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Electrolytic capacitor reformer and tester Last month we introduced our new electrolytic capacitor reformer and tester – ideal for anyone working with vintage radios, valve equipment or indeed the hobbyist who has gathered a collection of electrolytics over the years. Now you can not only test them, you can (usually!) breathe new life into them if they’ve suffered from the ravages of time! W ith the exception of the power supply, microswitch (S6) and of course the capacitor under test/reforming, virtually all of the circuitry and components used in the Electrolytic Capacitor Reformer and Leakage Meter are mounted on a single PC board measuring 222 x 120mm and coded 04108101. This is supported behind the transparent lid of the case – in fact, a modified storage organiser – which houses the instrument. As you can see from the photos and assembly diagrams, the main board is suspended from the lid of the enclosure and label (which becomes the instrument’s front panel) via four 25mm long M3 tapped spacers. The LCD display module mounts just above the centre of the main board on four 12mm long M3 tapped Nylon spacers (or two such spacers if you use the Altronics LCD module). The DC/DC converter’s step-up transformer T1 (wound on a 26mm ferrite pot core) mounts on the main board at upper left using a 25mm long M3 Nylon screw and nut, while voltage selector switch S1 also mounts directly Part 2: by JIM ROWE on the board at lower left. The only components not mounted directly on the main board are power switch S2, pushbutton switches S3-S5, the two test leads (fitted with alligator clips) and, as mentioned earlier, the microswitch. All switches are mounted on the front panel, with their rear connection lugs extended down via short lengths of tinned copper wire to make their connections to the board. All of these assembly details should be fairly clear from the diagrams and photos. To begin fitting the components on the main board we suggest you fit the fixed resistors. These are all 1% tolerance metal film components, apart from the 0.27Ω, 2.2kΩ and 8.2kΩ 5W resistors and the 2 x 1kΩ 1W resistors. When you are fitting all of the resistors make sure you place each value in its correct position(s), as any mixups may have a serious effect on the meter’s operation and/or accuracy. Check each resistor’s value with a DMM if you want to make sure of no mistakes. It’s also a good idea to fit the 1W and 5W resistors with their bodies about 2mm above the top of the board, rather than resting on it. That’s because these resistors can become quite warm during an extended ‘electro reforming’ test run. It’s logical to follow with the wire links, most of which are 0.4mm long, so they’re easily fashioned from resistor lead offcuts. There are quite a few of these links, of which five are located underneath the position where the LCD module is fitted later. Next place the eleven 1mm terminal pins in the board – two for each of the three test point locations, two for the DC input connection and three for the high voltage output (to the micro-switch and capacitor). Follow these with the sockets for IC1 and IC2 (both 8-pin sockets) and IC3 (an 18pin socket). After these are in place you can fit 25-turn trimpot VR1 at centre left and trimpots VR2 and VR3 at upper right. Next are the small low-value capacitors, followed by the two larger 470nF/630V metallised polyester units and finally the two high voltage elec- WARNING: SHOCK HAZARD! Because the voltage source in this instrument can be set to provide quite high DC voltages (up to 630V) and can also supply significant current (tens of milliamps), it does represent a potential hazard in terms of electric shock. We have taken a great deal of care to ensure that this hazard is virtually zero if the instrument is used in the correct way – ie, with the lid closed and secured – even to the extent of quickly discharging any capacitor when the lid is opened. However, if the safety switching is bypassed, especially when it’s set to one of the higher test voltages, it is capable of giving you a very nasty ‘bite’ should you become connected across the test clips or a charged high voltage capacitor. There are some situations where such a shock could potentially be lethal. Do NOT bypass the safety features included in this design. We don’t want to lose any SILICON CHIP readers to electrocution. 70  Silicon Chip siliconchip.com.au The completed reformer and tester built into its modified “storage organiser” case. The circuitry, including the test clips, is completely isolated when the lid is closed and any charge on the capacitor under test/reforming is bled away safely when the lid is opened. There is plenty of room inside the case for the 12V DC power supply and in this case its IEC lead, which in use emerges from a hole cut in the side of the case alongside the supply. trolytics, which lie on their side at the top of the board with their leads bent down by 90°. They are each held down using a Nylon cable tie which goes through the hole in the PC board and around the edge. Once the high voltage electros are in place you can mount the low voltage electros, three of which go at far right and the remaining 47F unit at lower centre just near TP2. Don’t forget to fit all of the electros with their orientation as shown in the PC board overlay diagram (Fig.3), as they are all polarised. Next fit the two relays, making sure that they too are orientated as shown in Fig.3. Then you can solder in voltage selector switch S1, which as you can see mounts with its indexing spigot in the ‘1:30’ position. Before you fit the switch you should cut its spindle to