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Brownout Protector for Induction Motors By JIM ROWE Brownouts occur when the mains voltage drops to a very low level, say below 100VAC and this causes incandescent lamps to be very dim or “brown”. But as well as making your lights go dim, brownouts can cause induction motors to burn out because they cannot start properly. Y EARS AGO, BROWNOUTS were quite rare and generally confined to rural districts where the power lines had very long runs. A falling tree or an electrocuted possum might cause the mains voltage to drop to a low level and lights would go dim. This has always been a hazard for the induction motors used in pumps and refrigerators. Nowadays though, because the electricity grid is running much closer to total capacity, brownouts can be experienced much more commonly in the cities and suburbs. Our own offices in the Sydney suburb of Brookvale have had brownouts 34  Silicon Chip on a number of occasions in the last few years. Each time one has occurred, we have made sure that the air conditioner, fridges, compressors and other machinery in the building were turned off until full AC mains supply was restored. Had we not done so, all the motors in that equipment were liable to burnout. So how many motors in your home are at risk right now if a brownout was to occur? The list can be quite long: fridge, freezer, washing machine, dishwasher, air conditioner, pool pump, spa pump and perhaps one or two garage door openers; typical of many homes. All this equipment could attempt to turn on during a brownout and the motor(s) would probably burn out. Maybe your insurance policy covers motor burnouts but you would need to read the fine print. The insurance company might also look askance at your claim if there was more than one motor burnout or if the appliances were more than a few years old. The problem is that if induction motors try to start when the mains voltage is very low, they will never come up to correct speed and they will consequently draw very heavy currents. Unless they are turned off within a minute or so, they are very siliconchip.com.au likely to burn out their windings. heavy duty relay to perform the The risk applies to all induction switching. motors in appliances which can The relay contacts have a conswitch on at any time, as in refrigtinuous current capacity of 30A A low cost brownout protector for single phase erators, airconditioners, water/ and an inrush current capacity 230VAC induction motors with power ratings up to sewer pumps on rural properties of 65A, ensuring that it is more 2300W. and the other appliances listed than capable of switching loads Features include an adjustable voltage threshold, above. of up to 2300W (= 10A at 230V). switch-on delay and indication of both normal But you can take out your own The circuit also has a time power and brownout conditions. “insurance” against this possidelay of approximately five bility by building our Brownout seconds after the mains voltage Maximum control power: 2300W Protector. drops below the threshold level, Switch-on delay: 5 seconds (approx) It monitors the AC mains voltbefore the relay switches off age and disconnects power to power to the motor. Standby power consumption: <5W with relay on the appliance when the voltage There is also built-in hysBrownout threshold voltage: typically set to 200V drops below a preset level, only teresis, to make sure that the reconnecting it when the voltage mains voltage has to rise above returns to its normal level. the threshold level by about 10V This would make it cheaper to build before the motor power is switched This project is a considerably revised version of the Brownout Protec- multiple units, to protect each vulner- back on again. This ensures that the tor published in our December 2008 able appliance in a home. relay is prevented from “chattering”, Hence this new Brownout Protector or rapidly switching on and off if the issue. That project worked well but the is smaller and will cost less to build, mains voltage lingers at the threshold original kit and PCB is no longer avail- while still offering all of the features level. able and we’ve