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Mk.3 Lead-Acid Battery Zapper and Desulphator Here is a revised version of the popular Lead-Acid Battery Zapper featured in the May 2006 issue of SILICON CHIP. It is now separate from the Battery Condition Checker and much easier to build. At the same time it has been revamped for more reliable long-period operation with 6V, 12V & 24V batteries. By JIM ROWE T HE LEAD-ACID Battery Zapper & Condition Checker published in the May 2006 issue has been a very popular project but since it was published a few shortcomings have become apparent. The metering circuit on the Battery Condition Checker sometimes had a tendency to “lock up” on the 6V range and the current pulse Disclaimer! Not all batteries can be rejuvenated by zapping. They may be too heavily sulphated or may have an open-circuit cell connection. Nor can the zapper restore a battery which is worn out; ie, one in which the active material on the plates has been severely degraded. Depending on the battery, it is also possible that any rejuvenation effect may only be temporary. 26  Silicon Chip loading circuit was sometimes un­ stable with 24V batteries, if the power switching MOSFETs were at the high end of their transconductance range. In addition, the test current pulse amplitude was fixed at about 30A; OK for car batteries but too high for batteries used in motorbikes and for sealed lead acid (SLA) batteries. Many readers also found the combination of the Battery Zapper & Condition Checker fairly tricky to assemble and disassemble because it was a bit of a shoe-horn job into the plastic case. In view of this, we recently decided to develop improved versions of both the Checker and the Zapper but to feature them as separate projects, to make them easier to build and use. The revised Battery Condition Checker is planned for publication next month. What the Zapper does First of all, let’s have a quick recap about zapping and what it’s all about. Lead-acid batteries have been used to store electrical energy for over 170 years – ever since Gaston Plante built the first one back in 1834. But lead-acid batteries are not without their faults. Probably their main drawback is that they tend to have a relatively short working life, typically no more than about three years although with care, they can last much longer than that. So why such a short life? Well, every time energy is drawn from a leadacid battery, lead and sulphate ions from the electrolyte combine and are deposited on the plates in the form of soft lead-sulphate crystals. Then when the battery is recharged, these crystals dissolve again in the sulphuric acid electrolyte. At least MOST of them redissolve – but not all. Even if the battery is never over-discharged and always recharged promptly after it has been discharged, a small proportion of the lead sulphate crystals tend to remain on the plates, siliconchip.com.au where they harden into crystals of a much less soluble and less conductive “hard” lead sulphate. The formation of these hard lead sulphate crystals gradually reduces the energy storage capacity of the battery, both by masking the active areas on the plates and also by reducing the concentration of lead and sulphate ions in the electrolyte. This “sulphation” effect has been known about for many years. It’s also well known that the effect happens much faster if a battery is overdischarged, left in a discharged state for long periods, or frequently undercharged. Batteries mistreated in these ways tend to have a particularly short working life. For a long time, sulphation was regarded as non-reversible and batteries that had lost too much of their capacity from it were simply junked. This was not only wasteful but caused an environmental problem, because siliconchip.com.au LITTLE GEM DIGITAL MULTIMETER 37.25 v WOW WOW WOW WOW ZAPPER WOW V + + – – METER ZAPPING 20A DIGITAL MULTIMETER WOW WOW SILICON CHIP A WOW WOW WOW  WOW 2A COM +V – + LEAD-ACID BATTERY ZAPPER/DESULPHATOR + + FUSE 3A BATTERY FU SE – 24V BATTERY CHARGER 6V/12V ON ON + – + BATTERY CHARGER CHARGER – – MIGHTY QUICK BATTERY CHARGER 0 1 2 3 4 + – 5 BATTERY + – Fig.1: here’s how the Battery Zapper is connected to a battery and charger. The multimeter monitors the zapping pulses and should be set to a range of 100V DC or more. In addition, make sure that the Battery Voltage switch (S1) is set in the correct position for the battery you’re going to be