a length of about 12mm and file off any burrs, so it’s ready to accept its knob. After switch S1 has been fitted to the board, remove its main nut/ lockwasher/position stopwasher combination and turn the spindle by hand to make sure it’s at the fully antisiliconchip.com.au clockwise limit. Then refit the position stopwasher, making sure that its stop pin goes down into the hole after the moulded ‘11’ digits. Next refit the lockwasher and nut to hold it down securely, allowing you to check that the switch is now ‘programmed’ for the correct eleven positions – simply by clicking it around through them by hand. You’ll probably need to temporarily attach the knob first to get enough grip to turn it. If all is OK, remove the knob for now. The next step is to wind the step-up autotransformer T1. This might sound a bit daunting, but it’s not. You can find step-by-step instructions in the box titled ‘Winding Transformer T1’, which also explains how to fit the completed transformer to the main PC board. The final components With the transformer wound and fitted to the board, you’ll be ready to install diodes D1-D6. These are all polarised, so make sure you orientate each one correctly as shown in Fig.3. Also ensure that D1-D3 are the three 1N4148 diodes, D4 is the UF4007 and the two 1N4004 diodes for D5 and D6. When fitting the two zener diodes ZD1 and ZD2, note that they are NOT the same voltage – and of course they too are polarised. After the diodes install transistors Q1, Q2, Q4 and Q5, which are all TO-92 devices. Make sure that you fit the two BC337 (NPN) devices as Q1 and Q4, with the BC327 (PNP) devices as Q2 and Q5. You can follow these with voltage reference IC4, which is also in a TO-92 package. If in doubt, use a magnifying glass to confirm the type numbers. Next come REG1 and Q3, which are both in TO-220 packages. In this project they each lie flat on the top of the board with a 19mm-square (6073B type) heatsink underneath and with their leads bent down by 90 degrees at a point about 6mm away from the body. Each device is then held in position on the board using a 6mm long M3 machine screw and nut. These should be tightened before the leads are soldered to the pads underneath to prevent stress on the pads. Next fit LED1 to the board. It is located just to the right of the socket for IC1, with its cathode ‘flat’ side towards rotary switch S1. Note that it is fitted vertically, with its leads left almost at their full length – so that the bottom of the LED’s body is about 22mm above the top of the board. This should mean that the top of the LED’s body will just protrude from the matching hole in the case lid, after final assembly. The final component to be mounted directly on the board is the connector for whichever LCD module you are going to use. In the case of the Jaycar QP-5516 module, this will be a 14-way (7x2) length of DIL (dual inline) socket strip, fitted vertically at the left-hand end of the module position; whereas if you are using the Altronics Z-7013 module, you will need to fit a 16-way September 2010  71 12-15V DC INPUT + 1000 F 1000 F REG1 7805 4004 D2 VR2 2.4k 4148 10k 22 VR3 D5 D3 4148 TP1 LCD CONT 220 F + TPG POWER 10k RE MR OFER CITYL ORT CELE E GAKAEL R OTI CAPA C & RETE M T NERRU C CABLE TIE SECURES DC LEAD – S2 SET 2.49V REF RLY1 0102 © 10k 1M IC2 LM358 10nF 47 F 1k + 100nF TPG 6V2 ZD1 1k 2 22k 4 6.8k 1 2 5 11 6 S 2.0k 100 K 3.0k A T 100 7 8 9 2.4k 560 30 LED1 560 F 16 110 10 SET APPLIED VOLTAGE 150 270k 33 220 S1 4.7k TP2 PIC16F88 IC3 100nF 13 11 9 7 5 3 1 14 S5 3.0k 56 6.8k Q3 IRF540N NC 100nF 2.2k 820k BC327 VR1 50k 1k 1W T+ Q2 (NO) (NC) TPG TP3 1k 1W T– CABLE TIE SECURES 3-CORE FLEX TO MICROSWITCH 0.27  5W 1k 2.2k 5W ZD2 BC337 75k IC1 34063 1nF 75k Q1 2.2k 75k 4V7 680k 100k JAYCAR QP-5516 LCD MODULE 560 D4 UF4007 T1 COIL DECREM TIME INCREM TIME S4 !VH+ RLY2 100 2.2k 10k 100nF 75k COMMON 3 10180140 D1 4148 47 100k 390k 470nF 630V 470nF 630V 390k 4.7k D6 4004 NO 390k 8.2k 5W Q4 BC337 10k 10k 10k K A 100k TEST S3 Q5 BC327 + – 47 F 450V IC4 LM336Z -2.5 390k 100k + 100k – 47 F 450V CABLE TIE SECURES CAPACITOR (TEST CAPACITOR NEGATIVE) Fig.3: Apart from the 12V plugpack, interlock microswitch and test leads/clips, everything mounts on or is attached to the one large PC board, as shown here. The cable ties reduce the flexing on the soldered joints as the case is opened. 72  Silicon Chip length of SIL socket strip horizontally, along the lower long side. Once this connector has been fitted and its pins soldered to the pads underneath, you’ll be almost ready to mount the LCD module itself. All that will remain before this can be done is to attach to the board either four or two 12mm long M3 tapped Nylon spacers, in the module mounting positions. This will mean two at each end in the case of the QP-5516 module, or only one at each end in the case of the Z-7013 module. In each case attach the spacers using a 6mm M3 screw passing up through the board from underneath – but in the case of three of the four screws for the QP-5516 module, you’ll need to fit an M3 Nylon flat washer under each screw head as these screws are unavoidably close to tracks under the board. Next ‘plug’ a 7x2 length of DIL pin strip into the socket strip you have just fitted to the board for the QP-5516 module, or a 16-way length of SIL pin strip into the socket strip for the Z-7015 module. Make sure the longer ends of the pin strip pins are mating with the socket contacts, leaving the shorter ends uppermost to mate with the holes in the module. Now remove the LCD module from its protective bag, taking care to hold it between the two ends so you don’t touch the board copper. Lower it carefully onto the main board so