had requests asking of the 2008 design. These include the ability to adjust Circuit operation if we could come up with a revised version which would be physically the low-voltage switching threshold The full circuit is shown in Fig.1. It (typically set to 200VAC), plus a uses only a small number of low-cost smaller and lower in cost. Specifications INPUT CABLE MAINS TERMINAL STRIP OUTPUT CABLE E E N N A F1 10A A SLOW BLOW RLY1 REG1 7812 T1 15V/3VA K 7.5V ~ K GND D1 A + – 7.5V 230V WARNING: WIRING & COMPONENTS IN THIS SHADED AREA MAY BE AT MAINS POTENTIAL. CONTACT MAY BE FATAL! OUT IN BR1 W04 470F 25V A POWER ~ LED2 K 2 TP1 8 1 IC1a IC1: LM358 SET VR1 SO DC VOLTS AT TP1 = (Vmains/100) E.G., 230V/100 = 2.3V SET VR2 SO DC VOLTS AT TP2 = (Brownout Volts/100) E.G., 200V/100 = 2.0V 100k 10k ZD1 3.9V BROWNOUT PROTECTOR MK2 C 6 A IC1b E K 7 2.2k B 100nF C Q2 BC337 LEDS Q1 BC337 E 4 VR2 50k B D3 5 TP2 K K A 470 BC337 A B ZD1 A E D1–D2: 1N4004 K Fig.1: the circuit has only a few low-cost components, with the exception of the relay, all mounted on a single PCB. It’s designed to disconnect any motor-driven appliance if the mains voltage drops below a preset level. siliconchip.com.au K 10k 10F 16V 560 3  TPG +~~– VR1 50k A BROWNOUT +12V 100F 16V 2.2k A 10F 16V  LED1 W04 SC 100F 16V D2 2.2k 120k 2016 30A AC CONTACTS +12V A K D3: 1N4148 A K C 7812 GND IN GND OUT July 2016  35 In contrast, the measured averaged voltage across VR1 was 3.7V with the relay on and 3.8V with the relay off, a variation of just over 2.5%. This is important because in the worst case, the brownout detector needs to respond to an actual variation in the mains voltage from 216VAC (the normal minimum mains voltage) to 200VAC (the switching threshold). This is a variation of only 7.5% and we don’t want the circuit being confused by variations in the supply waveform. Trimpot VR1 is included so that the sample voltage fed to IC1a (which is connected as a unity gain buffer) can be set to exactly 1/100th of the mains AC voltage value. To give an example, if the mains voltage is 230VAC, VR1 is adjusted so the DC voltage at the output of IC1a (ie, at TP1) is exactly 2.3V. This is part of the calibration procedure and just why we do this should become clear shortly. The voltage at TP1 is fed to the noninverting input (pin 5) of IC1b, which is connected as a comparator. A nominal 3.9V reference voltage is provided by zener diode ZD1, which is fed via a 560Ω resistor from the +12V supply. Trimpot VR2, connected across VR2 – SEC 2 100F REG1 7812 1 (HEATSINK) TP1 10F 10k C 2016 100k BC337 4148 2.2k 470 VR2 50k 10107161 TPG 100nF BROWNOUT PROTECTOR A TP2 ZD1 3.9V 560 CABLE TIES A 2.2k K 2.2k D2 4004 COIL CON2 RLY1 RLY1 Q2 BC337 COIL 10k 100F + SY-4040 4004 + VR1 50k 10F 120k D1 Q1 30A CONTACTS 470F D3 N MAINS OUTPUT CABLE SEC 1 POWERTRAN 102 C M6 7015A 240V/7.5V+7.5V 16170101 TRANSFORMER ROTCETORP TUONWORB E ~ IC1 LM358 FI FUSE HOLDER CON1 HEATSHRINK SLEEVES ~ ~ – ~ + PRIMARY T1 CABLE TIES OUTPUT CABLE GLAND BR1 W04 + MAINS INPUT CABLE + (UB1 BOX) INPUT CABLE GLAND + 100µF capacitor form an averaging filter to give a lower voltage (Vp x 0.636 x 50kΩ ÷ 170kΩ = ~3.6V). But why go to all this trouble rather than just monitoring the DC voltage across the 470µF main filter capacitor? After all, if the mains voltage varies, the voltage across the 470µF capacitor will vary in proportion, won’t it? The reason for using this averaging filter method is twofold. First, the actual AC waveform of the mains supply is usually “flat topped” due to the loading of gas discharge lighting (eg, fluorescents) and the capacitor-input switchmode power supplies used in most of today’s computers and other electronic equipment. Using the peak of the waveform to represent the actual mains voltage is not sufficiently accurate because the degree of “flat topping” varies during the day, depending on whether it is a peak or off-peak period. Second, when the relay switches on and off, it causes a considerable variation in the voltage across the 470µF main filter capacitor. For example, we measured a voltage of 16.1V across this capacitor when the relay was energised (on), but around 18.2V when the relay was off – a variation of more than 10%. + components. These include dual op amp IC1, two BC337 transistors (Q1 and Q2), a 12V regulator (REG1) and the heavy-duty relay RLY1. Power for the circuit is derived from the mains via a small 15VAC 3VA stepdown transformer, T1. This drives bridge rectifier BR1, with diode D1 used to couple the bridge output to the 470µF filter capacitor. The resulting nominal 19V DC is then fed to the input of regulator REG1. The output of REG1 then provides the 12V DC to power IC1, the 12V relay and both LED1 and LED2. To detect a brownout condition, the circuit needs to monitor the AC voltage from the transformer secondary winding. But we don’t do this directly; instead we monitor the rectified DC waveform at the output of BR1 and the anode of D1. This is filtered using the 120kΩ resistor and the 100µF capacitor across trimpot VR1. The resulting DC voltage across VR1 is about 3.6V. Note that this voltage does not necessarily track the 19V or so that appears across the 470µF main filter capacitor. This is because the 470µF capacitor charges up to the peak value of the rectified 15V waveform, whereas the 120kΩ resistor, trimpot VR1 and K LED2 BROWNOUT A LED1 POWER Fig.2: same size diagram showing the component overlay on the PCB, along with the mounting of the board and various hardware in the UB1 jiffy box. Note the extensive use of cable ties to hold mains wiring securely in place. 36  Silicon Chip siliconchip.com.au sets the switching threshold for IC1b, with its wiper connected to IC2b’s inverting input (pin 6) and to TP2. This allows the voltage at pin 6 to be set to about 2.0V, representing a brownout threshold detection point of 200VAC. So with a normal mains voltage, the voltage at pin 5 of IC1b will be 2.3V (230VAC÷100). This voltage is higher than the 2.0V at pin 6 and as a result the output of IC1b will be high (close to +12V). This switches on transistor Q1, which powers relay RLY1. The relay contacts then supply power to the appliance connected to the Brownout Protector’s output cable. When IC1b’s output is high, diode D3 will be reverse biased and so the 100kΩ resistor connecting back to pin 5 has no effect on circuit operation. However, should the mains voltage drop just below 200VAC, the voltage at pin 5 of IC1b will go below the 2.0V threshold set at pin 6 and so output pin 7 will go low. This will switch off transistor Q1 and the relay, disconnecting power from the appliance connected to the output cable. Diode D2 quenches the back-EMF from the relay coil when its magnetic field collapses, protecting Q1 from damage. Simultaneously, transistor Q2 switches on to light the brownout indicator LED2 – connected to the +12V supply via a 2.2kΩ resistor. Hysteresis When IC2b’s output is low, diode D3 conducts and pulls pin 5 even lower than 2.0V due to the voltage divider action of the 100kΩ and 10kΩ resistors. For example, if the voltage at TP1 is at slightly less than +2.0V, the output of IC1b will be very close to 0V. The anode of D3 will be at about +0.6V and so the divider action caused by the 10kΩ resistor connecting to +2.0V and the 100kΩ resistor connected to +0.6V will give a voltage at pin 5 of ((2.00.6V) x 100÷110) + 0.6V, or +1.87V. This is a drop in voltage of 130mV. So instead of pin 5 now being at +2.0V, the action of the 100kΩ resistor, diode D3 and the 10kΩ resistor reduces the voltage by about 130mV, to +1.87V. Before IC1b’s output can go high again, the mains voltage would have to rise by the extra amount to make up this 130mV difference. This requires an increase in mains voltage of 13VAC, to around 213VAC. In practice, because the average voltage at TP1 is higher when the relay is off compared to when it is on, the extra voltage required from the mains for the relay to switch back on again is around 10VAC. This voltage difference effect is called “hysteresis”, and is included to prevent the relay from rapidly switching on and off at the brownout threshold. Provided that the mains voltage remains below the brownout threshold, the relay will remain off. In fact the relay remains off at any voltage below the threshold level, including voltages down to 0VAC (ie, a true blackout). A