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Deluxe Lead-Acid BATTERY ZAP & Condition Checker This photo shows the same setup as depicted in Fig.6. A battery charger is needed to provide current for the zapping function. Here’s an improved design for a lead-acid battery desulphator or “zapper”, combined with a battery condition checker. It has output jacks which let you monitor the zapping pulses with an external multimeter as zapping progresses, while an inbuilt isolating choke makes it easy to connect a charger to the battery during zapping. T HE SIMPLE LEAD-ACID battery zapper we described in the July 2005 issue of SILICON CHIP has been very popular with readers but a few shortcomings did become apparent as people started putting it to work desulphating their batteries. For a start, when the zapper was connected to a battery with a high 6  Silicon Chip level of sulphation, the high voltage zapping pulses could rise in amplitude above the 100V rating of the switching MOSFET, causing it to suffer breakdown. A circuit modification to limit the maximum pulse voltage was published in the Notes & Errata section of the September 2005 issue (page 107). We also showed how to connect a switch in series with one of the leads between the zapper and battery, to avoid dangerous sparking at the battery terminals when the connection was made or broken. A number of readers also enquired if they could fit an indicator to show when zapping was taking place, as it wasn’t easy to siliconchip.com.au By JIM ROWE PER The circuit fits inside a standard UB2 plastic box and has output jacks so that you can monitor the “zapping” progress using a multimeter. be sure of this unless you connected an oscilloscope across the battery terminals. Another complication arose regarding the power MOSFET’s over-voltage protection, because the MOSFET used in the July 2005 design became unavailable and the only replacements we could find were rated at just 60V. So the over-voltage limiting had to be changed again. It also became clear that batteries needing desulphation must be connected to an external charger at the same time, because they couldn’t provide the zapper with sufficient current. Although we had shown how this could be done, it did involve the use of an external “floating” inductor in series with one of the charger leads. siliconchip.com.au Now we have incorporated the extra inductor inside the box. Finally, the original design was only suitable for 12V batteries but many readers needed to desulphate 6V or 24V batteries as well. Clearly, the best way of sorting out these drawbacks was to develop an improved Mk.2 zapper. At the same time, we decided to incorporate a battery condition checker, so that users would be able to check the condition of their batteries quickly and easily – either to see if zapping was necessary or after a zapping session, to see if there had been an improvement. So that’s the story behind this new unit. It’s largely based on the July 2005 design but with a higher zap output and the ability to be used with 6V, 12V and 24V batteries. It also has the bonus of a built-in battery condition checker. How it works The zapper section of the new unit is very similar to the earlier unit. As we went into a fair amount of detail explaining how this worked in the July 2005 article, we won’t repeat it in the same detail. It is illustrated in the three diagrams of Fig.1. The zapping section of the circuit is shown in the upper part of Fig.2 (from the negative battery terminal upwards). In this case, it only operates when switch S1 is in the “Zap” position, connecting this part of the circuit to the battery and/or charger. Current from the battery and/or May 2006  7 Fig.1(a): during the first phase of the circuit’s operation, current flows from the battery (or charger) and charges a 100mF electrolytic capacitor via inductor L2. Fig.1(b): next, the switch 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. charger flows through 1mH inductor L2 and charges the 470mF capacitor connected between the inductor’s lower end and earth (battery negative). At the same time, current flows through RF choke RFC1 and its 100W 5W series resistor, applying battery voltage to IC1, a 555 timer. Zener diode ZD1 is there to limit the supply voltage for IC1 to 16V when the unit is used with a 24V battery (and an accompanying charger). IC1 is configured as an astable oscillator running at 1kHz, with an output consisting of narrow positive pulses about 100ms wide and with spaces of about 900ms between them (ie, 1:10 mark-space ratio). The narrow pulses are used to turn on switching MOSFET Q2, with diode D2 and transistor Q1 used to ensure that Q2 is switched on and off as rapidly as possible. So Q2 is turned