the holes along its left-hand end (QP-5516) or along its lower front edge (Z-7015) mate with the pins of the pin strip, allowing the module to rest on the tops of the 12mm long nylon spacers. Then you can fit either one or two more 6mm M3 screws to each end of the module, passing down through the slots in the module and mating with the spacers. When the screws are tightened (but not OVER tightened!) the module should be securely mounted in position. The final step is then to use a finetipped soldering iron to carefully solder each of the 14 or 16 pins of the pin strip to the pads on the LCD module, to complete its interconnections. After this is done you can plug the three main ICs into their respective sockets, making sure to orientate them all as shown in Fig.3. Your PC board assembly should now be just about complete. Before finishing it off (ie, putting it in the case), we will run a few checks on it to make siliconchip.com.au Winding Transformer T1 Many constructors are put off projects which involve of the pot core, though, there’s a small plastic washer to winding a transformer but in most cases, it’s not too difprepare. This is to provide a thin magnetic ‘gap’ in the ficult a job and requires just a little care and attention pot core when it’s assembled, to prevent the potcore from to detail. saturating when it’s operating. In the case of the Electrolytic Capacitor Reformer and The washer is very easy to cut from a piece of the thin Tester, step-up autotransformer T1 has only 90 turns of clear plastic that’s used for packaging electronic compowire in all, with an initial primary winding of 10 turns nents, like resistors and capacitors. This plastic is very of 0.8mm diameter enamelled copper wire followed by close to 0.06mm thick, which is just what we need here. four 20-turn layers of 0.25mm diameter enamelled copSo the idea is to punch a 3-4mm diameter hole in a per wire to form the secondary. piece of this plastic using a leather punch and then use And as you can see from the coil assembly diagram a small pair of scissors to cut around the hole in a cir(Fig.4, below), all five layers are cle, with a diameter of 10mm. wound on a small Nylon bobYour ‘gap’ washer will then be bin which fits inside a standard ready to place inside the lower UPPER SECTION OF FERRITE ferrite pot core (bobbins are half of the pot core, over the POT CORE sold to match the cores). centre hole. Here’s the procedure: first Once the gap washer is in poBOBBIN WITH WINDING you wind on the primary ussition, you can lower the wound (10T OF 0.8mm DIAMETER ing 10 turns of the 0.8mm bobbin into the pot core around ENAMELLED COPPER WIRE WITH END BROUGHT OUT. diameter enamelled copper it and then fit the top half of the THEN START OF 0.25mm DIA wire primary, which you’ll find pot core. Your autotransformer ENAMELLED COPPER WIRE TWISTED TO IT, BEFORE will neatly take up the width should now be ready for mountWINDING 4 x 20T LAYERS of the bobbin providing you ing on the main PC board. OF SECONDARY. NOTE THAT ALL FIVE LAYERS wind them closely and evenly. To begin this step, place a SHOULD BE COVERED Then cover this first layer with Nylon flat washer on the 25mmWITH INSULATING TAPE) a 9mm-wide strip of plastic long M3 Nylon screw that will FINISH (OF SECONDARY) insulating tape or ‘gaffer’ tape, be used to hold it down on the to hold it down. board. Then pass the screw TAP (END OF PRIMARY, START OF SECONDARY) Now twist the start of the down through the centre hole START (OF PRIMARY) 0.25mm wire around the ‘finin the pot core halves, holding ish’ end of the primary winding them (and the bobbin and gap 'GAP' WASHER OF 0.06mm and proceed to wind on the first washer inside) together with PLASTIC FILM layer of the secondary – windyour fingers. ing in the same direction as you Then lower the complete aswound the primary, of course. sembly down on the upper left LOWER SECTION In this case you should find of the board with the ‘leads’ OF FERRITE POT CORE that 20 turns will neatly take towards the bottom, using the up the width of the bobbin, bottom end of the centre Nylon providing you again wind them screw to locate it in the correct closely and evenly. position. (ASSEMBLY HELD TOGETHER & SECURED TO After winding this first layer When you are aware that the PC BOARD USING 25mm x M3 NYLON SCREW & NUT) of the secondary, cover it with end of the screw has passed another layer of insulating through the hole in the PC tape. Then wind on another layer, again of 20 turns and board, keep holding it all together but up-end everything cover it with a layer of insulating tape as before. so you can apply the second M3 Nylon flat washer and Exactly the same procedure is then followed to wind M3 nut to the end of the screw, tightening the nut so that on the third and fourth layers of the secondary. the pot core is not only held together but also secured to Each of these extra layers should be covered with the top of the PC board. another 9mm-wide strip of plastic insulating tape just Once this has been done, all that remains as far as the as you did with the first layer, so that when all five laytransformer is concerned is to cut the primary start, ‘tap’ ers have been wound and covered, everything will be (primary finish/secondary start) and secondary finish nicely held in place. leads to a suitable length, scrape the enamel off their The ‘finish’ end of the wire can then be brought out of ends so they can be tinned and then pass the ends down the bobbin via one of the slots (on the same side as the through their matching holes in the board so they can be primary start and primary finish/secondary start leads) soldered to the appropriate pads. and your wound