure. You will need to drill and shape holes in one end of the case for the IEC connector and Earthing screw. You might as well prepare the lid at the same time, which needs holes made for the GPO socket, Earthing screw and speed control potentiometer. Fig.5 is a guide for the required cutouts; it can be copied or downloaded and used as a template. The large cutouts for the mains GPO and IEC connector can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece and filing the job to a smooth finish. Alternatively, you can use a speed bore drill to remove a large portion of the required area and then file it to the final shape. The Earth screw positions are not critical. Use the wiring diagram (Fig.6) to decide where to place the holes. One 4mm hole is required on the lid, and one in the enclosure base. Two 3mm holes are needed to secure the IGBT (Q1) and BR1 against the side of the siliconchip.com.au The underside of the Motor Speed Controller’s PCB. There are five components that are soldered to this side, the four 0.022W shunts (shown in the left insert) and the 10kW resistor (shown at right). The extra through-hole resistor shown at the bottom of the PCB was only for our prototype, and is fitted on the topside with the final PCB. Australia's electronics magazine August 2024  81 Fig.5: the required holes in the lid and base of the diecast aluminium case. Ensure the IEC and GPO socket holes are shaped correctly (filed carefully to size) so they are not loose. The exact Earth screw positions are not critical, so they are not marked. enclosure. Temporarily place the PCB into the enclosure and mark where the holes for Q1 and BR1 are needed. The holes for Q1 and BR1 need to be slightly countersunk on the inside of the enclosure to provide a flat mounting surface. There must not be any sharp edges around the hole or any remaining swarf that could puncture the silicone insulating washer. 3.5mm diameter holes are needed for the fibre-optic LED bezels on the front panel. These are not directly above the LED position on the PCB to give the fibre optic cables room to flex in an ‘S’ shape when the lid is attached. Once the drilling and filing is complete, install the IEC connector using countersunk head 10mm-long M3 machine screws and nuts. The PCB can then be placed inside the case but wait to secure it to the corner posts. Q1 needs to be insulated from the enclosure using a TO-247-sized silicone insulating washer. Its package has an insulated hole, so no insulating bush is required to insulate the package from the screw. A 12mm-long M3 screw and M3 nut can be used to secure Q1 to the side of the enclosure. Check that the enclosure is insulated from all three of Q1’s leads by measuring the resistance between each lead and the enclosure. There should be high resistance reading in each case, in the megohms region. BR1 does not require an insulating washer since the metal tab on the back of the package is insulated from the internal diodes. Before attaching the mains GPO, you can print out the front panel label (Fig.7), available to download from our website at siliconchip.au/ Shop/11/436 Details on making a front panel are found at: siliconchip.au/ Help/FrontPanels Now wire everything up per Fig.6. All wiring must be run using mainsrated cable. Be sure to use 10A cable where indicated, and note that brown wire is used for the Active wiring and blue for Neutral. Green/yellow-striped wire must be used for the Earth wiring only, and the Earth lead from the IEC connector is attached via a crimp eyelet to the enclosure Earth. The wiring not marked as 10A can be lighter-duty 7.5A mains wire, such as for the speed potentiometer VR1, or use 10A wiring throughout. The IEC socket and Earth screw are on the lefthand side of the case. 82 Silicon Chip Australia's electronics magazine The terminals on relay RLY3 will be too tall for the lid to fit, so they need to be cut down, with the wires soldered directly to the shortened terminals and covered in heatshrink insulation. These terminals are brittle, so hold the lower part of the terminal with small flat-nosed pliers while you break off the top part with another set of pliers. The terminals will break at the wire hole location. Be sure to insulate all the connections with heatshrink tubing for safety, and cable tie the wires to prevent any wire breakages coming adrift, as shown in Fig.6. The Active and Neutral leads are secured to the GPO using cable ties that pass through the holes in its moulding. Use neutral-cure