on for 100ms, off for 900ms and so on. During the 900ms “off” periods, the 470mF capacitor is able to charge up to the battery voltage via inductor L2. When Q2 turns on, it connects the lower end of 220mH inductor L1 to ground, allowing some of the energy stored in the capacitor to be transferred into the magnetic field around L1. Then when Q2 turns off 100ms later, the magnetic field in L1 collapses again, delivering the stored energy back into the circuit in the form of a high voltage pulse (positive at the drain of Q2). Most of the energy in the high voltage pulses is fed to the battery via fast switching diode D3. A number of small changes to the original zapper circuit have substantially increased the pulse energy. Over-voltage protection Fig.1(c): finally, the switch 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. 8  Silicon Chip Diode D4 and zener diodes ZD2 and ZD3 form the over-voltage protection circuit for Q2, limiting the maximum pulse voltage at its drain to about 60V. At the same time, diode D4 also functions as a half-wave rectifier and feeds a low-pass filter comprising a 47kW resistor and 100nF capacitor. This provides a DC voltage proportional to the maximum pulse amplitude to the “Meter” terminals. This allows monitoring of the pulse level with a standard multimeter. As zapping progresses, the pulses will initially be quite high in amplitude. But if the zapping is working to Fig.2 (right): IC1 and MOSFET Q2 provide the zapper function while the lower section of the circuit involving IC2-IC5 and MOSFETs Q3-Q6 provide a battery condition checker. successfully desulphate the battery, its internal impedance should drop and so the zapping pulses will be reduced in amplitude. So if you are monitoring the progress with a multimeter, the voltage should gradually reduce. If it doesn’t, you know that the battery is effectively beyond redemption. Visual indication LED1 is provided to show when the zapper is generating pulses and also to give a rough idea of their amplitude. Because the pulses are quite narrow, diode D13 is used to charge the 22nF capacitor to their full voltage (less the battery voltage across the 470mF capacitor) and LED1 is able to draw a steady current from the capacitor via the 6.8kW resistor. Incidentally, the 22nF capacitor, in conjunction with diode D13, also functions as a snubber circuit to provide further damping of the high-voltage pulses produced at the drain of Q2. The circuitry at upper right in Fig.2 is to allow safe connection of a standard battery charger to the battery at any time (ie, during zapping, condition checking or when neither is being carried out). Inductor L3 acts as a blocking choke for the zapping pulses, preventing the charger from possibly being damaged, while switch S3 with its 10nF spark suppressor allows the charger to be safely connected or disconnected, without producing any sparks. The 10W 5W resistor in series with the negative charger lead is to limit the current that can be drawn from the charger, preventing damage when heavy current pulses are drawn from the battery during condition checking. It also reduces the likelihood of overcharging the battery if it is connected to the Zapper for a period of days. Condition checking The condition checking circuit is broken into two distinct parts: the centre section of Fig.2 incorporating IC2, IC3 and transistors Q3-Q8 and the lowest section involving IC4, IC5 and LEDs 2-9. Essentially, the centre section is a pulsed current load which draws a sequence of three very short siliconchip.com.au siliconchip.com.au May 2006  9 Par t s Lis t 1 PC board, code 14105061, 101 x 185mm 1 UB2 size plastic box, (197 x 113 x 63mm) 1 3-pole 3/4-position rotary switch (S2) 1 DPDT centre-off mini toggle switch (S1) 1 SPDT mini toggle switch (S3) 1 SPST momentary contact pushbutton switch (S4) 1 1mH RF choke (RFC1) 1 220mH air cored inductor (L1) 2 1mH air cored inductors (L2, L3) 1 20mm knob 1 130mm length of 0.5mm tinned copper wire (PC board links) 1 150mm length of 2.5mm heatshrink sleeving 2 dual red/black binding posts, 19mm spacing 1 pair of 4mm panel-mount banana jack sockets (red/black) 1 M205 LV panel-mounting fuseholder 1 3A slow blow M205 fuse cartridge (F1) 4 15mm long M3 tapped metal spacers 4 6mm long M3 machine screws, countersink head 4 6mm long M3 machine screws, round head 3 200mm long x 2.5mm cable ties 1 1.5m length of light duty figure8 flex (for LED connections) 1 600mm length of 13 x 0.12mm wire, red PVC insulation 1 200mm length of 13 x 0.12mm wire, black PVC insulation 1 300mm length of 24 x 0.2mm wire, green PVC insulation 1 100mm length of 41 x 0.3mm wire, red PVC insulation 1 100mm length of 41 x 0.3mm wire, black PVC insulation 1 200mm length 13 x 0.12mm