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A fast charger for nicad batteries This nicad charger lets you fast charge nicad battery packs from a 12V car battery. It can charge packs of 5 to 10 cells at once and automatically reverts to trickle mode at the end of the charging cycle. By JOHN CLARKE Nicad battery packs seem to have a habit of going flat just when you want to use them, particularly when there is no readily available source of mains power to operate a recharger. Of course you can always call upon a spare battery but what happens when it also goes flat after some use? This Extra Fast Nicad Charger is the answer to your nicad battery problems. It operates from a car battery so you don’t need mains power and it can recharge a nicad battery pack in far less 54  Silicon Chip time than it takes using a conventional charger. At the maximum charge current of 4A, you can charge a 1.4Ah battery in less than 30 minutes. For higher capac­ity batteries, the charge time will be longer but most batteries with less than a 2Ah capacity can be charged in under 45 minutes. Sensing techniques With high charge rates, nicad batteries can be damaged if they are not charged correctly. As a result, the Extra Fast Nicad Charger employs four sensing methods to ensure that charging ceases before any damage is done to the cells. These are as follows: (1). Over-temperature sensing: If nicad cells are overcharged, they become hot and this causes cell damage. To prevent this from happening, the circuit monitors the temperature of the battery pack using a thermistor and switches the circuit to the trickle charge mode if the temperature rises above a preset level (45°C). (2). Low voltage sensing: Nicad cells that have been discharged to a very low voltage can be damaged if initially fast charged. The circuit prevents this by monitoring the battery voltage and initially trickle charging the battery until it reaches a preset value. It then automatically switches over to fast charging. (3). Voltage sensing: When a nicad VP 12 VS 6 Vref 10 Rn 11 IB 5 NTC 3 CP 9 Vr1 In SUPPLY GND 16 Vhigh PROTECTION Vr3 MAINS ON RESET V LSP Iref > t AO 2 A2 Vr2 Vlow PROTECTION Vr4 LS 4 A1 > > OSC DISABLE TIME OUT > R s+h BATTERY FULL DETECTION VAC 7 PWM 1 PWM & R TIME OUT PROTECT LED 15 > R 1/10 OSC TO PWM :1:2:4 PRESCALER COUNTER CONTROL CURRENTLESS SENSING AUX PULSES 13 OSC 8 PR 14 SYNC Fig.1: block diagram of the TEA1100 which is designed specifically for nicad battery charging. It includes automatic timeout and -dV detection circuitry and features both linear and PWM outputs. the LED flashes, the charger is in trickle charge mode. Battery charger IC battery pack is fully charged, further charging causes its output voltage to fall slightly. This slight voltage drop is sensed using a method known as -dV detec­tion, at which point the circuit is switched to the trickle charge rate. (4). Automatic timeout: As a final precaution, the circuit em­ ploys a timer which can be set to one of six intervals ranging from 30-180 minutes. If, for some reason, the battery voltage does not drop within a certain time, this timer automatically switches the circuit to trickle charge mode. Note that -dV detection can be unreliable if it takes longer than one hour to fully recharge a battery. This is because the output voltage drops very slowly after full charge at the lower charging currents and may not be detected. The timer is a “belts-’n-braces” feature – it’s there as a backup if the -dV sensing circuit fails to detect full charge. compact plastic case. There are just three switches on the front panel: (1) an on/off switch; (2) a 6-position rotary switch to set the timer (30-180 minutes); and (3) a 5-position rotary switch to set the charging current (1-4A). A table on the front panel shows the required switch set­tings for the various battery capacities available. These set­tings must be used in order to prevent battery damage. Also on the front panel is a LED indicator which shows the charging mode. When the LED is continuously lit, the charger is fast charging. When Main Features • • • Indicators & controls As shown in the photos, the Extra Fast Nicad Charger is housed in a The circuit is based on a Philips TEA1100 charger IC which is specifically designed for nicad cells. Its schematic is shown in Fig.1. Most of the IC circuitry is controlled by a single oscilla­tor which is used for timeout