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An Improved Lead-Acid BATTERY CONDITION CHECKER In July 2009 we presented an improved version of the Battery Zapper & Desulphator. Here we present the companion Battery Condition Checker. It gives more stable readings for all three main battery voltages (6V, 12V & 24V) than our earlier model, as well as giving a choice of test current pulse levels to suit batteries of different capacities. As a result, it’s now also suitable for testing sealed lead acid (SLA) batteries. By JIM ROWE 62  Silicon Chip siliconchip.com.au The lower section of the circuit is basically a sample-and-hold digital 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 drawn from the battery enable us to measure its output impedance. If the battery voltage doesn’t droop much at all, blue LED8 will light, indicating GOOD; if it droops by only a small amount, green LED7 lights (OK); if it droops more but not too much, green LED6 glows (FAIR). If it droops even more than this, either yellow LED5 (POOR) or red LED4 (FAIL) will glow, 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. Current pulser The Battery Condition Checker circuit fits inside a standard UB2 plastic box and is suitable for checking 6V, 12V & 24V lead-acid & SLA batteries. A S NOTED IN the July 2009 article, the May 2006 Lead-Acid Battery Zapper & Condition Checker has been a very popular project but since it was published a few shortcomings have become apparent. The metering circuit sometimes had a tendency to “lock up” on the 6V range and the current pulse loading circuit was sometimes unstable with 24V batteries, if the power switching MOSFETs were at the high end of their transconductance range. 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 siliconchip.com.au Checker and the Zapper but to feature them as separate projects, to make them easier to build. As noted, the new Battery Zapper was presented in July and here we present the companion Battery Condition Checker. How it works The circuit of the new Battery Condition Checker is shown in Fig.1 and comprises two distinct parts: an upper section incorporating ICs1-3 and transistors Q1-Q7 and a lower section involving IC4, IC5 and LEDs 1-8. Essentially, the upper section is a pulsed current load which draws a sequence of three very short high-current pulses from the battery, after you press the CHECK pushbutton S1. In more detail, the heart of the pulsed current load section is IC2, a 4017B decade counter. This can count clock pulses from gate IC1d, which is configured as a relaxation oscillator running at about 66Hz. This oscillator only runs when pin 12 is high and this is controlled by a “run flipflop” comprising gates IC1a & IC1b. When battery power is first applied to the circuit, the flipflop immediately switches to its “stopped” state, with pins 3 & 5 low and pins 2 & 4 high. So IC1d is prevented from oscillating and at the same time IC2 is held in its reset state by the logic high applied to its MR pin (15). The only output of IC2 at logic high level is O0 (pin 3). No further action takes place until you press the CHECK pushbutton S1, whereupon one side of the 22nF capacitor connected to pin 1 of IC1a is pulled down to ground, forcing it to charge via the 10kΩ resistor. Until it charges, pin 1 of IC1a is pulled low, causing pins 3 & 5 to swing high and pins 2 & 4 to swing low. Thus clock oscillator IC1d is enabled and at the same time the reset is removed from pin 15 of IC2. IC2 now begins to count the pulses from IC1d and its outputs switch high in sequence: O1, O2, O3 and so on up August 2009  63 Parts List 1 plastic box, 197 x 113 x 83mm 1 PC board, code 04108091, 185 x 100mm 1 SPST momentary pushbutton switch (S1) 1 220µH choke (Jaycar LF-1104 or Altronics L6225) 2 3-pole rotary switches (S2,S3) 1 ‘Speaker box’ binding post, red (Jaycar PP-0434 or equivalent) 1 ‘Speaker box’ binding post, black (Jaycar PP-0435 or equivalent) 1 8-pin DIL IC socket 2 14-pin DIL IC sockets 1 16-pin DIL IC socket 1 18-pin DIL IC socket 4 M3 x 25mm tapped spacers 9 M3 x 6mm machine screws, pan head 4 M3 x 6mm machine screws, countersink head 5 M3 hex nuts 2 knobs, 20mm diameter 5 PC stakes 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 IC1b feeds a negative-going pulse back to IC1b, which resets the flipflop. This stops the clock and activity again ceases until S1 is pressed again. So IC1a, IC1b, IC1d & IC2 form a simple digital sequencer which generates nine 15ms long pulses when pushbutton S1 is pressed. Diodes D2, D3 & D4 are connected to the O9, O5 and O1 outputs of IC2 to form an OR gate feeding the commoned inputs of IC1c, which are normally pulled down to 0V via a 22kΩ resistor. When the sequencer runs and outputs O1, O5 and O9 switch high in turn (with 45ms gaps between them), the inputs of IC1c are also pulled high. As a result, IC1c’s output (pin 10) switches LOW during the three corresponding 15ms periods. Because the output of IC1c is connected to the gate of FET Q1 via a 150Ω suppressor resistor, this transistor is normally turned on but is turned off during the three 15ms pulses. This means that during each pulse, the 64  Silicon Chip 1 180mm length 0.8mm tinned copper wire Semiconductors 1 4093B quad Schmitt NAND gate (IC1) 1 4017B decade counter (IC2) 1 MC34063 DC-DC converter (IC3) 1 4066B quad bilateral switch (IC4) 1 LM3914 dot/bar LED driver (IC5) 1 LM2940-5V regulator (REG1) 1 2N7000 N-channel FET (Q1) 2 BC338 NPN transistors (Q2,Q3) 4 IRF1405 55V/169A MOSFETs (Q4-Q7) 3 5mm green LEDs (LED1, LED6, LED7) 2 5mm yellow LEDs (LED2,LED5) 2 5mm red LEDs (LED3,LED4) 1 5mm blue LED (LED8) 7 1N4148 diodes (D1-D4,D6-D7, D10) 2 1N5819 40V/1A Schottky diodes (D5,D11) drain voltage of Q1 rises to about +12V, being pulled up by the 4.7kΩ drain load resistor. When this happens transistor Q2 turns on, delivering about 11.3V to the top of the 470Ω emitter resistor connected to the collector of Q3 and the gates of our main switching MOSFETs Q4-Q7. So during each of the three 15ms pulses, Q4-Q7 are switched on to draw heavy pulses of current from the battery. MOSFET gate supply IC3, an MC34063 DC-DC converter, is used to generate a +12V supply rail purely for Q1 and Q2, from the +5V rail. This is done because MOSFETs Q4-Q7 need a gate drive voltage of at least +9-10V in order to switch on properly. IC3 operates in switchmode at around 40kHz, storing energy in inductor L1 and then releasing it through diode D5 to charge the 220µF capacitor. The 10kΩ and 1.2kΩ resistors form a divider which feeds back a proportion of this output voltage to a comparator inside IC3, to allow it to maintain the output voltage at +12V. So Q1 and Q2 are basically a level translating inverter which turns on Q4-Q7 whenever the output of IC1c 2 6A1 100V/6A diodes (D8,D9) Capacitors 1 470µF 35V RB electrolytic 2 220µF 16V low-ESR RB electrolytic 1 10µF 16V tag tantalum 1 2.2µF 16V tag tantalum 2 100nF MKT metallised polyester 4 100nF monolithic 1 22nF MKT metallised polyester 1 820pF disc ceramic Resistors (0.25W, 1%) 1 10MΩ 2 1.2kΩ 1 270kΩ 1 680Ω 2 100kΩ 2 470Ω 1 22kΩ 8 220Ω 1 15kΩ 1 150Ω 2 10kΩ 4 100Ω 3 4.7kΩ 1 1.0Ω 4 0.22Ω 5W wirewound switches low during each 15ms pulse from the sequencer. MOSFETs Q4-Q7 are effectively in parallel, with their drains connected to battery positive via 6A polarity protection diodes D8 & D9 and their sources connected to battery negative via separate 0.22Ω 5W resistors. The MOSFET gates are each fitted with 100Ω suppressor resistors and are also pulled down to 0V via a 4.7kΩ resistor, so normally they are switched off and not conducting. Pulse current limiting The current pulses are limited by the circuit involving transistor Q3 and diodes D6 & D7 in series with its emitter. The base of Q3 is