silicone sealant (eg, Roof and Gutter silicone) to cover the Active bus piece that connects the Active pin to the fuse at the rear of the IEC connector. Take great care when making the connections to the mains socket (GPO). In particular, be sure to run the leads to their correct terminals; the GPO has the A, N and E clearly labelled. Do the screws up tightly so that the leads are held securely. Similarly, make sure that the leads to CON1’s screw terminals are firmly secured. Warnings Almost all of the circuitry operates at mains potential, so it is dangerous to make contact with any part of the circuit when it is powered. The speed potentiometer connections are also at mains potential. siliconchip.com.au Fig.6: all wires must be mains-rated; the wires marked with an * need to handle 10A, while the others can be rated at 10A or 7.5A. Some adjustments can be made more safely by disconnecting the mains supply from some parts of the circuit. This leaves the circuit floating at mains Neutral potential instead of Active. You still need to be very careful, but the risk of electrocution should you touch the circuitry is much lower. Some adjustments will need to be made when the circuit is live. We recommend using a 1000V-rated screwdriver with a 0.4mm-thick, 2.5mm-wide flat tip. That size of screwdriver suits the trimpot adjustment screws and has a sufficient voltage rating to protect against electrical shocks. We used a Wiha 1000V screwdriver that has an insulated shank. Similarly, when measuring voltages in the circuit, use a 600V CAT III (or higher, eg, CAT IV) rated multimeter and probes. We provide indicator LEDs that show when the circuit is powered and live. So don’t touch the circuit when any LED is lit, and always unplug it siliconchip.com.au from the mains before working on it (except during the part of the setup where it needs to be operating). Another LED shows the PWM duty cycle by varying brightness with PWM duty. A separate LED shows when the speed potentiometer is rotated fully anti-clockwise. Finally, there is one LED that shows when the motor can be started. Testing Ensure that the mains power point you connect to when testing and adjusting the 180V DC Motor Controller is connected to an Earth-­leakage core balanced relay, also known as a Residual Current Device (RCD) or mains safety switch. This can be installed in the fusebox, as a separate unit within the power point or as a plug-in device. The RCD is designed to cut the power should you receive an electric shock that passes through your body to Earth. However, an RCD will not Australia's electronics magazine Errata: in Fig.2 last month, the labels for REG1 and REG2 were transposed. The top regulator should be REG2 (7815), while the middle one should be REG1 (7812). protect you if current flows through your body from Active to Neutral (eg, by touching two points in the circuit with different hands). Thus, it is a good idea to use one hand only when there is any possibility of making contact with the live circuitry within the Motor Controller. If you are building the Controller in a different arrangement than the one we described, eg, with the motor hardwired to it, any wiring that goes outside the enclosure must be run in sheathed mains-rated cable that is secured to the enclosure with cordgrip grommets. This includes the safety/ emergency stop switch wires. The safety/emergency stop switch must be mains-rated and enclosed in an Earthed enclosure with its contacts covered in heatshrink tubing and the wiring cable tied together. Treat all connections to it as if they are live! Additionally, the wires from the safety switch need to be secured to its enclosure with a cordgrip grommet. August 2024  83 Fig.7: this panel label is also available as a PDF download from the Silicon Chip website. It can be printed, laminated and attached to the lid. This panel is shown at 83.3% actual size, and so needs to be enlarged by exactly 20%. Initial settings that can be made with the power off include setting the torque trimpot to near 0W. This resistance can be measured between the Vt and Rt test points. IC1b’s gain is set by varying VR2’s resistance (referred to as R1) to provide the required current measurement output voltage at the rated current of the motor that’s used. Table 1 shows the resistance setting for R1 versus motor ratings and shunt resistances. We show values based on ¼HP increments from ¼HP through to 2½HP. This closely corresponds to 1A to 10A motor ratings in 1A steps. That’s