counting, driving a pulse width modulator (PWM) for switch mode operation, and for various timing processes. These timing processes include a periodic “quiet time”, during which battery charging ceases so that its voltage can be measured without switchmode noise. In the trickle charge mode, the PWM output is applied in short • Fast charging Powered from a car battery Charging stopped using three detection methods: by monitoring battery temperature, drop in battery voltage at full charge and charging time Five charging currents from 1-4A • Suits most battery packs with 5-10 cells • • • Charging indicator LED • Trickle charging after fast charge Fuse protection for reverse polarity and shorts Short-circuit proof October 1995  55 F1 10A S1 12V BATTERY 10  4700 50VW 4700 50VW 4700 50VW 0.47 +8V 4 1.8k 6 8 IC2 7555 2 6.8k 3 10  2.2k 0.1 C A Q3 BC328 D1 MBR735 K A 56k NICAD BATTERY N2 Q1 IRF540 D 0.1  5W 2.2k 3.9k 1 S2 : 1 : 4A 2 : 3.5A 3 : 2A 4 : 1.8A 5 : 1A 1k 3 2 CURRENT SET S2 2k 7 VAC 1.1k 4 5 IB K A EXTRA FAST NICAD CHARGER K MINUTES S3 : 1 : 180 2 : 120 3 : 90 4 : 60 5 : 45 6 : 30 .001 TIME SET S3b 2 1 3 4 5 6 56  Silicon Chip VS 6 NTC GND 3 16 TEMP SET VR1 500k * DSE R1797  100k 6 5 .033 10 47k .001 11 220k 9 56k 27k VREF 10 PR 8 1 TIME SET S3a 2 4 3 *OR 100k Fig.2: the circuit of the charger. IC2, Q2 & Q3 together drive Mosfet Q3 and this switches transformer T1 to form a boost converter. This steps up the 12V input voltage to a level sufficient to charge as many as 10 nicads in a battery pack; ie, a maximum of about 18V. The boost convert­er is under the control of IC1, the TEA1100 battery monitor. bursts for about one period on to 10 periods off. Apart from the oscillator, the IC circuitry is also con­trolled by a resistor which is connected between Vref (pin 10) and ground. This resistor sets up a current reference (Iref) for the circuit. The actual charge current is then set by this refer­ence current and the value of an external current set resistor. In operation, the IB pin monitors the voltage across an external dropping resistor which carries the nicad charge cur­rent. This voltage is then fed to internal op amp A1. Any error will be amplified by A1 and compared with the oscillator waveform in a PWM comparator. The result is a pulse train at pin 1 with a duty cycle varying according to the error signal at the A1 output. The CP input, pin 9, controls the RN CP .0015 A 15 LED 4 LS IC1 TEA1100 .01 B E C VIEWED FROM BELOW 12 V+ 5 1 PWM OSC 13 GD S 1 16VW 15k C 4.3k I GO  K 0.1  5W S E 10 16VW LED1 N1 E 10W G B 5 1 B GND 100 16VW OUT T1 0.1 Q2 BC338 ZD1 16V +12V 1W 0.47 +12V 0.1 IN REG1 7808 output polarity at pin 1. In addition, an analog output appears at pin 2 and is used to control circuits employing linear regulation. This latter output is not used in this design, which employs PWM control only. During trickle charge, a resistor at Rn (pin 11) controls the current into the battery. The current is also deter­ mined by the state of the PR pin (pin 8) which controls a pre­scaler to divide the oscillator signal by 1, 2 or 4. Pin 7, the VAC input, monitors the voltage of the battery being charged. For normal (ie, fast) operation, this voltage must be between 0.385V and 3.85V and is set using a voltage divider network to suit the batteries that are to be charged. A voltage on pin 7 that’s outside this range initiates the trickle charge mode. In addition, the battery full detection circuitry initiates the trickle charge mode when it detects a 1% fall in battery voltage. The NTC input at pin 3 is used to monitor the voltage across a thermistor. This is the temperature sensing circuit. As shown, it drives a couple of internal Schmitt trigger compara­tors. When the temperature of the battery pack exceeds a certain value (ie, when the voltage at pin 3 drops below a critical level), one of the Schmitt triggers toggles and the current is reduced to trickle mode (the other Schmitt trigger is used for under-temperature sensing but this is not a problem in Aus­tralia). Finally, the LED output at pin 15 goes low when the IC is in fast charge mode. Alternatively, this pin switches between high and low (to flash the LED) when the IC reverts to the trick­le charge mode. Circuit details Refer now to Fig.2 for the full circuit details. Apart from the TEA1100 This inside photo shows the general arrangement of the PC board in the case. Note how mica washers have been used to