zapping. July 2009  27 Parts List 1 ABS Jiffy box, UB2 size (197 x 113 x 83mm) 1 PC board, code 04107091, 185 x 100mm 3 SPDT mini toggle switches (S1S3) 2 speaker box binding posts, red (Jaycar PP-0434 or equivalent) 2 speaker box binding posts, black (Jaycar PP-0435 or equivalent) 1 Premium binding post, red (Jaycar PT-0460 or equivalent) 1 Premium binding post, black (Jaycar PT-0461) 1 M205 LV panel-mounting fuseholder 1 3A slow blow M205 fuse cartridge (F1) 2 6073B type TO-200 heatsinks (HS1, HS2) 1 8-pin DIL IC socket 1 220µH air-cored inductor (L1) both lead and sulphuric acid are highly toxic materials. Around the middle of last century though, farmers in rural areas discovered that they seemed to be able to resuscitate sulphated batteries and extend their life by zapping them with the high-voltage pulses from their electric fence controllers. They didn’t quite know how this method worked but kept using it simply because it did. Then in 1976, the US Patent Office granted a patent to William H. Clark of Salt Lake City, Utah, for a method 2 1mH air-cored inductors (L2, L3) 3 Nylon cable ties, 250-300mm 4 M3 x 25mm tapped spacers 6 M3 x 6mm machine screws, pan head 4 M3 x 6mm machine screws, countersunk head 8 M3 flat washers 2 M3 hex nuts 1 400mm length 1mm tinned copper wire 1 300mm length 0.7mm tinned copper wire Semiconductors 1 555 timer (IC1) 1 BC327 PNP transistor (Q1) 1 IRF540N MOSFET (Q2) 2 6.8V 1W zener diodes (ZD1,ZD2) 1 30V 1W zener diode (ZD3) 1 27V 1W zener diode (ZD4) 1 5mm red LED (LED1) of charging lead-acid batteries by means of narrow high current pulses – claimed to dissolve the lead sulphate crystals and hence prolong battery life. Since then, a number of designs for pulse-type battery rejuvenators or “zappers” have appeared in electronics magazines around the world. We should point out that there is still argument and controversy about whether or not the sulphation of flooded lead-acid batteries can be reversed. That in turn means there is still argument about the effectiveness +12V + K L2 1mH – A SWITCH (Q2) 28  Silicon Chip + – 470 F Fig.2(a): during the first phase of the circuit’s operation, current flows from the battery (and/or battery charger) and charges a 470mF electrolytic capacitor via 1mH inductor L2. of zapper-type pulse rejuvenators. However, many people have reported achieving a useful amount of rejuvenation on badly sulphated batteries, using zappers – including our earlier designs. That’s why we’re describing this new version. At the same time, we should also point out that this zapping process does not appear to work with sealed lead acid (SLA) batteries with a “gel” electrolyte. So we don’t recommend building the Battery Zapper to try rejuvenating this type of battery. L2 1mH K L1 220 H A CAPACITOR CHARGING PHASE Resistors (0.25W, 1%) 1 1MΩ 1 470Ω 5W wirewound 1 270kΩ 1 150Ω 1 27kΩ 1 100Ω 1 15kΩ 1 15Ω 5W wirewound 1 6.8kΩ I pulse (D3) A Capacitors 1 470µF 63V low ESR RB electrolytic 1 470µF 16V low ESR RB electrolytic 1 470nF 100V MKT polyester 1 100nF 100V MKT polyester 1 22nF 100V MKT polyester 3 10nF 100V MKT polyester 1 4.7nF 100V MKT polyester +12V FROM BATTERY AND/OR CHARGER I charge (D3) 2 1N4148 diodes (D1,D2) 1 BY229-200 fast recovery diode (D3) 2 UF4003 ultra-fast diodes (D4,D5) SWITCH (Q2) B L2 1mH K 12V (D3) L1 220 H I transfer A – + 470 F ENERGY TRANSFER PHASE Fig.2(b): next, switch Q2 is closed for 50ms, and current flows from the capacitor into L1. As a result, the energy stored in the capacitor is transferred to the inductor’s magnetic field. L1 220 H 470 F SWITCH (Q2) C DISCHARGE/PULSE GENERATION PHASE Fig.2(c): finally, switch Q2 opens again, interrupting the inductor current and causing a high-voltage pulse across the inductor with the polarity shown. The green arrow shows the discharge current path. siliconchip.com.au 24V BATTERY S1 VOLTS 6/12V 100 K 470 F 16V LOW ESR 100nF 27k K A A BATTERY 470  5W A ZD1 6.8V 1W LED1 ZD2 6.8V 1W K L2 1mH AIR K D3 BY229-200 A 7 6 D1 K 8 4 6.8k 3 IC1 555 A A Q2 IRF540N 4.7nF E B C K D G A S Q1 BC327 CHARGE ON/OFF S3 CHARGER + 10nF 100V D5 UF4003 A 150 15  5W D4 UF4003 K 1 10nF L3 1mH AIR L1 220 H AIR 5 2 22nF 100V K D2 BATTERY + 10nF 100V  A 270k S2 F1 3A K 15k A ZD3 30V 1W ZD4 27V 1W METER + K 470 F 63V LOW ESR 470nF 100V 1M METER – CHARGER – BATTERY – D1, D2: 1N4148 A K D4,D5: UF4003 A SC  2009 K ZD1–ZD4 A K K A BY229-200 BC327 LED IRF540N K D B E C K LEAD-ACID BATTERY ZAPPER MK3 G A D