power-on delay is included so that the relay only switches on about five seconds after power is applied. This delay is due to the values of the 120kΩ and 100µF filter components that monitor the average voltage from rectifier bridge BR1. These are sufficiently large so that it takes time for the 100µF capacitor to charge up to above the voltage provided at TP2. This delay is also important to allow for the inevitable momentary drop in mains voltage caused by high surge currents every time an induction motor starts up. Normally, these high currents only last a second or two, depending upon the appliance – and we want to be sure that they do not cause the Brownout Here’s a photo of showing the same things as the drawing at left. All exposed mains wiring (eg, to relay, fuse, etc) is insulated with either appropriate crimp connector shrouds or, in the case of the fuseholder, heatshrink tubing. siliconchip.com.au July 2016  37 Protector to erroneously switch off the power. Construction The Brownout Protector is housed in a standard low cost UB1 jiffy box, measuring 158 x 95 x 53mm. All of the parts except for the mains fuseholder and mains switching relay RLY1 are mounted on a small PCB, coded 10107161 and measuring 85 x 76mm. This mounts inside the right-hand half of the box, using four 15mm long M3 tapped Nylon spacers and eight M3 x 6mm long screws. Because this is a mains device, it’s essential to use Nylon spacers and relatively short screws to maintain insulation integrity between the inside of the box and the outside world. Relay RLY1 mounts in the left-hand half of the box, using two M4 x 10mm long Nylon screws, flat washers, lockwashers and M4 hex nuts. Two cable entry glands, used to secure the mains input and output cables, mount in the end of the box, with a 3AG safety fuseholder between them. The Active (brown) wire from the mains input cable solders directly to one of the fuseholder terminals while the other fuseholder terminal is connected to the Protector’s PCB via a short (50mm) length of mains (brown) cable, cut from the input cable. Both soldered joints are covered with with heatshrink sleeves for safety. All connections between the input and output cables and the Protector’s PCB are made via a four-way barrier terminal strip – although only three of the terminals are actually used. The mains active connections to the contacts of RLY1 are made using 6.5mm insulated crimp connectors, which slide down over the relay contact lugs. The connections to the coil of the relay (RLY1) are made via two short leads terminated with 4.8mm insulated crimp connectors at the relay ends, and connecting to a small two-way terminal strip (CON2) at their PCB ends. All of these off-board wires are secured together using cable ties, as shown in both the overlay/wiring diagram of Fig.2 and the photograph alongside. Also shown in this diagram and photo are the two indicator LEDs, which are mounted near the front edge of the PCB with their leads bent by 90° so that 38  Silicon Chip the LEDs become visible via two 3mm holes drilled in the front of the box. This overall assembly setup should all be fairly clear from the internal photos along with the overlay/wiring diagram. Building it Begin construction by fitting all of the components to the PCB in the usual order: first the fixed resistors, followed by the non-polarised capacitor and then the polarised electrolytic capacitors – making sure the latter are fitted with the correct orientation. After this mount the diodes (again watching their polarity) and bridge BR1, followed by transistors Q1 and Q2 and then IC1. Then fit regulator REG1, which mounts horizontally on a small Ushaped heatsink with its three leads bent down by 90° at a distance of 7mm from the body of the device so they pass down through the matching holes in the PCB. A 10mm long M3 screw and nut are used to clamp the tab of REG1 to the heatsink and also both of them to the PCB. Next solder the two trimpots to the PCB, orientating them as shown in Fig.2. Then fit the four-way barrier terminal strip CON1, making sure all four of its connection pins are soldered securely to the pads under the PCB so the terminal strip is