set the gap between the transformer cores (see text). IC, it employs a 7555 timer (IC2) two tran­sistors, an N-channel Mosfet and a 3-terminal regulator (REG1). The resistors at pins 10 & 11 of IC1 set the reference currents for the fast and trickle charge rates, as described previously. The oscillator control input is at pin 13 and this pin is connected to ground via one of two capacitors, as selected by S3b. When the .0015µF capacitor is selected, the oscillator runs at 25kHz. Conversely, when the .001µF capacitor is selected, the frequency increases to 37kHz. S3a selects the prescaler value. In positions 1 & 2, pin 8 is grounded and the prescaler divides the oscillator frequency by 4. Similarly, positions 3 & 4 set the prescaler to divide by 2 (pin 8 open circuit), while positions 5 & 6 set the prescaler to divide by 1 (pin 8 connected to the 4.2V bias voltage Vs at pin 6). Combined with switch S3b, S3a sets the timeout period to one of six values: 30, 45, 60, 90, 120 & 180 minutes. The NTC input (pin 3) is connected to a thermistor and also to the 4.2V bias voltage via VR1 and a 100kΩ resistor. Normally, the thermistor resistance is about 100kΩ at 25°C. However, as the temperature rises, the thermistor resistance falls and this reduces the voltage at the NTC input. If the voltage at the NTC input falls below 0.8V, the IC immediately switches to trickle mode and remains there until the voltage increases to about 0.9V. VR1 allows the temperature trip point to be adjusted, while the adjacent .033µF capacitor prev­ents false triggering by bypassing any high frequency signals from the switchmode supply. The PWM output at pin 1 of IC1 is designed to drive a step-up converter and this is based here on Mosfet Q1, transform­er T1 and Schottky diode D1. In practice, however, the PWM wave­ form at pin 1 is not suitable for directly driving the Mosfet. This is because the voltage does not swing sufficiently high to fully turn on the device, nor is the output current sufficient to charge the gate capacitance of the Mosfet in the time allowed. To overcome this problem, 7555 October 1995  57 Q1 BC328 10  0.47 NICAD+ GND T1 Q3 GND 0.1 D1 Q2 0.47 4700uF +12V 0.1  5W 4700uF 1 56k BC338 0.1  5W 15k .0015.001 0.1 0.1 56k 1k K LED1 A 220k 27k S3b 4700uF 1uF S3a 1,2 10uF REG1 4.3k S2 WIPER 5 4 3 S2 2 1 Fig.3: install the parts on the PC board as shown in this wiring diagram, taking care to ensure that all polarised parts are correctly oriented. Note that Q2 is a BC338 transistor while Q3 is a BC328 type, so don’t get them mixed up. timer IC2 is used as a buffer stage. This is a rather unusual application for a 7555 timer IC, since it does not function as a timer at all. Instead, it is used to convert the 0-7V PWM signal to a 0-12V signal at its pin 3 output. As shown on Fig.2, the upper threshold of the 7555 is set to about 2V by the 6.8kΩ and 2.2kΩ resistors at pin 5. This, in turn, sets the pin 2 threshold to 1V. As a result, when pins 6 & 2 are taken above 2V, pin 3 goes low. Conversely, when the input goes below about 1V, pin 3 goes high. Because IC2 is powered from +12V, it effectively converts the PWM output from IC1 into a 0-12V signal. It also inverts the signal and so to maintain the correct output phase, the PWM output from IC1 is inverted by connecting a 56kΩ resistor to the CP input at pin 9. 58  Silicon Chip 10  3.9k .001 S3a 5,6 2.2k 47k .01 VR1 1 2k 100k 1.1k 1 IC2 7555 ZD1 2.2k 100uF S3a WIPER 6.8k NTC1 IC1 TEA1100 10 .033 NTC2 1.8k 10uF The output from IC2 drives complementary pair Q2 & Q3 which in turn provide the current pulses to drive the gate of Q1. Q1 is used to switch the N1 winding of transformer T1. This transformer has a turns ratio (N1:N2) of 1:1.7, to provide suffi­cient voltage step-up for recharging battery packs above 12V. Diode D1, an MBR735 fast recovery type, rectifies the transformer output so that the battery is charged with the correct polarity. The charge current through the batteries is sensed by the two 0.1Ω 5W resistors and the voltage developed across them is fed via one of five resistors, as selected by S2, to op amp A1 inside IC1 (at pin 5). This op amp compares the voltage developed across the current sensing resistors and produces an error signal to control the PWM oscillator. This, in turn, adjusts the PWM output signal at pin 1 so that the charging current is correct. The .01µF capacitor at pin 5 filters out any transient