wire, blue PVC insulation 4 QC “eye” connector lugs, 5.3mm ID/9.5mm OD Semiconductors 1 555 timer IC (IC1) 1 4093B quad Schmitt NAND gate (IC2) 1 4017B decade counter (IC3) 1 4066B quad bilateral switch (IC4) 10  Silicon Chip 1 LM3914 LED display driver (IC5) 2 BC327 PNP transistors (Q1,Q7) 5 STP60NF06 N-channel MOSFETs (Q2-Q6) 1 BC338 NPN transistor (Q8) 5 5mm red LEDs (LED1, LED2, LED7-9) 2 5mm green LEDs (LED5, LED6) 1 5mm yellow LED (LED4) 1 5mm orange LED (LED3) 1 16V 1W zener diode (ZD1) 1 27V 1W zener diode (ZD2) 1 30V 1W zener diode (ZD3) 1 12V 1W zener diode (ZD4) 1 10V 1W zener diode (ZD5) 9 1N4148 diodes (D1, D2, D6D12) 1 1N4004 1A diode (D5) 1 BY229-200 fast recovery diode (D3) 2 UF4003 fast power diodes (D4,D13) Capacitors 1 2200mF 16V RB electrolytic 1 470mF 63V low ESR RB electrolytic 2 470mF 25V RB electrolytic 1 10mF 16V tantalum 3 100nF 100V MKT metallised polyester 3 100nF 50V monolithic 2 22nF 100V MKT metallised polyester 2 10nF 100V MKT metallised polyester 1 4.7nF 100V MKT metallised polyester Resistors (0.25W, 1%) 1 4.7MW 1 6.8kW 1 270kW 3 4.7kW 3 100kW 1 2.2kW 1 82kW 1 1.2kW 1 47kW 2 1kW 1 27kW 1 470W 1 22kW 1 270W 2 15kW 4 220W 2 10kW 1 100W 2 100W 5W wirewound 1 10W 5W wirewound 3 0.22W 5W wirewound Where To Buy A Kit This project was sponsored by Jaycar Electronics and they own the design copyright. A kit of parts is available from Jaycar for $A99.00 – Cat. KC-5427. high-current pulses from the battery, shortly after you press the CHECK pushbutton S4. The lowest section of the circuit is basically a sample-and-hold voltmeter, which samples the battery voltage only during the last of the three current pulses and compares it with the battery’s no-load voltage. This indicates the battery’s condition by showing how much its terminal voltage droops under load. In effect, the heavy current pulses across the battery enable us to measure its output impedance. If the battery voltage doesn’t droop much at all, green LED6 (GOOD) will light; if it droops by only a small amount, green LED5 (OK) lights up; if it droops more but not too much, yellow LED4 (FAIR) lights up. And if it droops even more than this, either orange LED3 (POOR) or red LED2 (FAIL) will light, giving you an idea of how urgently the battery should be replaced. This assumes that you have just charged the battery, of course. If none of the LEDs light, your battery is dead or flat. If charging and zapping does not fix it, it is beyond redemption. In more detail, the heart of the pulsed current load section is IC3, a 4017B decade counter. This can count clock pulses from gate IC2c, which is configured as a relaxation oscillator running at about 66Hz. Switch S2a increases the feedback resistance when the circuit is connected to a 6V battery, to maintain about the same clock frequency. The oscillator only runs when the level on pin 9 of IC2c is high and this is controlled by the “run flipflop” made up of gates IC2a and IC2b. When power is first applied to the circuit (ie, when S1 is switched to the CHECK position), the flipflop immediately switches to its “stopped” state, with pins 3 & 5 low and pins 2 & 4 high. So IC2a is prevented from oscillating and at the same time, IC3 is held in its reset state by the logic high applied to its MR pin (15). The only output of IC3 at logic high level is O0, pin 3. No further action takes place until you press the CHECK pushbutton (S4), whereupon one side of the 22nF capacitor connected to pin 1 of IC2a is pulled down to ground, forcing it to charge via the 10kW resistor. Until it charges, pin 1 of IC2a is pulled low, causing pins 3 & 5 to swing high and pins 2 & 4 to swing low. Thus, clock siliconchip.com.au Fig.3: the scope waveforms at left were measured using a 12V battery with a series resistor of 2.7W to simulate a sulphated battery. The lowest trace (yellow) is the pulse train fed to the gate of Q2 while the top trace (purple) is the resultant high-voltage pulse developed at the drain of Q2. The blue trace shows the accompanying ripple voltage across the 470mF low-ESR capacitor. At right is the sequence of three current pulses used by the condition checker (measured across the paralleled 0.22W source resistors). oscillator IC2c is enabled and at the same time the reset is removed from pin 15 of IC3. The counter begins to count the pulses from IC2c and its outputs then switch high in sequence: first O1, then O2, O3 and so on up to O9. Each counter output switches high for around 15ms (milliseconds), so the complete sequence takes 9 x 15 = 135ms. When output O9 finally drops low again at the end of the ninth clock period, the 100nF capacitor connected between this output and pin 6 of IC2b feeds a negative-going pulse back to IC2b, which resets the