S Fig.3: the circuit uses 555 timer IC1 to turn MOSFET Q2 on for 50µs every 1ms (ie, at a 1kHz rate). Transistor Q1 turns on and shorts Q2’s gate to ground each time IC1’s pin 3 output switches low to ensure a fast turn off, while zener diodes ZD3 and ZD4 form an over-voltage protection circuit for Q2, which has a maximum voltage rating of 100V. It’s also worth noting that even on flooded lead-acid batteries, pulse desulphation is not quick. It can involve tens or even hundreds of hours to achieve a significant amount of rejuvenation. How it works As with our earlier units, the new Battery Zapper converts some of the energy from the battery itself (usually aided by a battery charger) into narrow high-voltage pulses which are fed back to the battery. This is done using the basic circuit configuration shown in Fig.2, which also shows its three operating phases. In the first phase (A), current flows from the battery and/or charger through 1mH inductor L2 and charges a 470µF capacitor connected between the inductor’s lower end and earth (battery negative). This phase lasts for about 950µs – long enough for the capacitor to charge up to the battery voltage. siliconchip.com.au At the end of this charging phase, switch Q2 (a power MOSFET) is closed for about 50µs (B), shorting the lower end of 220µH inductor L1 to ground and effectively connecting it right across the charged 470µF capacitor. As a result most of the energy stored in the capacitor is transferred into the inductor’s magnetic field. Hence this second phase is known as the energy transfer phase. The third phase (C) begins when switch Q2 is opened again. This breaks the inductor’s transfer current, which causes a high voltage back-EMF pulse to be generated across L1 with the polarity shown. Fast recovery diode D3 then feeds this high voltage pulse back to the battery, as shown in Fig.1(c). The third phase is therefore known as the discharge/pulse generation phase. Circuit details Refer now to Fig.3 for the full circuit details of our new Lead Acid Battery Zapper. You should now be able to identify this basic pulse generation circuit in the centre of the diagram. The discharging switch Q2 is now shown in its true form as an IRF540N power MOSFET, which we’re using here as a fast electronic switch. Virtually all of the circuitry to the left of Q2 is used to switch it on and off repeatedly, so that the pulse generating circuit produces a stream of zapping pulses. The pulses used to switch Q2 on and off are generated by IC1, a 555 timer. This is configured as an astable oscillator running at about 1kHz but with an output consisting of narrow positive pulses about 50µs wide, with spaces of about 950µs between them (ie, a 1:19 mark-space ratio). Each of these narrow pulses is used to turn on Q2, with diode D2 and transistor Q1 used to ensure that Q2 is switched both on and off as rapidly as possible. So Q2 is turned on for 50µs, then off for 950µs and so on. The 150Ω resistor in series with Q2’s gate is included to July 2009  29 UF4003 6.8k F S K BT229-200 D4 L2 1mH A D3 + ZAPPING LED1 METER- CABLE TIE 15k Q1 BC327 63V 22nF +B 9002 © FU SE 3A CHARGER BATTERY S2 S1 10nF BAT VOLTS 10nF 470  5W DI CA-DAEL YRETTA B 3K M REPPA Z 19070141 BATTERY- F1 BATTERY+ CABLE TIE 470 F S3 +C L3 1mH 15  5W S CHARGER+ 100 METER+ 1M 150 D2 4148 F S 470nF 10nF 4.7nF 27k 4148 270k ZD1 ZD2 D5 +M L1 220 H D1 470 F 27V UF4003 IC1 555 6V8 ZD4 30V Q2 IRF540N 100nF 6V8 ZD3 CHARGER- CABLE TIE F Fig.4: follow this parts layout diagram to assemble the PC board and make sure that all polarised parts are orientated as shown. The large inductors (L1-L3) are secured to the board using plastic cable ties which pass through holes on either side. suppress any tendency for it to oscillate during the switching transitions. That’s all there is in the basic zapping circuit. Now let’s look at the refinements. Zener diodes ZD1 and ZD2 are included to prevent the supply voltage for IC1 from rising above 13.6V, espe30  Silicon Chip cially when the Battery Zapper is being used with a 24V battery. They do not conduct any significant current when 6V batteries are being zapped and for 12V batteries they only serve as a limiter for any zapping pulses which find their way back from the cathode of D3, via the 100Ω series resistor. Note that switch S1 inserts a 470Ω 5W resistor in series with the 100Ω resistor when the unit is being used with a 24V battery, to limit the dissipation in