connected to the top of each source resistor via a 220Ω base current-limiting resistor, so that when the MOSFETs conduct and current flows in the 0.22Ω resistors, the resulting voltage drops provide forward bias for Q3. If switch S2 is in the 40A position, diodes D6 & D7 are connected in series between the emitter of Q3 and 0V. As a result, Q3 doesn’t conduct collector current to any significant extent until the voltage drop across the MOSFET source resistors rises above 2.1V, where it matches the forward voltage siliconchip.com.au siliconchip.com.au August 2009  65 6V 12V LED2 K  A 24V LED3 12V K  A 24V 4 3 270k IC1d 14 11 220 220 220 15 13 14 6V MR 220 CP1 CP0 24V 12V 470 100nF 100nF 13 12 IC1: 4093B O6 O7 O8 O9 10 5 6 9 11 S3a D10 8 Vss A K O0 O1 O2 O3 O4 3 2 4 7 IC2 O5 1 4017B 16 Vdd A A A D4 D3 D2 22k 9 8 820pF 6 11 12 10 3 1 7 10 8 1 10M 1.2k S 2.2 F A K D8-D9: 6A1 – 1.2k 10k A 5 4 8 7 6 2 K A IC5 LM3914 3 LEDS 1 18 17 16 15 14 13 12 11 10 40A K K K K K 25A Q3 BC338 B +12V PEAK CURRENT 12A S2 220 F 16V LOW ESR 4.7k K D5 1N5819 Q1 2N7000 D 15k 100nF G + 10 F +VBATTERY 150 CinSwE 2 5 +1.25V 7 Ips 8 DrC L1 220 H 1 IC3 SwC MC34063 GND 4 2 13 5 4 9 14 6 Vcc 100nF Ct IC4 4066B +5V 3 IC1c THIRD PULSE 4.7k K K K LEAD-ACID BATTERY CHECKER MK3 K  A 6V 7 IC1b IC1a S3b 6 5 2 1 10k 220 F 16V LOW ESR K A IN A A A A GND LED4  LED5  LED6  LED7  A D7 D6 B 470 LED8  E C E Q2 BC338 C GND G Q4 Q5 A S D K A S D Q7 D9 4.7k S D BATTERY – 0.22  5W G K A G GND S A K D E B C BC338 K S Q4–Q7: IRF1405 A D5, D11: 1N5819 2N7000 G Q6 0.22  5W G D8 BATTERY + D D1–D4, D6, D7, D10: 1N4148 0.22  5W G D LM2940 OUT FAIL POOR FAIR OK GOOD 0.22  5W S D 470 F 35V K D11 1N5819 4x220 IN Fig.1: the circuit has two distinct sections. The top section consisting of ICs1-3 & transistors Q1-Q7 forms a pulsed current load which draws a sequence of three very short high-current pulses from the battery when the CHECK switch (S1) is pressed. The bottom section involving IC4, IC5 & LEDs 1-8 forms a sample-and-hold digital voltmeter which samples the battery voltage during the final current pulse and compares it with the battery’s no-load voltage. 2009 SC  A 680 100k LED1 K D1 S1 CHECK 22nF 100k 100nF OUT 100 REG1 LM2940T–5V 100 100nF +5V 100 +5V 100 Fig.2: these three scope screen grabs show the operation of the MOSFET pulser which draws heavy current pulses from the battery on test. In each case, the top (yellow) waveform is the signal fed to the MOSFET gates. It is the same amplitude, regardless of the current setting and voltage of the battery under test. The lower (green trace) is the corresponding voltage across one of the MOSFET’s 0.22Ω source resistor. In the top-left screen grab, the peak-peak voltage across the 2.2Ω resistor is 2.18V, corresponding to a 10A pulse current through each of the four MOSFETs and giving a total of 40A. In the top-right screen grab, the corresponding peak-peak voltage is 1.46V, corresponding to a 6.6A pulse current through each of the four MOSFETs and giving a total of 26.5A. Finally, in the screen grab at right, the corresponding peakpeak voltage is 680mV, corresponding to a 3A pulse current through each of the four MOSFETs and giving a total of 12A. drop of D6, D7 and Q3’s own baseemitter junction. When that voltage level is reached, Q3 begins to conduct, shunting away some of the MOSFETs’ gate voltage. As a result the MOSFET current is automatically limited to a value which produces about 2.1V of drop in the source resistors: around 2.1V/0.22Ω = 9.5A. This is for each MOSFET, so the total current is around 38A, or pretty close to 40A. So when you press pushbutton S1, a sequence of three 15ms 40A pulses is drawn from the battery, each 45ms apart. When switch S2 is set to its centre 25A position, exactly the same sequence of pulses takes place except that they are now limited to around 4 x 6.3A = 25A. This is because S2 shorts out diode