voltages which could otherwise cause false current settings. In addition, the output of error amplifier A1 is fil­tered using a 47kΩ resistor and a .001µF capacitor at pin 4. As the battery charges, its voltage is monitored via a voltage divider network (56kΩ & 15kΩ). The resulting voltage sample is filtered using a 1µF capacitor and applied to pin 7 (VAC) of IC1. When the battery is fully charged, the IC detects the slight drop in battery voltage and automatically switches to the trickle mode as described above. Power for the circuit is fed from a 12V car battery via fuse F1. This fuse protects against shorts and reverse polarity connections. If the 12V battery is wrongly connected, an internal reverse diode in Q1 will conduct and blow the fuse. tor and transistors Q2 & Q3 can now be installed. Make sure that these parts are all correctly oriented and don’t get the two transistors mixed up. REG1 must be installed with its metal tab towards ZD1. Diode D1 and transistor Q1 are installed with their metal tabs towards the edge of the board. Install them with their mounting holes about 22mm above the board, so that they can later be bolted to the rear panel. Next, install the capacitors on the board, starting with the smaller devices and finishing with the three 4700µF electrolytics. The temperature sensing feature may not be needed for some applications. If you don’t wish to use it, connect a 100kΩ resistor across the NTC1 and NTC2 terminals. Winding the transformer The PC board is secured to integral standoffs in the base of the case using four self-tapping screws. Note the use of plastic cable ties to beep the internal wiring neat and tidy. The 12V rail is decoupled using three 4700µF capacitors and two 0.47µF capacitors. These provide the high current pulses required by T1. A 10Ω resistor and 16V zener diode ZD1 protect IC2 from high voltage transients on the 12V rail, while 3-termi­nal regulator REG1 supplies 8V to IC1. In addition, the output of REG1 supplies power to LED 1, the other side of which is connect­ed to pin 15 of IC1 via a 1kΩ current limiting resistor. Construction Most of the parts for the Extra Fast Nicad Charger are mounted on a PC board coded 14309951 and measuring 11 12 13 14 15 16 17 18 19 171 x 140mm. Fig.3 shows the parts layout. Begin by carefully checking the PC board against the pub­lished pattern. In particular, check for broken or shorted tracks. When you are satisfied that the board is OK, begin the assembly by installing PC stakes at all the external wiring points (19 in all). This done, install the wire links, followed by the ICs and the resistors. Table 1 shows the resistor colour codes but it is always a good idea to check them using a digital multimeter, as some colours can be difficult to read. The zener diode, 3-terminal regula- Transformer T1 is wound using 0.8mm-diameter enamelled copper wire – see Fig.4. Begin by cutting four 1700mm lengths of wire and soldering these to pins 9, 8, 7 and 6 of the transformer bobbin. This done, wind these four wires together (ie, side-by-side) onto the bobbin in the direction indicated until you have completed 24 turns. Terminate the free ends to pins 12, 13, 14 & 15 respectively (ie, 9 to 12, 8 to 13, etc), then insulate the winding with a single layer of paper held with insulating tape. Next, cut two 3500mm lengths of wire and connect these to pins 2 & 3. These two wires are then wound on together for 41 turns in the same direction as the previous winding – see Fig.4. Terminate their free ends on pins 19 & 18 (ie, 2 to 19; 3 to 18) and again CASE 20 HEATSINK PRIMARIES SECONDARIES FINISH FINISH T1 WINDINGS VIEWED FROM BELOW NUT WASHER INSULATING BUSH TO3P (TO220) DEVICE MICA WASHER 3mm SCREW PRIMARY : 4x0.8mm DIA ENCW 24T SECONDARY : 2x0.8mm ENCW 41T PRIMARIES START 10 9 8 7 6 SECONDARIES START 5 4 3 2 Fig.4: this diagram shows the winding details for transformer T1 (see text). 