transformer bobbin should be ready to Don’t forget to scrape, tin and solder BOTH wires fit inside the two halves of the ferrite pot core. which form the ‘tap’ lead – if this isn’t done, the transJust before you fit the bobbin inside the bottom half former won’t produce any output. siliconchip.com.au eptember 2010  73 2010  73 SSeptember The finished PC board, ready for mounting in the case. While pushbutton switches S3, S4 and S5 are shown in position here for the photograph, they are normally not soldered in until the board is mounted on the front panel – they have to pass through the panel from above and are connected to the PC board via lengths of tinned copper wire. sure everything is according to Hoyle. Checkout and setup NOTE: the following checks MUST be done with S1 on a low voltage setting (say 35V or less). NEVER apply power to the unit with S1 on a higher voltage setting without the PC board fitted to the case and the safety interlock in place. If you connect the 12V DC plugpack to the mains and then switch on the power using S2, a reassuring glow should appear from the LCD display window – from the LCD module’s backlighting. You may also be able to see the Meter’s initial greeting ‘screen’. If not though, you’ll need to use a small screwdriver to adjust contrast trimpot VR3 until you get a clear and easily visible display. (VR3 is adjusted through the upper small hole just to the right of the LCD window.) After a few seconds, the display should change to the Meter’s measurement direction ‘screen’, where it tells you to set the appropriate test voltage (using S1) and also the test time period (using S4 and/or S5), before pressing the Start/Stop Voltage Application button (S3) to begin the test. Note that if you make no adjustments to the test time period using S4 or S5, the default time period will be 74  Silicon Chip 10 seconds. If you just set the test voltage and press S3 at this stage, without any capacitor connected to the alligator clips (make sure the alligator clips cannot short!), LED1 should begin glowing to indicate that the test voltage is being presented to the test terminals and the LCD display should change to read: Vtest=ON 0m09s Cap Lkg= 0.00A where the time displayed on the right end of the upper line will be decrementing to show the ON time remaining. Then when the remaining time falls to zero, you’ll hear a soft ‘click’ and LED1 will go dark to indicate that the test voltage has been removed. At the same time the top line of the display will change to read: Vtest=OFF 0m 0s while the lower line will remain unchanged. Assuming all has gone well at this point, your unit is probably working correctly. However if you want to set its calibration to ensure maximum accuracy of the readings, try connecting your DMM between the terminal pins TP1 and TPG (at upper right on the board, accessible via the gap between the board and front panel). You should get a reading of close to 2.5V and assuming this is the case try adjusting trimpot VR2 with a small screwdriver until you get a reading as close as possible to 2.490V. Now set your DMM to a range where it can read a voltage of 63V accurately and connect its probes between the Meter’s test terminals. Then turn S1 to the ‘63V’ position and press S3 to turn on the test voltage source. The DMM reading should quickly rise to read very close to 63.0 volts and if so there’s no need to go further. But if the reading is not within the range of 62.5 - 63.5V, you’ll need to bring it inside this range (and ideally to 63.0V) using a small screwdriver or insulated alignment tool passed down through the hole in the front panel midway between the test terminals, to adjust the setting of VR1. Once you set the test voltage on the 63V range in this way, all of the other voltage settings will be correct as well. Note that if you haven’t set the Meter’s timer to increase the testing time period from its default 10 seconds, the timer will turn off the test voltage after this time. So if you want to take your time to adjust the voltage to 63V using VR1, you might want to crank up the time period using S4, to keep the test voltage present for as long as you need. Once the 2.49V reference voltage and the 63V test voltage have been set in siliconchip.com.au this way, your Electrolytic Capacitor Reformer/Leakage Meter has been set up correctly and will be ready to be fitted into the case. Preparing the “case” As mentioned earlier, the case we have used is a little unusual. It’s sold as a “Storage Organiser” and is made by Trojan. Ours came from Bunnings Hardware for the princely sum of $9.95. It has a transparent hinged lid and in the “body” it has three rows of fixed dividers plus quite a number of movable dividers which fit into slots moulded into the fixed dividers. First determine where your PC board will lie inside the case. Use an enlarged photocopy of the front panel (see Fig.7) or a same-size copy of the PC board layout and use it on the outside of the case as a template for drilling. The left-to-right position is fairly unimportant (just make sure you leave enough room for the leakage current guide if you use the PC board layout diagram). However, you need to make sure that the PC board lies exactly in the space between the vertical dividers so that when the lid is closed, it fits! There are four holes to be drilled to mount the PC board and nine for controls/indicators. You don’t need to cut a slot for the LCD readout because the lid is transparent enough to read through it. (Yeah, we know, our photos show a cutout – we did that before we realised it was transparent enough! D’oh!) You will, however, need a cutout in the front panel label. We modified