ZD1 and ZD2. Zener diodes ZD3 and ZD4 form an over-voltage protection circuit for Q2, which has a maximum voltage rating of 100V. These zener diodes limit the maximum pulse voltage to about 70V under all conditions. Pulse level monitoring D5 is an ultra-fast diode which forms part of a simple half-wave rectifier circuit with the 1MΩ resistor and 470nF reservoir capacitor. These provide a DC voltage proportional to the maximum pulse amplitude between the “Meter” terminals, to allow monitoring the pulse level with a standard (high-impedance) digital multimeter. LED1 indicates when the Battery Zapper is generating pulses and also gives a rough idea of their amplitude. Because the pulses are quite narrow, diode D4 is used to charge the 22nF capacitor to their full voltage (less the battery voltage across the 470µF capacitor) and the LED is able to draw a steady current from the capacitor via the 6.8kΩ resistor. This allows LED1 to glow fairly brightly, without taking too much of the energy in the zapping pulses. Fuse F1 is provided mainly to protect inductors L2 and L1 against damage in the event of Q2 developing a short circuit or being switched on continuously due to a fault in IC1 and its associated components. The circuitry at upper right is to allow safe connection and disconnection of the unit to a battery (via switch S2) and also to allow safe connection or disconnection of a standard battery charger to the battery at any time, via switch S3. Inductor L3 acts as a choke for the zapping pulses, preventing the charger from absorbing them and possibly being damaged, while the 10nF capacitors across both S2 and S3 are spark suppressors. The 15Ω 5W resistor between L3 and S3 is there to limit the current that can be drawn from the charger, preventing damage should the battery develop a short circuit during zapping. Construction To make the new Battery Zapper as easy as possible to build, virtually all the components are mounted on a PC siliconchip.com.au This view shows the fully assembled PC board. Note that the three toggle switches would not normally be mounted on the board at this stage but are instead fitted with extension leads and mounted on the lid of the case – see text. Warning! (1) This circuit generates highvoltage pulses which could easily damage the electronics in a vehicle. Do not connect it to a car battery installed in a vehicle. (2) Hydrogen gas (which is explosive) is generated by lead-acid batteries during charging. For this reason, be sure to always charge batteries in a well-ventilated area. board coded 14107091 and measuring 185 x 100mm. This PC board has rounded cut-outs in each corner so it will fit snugly inside a standard UB2size ABS utility (Jiffy) box. The only components which don’t mount directly on the PC board are switches S1-S3, the fuseholder for fuse F1 and the various input terminals. All of these off-board components mount on the box lid (which becomes (3) Never connect high-current loads directly to a battery’s terminals. This can lead to arcing at the terminals and could even cause the battery to explode! Note too that the electrolyte inside lead-acid batteries is corrosive, so wearing safety glasses is always a good idea. the front panel) and are connected to the board beneath via short lengths of tinned copper wire, as you can see from the parts layout diagram of Fig.4 and the cross-section diagram of Fig.6. Begin assembly of the PC board by fitting the wire links. There are only two of these and they’re both only 10mm long (horizontal section), so they are easily made from resistor lead off-cuts. After the links, fit the (4) This unit is not suitable for use with SLA batteries. Table 1: Resistor Colour Codes o o o o o o o o o o siliconchip.com.au No.   1   1   1   1   1   1   1   1   1 Value 1MΩ 270kΩ 27kΩ 15kΩ 6.8kΩ 470Ω 5W 150Ω 100Ω 15Ω 5W 4-Band Code (1%) brown black green brown red violet yellow brown red violet orange brown brown green orange brown blue grey red brown not applicable brown green brown brown brown black brown brown not applicable 5-Band Code (1%) brown black black yellow brown red violet black orange brown red violet black red brown brown green black red brown blue grey black brown brown not applicable brown green black black brown brown black black black brown not applicable July 2009  31 36 A 36 A C 41 19 C B 45 5 37 56 D 19 E D 23 F F F 40.5 20 20 D 57 28 D 10 A 10 36 A 36 HOLES A: 3.5mm DIAMETER, CSK HOLE B: 5.0mm DIAMETER HOLES C: 10.0mm DIAMETER CL HOLES D: 6.0mm DIAMETER HOLE E: 13.0mm DIAMETER HOLES F: 6.5mm DIAMETER ALL DIMENSIONS IN MILLIMETRES Fig.5: the drilling template for the front panel (ie, the lid of the case). Drill small pilot holes first & use a tapered reamer to make the larger holes. 