held firmly in place. Install the smaller two-way terminal block CON2 for the relay coil connections, along with the pair of wires connecting this and the relay coil. While this connection is low voltage, the wire is in an area with lots of mains connections, so its insulation should be rated at 250V. This is followed by the largest component of all: power transformer T1. Take care again to solder all seven of its connection pins to the pads under the PCB, so the transformer will be held firmly in place. The final items to be fitted to the PCB are the two LEDs, which should each have both their leads bent down by 90° at a distance of 9mm away from the body. These are then soldered to the appropriate pads on the PCB with the axis of the LEDs and their leads as close as possible to 7.5mm above the PCB. This is to allow them to protrude slightly through the matching holes in the box after final assembly. When you are bending the LED leads before soldering them to the PCB, you need to make sure that they’re being bent the correct way – so the longer anode lead of each LED will be able to pass through the right-most hole in the PCB. Your PCB assembly can be placed aside while you prepare the box for final assembly of the project as a whole. There are only 11 holes to be drilled in the main part of the box. You’ll find full details of all of the holes in the drilling diagram, which you can download from www.siliconchip.com.au We suggest that you drill all the holes first with a 3mm drill, then enlarge holes D with a 3.5mm drill and holes E with a 4mm drill. You can also enlarge holes B and hole C at the same time, and then use an 8mm drill to enlarge them further. Then holes B and C can be enlarged to their final sizes of 12.5mm and 15mm using either a “stepped” drill bit or a tapered reamer. When all holes have been drilled, remove any swarf on both sides of each hole using a countersink bit or a small rat-tail file. Although there are no holes to be drilled in the box lid, you might like to attach to it a small dress panel like the one in our photos. The artwork for this is shown in Fig.3, or it too can be downloaded and printed in colour from www.siliconchip.com.au We printed this out on plain paper, hot laminated it and then cut it out to size using sharp scissors. Then it An extension cord is cut to form the mains input and out leads. siliconchip.com.au was attached to the box lid using thin double-sided adhesive tape (spray adhesive also works well!). Final assembly Final assembly should not give you any problems if you do the steps in the following order. First, mount relay RLY1 in the bottom of the box on the left, with its larger staggered mains connection lugs towards the left as shown in Fig.2. Secure it in position using two M4 x 10mm Nylon machine screws with flat washers, lockwashers and nuts above each of the relay’s mounting flanges. Make sure you tighten both screws up firmly using a screwdriver and nut driver or spanner. Now fit the four M3 tapped 15mm long Nylon spacers to the bottom of the box on the right, using M3 x 6mm screws passing up through holes A from underneath. Do not tighten these screws up too firmly at this stage though, because the spacers may need to be nudged slightly during the next step, which is to lower the PCB assembly down into that side of the box until it’s sitting on the spacers. Make sure you don’t damage the two LEDs or bend their leads too much when you’re lowering the board into place. It should now be possible to line up the LED bodies with the holes in the front of the box and just poke them through so they can be seen from outside the box. You should now be able to fit the four remaining M3 x 6mm screws near the corners of the PCB, to mesh with the holes in the tops of the four spacers, thus fastening the PCB assembly in position. Complete the tightening of the lower screws as well, to ensure that the PCB assembly is firmly locked in place. Now fit the two cable glands into holes B in the left-hand end of the box, fastening them in position using a pair of small spanners – one to hold the hex nut moulded into the body of the gland, and the other to turn the actual mounting nut