the case to accommodate the PC board by removing a 30mm deep by 215mm long section from one of the fixed dividers, then cut notches along the moulded slots about 10mm wide and about 25mm down from the top. The photo of our modified case gives a better idea. The PC board sits down in the removed divider section and along the slot notches each side. 25mm threaded standoffs then mount the PC board to Resistor Colour Codes o o o o o o o o o o o o o o o o o o o o o o o o o o o No. Value 4-Band Code (1%) 5-Band Code (1%) 1 1MΩ brown black green brown brown black black yellow brown 1 820kΩ grey red yellow brown grey red black orange brown 1 680kΩ blue grey yellow brown blue grey black orange brown 4 390kΩ orange white yellow brown orange white black orange brown 1 270kΩ red violet yellow brown red violet black orange brown 5 100kΩ brown black yellow brown brown black black orange brown 4 75kΩ violet green orange brown violet green black red brown 1 22kΩ red red orange brown red red black red brown 5 10kΩ brown black orange brown brown black black red brown 1 6.8kΩ blue grey red brown blue grey black brown brown 2 4.7kΩ yellow violet red brown yellow violet black brown brown 1 3.0kΩ orange black red brown orange black black brown brown 2 2.4kΩ red yellow red brown red yellow black brown brown 4 2.2kΩ red red red brown red red black brown brown 1 2.0kΩ red black red brown red black black brown brown 5# 1kΩ brown black red brown brown black black brown brown 2 560Ω green blue brown brown green blue black black brown 1 220Ω red red brown brown red red black black brown 1 150Ω brown green brown brown brown green black black brown 1 110Ω brown brown brown brown brown brown black black brown 3 100Ω brown black brown brown brown black black black brown 1 56Ω green blue black brown green blue black gold brown 1 47Ω yellow violet black brown yellow violet black gold brown 1 33Ω orange orange black brown orange orange black gold brown 1 30Ω orange black black brown orange black black gold brown 1 22Ω red red black brown red red black gold brown 1 16Ω brown blue black brown brown blue black gold brown (All 5W resistors will have values printed on them. # 2 1kΩ are 1W. ) siliconchip.com.au the underside of the lid, onto which we had previously glued the front panel and drilled the required holes (actually we melted the holes with a fine soldering iron but don’t tell the boss!). You’ll also need to mount the microswitch so that it is actuated when the lid is closed. The microswitch has two mounting holes through the body which make this fairly simple. It doesn’t have to be horizontal when mounted, in fact a little bit an angle makes the action on the actuator arm more certain. Holes also need to be drilled (or melted) through the divider walls to allow the HV wires (from PC board to microswitch/negative capacitor terminal) to pass through, along with the wires from the plugpack to the PC board. Power supply While we have built the prototype with a switch-mode 12V 2A plugpack, that’s not the only option. The supply can be virtually any 12-15V DC type with a minimum of about 1.5A output – just so long as it fits inside the case. If you use a plugpack, it obviously needs to be outside the unit when in operation. Therefore a small slot can be cut in the outside vertical wall of the case, just deep enough to allow the figure-8 cable to pass through when the lid is closed and locked. An alternative is to use a switchmode adaptor supply – one we had on hand was a 12V, 4A type which came from Altronics (Cat M8938). At 60mm wide, this particular supply fits nicely into the case, as our photo shows. Yet another, often much cheaper, alternative, is to use what is commonly sold as a “hard disk drive” supply – they’re usually about the same size as the above model (or a little less), and have a 12V, 2A DC ouput (along with a 5V 2A ouput which can be ignored). The latter supply is often sold with, or is available for, external hard disk drives and we’ve seen them advertised for less than $5 each! Both of these supplies generally have Capacitor Codes Value F value IEC Code EIA Code 470nF 0.47uF 474 470n 100nF 0.1uF 104 100n 10nF 0.01uF 103 10n 1nF 0.001uF 102 1n eptember 2010  75 2010  75 SSeptember LAMINATED LABEL GLUED TO UNDERSIDE OF CASE LID S2 S5 (WITH & S5 S4 S4 BEHIND) S3 CASE LID LED1 0.1  5W (Q3) LCD MODULE S1 (IC2, WITH IC3 BEHIND) (REG1) (RLY2) PC BOARD Fig.5: the PC board “hangs” from the case lid, which becomes the front panel. The label is on the inside of the lid. an IEC socket so a standard IEC power cable can be used. To do this, a 30mm hole could be cut in the case side to allow the supply’s IEC plug to fit through, which would then allow the supply to remain inside the case when in use. There’s even room to store an IEC cable inside the case in the area you would normally connect the capacitor under test/reforming. We used the front 1/3 of the case for the capacitor under re-forming or test and storage for the supply. One of the supplied orange dividers makes neat separate compartments for both the capacitor and the supply. Fitting the front panel Before proceeding to final assembly, tinned copper extension wires need to be soldered to the three pushbutton switches (S3-S5) which will go through the front panel from above and soldered to the underside of the PC board when it is in position. A tip here is to make all of the S3S5 extension wires slightly different lengths and longer than you’d think necessary (say from 30 to 50mm) so that when one goes in, it doesn’t pop out doing the next one! Unfortunately, the front panel is longer than a SILICON CHIP page so we haven’t been able to provide a samesize artwork as normal. The