flipflop. This stops the clock and activity again ceases until S4 is pressed again. So IC2a, IC2b, IC2c & IC3 form a digital sequencer which generates nine 15ms long pulses when pushbutton S4 is pressed. Diodes D9, D8 & D7 are connected to the O1, O5 & O9 outputs of IC3. These diodes form an OR gate to feed the inputs of IC2d which are normally pulled down to 0V via a 22kW resistor. But when the sequencer runs and outputs O1, O5 & O9 switch high in turn (with 45ms gaps between them), the inputs of IC2d also switch high for 15ms each time. As a result, IC2d’s output (pin 11) switches low during these three 15ms periods, providing pulses of base current to turn on transistor Q7 for the same periods. And when Q7 conducts, it turns on MOSFETs Q3-Q6, to draw pulses of current from the battery. siliconchip.com.au Q3-Q6 are enhancement-mode MOS­ FETs connected in parallel, with their drains connected to battery positive and sources connected to battery negative via a parallel combination of three 0.22W resistors, giving an effective common source resistance of 0.073W. The MOSFET gates are pulled down to 0V via a 4.7kW resistor, so normally they are switched off and not conducting. But when the sequencer turns on Q7 for three 15ms pulses, this also turns on the MOSFETs and they draw pulses of current from the battery. Pulse current limiting The battery current pulses are limited by transistor Q8 and the two diodes connected in series with its emitter, in conjunction with the three 0.22W resistors in the source circuit of the MOSFETs. The base of Q8 is connected directly to the top of the source resistors, so that when the MOSFETs conduct, the resulting voltage across the source resistors provides forward bias for Q8. Q8 doesn’t conduct to any significant extent until the voltage drop across the MOSFET source resistors rises above 1.95V, where it matches the forward voltage drop of D11, D10 and Q8’s own base-emitter junction. When that voltage level is reached, Q8 begins to conduct, draining away some of the MOSFET forward bias reaching their gates via the 470W and 100W resistors. As a result, the MOSFET current is automatically limited to a value which produces about 2V across the source resistors; ie, around 2V/0.073W, or 28A. So when you press pushbutton S4, a sequence of three pulses of around 28A is drawn from the battery, each around 15ms in duration and 45ms apart. Checking the droop As explained earlier, the circuitry around IC4 and IC5 forms a sampleand-hold voltmeter. It compares the battery voltage during the last of the Warning! This circuit generates high voltage pulses which could easily damage the electronics in a vehicle. Do not connect it to a car battery installed in a vehicle. 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. May 2006  11 Fig.4: follow this parts layout diagram to assemble the PC board and complete the external wiring. Make sure that all polarised parts are installed with the correct orientation. three 15ms pulses against the voltage when no current is being drawn, because this “droop” is a fairly good indicator of the battery’s condition. The heart of the voltmeter is IC5, an LM3914 LED driver IC. The LM3914 is basically a set of 10 voltage comparators, with the reference inputs of the comparators connected to taps on an 12  Silicon Chip internal voltage divider. The top of the divider connects to pin 6, while the bottom connects to pin 4. The second input of all 10 comparators is fed with the input voltage from pin 5, via an internal buffer amplifier. The outputs of the comparators are used to drive current sinks, one for each LED driver output pin. Only five LEDs are used, with each LED connected to an adjacent pair of outputs so they provide a resolution of only five voltage ratio levels. Although the LM3914 has an internal voltage reference, it’s not used here. The reference pin (pin 7) is simply connected to ground via a 1.2kW siliconchip.com.au Our proto­type has the LEDs mounted on sleeved standoffs, for clarity. In practice, the LEDs are wired with flying leads and fitted into bezels in the lid. Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o o o o o No.   1   1   3   1   1   1   1   2   2   1   3   1   1   2   1   1   4   1 Value 4.7MW 270kW 100kW 82kW 47kW 27kW 22kW 15kW 10kW 6.8kW 4.7kW 2.2kW 1.2kW 1kW 470W 270W 220W 100W resistor, to set the LED current levels correctly. So that we can use the circuit to compare the on-load battery voltage with its off-load value, we use the offload battery voltage as the voltmeter’s reference. Actually, we use a proportion of the battery voltage, as selected by switch S2b, because the LM3914’s siliconchip.com.au 4-Band Code (1%) yellow violet green brown red violet yellow brown brown black yellow brown grey red orange brown yellow violet orange brown red violet orange brown red red orange brown brown green orange brown brown black orange brown blue grey red brown yellow violet red brown red red red brown brown red red brown brown black red brown yellow violet brown brown red violet brown brown red red brown brown brown black brown brown input voltage range must be limited for linear operation. So S2b selects a suitable proportion of the battery voltage, depending on whether a 6V, 12V or 24V battery is being tested. This voltage is fed through a 1kW resistor and diode D12 to charge the 470mF capacitor and this provides our ‘no load” voltage reference for the LM3914. 5-Band Code (1%) yellow violet black yellow brown red violet black orange brown brown black black orange brown grey red black red brown yellow violet black red brown red violet black red brown red red black red brown brown green black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown red red black brown brown brown red black brown brown brown black black brown brown yellow violet black black brown red violet black black brown red red black black brown brown black black black brown Table 2: Capacitor Codes Value 100nF 22nF 10nF 4.7nF μF Code 0.1µF .022µF .01µF .0047µF EIA Code   104   223   103   472 IEC Code   100n   22n   10n   4n7 May 2006  13 Fig.5: this cross-sectional diagram shows the mounting details for the LEDs and the rotary switch. The top of the LM3914’s internal voltage divider is connected to the top of the capacitor, while the bottom of the divider is connected to ground/battery negative via a 15kW resistor. This expands the range of the LM3914’s comparator voltage divider to the upper 40% of the total reference voltage. Voltage sampling Sampling of the on-load voltage is performed by IC4, a 4066B quad bilateral switch with all four switches connected in parallel to minimise on-resistance. The control inputs of the switches are connected to the O9 output of IC3, so the switches are normally “off” and are only turned on during the third pulse of each load pulse sequence. When this occurs, the switches allow the 10mF capacitor connected to pin 5 of IC5 to charge up to the proportion of battery voltage selected via S2b – the same voltage proportion used to charge the 470mF capacitor but in this case it samples what happens to it when the battery is attempting to provide 30A pulses of current. The LM3914 therefore compares the selected proportion of the battery’s no-load voltage (pin 6) with the same proportion of its on-load voltage (pin 5). If the voltage droops very little, LED6 will light; if it droops a little 14  Silicon Chip more, LED5 will light and so on. Note that if the on-load battery voltage drops below 60% of its no-load value, none of the LEDs will light – that’s why a “no glow” indicates that the battery is either flat or completely dead. Note too that regardless of which LED lights during the test to indicate battery condition, after a few seconds the glow will transfer down through the lower LEDs and then finally they’ll all go dark again. That’s because the sampled on-load voltage held by the 10mF capacitor is gradually leaked away by the parallel 4.7MW resistor, to ready the circuit for another test. The 10V 1W zener diode (ZD5) connected to the wiper of switch S2b is there to protect the inputs of IC4 & IC5, in case the 6V battery position is selected while a 24V battery is connected. Without ZD5, both IC4 & IC5 could be destroyed by this mistake. The third pole of switch S2 (S2c) is used to indicate which battery voltage has been selected, via LED7-LED9. Construction To make the new Battery Zapper & Checker reasonably easy to build, almost all of the components used are mounted directly on a PC board coded 14105061 and measuring 101 x 185mm. This has rounded cutouts in each corner so it will fit snugly inside a standard UB2-size plastic utility (Jiffy) box. The only components which don’t mount on the PC board are the LEDs, switches S1, S3 & S4, the fuseholder for fuse F1 and the various input terminals and banana sockets. The three switches mount on the lid of the box, while the fuseholder and terminals mount on the sides of the box. All of these off-board components connect to the board via short lengths of insulated wire – see Fig.4. Begin the board assembly by fitting the seven wire links. Don’t forget the short link between diodes D7 and D9, just to the right of rotary switch S2, or the longer link just to the left of the same switch. Next, fit the smaller resistors and the small RF choke (RFC1), followed by the 5W wirewound resistors. Take care to fit the three 0.22W resistors in their correct positions just below the indicated position for inductor L3. Next, fit the