8-pin socket for IC1, making sure you orientate it with the notch end to the left so it will guide you later when plugging in IC1. 32  Silicon Chip Next, fit the smaller resistors, then fit the two larger 5W resistors which are in ceramic block packages. It’s a good idea to fit these about 1mm above the board rather than flat down on it. This will provide them with a small amount of ventilation and also protect the board from damage if they should become overheated. Follow these parts with the capacitors, starting with the smaller nonpolarised MKT parts and then moving to the electrolytics. There are only two of the latter but be sure to fit them in the correct places and with the correct orientation, otherwise you’ll strike trouble later. Now you can fit the semiconductor parts, starting with diodes D1, D2, D4 & D5 and then zener diodes ZD1-ZD4 and transistor Q1. Once they’re in, fit diode D3 and power MOSFET Q2. These are both in TO-220 packages and are mounted flat on the top of the PC board along with small 6073B-type heatsinks. In both cases, their leads must be bent down by 90° about 6mm away from the bodies, so they’ll pass down through the matching holes in the PC board. The tabs of both devices are then secured down against the heatsink using an M3 x 6mm machine screw and M3 nut. Then when the screws are nuts are tightened, the board is upended and the device leads soldered to the pads underneath. Don’t solder the leads before bolting them down, otherwise you could crack the copper tracks as the screws are tightened. Once D3 and Q2 are in place you can fit LED1. This mounts vertically in the upper centre of the board, with its leads straight and with the underside of its body spaced about 24mm above the board so that it will later just protrude through its matching hole in the front panel. With LED1 in place, now is the time to fit the largest components which mount on the board: the three aircored inductors. During this process, it’s important to dress each inductor’s leads carefully so they’re straight and at 90° to the side cheeks of the inductor bobbin. This will allow the leads to be fed through their matching board holes without strain as each inductor is lowered into position. Be sure to orientate each inductor so that its “start” lead (near the centre of the bobbin) passes through the matching “S” hole on the board, while its “finish” lead (on the outside) passes through the hole marked “F”. When each inductor is sitting flat down against the top of the board, siliconchip.com.au CHARGER NEGATIVE TERMINAL M205 BOX LID/ FUSEHOLDER FRONT PANEL CHARGER POSITIVE TERMINAL BATTERY POSITIVE TERMINAL S1,S2,S3 S1 L3 1mH/20AWG 470  5W 15  5W PC BOARD MOUNTED BEHIND PANEL VIA FOUR M3 x 25mm TAPPED SPACERS WITH 2x FLAT WASHERS UNDER EACH ONE CABLE TIE SECURING L3 TO PC BOARD PC BOARD NOTE: BATTERY NEGATIVE TERMINAL OMITTED FOR CLARITY Fig.6: this end-elevation diagram shows how the PC board is mounted on the back of the lid on M3 x 25mm tapped spacers & washers. The front panel parts are connected to the PC board via “extension” wires. Left: the charger, battery & meter terminals are all mounted on the lid of the case, along with the fuse and toggle switches (not shown here), before the PC board is attached. XYBER Data Recovery Data recovery for the rest of us: reliable, affordable, thorough, fast, professional. MacOS•Windows•Novell•Linux•Servers Disk•Flash•Optical•MO•RAID•NAS•SAN Data•Photo•Audio•Video•Forensics Wholly Australian and proud of it :-) www.xyber.com.au Xyber. At your service. Since 1985. 