easiest way to get the panel is to download the PDF from siliconchip.com.au and print it. A colour printer is the best but you will need to be able to print A3 paper. To provide a little more protection and rigidity, we laminated ours (again, an A3 laminator is required), cut out all the holes (including the LCD hole) then glued it, face-side up, inside the lid of the case using spray adhesive. Hopefully all the holes you previously drilled in the panel will line up with those you drilled earlier. Allow the glue to dry and you should now be ready for the only slightly fid76  Silicon Chip dly part of the assembly operation: attaching the PC board assembly to the rear of the lid/front panel. This is only fiddly because you have to line up all of the extension wires from switches S2-S5 with their matching holes in the PC board, while you bring the lid and board together and at the same time line up the body of LED1 along with switches S1 and S2 with their matching holes in the front panel. Just take your time and the lid will soon be resting on the tops of the board mounting spacers. Make sure LED1 is poking through its hole, then you can secure the two together using the four remaining 6mm long M3 machine screws, with washers underneath the heads to protect the relatively soft plastic of the case lid. Now it’s a matter of soldering each of the switch extension wires to their board pads. Once they are all soldered you can clip off the excess wires with sidecutters. Place the power switch washer and nut on the thread and tighten (adjust the underside nut up or down as necessary so you don’t bow the plastic) and finally make sure the LED is poking through its front panel hole. Final wiring Power wiring (from the 12V power supply/plugpack) and high voltage wiring (to the microswitch and capacitor negative) can be attached to the PC stakes even with the board in position. It’s a bit fiddly and you have to be careful not to damage the plastic lid but the stakes are close enough to the outer edges of the PC board to make this possible. To protect the soldered joints, as much as possible, as the lid is opened and closed, we secured both the power supply and output cables to the PC board using small cable ties. Remember to run the various wires through the holes you have drilled in the divider walls before soldering to the PC board. The power supply connections are straightforward (remember the polarity!) but the high voltage wiring is just a bit more difficult. Note our comments earlier about the type of cable used for the high voltage cable: it must be rated at 250V or higher. • The wire from the HV+ terminal goes to the microswitch “NO” terminal. • The wire which connects to the 2 x 1kΩ 1W bleed resistors on the PC board goes to the microswitch “NC” terminal. • The wire from the microswitch “COM” terminal goes direct to the capacitor positive (red) alligator clip. • The wire from the T- terminal goes direct to the capacitor negative (black) alligator clip. By the way, if you find this description a bit confusing, refer to the diagrams of Figs. 3&5 and also the inside photos shown last month. These will hopefully make everything clear. Using it The new Electrolytic Capacitor Reformer is very easy to use, because literally all that you have to do is connect the capacitor you want to test between the alligator clips (with the correct polarity in the case of solid tantalums and electrolytics), close the lid, set selector switch S1 for the correct test voltage and then turn on the power using S2 (assuming you have already plugged in your plugpack supply). When the initial greeting message on the LCD changes into the ‘Set Volts & Test Time, Press Strt’ message, press S4 and/or S5 to set the time period to whatever you need. Then it’s simply a matter of pressing the Start/Stop Voltage Application button (S3) to start the test. What you’ll see first off may be a reading the capacitor’s charging current, which can be almost 20mA at siliconchip.com.au first (with high value caps) but should table attached to the front panel, the then drop back as charging continues. leakage currents for tantalum and aluHow quickly it drops back will minium electrolytics also never drop depend on the capacitor’s value. down to zero but instead to a level of With capacitors below about 4.7F, somewhere between about 1A and the charging may be so fast that the 9200A (ie, 9.2mA) depending on both first reading you see may be less than their capacitance value and their rated 100A, with the meter having immeworking voltage. diately downranged. So with these capacitors, you will If the capacitor you’re testing is of need to set the Meter’s testing time the type having a ‘no leakage’ dielectric period to at least 3 minutes to see if the (such as metallised polyester, glass, leakage current reading drops down ceramic or polystyrene), the current to the ‘acceptable’ level as shown in should quickly drop down to less than the front panel table and preferably a microamp and then right down to even lower. zero. That’s if the capacitor is in good If this happens the capacitor can be condition, of course. judged ‘OK’ but if the current never On the other hand if the capacitor drops to anywhere near this level this is one with a tantalum or aluminium indicates that it is in need of either oxide dielectric with inevitable leakreforming or replacement. age, the current reading will drop more What about low leakage (LL) slowly as the test proceeds. electrolytics? In fact it will probably take up to a minute to stabilise at a reasonably Well, the current levels shown in the steady value in the case of a solid table are basically those for standard tantalum