because, for a 180V DC motor, each amp is 180W. Since 1HP is 746W, 180W is 0.24HP or near enough to 0.25HP. resistors in series to form a 0.1W shunt instead of the 0.022W shunts used for other ratings; in that case, less gain is required from IC1b. The gain for IC1b is set so that, at the full rated motor current, its output sits at 0.55V. For example, when the current shunt is 0.022W, and the motor is rated at 10A, the voltage across the shunt will be 0.22V at 10A. IC1b needs to amplify this to give the 550mV output, meaning a gain of 2.5. The formula for the required R1 resistance is (gain – 1) × 430W. That works out to 645W in this example. With the power off, connect your multimeter probes to the two R1 test points on the PCB and adjust VR2 for the value required for R1. Now insert IC1 and the remaining ICs in their sockets if you have not already done so. Shunt values Overload setting Note that the shunt resistance comprises series and parallel resistors to provide the required overall shunt resistance. For the 1A and 2A rated motors, you can use two 0.05W At the motor’s rated current, IC1b’s output delivers 0.55V. IC3d amplifies this by 4.68, giving a 2.57V output. VR6 provides adjustment of the current threshold (It) for motor Setting IC1b’s gain 84 Silicon Chip Australia's electronics magazine overload. To set the motor overload to 1.6 times the rated current, the ‘It’ setting should be 1.6 × 2.57V = 4.1V. This value assumes that the Vovl offset output from IC3d is set to 0V using VR5, which we will do later. The overload trip voltage needs to be set with the power on. Before applying power: 1. Check your wiring carefully and ensure all mains connections are covered in heatshrink tubing and the wiring is cable-tied. 2. Check the Earth connection between the enclosure and the Earth pin on the IEC connector. The reading should be steady and under 1W. 3. Install the fuse inside the fuse holder. Testing The initial testing and setting up can be done more safely by disconnecting the Active wire to BR1. This is done at CON1, by removing the wire between terminals 4 and 5 and only connecting the Active wire to terminal 5. Also disconnect the spade connector wire loop between CON5 and CON7. siliconchip.com.au The large relay’s terminals are cut down and the wires soldered and covered with heatshrink so the lid will fit. Because the circuit operates at mains potential, it is unsafe to make contact with any part of the circuit, including the terminals of VR1, when it is switched on, despite the above measures. Do not touch any part of the circuit except with the multimeter probes and 1000V-rated screwdriver. Attach the enclosure lid before switching on power for the first time. That will make it safer if something is wrong, such as a reverse-connected electrolytic capacitor or if a 16V capacitor is installed in a 25V position. Still, check those aspects again before fitting the lid and applying power. If all is quiet when power is applied (except for relays clicking), switch off the power and open the lid. Wearing safety glasses, switch on the power again and measure the AC voltage between Neutral (at terminal 3 of CON1) and the mains Earth connection to the enclosure. The reading should be no more than a few volts. You should read close to 230V AC between Earth and terminal 5 of CON1. If the Neutral reading is instead close to 230V AC, check that you have siliconchip.com.au wired up the IEC connector correctly. If the wiring is correct, your mains supply may have the Active and Neutral wires transposed. Have this corrected by an electrician before proceeding with testing the motor controller. Switching on power again, you should be greeted with power LED2 lighting to show that the +12 and -12V supplies are up. Check the regulators for the correct output voltages. There should be +12V between the 0V and +12V test points. Similarly, there should be +15V at the +15V test point and -12V at the -12V test point. These voltages should be within 5% of the designated voltages. That means between 11.4V and 12.6V for 12V, -11.4V to -12.6V for -12V and between 14.25V and 15.75V for +15V. Verify that when VR1 is fully anti-clockwise, LED4 is off and only switches on once the speed pot (VR1) is rotated clockwise slightly. It is important to test the Controller Australia's electronics magazine initially using a filament light bulb. A halogen 25-100W bulb is sufficient, eg, in a table lamp. This way, nothing bad will happen if the ‘motor speed’ oscillates; any changes in ‘speed’ can be seen by observing the lamp brightness. Setup and adjustment With the lamp connected, perform the following tests and adjustments. All voltage measurements below are with respect to the 0V test point. 