on the inside. Now you can fit the safety 3AG fuseholder into the 15mm diameter hole in the centre of the left-hand end of the box, tightening up its mounting nut with a small spanner while holding the fuseholder’s outer barrel with your hand so it doesn’t rotate far enough to make its connection lugs too difficult to access for soldering the active wires. Next take the 3m long 230V/10A extension cord and cut it in two equal lengths. The half with the 3-pin plug on the end will be used for the Protector’s input cable, while the other half (with the 3-pin socket) will be used for the output cable. Cut off a length of around 150mm from the cut end of the input cable, which will be used to provide the two short lengths of brown (active) mains lead for making the connections between the fuseholder, barrier terminal strip and one of the relay contact lugs. Now remove about 90-100mm of the outer sheath from the cut ends of both the input and output cables, freeing the three internal wires. Remove 10-15mm of insulation from these six wires. Then remove the outer clamping ‘nuts’ from the two cable glands, and slip each nut onto one of the cut ends of the cables (outer end first). After this you need to push the end of each cable into and through its corresponding cable gland, until about 10mm of the cable’s outer sheath is protruding through the gland into the interior of the box. Then bring the outer clamping nut for that gland back up the cable and thread it back onto the gland’s outer thread, tightening it up to make sure the cable is being clamped securely in The two LEDs are mounted at rightangles to the PCB so they just poke through appropriate holes drilled in the side of the case. For a detailed case drilling diagram, refer to www.siliconchip.com.au siliconchip.com.au MaxiMite miniMaximite or MicroMite Which one do you want? They’re the beginner’s computers that the experts love, because they’re so versatile! And they’ve started a cult following around the world from Afghanistan to Zanzibar! Very low cost, easy to program, easy to use – the Maximite, miniMaximite and the Micromite are the perfect D-I-Y computers for every level. Read the articles – and you’ll be convinced . . . You’ll find the articles at: DETAILS VISIT SILICONCHIP.COM.AU FOR ALL Maximite: Mar, Apr, May 2011 siliconchip.com.au/project/mite miniMaximite: Nov 2011 Maximite: Mar, Apr, Colour MaxiMite: Sept,May Oct 2011 2012 miniMaximite: NovAug 2011 MicroMite: May, June, 2014 Colour MaxiMite: Oct 2012 MicroMite Mk Sept, 2: Jan 2015 MicroMite: May, Jun, Aug MicroMite LCD Backpack: Feb2014 2016 plus loads of Circuit Notebook Boat Computer (MicroMite Backpack):ideas! Apr 2016 plus more MicroMite and ideas! PCBsmany & Micros availableprojects from PartShop Want to know more? Go to siliconchip.com.au PCBs & micros available from SILICON CHIP OnLine Shop July 2016  39 Parts List 1 UB1 size jiffy box, 158 x 95 x 53mm 1 Double-sided PCB, 85 x 76mm, code 10107161 1 240V to 15V power transformer, 3VA, PCB mounting (Powertran M7015A or similar) 1 SPST relay with 12V coil and 30A/230V contacts (Jaycar SY-4040 or equivalent) 2 M4 x 10mm machine screws, nuts, flat washers and lockwashers 2 6.5mm spade connectors (for relay contacts) 2 4.8mm spade connectors (for relay coil) 1 Panel mounting 3AG fuseholder, ‘very safe’ type (Jaycar SZ-2025 or equivalent) 1 10A slow-blow 3AG fuse cartridge 2 Panel mounting cable glands for 3-6.5mm diameter cable (Jaycar HP-0720 or similar) 2 20mm lengths of 5mm heatshrink sleeving 6 Nylon cable ties, 100-150mm long 1 3m long 230V 10A extension cord (cut in half to use for the Protector’s input and output cables) 4 15mm M3 tapped Nylon spacers 2 10mm M3 Nylon machine screws 8 6mm M3 machine screws 1 10mm M3 machine screw 3 M3 hex nut 1 U-shaped TO-220 heatsink, 19 x 19 x 9.5mm 1 4-way PCB mounting barrier terminal strip (Altronics P-2103 or equivalent) 1 2-way PCB mounting terminal block 3 1mm PCB terminal pins Semiconductors 1 LM358 dual op amp, DIL8 (IC1) 1 7812 12V regulator (REG1) 2 BC337 NPN transistors (Q1, Q2) 1 3mm green LED (LED1) 1 3mm red LED (LED2) 1 W04 400V/1A bridge rectifier (BR1) 2 1N4004 1A diodes (D1, D2) 1 1N4148 signal