capacitors, starting with the smaller non-polarised multilayer monolithic and MKT parts and then progressing through to the polarised tantalum and electrolytic types. There are not many of these but take care to fit them with the correct orientation. Now you can fit the semiconductors, starting with the various diodes and then the bipolar transistors (Q1, Q7 & Q8), the ICs (or sockets for them if you wish) and the power MOSFETs. The semiconductors are all polarised, so be sure to install them correctly. When fitting MOSFETs Q3-Q6, leave about 5mm of their leads above the board (ie, the wider 4mm long sections plus a further 1mm). This is necessary because they need to be bent over at about 45° later, so that their top tabs clear the contacts of switch S1 when everything is assembled. Although not shown in the photos, the two lower MOSFETs must be bent downwards towards D11, while the upper MOSFETs are bent upwards towards L3. Mounting the LEDs The LEDs are all connected to the PC board using 150mm lengths of light-duty figure-8 flex and the LEDs themselves fitted into bezels on the front panel. Each LED is fitted with its connecting lead first. Do this by separating the two lead wires at one end for about 20mm and then removing about 6mm of insulation from each. Then slip a 15mm length siliconchip.com.au of 2.5mm heatshrink sleeving down over each wire, before soldering the two wires to the LED leads (which have been previously cut short, to about 12mm long). When you solder the wires, make sure you solder the wire with the black stripe to the LED’s cathode lead. After both joints are made, slide the heatshrink sleeves up and over the solder joints, so they are fully covered, and heat them with a hot-air gun or by rubbing them with the barrel of your soldering iron, so they shrink into place. Once the leads have been fitted, the LEDs can all be attached to the PC board. Be sure to fit them in the correct positions and with the correct polarity. Special note: our photograph of the prototype shows all LEDs except LED1 mounted on sleeved standoffs about 40mm high, just high enough to let the LEDs protrude through the lid. This has the advantage of showing an uncluttered board in our photographs and allowing more easy comparison with the wiring diagram of Fig.4. That done, it’s time to fit the largest components to the board – ie, rotary switch S2 and the three air-cored inductors. There’s no need to cut S2’s control shaft before it’s fitted to the board. Instead, it’s left at full length so that it will later protrude far enough through the box lid to accept the control knob. However, you do need to make sure that the switch is set for only three positions. This is done by first turning the control shaft as far as it will go in the anticlockwise direction and then unscrewing the mounting nut and removing this from the threaded ferrule, along with the star lockwasher. That done, use a small screwdriver to prise up the indexing pin washer from its position under the star lockwasher and then carefully replace it so that its indexing pin slips down into the rectangular hole between the numerals ‘3’ and ‘4’ which are moulded into the plastic. Make sure the washer is sitting down flat before replacing the lockwasher and mounting nut. If you now try turning the control shaft by hand, it should have three only possible positions. You can now fit the switch in position, making sure that all its connection pins pass through the board holes siliconchip.com.au This is the view inside the completed prototype. Note that in the kit version, the LEDs are connected to flying leads and clipped into bezels mounted on the front panel. and that the bottom of the switch sits flush against the board. Note that in this project, the switch orientation is NOT with the locating spigot pin at 12 o’clock but at the 5 o’clock position. This is shown clearly on the overlay diagram (Fig.4). When you are happy that the switch is orientated correctly and is sitting flat on the board, turn the board over and solder all of the pins to the pads underneath. Air-cored inductors The air-cored inductors are also mounted directly on the PC board. It’s important to dress each inductor’s leads carefully so they’re each straight and at close to 90° to the side cheeks of the inductor bobbin, to prevent strain as the inductor is lowered against the board. Make sure also that you orientate each inductor so that its “start” lead (nearer the centre of the bobbin) passes through its matching “S” hole on the board. The “finish” lead (further out) goes through the hole marked “F”. When each inductor is sitting flat against the top of the board, you can solder its leads to the pads underneath and trim off any excess. That done, use