1. Adjust VR3 for -7V at Vt. 2. Adjust VR1 for 0.5V at Vc. 3. Adjust VR7 so that LED3 is just lit, then back off anti-clockwise until the LED is off. Vs should measure 0.4-1.0V. 4. Adjust VR5 for a reading at Vovl as close to 0V as you can manage. 5. Adjust VR6 for 4.1V at ‘It’. This sets the motor overload threshold to 1.6 times its rating. Now switch off the power, unplug the unit and restore the Active connection between terminals 4 and 5 of August 2024  85 The assembled module, ready for mounting in the case. CON1. Also reconnect the crimp spade lead from CON5 to CON7. Make sure VR1 is set fully anti-clockwise and connect the lamp. Apply power and wait for RLY1 to switch off (indicated by LED4 switching off). Check that the lamp begins to glow at low speed settings and reaches full brightness with the potentiometer fully clockwise. Once the operation is successful with the lamp, switch off the power and test it with the motor. Verify that the motor speed can be controlled, noting that the motor will not start unless the speed potentiometer is rotated fully anti-clockwise first (LED4 off). Wait for RLY3 to be powered (LED5 lit) before bringing it up to speed. Test the motor under load at around 25-50% of full speed and adjust the Torque trimpot, VR4, so that the motor does not drop markedly in speed when a load is applied. Anti-clockwise rotation of VR4 increases the feedback control, meaning that more torque will be applied when the motor is under load. Too much speed compensation can cause the motor to speed up under load, so minor adjustments between tests are necessary to get it right. Note also that the torque adjustment will affect the Vs value set with VR7, which ensures the PWM output is zero when the speed potentiometer is brought fully anti-clockwise. Check this by repeating steps 2 and 3 above after adjusting VR4. Suppose the motor drops in speed too much under load even with 86 Silicon Chip maximum torque adjustment. In that case, the output from IC1b (current feedback) can be boosted by increasing the gain of this amplifier via clockwise adjustment of VR2. Again, make small adjustments between load tests. Increasing the gain of IC1b will also require increasing the overload threshold (It) using VR6 by the same percentage. Adding a reversing switch If you need a motor reversing switch, you can use a 3PDT switch, as shown in Fig.8. One suitable switch is the “Lovato 3PDT 3 Position 60° Motor Reversing Cam Switch”, rated at 20A. It has a knob actuator and is available from RS Components (Cat 8405624). Two poles of the switch are used to reverse the motor polarity. The third switch pole ensures the motor is disconnected from power during the switching. It does this by opening the safety switch connection at terminals 7 and 8 of CON1. This prevents the motor from being switched into reverse while the motor is running. After reversing, the motor can only be started once the speed pot is returned to its anti-clockwise position. If a safety/emergency stop switch is also used, this will need to connect in series with the reversing switch pole at terminal 8 of CON1. There is insufficient room inside the enclosure to install a reversing switch. Consequently, mains wiring for the motor connections and safety/ emergency stop switch will need to run outside the enclosure using 10A sheathed mains cable, with the cables secured to the enclosure using cordgrip grommets. The reversing switch must also be enclosed in an Earthed metal enclosure with cables secured using cordgrip grommets. Altronics H4280 grommets are suitable. Note that if you have an on/off switch in series with the motor wiring, the switch needs to be a double-pole, double-throw type (DPDT) so that one pole connects or disconnects the power to the motor, with the second pole connected in the same way as shown for the third pole in the reversing switch. That way, the motor can’t suddenly be reconnected, which could SC damage the Speed Controller. Fig.8: a 3PDT or 3P3T switch can be used to reverse the motor. The third pole (terminals 9-12) is used to shut down the Controller when the direction is changed. The speed pot needs to be reset to zero each time the switch is thrown before the motor will be powered again. Australia's electronics magazine siliconchip.com.au