capacitor and as long as 3 electrolytics rather than for those rated minutes in the case of a ‘good’ aluas low leakage. minium electrolytic. (That’s because So when you’re testing one which these capacitors generally take a few is rated as low leakage, you’ll need minutes to ‘reform’.) to make sure that its leakage current RDG_SiliconChip_0910.pdf 1 6/08/10 1:36 PM As you can see from the guide drops well below the maximum val- ues shown in the guide table. Ideally it should drop down to no more than about 25% of these current values. Another tip: when you’re testing non-polarised (NP) or ‘bipolar’ electrolytics, these should be tested twice – once with them connected to the alligator clips one way around and then again with them connected with the opposite polarity. That’s because these capacitors are essentially two polarised capacitors internally connected in series backto-back. If one of the dielectric layers is leaky but the other is OK, this will only show up in one of the two tests. Reforming old electros While reading the preceding paragraphs about testing capacitors, you’ve perhaps been wondering about the Reformer’s main function: reforming electrolytics that may have high leakage currents due to a long period of inactivity. How do you use it for this function? In exactly the same way as you use it for testing capacitors, except that for reforming you set the timer for a much longer testing time period. The idea here is that you still set S1 CC MM YY CM CM MY MY CY CY CMY CMY KK siliconchip.com.au September 2010  77 630V 450V 400V 250V DECREASE APPLICATION TIME START/STOP VOLTAGE APPLICATION INCREASE 100V 63V 16V 25V * Figures for Solid Tantalum capacitors are after a charging period of one minute. # Figures for Aluminium Electrolytics are after a charging/reforming period of three minutes. 9200 8230 5970 4110 3300 2900 2450 2060 1300 4700 F 1590 600 1000 F 730 1500 1340 1130 950 1900 2740 3790 4250 3850 3500 3130 2250 500 680 F 600 1300 1100 950 780 1560 1640 1470 1050 230 150 F 280 600 520 430 370 730 1470 1350 1200 900 50 100 F 230 500 420 330 300 600 460 570 530 420 380 460 340 270 50 11 15 F 13 8.0 8.0 10 F 5.0 5.0 4.7 F 19 6.0 35 38 25 78  Silicon Chip 100 25 18 230 320 290 250 60 15 12 8.0 23 1800 TEST VOLTS ON! 35V 10V 50V SELECT CAPACITOR WORKING VOLTAGE SET TEST VOLTAGE 270 240 220 5.0 Standard Aluminium Electrolytic# <3.3 F 5.0 5.0 17 10 8.0 6.0 50 59 54 48 15 19 24 17 16 36 22 20 18 9.0 7.0 6.5 10 47 F 10 1.5 6.8 F 2.0 3.0 4.0 14 19 17 15 12 7.5 5.0 3.5 3.0 1.0 Solid Tantalum* < 4.7 F 1.5 2.5 LEAKAG E C URREN T SH OULD BE ZERO FOR ALL OF TH ESE TYPES, AT RATED VOLTAG E Ceramic, Polystyrene, Metallised Film (MKT, Greencap etc.), Paper, Mica POWER SET 2.49V REFERENCE SET LCD CONTRAST ELECTROLYTIC CAPACITOR RE-FORMER & TESTER 450V 400V 250V 100V 63V 50V 35V 25V Maximum leakage current in microamps  A) at rated working voltage 16V 10V TYPE OF CAPACITOR CAPACITOR LEAKAGE CURRENT GUIDE 630V SILICON CHIP 320mm Fig.6: the front panel, which incorporates the leakage table, is too big to fit on the page, so is reproduced at exactly 75%. If you photocopy this at 133% (which in this case you can do without infringing copyright) it will come out right size. Obviously, you’ll need a copier that can handle A3 paper. Alternatively, you can download the PDF file from siliconchip.com.au You’ll still need a printer that can handle A3 paper! for the capacitor’s rated voltage but simply crank up the testing time period using S4 until it’s set for either 30 or 60 minutes. Then connect the capacitor to the alligator clips (making sure of the polarity) and finally press the Start/Stop Voltage Application button (S3) to start the test/reforming operation. Because the metering part of the instrument will continue to make measurements during the reforming period, this allows you to keep track of the leakage current as it slowly falls from its initial high figure (which may well be up in the region of 20mA). This is due to the oxide dielectric inside the electro slowly regrowing (reforming) as a result of the current passing through it. Needless to say if the current readings don’t fall, even slowly, the electro concerned is beyond being reformed and should be scrapped. On the other hand if the current readings do fall significantly but still don’t come down to an acceptable level, this indicates that the electro will probably benefit from another reforming operation. There’s no problem about giving a capacitor repeated reforming operations, provided that it doesn’t get overheated. In fact, significant heating is really a sign that the electro is beyond reforming and is not worth any further rescue efforts. So this is the basic procedure, when dealing with electrolytics: 1. First give it a standard 3-minute test run at rated voltage and see if the leakage current tapers down to an acceptable level during this time. If it does, the capacitor is OK. 2. If the current doesn’t taper down significantly and/or the capacitor becomes overheated, it is beyond help and should be discarded. 3. If the current does taper down significantly but doesn’t reach an acceptably low level, it can be regarded as a candidate for reforming. Give it a test/reforming run of 30 or 60 minutes. 