1 Fig.5: here are the mounting details for Mosfet (Q1) and the fast recovery diode (D1). They must be isolated from the case and the heatsink using TO-220 mounting kits. October 1995  59 F1 RED+ SOLDER LUG CORD GRIP GROMMET D1 CORD GRIP GROMMET Q1 D RE C1 NT CK LA C2 -B D NT CA NI BLACKNICAD+ RED 1 NTC2 NTC1 S1 B 12 1 A 5 1 2 K LED1 S3 A 60  Silicon Chip 3 4 S2 Fig.6: use this diagram to complete the wiring to the switch­es and the PC board. Tucked in behind the 4700µF filter capacitors are the T0220 Mosfet and fast recovery diode. The mounting details for these devices are shown in Fig.5. finish with a layer of paper held with insulating tape. The transformer can now be assembled by first inserting one ferrite core half into the bobbin and installing its metal re­taining clip. The other ferrite core half is then inserted and 0.5mm spacers (eg, 4 x TO-220 mica washers) slid in between the two halves to provide an air gap (see photo). The second core half is then secured by installing its retaining clip. Once the transformer assembly has been completed, it can be installed on the PC board. Make sure that pin 1 is adjacent to the 56kΩ resistor. Final assembly The Extra Fast Nicad Charger is housed in a plastic case measuring 204 x 68 x 157mm. An aluminium panel The charger has optional temperature monitoring of the battery provided by a negative temperature coefficient (NTC) thermistor. measuring 194 x 65mm and a finned heatsink (125 x 42 x 34mm) are fitted at the rear. Position the PC board in the case and line up its mounting holes on the four integral standoffs at the corners. Use a large drill to shorten the unused standoffs so that the PC board will sit neatly in position. This done, secure the PC board in place with self-tapping screws, slide the metal panel into the slot at the rear of the case, and mark the positions for the Mosfet and diode mounting holes. Next, drill these holes in the rear panel, along with holes for the two cord­grip grommets and the fuseholder. The heatsink is also secured with a screw and nut at its centre. After all the holes have been drilled, remove any burrs, particularly around the Mosfet and diode mounting holes, to prevent punch-through of the insulating washers. The heatsink can now be secured to the rear panel using its central mounting screw. Fit an earth solder lug to this mounting screw and apply a smear of heatsink compound between the mating faces of the heatsink and rear panel before the final assembly. Fig.5 shows the mounting details for the the Mosfet transistor and diode D1. They each need to be isolated from the panel using an insu­lating washer and bush. If you are using mica washers, use a smear of heatsink compound between the mating faces before final assem­ b ly. If silicone-impregnated glass fibre washers are used, no heatsink compound is necessary. When you have tightened down the screw TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  1 ❏  3 Value 220kΩ 100kΩ 56kΩ 47kΩ 27kΩ 15kΩ 6.8kΩ 4.3kΩ 3.9kΩ 2.2kΩ 2kΩ 1.8kΩ 1.1kΩ 1kΩ 10Ω 4-Band Code (1%) red red yellow brown brown black yellow brown green blue orange brown yellow violet orange brown red violet orange brown brown green orange brown blue grey red brown yellow orange red brown orange white red brown red red red brown red black red brown brown grey red brown brown brown red brown brown black red brown brown black black brown 5-Band Code (1%) red red black orange brown brown black black orange brown green blue black red brown yellow violet black red brown red violet black red brown brown green black red brown blue grey black brown brown yellow orange black brown brown orange white black brown brown red red black brown brown red black black brown brown brown grey black brown brown brown brown black brown brown brown black black brown brown brown black black gold brown October 1995  61 PARTS LIST 1 plastic case, 204 x 68 x 157mm 1 aluminium rear panel, 194 x 65mm 1 heatsink, 125 x 42 x 34mm 1 PC board, code 14309951, 171 x 140mm 1 self-adhesive front panel label, 190 x 60mm 1 Philips ETD49/25/16 transformer assembly: 2 4312 020 38041 3F3 cores; 1 4322 021 33882 bobbin; 2 4322 021 33922 clips 2 0.5 x 10 x 15mm spacers to gap transformer (eg, 4 TO220 mica washers) 1 NTC thermistor (DSE Cat R-1797) 1 3AG panel fuse holder (F1) 1 10A 3AG fuse 1 SPST rocker switch (S1) (Altronics Cat S-3210) 1 single pole rotary switch (S2) 1 2-pole 6-position rotary switch (S3) 1 bezel to suit LED1 2 20mm diameter knobs 1 small cordgrip grommet 1 large cordgrip grommet 1 solder lug 2 TO-220 mounting kits 1 30A red alligator clip 1 30A black alligator clip 1 15-metre length 0.8mm enamelled copper wire 1 2-metre length automotive twin polarised cable 1 1-metre length red hookup wire 1 1-metre length black hookup wire 1 1-metre length yellow hookup wire 1 1-metre length green hookup wire 1 60mm length of 0.8mm tinned copper wire 19 PC stakes 2 25mm long x 3mm dia screws 6 cable