D7, reducing the voltage threshold where Q3 begins to conduct from 2.1V down to 1.4V. In the third position of S2, both D6 66  Silicon Chip & D7 are shorted out. Q3 will therefore begin to conduct as soon as the voltage drop in the MOSFET source resistors rises to above about 0.65V, the Vbe drop of Q3 itself. This limits the current pulses to around 0.65V/0.22Ω = 3A each, for a total of around 12A. If you have a look at the scope waveforms of these current pulses, you will see that our prototype produced pulses pretty close to the design values. However, the actual currents pulled from the battery will depend on the tolerances of the 0.22Ω resistors and other circuit variables, the resistance of the battery leads and the internal impedance of the battery itself. Checking the droop As explained earlier, the circuitry around IC4 and IC5 forms a sampleand-hold digital voltmeter. It compares the battery voltage during the last of the three 15ms current pulses against the voltage when no current is being drawn. This is a good indicator of the battery’s condition and its ability to deliver a high discharge current, as when starting a motor. The heart of the voltmeter is IC5 an LM3914 LED bargraph driver IC. The LM3914 is basically a set of 10 voltage comparators, with the reference inputs of the comparators connected to taps on an internal voltage divider between pins 6 & 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 for each LED driver output pin. Only five LEDs are used here, with each connected to an adjacent pair of outputs so they provide a resolution of five discrete voltage levels. Although the LM3914 has an internal voltage reference, we’re not using it here; the reference pin (pin 7) is simply siliconchip.com.au connected to 0V via the 1.2kΩ 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 selected by switch S3a, because the LM3914 input voltage range must be limited for linear operation. So S3a selects a suitable proportion of the battery voltage, depending on whether a 6V, 12V or 24V battery is being tested. Diode D10 is used to prevent the voltage at the rotor of S3a from rising above the +5V supply line by more than 0.6V, to prevent damage to either IC4 or IC5 if S3 is set to the incorrect battery voltage. The proportion of the battery’s voltage selected by S3a is normally fed to the reference input of IC5 (pin 6), where it also charges the 10µF capacitor at all times EXCEPT during the third current pulse drawn from the battery by Q3-Q6. The end result is that the 10µF capacitor becomes charged up to a voltage proportional to the battery’s off-load voltage. When the Checker’s sequencer is running and the third current pulse is being drawn from the battery, the voltage from S3a is switched to pin 5 of IC5, where it also charges up the 2.2µF capacitor. This means that the 2.2µF capacitor charges up to a voltage proportional to the battery’s loaded voltage. This switching of the voltage from the rotor of S3a is performed by CMOS switch array IC4, under the control of the pulse voltage from output O9 (pin 11) of IC2. When the voltage at IC2 pin 11 is low, which is most of the time, it turns off the uppermost switch element of IC4 (pins 9, 8 & 6) which is wired to function as a simple inverter. As a result, pin 9 of IC4 rises to +5V, pulled high via a 4.7kΩ resistor. This pulls pin 5 of IC4 high with it, turning on the second switch element (pins 3 & 4), which switches the voltage from S3a through to pin 6 of IC5. On the other hand, when pin 11 of IC2 switches high during the crucial third current pulse, this switches on the inverter element in IC4, dropping the voltage at pin 9 down to 0V and hence switching off the second switch element. At the same time, it switches on the two remaining elements in IC4 (pins 1-2 and pins 10-11), directing the siliconchip.com.au voltage from S3a through to pin 5 of IC5 and the 2.2µF