1800 88 31 77 into its socket, taking care to fit it with the correct orientation. The board assembly can then be placed aside while you prepare the box lid/front panel. Drilling the front panel you can solder its leads to the pads underneath and trim off any excess. A 250mm-long Nylon cable tie is then used to hold the inductor in place. As shown, this tie passes down through one of the edge holes provided in the board and up through the other. siliconchip.com.au Tighten the ties quite firmly to secure each inductor in place. Finally, cut off the excess ends of the cable ties, leaving only about 4mm. Once all three inductors have been fitted to the board, it is almost complete. All that remains is to plug IC1 Preparing the front panel requires 15 holes to be drilled and reamed. Their sizes and positions are shown in Fig.5, which is also shown actual size so you can use a photocopy as a drilling template if you wish. After all of the holes have been drilled and de-burred, you may want to fit the lid/panel with a stick-on escutcheon to give it a more professional finish. To make this step easier, we have produced an artwork for the front panel – see Fig.7. The easiest way to make a front panel is to photocopy the artwork onto an adhesive-backed A4 label sheet, over which is then applied a sheet of protective clear self-adhesive film (like “Contact” or “Duraseal”). Then the artwork can be cut to size and its backing sheet peeled off, allowing it to be placed carefully on the top of the box lid. Another option is to download the July 2009  33 artwork from the SILICON CHIP website and print it out. Once the label is in place you can then cut out the various holes in the escutcheon using a sharp hobby knife, guided by the holes already drilled in the lid. Fuseholder & switches The next stage is fitting the fuseholder, toggle switches and binding posts to the front panel. Don’t use excessive force to tighten the nut on the fuseholder, as you might strip the plastic thread. The three toggle switches are identical, so they can go in any of the three positions. After these fit the red and black plastic binding posts, which are used for the “Meter” terminals. The other two pairs of binding posts are gold-plated speaker terminals and they probably seem too good for this application. However, they have the advantage that they are readily available and will take heavier cables. They also have a top section which can be unscrewed completely to allow connections via crocodile clips. The binding posts with the red mounting 34  Silicon Chip The views above left & top show how the assembly goes together, while at right is the completed Battery Zapper. Make sure that all the extension wires fitted to the front-panel items go through their corresponding holes in the PC board. bushes are used for the two positive terminals. Extension wires Once all of these items have been fitted to the front panel, it can be turned over and their connection lugs or spigots fitted with “extension” wires made from short lengths of tinned copper wire. This is necessary to extend the leads down through the matching holes in the PC board when the latter is mounted up behind the panel. The extension wires for S1, S2 and S3 need only be about 25mm long but with one end bent into a tiny hook so that it can be attached firmly to the switch lug before soldering. The wires used for the fuseholder extensions should be about 15mm and 30mm long respectively, with the longer wire used for the holder’s side connection. As before, these wires should both be attached to the fuseholder lugs by forming them into a small hook before soldering. The extension wires used for the binding posts should be cut from siliconchip.com.au LEAD-ACID BATTERY ZAPPER and DESULPHATOR + METER – longer lengths of 1mm diameter tinned copper wire – about 60mm long. The centre of each wire is then wound tightly once around the notch near the lower end of each binding post’s spigot, before soldering. The two ends are then bent down along the axis of the post and finally twisted together to form a stout extension wire to pass down through the board. All of these extension wire details are shown clearly in the diagram of Fig.6. When all of these extension wires have been fitted the next step is to attach the PC board to the panel. This is done by first mounting an M3 x 25mm tapped spacer to the rear of the panel near each corner, with M3 x 6mm countersink head screws passing down through matching holes ‘A’ in Fig.5. Tighten these screws firmly to ensure that they don’t work loose later. Now offer up the PC board assembly underneath the panel, making sure both that the various extension wires pass through their matching holes in the board and that LED1 also passes up through its matching hole in the panel. Then once the board has moved up to almost touch the spacers (it won’t quite reach them because of the cable ties around the inductors), up-end everything to allow you to fit two M3 flat washers between the board and each spacer. Secure the assembly