ties and nut, use a multimeter (set to a high “Ohms” range) to confirm that the metal tab of each device is correctly isolated from the panel. Work can now be done on the front panel. Use the label as a guide for positioning the power switch, LED bezel and rotary switches. Drill out the holes for these items, then affix the label and cut out the holes with a sharp utility knife. This done, mount the switches and LED bezel on the front panel and complete the wiring in the case. If the wires passing through each grommet on the rear panel are not gripped securely, use some heatshrink tubing to increase the cable diameter. Use cable ties to keep 1 IRF540 N-channel Mosfet (Q1) 1 BC338 NPN transistor (Q2) 1 BC328 PNP transistor (Q3) 1 MBR735 Schottky diode (D1) 1 16V 1W zener diode (ZD1) 1 5mm green LED (LED1) Capacitors 3 4700µF 50VW PC electrolytic with support pin 1 100µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 2 0.47µF MKT polyester 3 0.1µF MKT polyester 1 .033µF MKT polyester 1 .01µF MKT polyester 1 .0015µF MKT polyester 2 .001µF MKT polyester Resistors (0.25W 1%) 1 220kΩ 1 3.9kΩ 1 100kΩ 2 2.2kΩ 2 56kΩ 1 2kΩ 1 47kΩ 1 1.8kΩ 1 27kΩ 1 1.1kΩ 1 15kΩ 1 1kΩ 1 6.8kΩ 3 10Ω 1 4.3kΩ 2 0.1Ω 5W Semiconductors 1 TEA1100 nicad battery monitor (IC1) 1 7555 CMOS timer (IC2) 1 7808 3-terminal regulator (REG1) Fig.7 (below): this full size artwork can be used as a drilling template for the front panel. the wiring neat and tidy. Terminate the 12V battery leads with 30A battery clips and the nicad leads with the correct plug for your battery. The thermistor can be permanently soldered to the NTC output lead or a small 2-pin connector plug connected to the lead end. In the first case, use heatshrink tubing on the leads to prevent shorts. In the second case, the thermistor is installed EXTRA FAST NiCad CHARGER 60 90 45 30 1.8 120 180 1 + 2 Amps 1 Mins 3.5 4 + 180 120 1.4AH 2.4AH 1.8AH 62  Silicon Chip TIMEOUT (Mins) CHARGE CURRENT (Amps) 2 3.5 4 4AH 90 1AH 60 600mAH 1.2AH 45 500mAH 800mAH 1AH 30 POWER 1.8 2AH 2AH 4AH 1.4AH 2.4AH 1.8AH 2AH 1.2AH 1.4AH BATTERY CAPACITY Fig.8: this is the full size artwork for the PC board. Check your board carefully for possible etching defects before installing any of the parts. in the nicad battery package with a corresponding 2-pin socket ready for connection every time the nicad is to be charged. Fit a short length of heat­ shrink tubing over the thermistor to prevent it shorting to the nicad case. If the thermistor is not permanently installed inside the nicad pack, we recommend using either masking tape or an elastic band to hold it in con­tact with the cells during charg­ing. Testing Apply 12V to the input terminals and check that there is +8V between pins 12 and 16 of IC1. There should Specifications Maximum charge current ������������������������������������������������������������������� 4A Charge current ranges (A) �����������������������������������������������4, 3.5, 2, 1.8, 1 Charging times (mins)........................................30, 45, 60, 90, 120, 180 -dV detection ��������������������������������������������������������������������������������������1% Trickle charge current.......................... 5% of main charge current for 30 and 45 mins timeout; 2.5% for 60 and 90 mins timeout; 1.25% for 120 and 180 mins timeout Thermistor cutout temperature ������������������������������������������������������<45°C Input voltage............................................................................ 11-14VDC also be about +4.2V at pin 6 and +12V at pins 4 and 8 of IC2. The LED should be glowing dimly. If not, check the fuse and your component place­ment and wiring. If the transformer makes a high pitched squeal, check the transformer windings – they are probably wound with incorrect phase. Short out the nicad battery output leads and check that the LED flashes. The standby current with the nicad output leads shorted is about 16mA. Now the unit is ready to test by charging a battery. Switch off the power and connect a discharged nicad battery to the output leads. Select the requisite timeout period and charge current. Apply power and check that the battery charges within the allotted time. Note that the charger will not operate if the NTC output leads are disconnected from the thermistor. During charging at the higher current levels, the heatsink and transformer windings will run hot. This SC is normal. October 1995  63