capacitor. So the reference input of IC5, pin 6, is fed with the “off load” battery voltage on the 10µF capacitor. Pin 4 of IC5 is not connected to 0V but via a 15kΩ resistor. This expands the range of the LM3914’s comparator voltage divider to the upper 40% of the total reference voltage. The LM3914 therefore compares the selected proportion of the battery’s off-load voltage at pin 6 with the same proportion of its on-load voltage at pin 5. If the voltage drops very little, LED8 will light; if it drops a little more, LED7 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 stored by the 2.2µF capacitor is gradually leaked away by the parallel 10MΩ resistor, to ready the circuit for another test. The second pole of switch S3 (S3b) is used to indicate which battery voltage has been selected, via LEDs1-3. This is mainly to remind you to set S3 for the correct battery voltage, because otherwise the Checker won’t give the correct readings. Note that except for Q1 & Q2 in the inverting level translator, all of the Checker’s logic circuitry operates from a +5V supply rail, derived from the battery voltage via REG1, an LM2940-5 low-dropout regulator. As explained before, Q1 & Q2 operate from a +12V rail generated by IC3, while MOSFETs Q4-Q6 are connected to the battery via diodes D8 & D9. Construction Most of the parts are mounted on a single PC board coded 04108091 and measuring 185 x 100mm. This fits neatly into a standard UB2 sized jiffy box (197 x 113 x 83mm). The battery terminals and switch S1 mount on the box lid, being connected to the board via short lengths of tinned copper wire. The board is mounted under the lid via 25mm-long tapped spacers. The component overlay diagram is August 2009  67 2.2 F LED8 + GOOD 10M IC4 REG1 LM2940 -5V 4066B LED5 POOR D10 D11 5819 LM3914 9002 © BATTERY + 6A1 D9 D8 220 F 6A1 DI CA-DAEL YRETTA B N OITI D N O C 3K M REK CE H C LED4 19080140 FAIL + 35V IC5 100nF LED6 FAIR 100nF + 470 F LED7 OK 4.7k 4148 1.2k 15k + 10 F 470 MC34063 TPG 1.0 1.2k 220 LED1 6V 220 Q5 D5 IRF1405 5819 100 220 TP1 +12V Q6 10k IRF1405 100 220 Q7 IRF1405 LED2 12V S3 0.22  5W LED3 24V 0.22  5W 0.22  5W 0.22  5W 220 IC3 Q4 IRF1405 100 100 L1 220 H BATTERY - 820pF S2 BATT VOLTS PK CURRENT + 4.7k 220 F 4148 D6 CHECK 100nF IC2 4017B 100nF 4148 4148 S1 22k 4148 100k 4093B 4148 D7 D1 10k IC1 100k 4148 270k 100nF BC338 2N7000 Q3 D3 Q2 D2 D4 150 220 220 100nF 680 Q1 BC338 220 4.7k 470 22nF Fig.3: follow this diagram to install the parts on the board. Make sure that all polarised parts are correctly orientated and take care also with the orientation of rotary switches S2 & S3 (see text) shown in Fig.3. Begin the assembly by fitting the five wire links, two near IC1 and D1, one just above IC2 and the remaining two at upper left near D10 and IC4. The links are all 10mm long (above the board) and can made from resistor lead off-cuts. Next, add the five IC sockets. Be sure to orientate all five so their end notches are as shown on Fig.3. Then fit 68  Silicon Chip all of resistors, including the four 5W wirewound units. Follow these with the multilayer monolithic and MKT capacitors, then fit the five polarised capacitors (the 2.2µF and 10µF tantalums, plus the 470µF and the two 220µF electrolytics), taking care to orientate these as shown in Fig.3. Fit the two rotary switches S2 and S3, although their spindles should first be cut to about 15mm long (from the threaded mounting sleeve). As indicated in Fig.3, both switches mount with their orientation spigot at about 5-o’clock. After both switches are soldered in place, make sure they’re both configured for three positions. Do this by turning their spindles anticlockwise as far as they’ll go and then removing siliconchip.com.au S1 BATTERY NEGATIVE TERMINAL PC BOARD MOUNTED ON REAR OF PANEL VIA FOUR M3 x 25mm TAPPED SPACERS BOX LID/FRONT PANEL LED1,2,3 S2,S3 Q7 IC1,IC2 Q6 Q5 Q4 D6, D7 (0.22  5W) (0.22  5W) (0.22  5W) (0.22 ) PC BOARD Fig.4: this side-elevation diagram shows how the PC board is mounted on the back of the lid on M3 x 25mm tapped spacers & washers. The battery terminals are connected to the PC board via “extension” wires, as is switch S1. Left & above: these two photos show how it all goes together. The cutouts in the corners of the PC board are necessary to clear the four integral corner pillars inside the case. Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o o siliconchip.com.au No.   1   1   2   1   1   2   3   2   1   2   8   1   4   1   4 Value 10MΩ 270kΩ 100kΩ 22kΩ 15kΩ 10kΩ 4.7kΩ 1.2kΩ 680Ω 470Ω 220Ω 150Ω 100Ω 1Ω 0.22Ω 5W 4-Band Code (1%) brown black blue brown red violet yellow brown brown black yellow brown red red orange brown brown green orange brown brown black orange brown yellow violet red brown brown red red brown blue grey brown brown yellow violet brown brown red red brown brown brown green brown brown brown black brown brown brown black gold gold not applicable 5-Band Code (1%) brown black black green brown red violet black orange brown brown black black orange brown red red black red brown brown green black red brown brown black black red brown yellow violet black brown brown brown red black brown brown blue grey black black brown yellow violet black black brown red red black black brown brown green black black brown brown black black black brown brown black black silver brown not applicable August 2009  69 36 36 A A B 7.5 B 7.5 B 7.5 54 B 7.5 B 16.5 C 19 C 37.5 60 8 8 B B B 19 D D 28 28 38 E A 10 A 6.5 36 ALL DIMENSIONS IN MILLIMETRES 36 CL HOLES A: 3.5mm DIAMETER, CSK HOLES B: 5.0mm DIAMETER HOLES C: 6.0mm DIAMETER HOLES D: 7.0mm DIAMETER HOLE E: 12.5mm DIAMETER 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. their mounting nuts, lockwashers and stopwashers. That done, replace the stopwashers with their stop tabs passing down through the hole between the moulded “3” and “4” digits, and finally refit the lock washers and nuts 70  Silicon Chip to hold them down in this position. The diodes can be fitted next, followed by FET Q1 and transistors Q2 & Q3, making sure you don’t inadvertently swap them. Then fit regulator REG1 and MOSFETs Q4-Q7. These are all in TO-220 cases, with REG1 mounted flat against the PC board with its leads bent down by 90° about 6mm from its body. In contrast, the MOSFETs are all mounted vertically, with their leads pushed through the matching board holes as far as they’ll go without strain. The MOSFETs don’t need any heatsinks as they are switched on too briefly for them to get hot. Before soldering the leads of REG1, you should bolt its tab to the board using an M3 x 6mm machine screw and nut. This avoids stress on the soldered joints, as can occur if you bolt the tab down after soldering the leads. The eight LEDs are mounted vertically above the board, with each LED’s body about 23mm above the board so that it will just protrude through the lid after assembly. Note also that LEDs1-3 are orientated with their cathode lead “flat” sides towards the top, whereas LEDs4-8 are orientated with the “flats” towards the right. Finally, plug the five ICs into their respective sockets, making sure you install each one with the correct orientation (see Fig.3). Notice that IC1 and IC2 have their notch ends towards the left, while IC3-IC5 have their notch ends towards the right. With the PC board finished, you need to drill the box lid. Fig.5 shows the size and location of the holes. After the holes are drilled, attach the front panel using the full-sized artwork of Fig.6. Next, fit pushbutton switch S1 to the 12.5mm hole near the bottom of the front panel, fastening it in place using the moulded nut that comes with it. Once it’s in place, solder a 15-20mm length of tinned copper wire to each of its connection lugs, so that they are ready to make the connections to