using M3 x 6mm machine screws (pan head). Finally, solder the ends of all of the extension wires to the copper pads on the board and clip off any excess wire. It might all sound complicated but it’s easier to do than to describe in words. Fig.6 shows the details. Your new Battery Zapper should now be fully wired up and you should be able to lower the complete front panel/PC board assembly down onto the box. The assembly can then be fassiliconchip.com.au ZAPPING + FUSE 3A BATTERY – 24V BATTERY CHARGER 6V/12V ON ON + CHARGER SILICON CHIP .com.au – Fig.7: this full-size front-panel artwork can be photocopied and used direct or you can download a PDF of the artwork from the SILICON CHIP website and print it out on a colour printer – see text. tened to the box using the self-tapping screws provided. Don’t forget to fit the small plastic bungs over each screw recess, to finish the job. Putting it to use It’s very easy to connect the Battery Zapper Mk.3 to a battery, charger and optional DMM – just follow the connection diagram of Fig.1. Before you start, make sure that the Battery Voltage switch (S1) is set in the correct position for the battery you’re going to be zapping. Switches S2 and S3 should both be in their upper “Off” positions. The other main thing to watch is that July 2009  35 Fig.8: this scope shot shows the unit working with a 12V battery. The yellow trace is the voltage waveform seen at the drain of MOSFET Q2, while the green trace shows the resulting spike waveform impressed across the battery itself. The blue trace shows the resulting ripple voltage across the 470µF capacitor. Fig.9: this scope shot shows the Battery Zapper working with a 24V battery. The yellow trace at top is the voltage waveform seen at the drain of MOSFET Q2 and is shown at 70V peak-peak. The spike waveform impressed across the battery (green trace) is 56V peak-to-peak, indicating a battery in need of zapping. the unit’s battery and charger terminals are connected to the battery and the charger respectively with the correct polarity, ie, positive-to-positive and 36  Silicon Chip negative-to-negative. If you connect the battery with incorrect polarity, you will blow the 3A fuse and the chances are that you will blow the MOSFET (Q2) as well. There, you have been warned! If you are using a DMM to monitor the zapping pulses, it is connected to the Battery Zapper’s meter jacks as shown. The DMM should be set for a DC voltage range of 0-100V or more. To begin zapping a battery which has a reasonable charge, all you do is switch S2 to its lower ON position. Zapping LED1 should begin to glow, showing that the high-voltage zapping pulses are being generated and applied to the battery. If you have a DMM connected, it should be giving a reading of more than the battery’s nominal voltage – up to about 70V DC, depending on the amount of sulphating in the battery. If you are in a quiet location, you may also hear a faint 1kHz whistle from the inductors – further evidence that the circuit is working. If Zapping LED1 doesn’t light and the DMM simply reads the battery’s nominal voltage (or less), this means that the battery doesn’t have enough charge at present even to operate the Zapper. In that case, apply power to the charger and turn on the Zapper’s charger switch S3, to allow the charger to provide enough current to support the zapping process. Zapping should then begin, unless the battery is beyond redemption. As the zapping progresses, LED1 will tend to glow less brightly, as the lead sulphate crystals in the battery are gradually dissolved and the amplitude of the zapping pulses slowly drops. But be aware that this may take a considerable time. At the same time the reading on the DMM should slowly drop as well, eventually returning to the battery’s normal “under charge” terminal voltage. By the way if you do need to use a battery charger to allow the zapping process to proceed, the 15Ω resistor inside the Battery Zapper will limit the charging current to less than 1A, mainly to prevent the battery from being damaged by over-charging if zapping needs to continue over several days. This means that after the zapping process has been completed, the battery may still need further charging. Note that, depending on the charge in the battery, the Battery Zapper circuit will draw up to 300mA. This means that you must connect a battery charger, otherwise the battery will end SC up fully discharged. siliconchip.com.au