a 200mm-long cable tie to hold the inductor in place, passing the tie down through one of the edge holes provided in the board and up through the other. All that remains now is to plug the ICs into their sockets (taking care to fit them with the correct orientation) and then prepare and fit the various short lengths of wire for the off-board connections. There are 14 of these connection wires to be prepared: two each for the charger and battery terminal connections; two for the meter jacks; two for the charger on/off switch (S3); two for the main function switch (S1); two for pushbutton switch S4; one for the end terminal of the fuseholder; and finally, one for the connection between the May 2006  15 fuseholder side lug and the centre lugs of switch S1. To make it easier to prepare all these wires, their details are shown in Table 1. Note that the wires for the meter terminals are of light-duty hookup wire and this also applies to the wires for S4, S1 and the fuseholder. On the other hand, the wires for charger switch S3 and especially the charger and battery terminals should be made from heavier wire, because they carry higher currents. Warning! 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. Never connect high-current loads directly to a battery’s terminals.This can lead to arcing at the battery 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. 16  Silicon Chip Note also that the wires for the meter jacks have matching large solder lugs fitted to their far ends, while the wires for the charger and battery terminals are fitted with suitable “QC eye” connector lugs (see parts list) for easy attachment to the rear of the terminals using the nuts provided. Once all of these wires are prepared, you can pass the “board end” of each wire through its corresponding hole on the board and solder it to the pad underneath. Your board assembly should then be complete and ready to be fitted into the box, although you should first give it a thorough inspection, to make sure there are no dry solder joints, joints that have been forgotten altogether or accidental solder bridges between pads or tracks. Final assembly Before lowering the board assembly into the box, secure the four 15mmlong tapped spacers inside the bottom of the box using countersink-head M3 x 6mm machine screws. That done, lower the board onto the spacers and secure it in place using four round- head M3 x 6mm machine screws. Next, fit the meter connection jack sockets, the charger and battery connection terminals and the fuseholder to the sides of the box. With both the meter jacks and the charger/battery terminals, you have to disassemble them first before you can fit them to the box and then reassemble them with a single nut inside. When you have tightened these nuts, slip the solder lugs or QC connectors over the ends of the threaded sleeves or shafts and then add a second nut to each connector to fasten them in place. The fuseholder is pushed through its mounting hole and the washer and nut refitted. Don’t use excessive force to tighten the nut though, as this may strip the plastic thread. Once the fuseholder is in place, you can solder the end of the wire from the PC board to its end connection lug. Next, fit toggle switches S1 & S3 to the box lid. S3 is a single-pole switch which mounts in the central hole of the lid, while S1 is a double-pole centre-off switch which mounts in the righthand hole. After these, fit pushbutton switch S4 in the centre hole at the bottom of the lid. You should now be ready to make the last off-board connections, so turn over the box lid and bring it close alongside the box itself. First of all, use the remaining loose length of prepared wire (80mm of 13 x 0.12mm, red PVC insulation) to connect the side lug of the fuseholder to the two centre terminal lugs of switch S1 (note: the two sections of S1 are connected in parallel, to give greater current handling capacity). That done, solder the free ends of the remaining red wires from the board (“S1a” and “S1b”) to the lugs at each end of switch S1 – see (Fig.2). The “S1a” wire goes to the two lower lugs of S1, while the “S1b” wire goes to the two upper lugs. Next, solder the leads to pushbutton switch S4. The switch wiring can then be completed by soldering the free ends of the two green wires coming from centre left of the PC board to the centre and uppermost lugs of S3 (the charger on/off switch). Panel-mounting the LEDs You can now fit the plastic bezels for the nine LEDs into their holes in the lid. When each bezel is in place, push its LED up from below until it clicks into place. Just make sure you fit each siliconchip.com.au LED into its correct position or you’ll get some strange results later! That done, you can lower the lid