diode (D3) 1 3.9V 1W zener diode (ZD1) Capacitors 1 470µF 25V RB electrolytic 2 100µF 16V RB electrolytic 2 10µF 16V RB electrolytic 1 100nF MKT polyester Resistors (1/4W, 1%) 1 120kΩ 1 100kΩ 2 10kΩ 3 2.2kΩ 1 560Ω 1 470Ω 2 50kΩ multi-turn vertical trimpots 40  Silicon Chip that position and can’t be pulled out. This should all be repeated for the second (output) cable. (If you want to prevent any possibility of the gland becoming loose and not providing proper cord anchorage, you can put a drop of super glue on the thread before tightening the nut. But don’t do this until you have made sure the project is fully working because it will make the nut impossible to remove!) Next cut off about 40mm from the input cable’s brown (Active) lead and strip off about 6mm of the insulation from the end of the remainder. This will allow it to be soldered to the rear lug of the fuseholder – but before doing so, slip a short length (say 20mm) of 5mm diameter heatshrink sleeving over the lead and slide it up to the end near the cable’s outer sheath. This is to avoid it shrinking prematurely. Solder the end of the lead to the fuseholder lug, and after the solder joint has cooled down you should be able to slide the heatshrink sleeve back up the lead until it has covered both the joint and the metal lug. Then apply heat to the sleeve using the side of your soldering iron’s tip (without touching it), so that it shrinks securely in position. A similar job needs to be done on the brown (Active) lead of the output cable, only in this case it needs to be shortened by about 50mm, again with 6mm of the insulation stripped from the remainder, and then fitted with a 6.5mm insulated crimp connector to attach to one of the relay contact lugs. The blue (Neutral) and green/yellow (Earth) are all left at their full length of 90-100mm but with about 12mm of insulation stripped from the end of each one. The bared wires of the two Earth leads should then be twisted tightly together. The same needs to be done with the two Neutral leads. They should then be fitted under the clamping plates of the matching terminals on the barrier strip, after the screws have been loosened. The Earth leads need to be fitted under the rearmost ‘E’ terminal screw, of course, while the Neutral leads go under the next ‘N’ screw. Make sure you retighten each screw firmly after the wires are in place under the screw’s clamping plate. The next step is to remove the brown (Active) lead from the 150mm length of cable you cut from the ‘input’ cable earlier, and cut it into two 75mm lengths. One of these will be used to make the lead connecting from the side lug of the fuseholder to the active (A) terminal of the barrier strip, while the other will be used to make the lead connecting the same barrier strip terminal to the second contact lug of RLY1. It’s probably easiest to strip 6mm of insulation from one end of each lead, and 12mm from their other ends. The shorter bared end of one lead will then be soldered to the side lug of the fuseholder, with another 20mm length of 5mm heatshrink sleeving slipped over the joint and lug once they have cooled down, then heated once more to shrink over them securely. The bared end of the other short brown lead should then be fitted with a 6.5mm insulated crimp connector, to attach to the second contact lug of the relay. Finally the wires on the 12mm bared ends of these two short active leads should be twisted tightly together and then clamped under the ‘A’ terminal screw of the barrier strip. Finally, cut two 60mm lengths of insulated hookup wire, strip off about 6mm of insulation from both ends, and then fit one end of each wire with a 4.8mm insulated crimp connector to mate with the coil lugs of RLY1. The other end of each wire should Resistor Colour Codes       No. 1 1 2 3 1 1 Value 120kΩ 100kΩ 10kΩ 2.2kΩ 560Ω 470Ω 4-Band Code (1%) brown red yellow brown brown black yellow brown brown black orange brown red red red brown green blue brown brown yellow violet brown brown 5-Band Code (1%) brown red black orange brown brown black black orange brown brown black black red brown red red black brown brown green blue black black brown yellow violet black black brown siliconchip.com.au Same-size “cover all” front panel artwork for the Brownout Protector, to fit a standard UB1 jiffy box. If you prefer, you can cut out the inner (gray) section and centre that on the lid. (This panel, along with a hole drilling diagram, can also be downloaded from www. siliconchip. com.au). 