the PC board pads. Now fit the two battery connection binding posts to the front panel, in the two 6mm holes on the upper righthand side. The binding post with red mounting washers should go in the upper hole and the post with black mounting washers in the lower hole. Secure them in place with the nuts provided, tightening these to ensure that the binding posts don’t become loose in the future. Now take two 70mm lengths of 0.8mm diameter tinned copper wire and wind the centre section of each one around the “groove” at the rear siliconchip.com.au end of each binding post’s mounting stud, before bending both ends down parallel with the stud’s axis and finally twisting them together to form an extension, ready to pass through a matching hole in the PC board. Finally solder the loop in each extension to the binding post lug, to make a good connection between them. The final step before attaching the PC board assembly to the rear of the front panel is to attach four M3 x 25mm tapped spacers to the rear of the front panel using four countersink head M3 screws (passing through the four 3mm countersunk holes marked “A” in Fig.5). Now if you offer the PC board assembly up behind the front panel, you should be able to position it so that the bodies of the LEDs and the spindles of S2 and S3 all pass up through their matching holes in the panel. At the same time the wire extensions from S1 and the two binding posts should all pass down through their matching holes in the PC board, until the top of the board is resting on the four 25mm spacers. Then you can fasten both parts together using four M3 x 6mm machine screws, passing up through the board holes and threading into the spacers. Once these screws are fitted and tightened, the complete assembly can then be up-ended and the extension wires from S1 and the binding posts soldered to their board pads. Fig.4 and the photos will clarify some of the foregoing assembly details. Your Battery Condition Checker is now finished, apart from attaching the PC board/panel assembly to the box using the screws provided. GOOD OK FAIR POOR FAIL BATTERY + SILICON CHIP – LEAD-ACID BATTERY CONDITION CHECKER BATTERY VOLTAGE 6V 12V PULSE CURRENT PEAK (AMPS) 24V 12 25 40 BATTERY CHECK Using it There are no internal setting up adjustments required, so you can use it immediately. First, set switch S3 to the nominal voltage (6V, 12V or 24V) and then set switch S2 to suit the battery’s size/capacity. For larger car and truck batteries this will mean setting S2 for 40A, with the 25A position more appropriate for smaller car batteries and the 12A position for motorbike and SLA batteries. Next, use a pair of clip leads to connect the unit to the battery. One of the LEDs associated with battery voltage switch S3 should immediately light, indicating that you have selected the correct range. Now briefly press Battery Check switch S1. siliconchip.com.au Fig.6: 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. If your battery is good, the blue and/or a green LED will immediately light and then fade as the lower LEDs light – this is the sampled voltage fading away. If your battery is only fair or worse, one of the other LEDs will light. Basically, the blue or a green LED should light, indicating that your battery is fully up to scratch. If not, you might want to put the battery on charge again or connect it to our Battery Zapper, presented in the July 2009 issue. What happens if only the “FAIL” LED lights or – even worse – none of the five condition LEDs lights at all? Well, this means that your battery is probably dead and ready for replacement. You might like to give it a few hours on the charger and the Zapper just to see if it can be rescued, before checking it again. There’s nothing to lose by doing so but if you still get the same result afterwards, the battery is SC definitely due for replacement. August 2009  71