4. At the end of the reforming run, test it again with a standard 3-minute test period. If the leakage current is now in the acceptable range (according to the guide on the front panel), the capacitor has successfully reformed and is now OK. But if it hasn’t quite finished reforming, it would be worth giving it another 30 or 60-minute session to see if this will ‘do the trick’. Errata In the parts list published last month, no mention was made of the mains power adaptor. As discussed in this month’s text, you’ll need a 12-15V DC supply at a minimum of about 1.5A. A more robust supply (ie higher current output) won’t hurt but it does need to be able to fit into the case! Also, six (not two) small cable ties are needed, the extras to secure the cables from the PC board to the microswitch/test leads and 11, not 10 PC pins are required. siliconchip.com.au All you need to know about . . . electrolytics! Most Silicon Chip readers So electrolytics have large ETCHED & ANODISED will be aware that all capacicapacitance because of these ALUMINIUM FOIL (ANODE) tors consist of two electrodes three factors, the very high separated by an insulating surface area of the anode, THIN OXIDE FILM ON ANODE IONISED ELECTROLYTE = ACTUAL CATHODE dielectric. the very thin aluminium oxide (THIS IS THE (IN PAPER SEPARATOR) DIELECTRIC) It’s the dielectric which dielectric and the relatively allows the capacitor to store high dielectric constant of energy (ie, a ‘charge’) in an around 8.5. ETCHED ALUMINIUM FOIL (APPARENT CATHODE) electric field between the The anodising process was two electrodes. The capacioriginally referred to as “formtance is directly proportional to the surface area of the ing” as in forming the oxide layer. electrodes on either side of the dielectric, and inversely The capacitor is wound with the etched/anodised foil, proportional to the thickness of the dielectric itself. So a paper separator and the non-anodised aluminium foil to achieve a high capacitance the electrode area must which becomes the negative electrode. The capacitor be as large as possible, while the dielectric must be as windings are usually then immersed in a bath of electhin as possible. trolyte and connected to a power supply to “re-form” the There’s also another factor which determines the anodised layer on the positive foil which is inevitably capacitance: the dielectric constant ‘k’ of the dielectric damaged during the winding process. material. The capacitance is again directly proportional After that, the windings have their terminations conto this property, so to achieve a high capacitance you nected to an aluminium can in the case of the negative need to use a dielectric material with as high a k value electrode and to the positive terminal for the anode. The as possible. Examples are polyester/Mylar with a k of can is sealed with a rubber bung and then it is recon3.0 and mica with a k value of 6.0. nected to a power supply for a final re-form and leakage Electrolytic capacitors were developed about 90 years current test. ago in an effort to produce high value capacitors which It should be noted that the electrolyte layer is critical were at the same time much more compact than other to the performance of the capacitor. Because it is a types. Over the years they have been greatly improved liquid, it can fill the etched pits in the oxide layer. This but they are still not quite as reliable and they don’t have means that the actual cathode is in intimate contact with the very low leakage of other capacitors such as mica, the dielectric layer, minimising dielectric thickness and ceramic or polyester. therefore maximising capacitance. As you can see from the diagram of Fig.7 (above), both New electrolytic capacitors typically have a shelf life electrodes in an electrolytic capacitor are made from of many years but the older they get, the higher their thin aluminium foil and between them is sandwiched a leakage current becomes as the oxide layer on the alusheet of paper soaked in a conducting liquid or ‘elecminium anode gradually deteriorates, due to the lack of trolyte’ (often sodium borate in aqueous solution, with a polarising DC voltage. In most cases, though, such additives to retard evaporation). capacitors can be rejuvenated by a re-forming process So superficially it would seem that we have a pair of whereby they are connected to a DC supply via a suitconducting electrodes separated not by an insulating able current limiting resistor. dielectric but by a sheet of paper soaked in conductive Initially, when the DC voltage is applied, the leakage electrolyte. current will be quite high but it should come down within But before the capacitor is assembled, the aluminium a minute or so to a value which is less than the capacifoil which is to become the anode (positive electrode) tor’s specified leakage current at the rated voltage. This has its surface etched in a caustic soda solution to project makes that process easy and safe for electrolytic greatly increase its surface area. This process covers capacitors with a wide range of voltage ratings, in addition the surface with an array of microscopic pits, which can to measuring the capacitor’s leakage current. have a total effective surface area of up to 60 times So that’s what is inside an electrolytic capacitor and greater than the original unetched area for high voltage that’s why it’s able to provide a very high capacitance electrolytics and even higher for low voltage electros. in a surprisingly small package. The main drawback of The etched aluminium foil is then subjected to an electrolytics is that they always exhibit at least a small anodising process, whereby a very thin aluminium oxleakage current – as shown in the front panel table. So they ide layer covers the surfaces of all of the microscopic are really only suitable for use in circuits where this small pits. This aluminium oxide is not only an insulating leakage current does not upset circuit operation. Luckily dielectric but it also has a relatively high k value of 8.5. SC this still gives them a great many applications. + – siliconchip.com.au September 2010  79