230V AC INPUT 10A FUSE (3AG) 230V AC OUTPUT SILICON CHIP BROWNOUT PROTECTOR FOR 230VAC INDUCTION MOTORS BROWNOUT be clamped under one of the two screw terminals on the smaller terminal strip (CON2) at the left front of the PCB. All of your off-board wiring will then be complete, and all that remains is to fit about six cable ties to the leads to prevent them from ‘wandering’ if one of the solder joints, screw terminals or crimp connectors should come adrift. The suggested positions of these cable ties are shown in Fig.2. Unscrew the front insert of the fuseholder and fit it with a 10A slow-blow 3AG fuse cartridge and then screw it all back together again. Don’t attach the lid to the box yet, because the two trimpots on the PCB still need to be adjusted to set up the Protector correctly. Setup procedure There’s not a great deal involved in setting up the Protector correctly, but you are going to need at least one good digital multimeter (DMM) – and ideally two of them. As the setting up must be done with the lid left off the box, be very careful while you’re doing it. Be especially careful not to touch either the active (A) or neutral (N) screw terminals on the barrier strip – this could be fatal! All other “bitey bits” should of course be shrouded or covered in heatshrink. Plug the Protector’s input cable siliconchip.com.au into a convenient power outlet and switch on the power. You should see LED1 glowing to show that the circuit is powered up. Don’t worry too much about whether LED2 also glows as well, or if you hear the relay click on instead. But if you want to make sure that the power supply circuit is working correctly, you can use your DMM (set to measure say 20V DC) and check the voltage between test point TPG and pin 8 of IC1. If you get a reading of +12V, this will confirm that all is well. Next, set your DMM to measure at least 250VAC and very carefully touch the tips of its test leads to the screws of the ‘A’ and ‘N’ terminals on the main barrier strip, making sure you don’t touch these yourself in the process, or touch them together. Note the reading and then remove the test leads. Now set the DMM to measure DC volts again, and clip its input leads to test points TPG and TP1, to measure the voltage between them. You’re aiming to get a reading here of 1/100th the AC mains voltage you just measured, ie, 2.30V DC if your measured mains voltage was 230VAC. The odds are that the reading you get will be some distance away from this correct figure, either higher or lower. Not to worry though; all you need to do is adjust trimpot VR1 (just to the POWER right of transformer T1) until the voltage reading rises or falls to the correct figure or as close as possible to it. Since the mains voltage can vary somewhat at different times of the day, the above measurements of the mains voltage and the DC voltage at TP1 should ideally be done at the same time – using two different DMMs. However, if you only have a single DMM just try to make one measurement soon after the other and perhaps recheck them both again after you believe you’ve found the right setting for VR1. Just make sure you remember to reset the DMM correctly to change from high voltage AC to low voltage DC and vice-versa! The remaining setup adjustment is even simpler. All that’s needed is to clip the DMM test leads to test points TP2 and TPG and adjust trimpot VR2 until you get a reading of 2.0V. (If you want the brownout voltage threshold to be other than 200VAC, set this to 1/100th the voltage you want). Once this second setup adjustment has been made, you can turn off the power, remove the DMM test leads and then screw the lid onto the Protector’s box to complete its assembly. Your Brownout Protector should now be ready to begin work, protecting the induction motor from damage in the event of one of those nasty power SC brownouts. July 2016  41