down onto the box, with the rotary switch spindle passing through its clearance hole. Fasten it with the selftapping screws provided, fit the small plastic bungs over each screw recess and fit the control knob on the rotary switch spindle. Using it Now for the smoke test. First, make sure that the Zapper’s switches are set as follows: S1 in its centre-Off position, S2 for the correct nominal battery voltage and S3 in its upperOff position. That done, connect it as shown in Fig.6. The Zapper’s battery terminals are connected directly to the battery using heavy-gauge cables. Just make sure you connect the positive terminal to battery positive and the negative terminal to battery negative, or very nasty things can happen. If you are going to zap the battery, you’ll also have to connect your charger to the Zapper’s charger terminals: again, positive to positive and negative to negative. This is because a sulphated battery cannot deliver the 200mA or so of current required by the Zapper. Once the charger is connected, switch S3 on the Zapper to “On” (assuming you’ve already connected the Zapper to the battery). Note that if you are using a multimeter to monitor the zapping pulses, it should be set for a DC voltage range of 20V or 50V. To begin zapping the battery, switch S1 to its “Zap” position. The Zapping LED should immediately light, showing that the high-voltage zapping pulses are being applied to the battery. If you have a multimeter connected, it should be giving a reading of about 30V DC or thereabouts; this is not the actual peak-to-peak pulse voltage but an average value proportional to it. As zapping progresses, this voltage reading should slowly drop, as the lead sulphate crystals in the battery are gradually dissolved. So let’s say you’ve been zapping the battery for a day or two and also charging it at the same time. Now you want to check the battery’s condition. This is done as follows: First, turn the Zapper’s Charger switch S3 to the Off position, so you’ll be checking the battery by itself and not the charger as well. Then, after siliconchip.com.au Fig.6: this diagram shows how the Zapper is connected to a battery and charger. The multimeter monitors the zapping pulses. making sure S2 is set for the battery’s nominal voltage (6V/12V/24V), move function switch S1 down to its lower Check position. One of the LEDs above the knob for S2 should light, confirming the battery voltage setting. The Good Condition LED (LED6) will also light briefly, then the OK LED, the Fair LED and so on, down to the Fail LED. This “ripple down” effect is caused by the time taken for the LM3914 reference voltage to stabilise after switch-on. Once the Condition LEDs have all gone dark again, simply press the Check pushbutton (S4) briefly. Now one of the Condition LEDs should light again, to show the battery’s actual condition – hopefully it will be the “Good” or “OK” LED, if the battery has responded to the zapping. After a few seconds, the lit LED will fade out and the LED next down from it will light instead. Then the next LED to its left will light and so on, until all Machine screws can be fitted to the Zapper’s charger terminals to provide handy contact points for the battery charger’s alligator clip leads. five LEDs are dark again. When they are all dark it’s a good idea to press S4 again for a second check, because a single check may give a reading that’s lower than the battery’s actual condition. So if you do press S4 again, you’ll very likely get a higher reading than the first time if the battery really is in “Good” or “OK” condition. If you only get a reading of “Fair”, “Poor” or “Fail”, even on the second check, your battery isn’t in good shape and needs more zapping. And if further zapping doesn’t give better readings, your battery is essentially dead and ready for replacement. By the way, you can check the battery condition any time you wish. Because each check only draws three very short pulses of current from the battery, it draws a negligible amount of charge – about 1.35 coulombs or 0.000375Ah. Your charger can probably replace this in a couple of seconds. You’ll also notice that when you exit the battery checking function by switching S1 back to its centre-off position, the Condition LEDs again light briefly, this time from the lowest to the highest. This occurs as the LM3914’s reference voltage decays and is nothing to worry about. By the way, note that regardless of the battery charger you use, the charge current is limited by the circuit to less than 1A. We did this because we did not want the risk of severely overcharging a battery during a period of zapping over several days. So after zapping successfully, the battery may SC still need further charging. May 2006  17