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 NiCads  NiMHs  SLAs  LiIONs  Bike batteries  Car batteries. . . IT'S THE ONLY BATTERY CHARGER YOU WILL EVER NEED, EVER AGAIN! Fast Universal Power Charger . Part 1 By JOHN CLARKE For power tools, camcorders, R/C equipment and car batteries Improved MkII version now charges Lithium-Ion and a huge range of Nicad, NiMH, SLA and lead-acid batteries. And YES, you can update the MkI version if you wish... 24  S 24  Silicon iliconCChip hip W aiting for your power tool batteries to charge can be a drag, particularly when you wish to use the tool immediately. This Fast Battery Charger can have your tools operational in a short time. It will charge your power tool batteries in less than 15 minutes for a 1.2Ah Nicad pack. It includes full battery protection and employs endof-charge detection to ensure that the cells are not damaged. Along with Nickel Cadmium (Nicad) and Nickel Metal Hydride (NiMH) batteries, you can also charge Lithium-Ion batteries, 6V and 12V Sealed Lead Acid (SLA) packs and Lead-Acid car and motorcycle batteries. This is an improved version of our very popular Multi-Purpose Fast Battery Charger which was first published in the February and March 1998 issues of SILICON CHIP. While the original charger provided for a host of battery types and voltages, inevitably there were calls from readers who wanted to use it for other voltages and for Lithium-Ion batteries. The original design also had a tendency to prematurely terminate charging on older batteries. Note that if you built the previous version, you can upgrade to the new design by transferring all the components to the new PC board and changing some of the wiring to the switches. Charger features For those not familiar with the previous design, we will now outline the features of this very flexible charger. It uses a Philips TEA11012 IC to perform all the control functions of the circuit. It monitors charging current, battery or cell voltage and battery temperature (optional) and incorporates a timer to shut down charging if other methods of charge detection fail. It is important when fast charging batteries that they are not overcharged. Both Nicad and NiMH types, if given too much charge, will overheat and be permanently damaged. LiION, SLA and Lead-Acid types should not be charged beyond a certain voltage or they too will be damaged and their life reduced. Nor should SLA and Lead-Acid batteries be undercharged since this will also lead to a shortened life. Nicad batteries should also be discharged before recharging in order to consistently provide their maximum capacity. Our new Fast Battery Charger provides accurate detection of full charge for Nicad and NiMH batteries and precise end-point voltage regulation for LiION, SLA and Lead-Acid types. It also has various protection features to prevent fast charge when the battery temperature is too high or low for Nicad and NiMH types and if the battery voltage is initially low for all battery types. An added feature of the charger is the Refresh cycle which is used for Nicad batteries. This discharges the battery so that each cell reaches a nominal 1V before the charger begins to fast charge. Nicad & NiMH batteries are then fully charged and this is detected when the voltage begins to drop off from a maximum value. If a thermistor is connected to monitor temperature of the battery pack, then the charger detects full charge when the temperature begins to rise at a rapid rate. Once charged with high current (fast charge), Nicad & NiMH batteries are topped up with a 200mA current for about 90 minutes and then trickle-charged at 62mA to maintain their capacity before use. This trickle charge comprises short bursts of current which average to 62mA. These bursts of current prevent dendritic growth within NiMH and Nicad cells. LiION, SLA and Lead-Acid batteries are initially fast charged and this current tapers off as the battery voltage approaches 4.1V for LiION and 2.4V per cell for SLA and Lead-Acid types. Charging stops at these voltages. For 12V SLA and Lead-Acid batteries, this end point corresponds to 14.4V. Charging automatically starts again when the cell voltage falls to 2.2V for SLA and Lead-Acid types and to 3V for LiION. Timer & LED indicators The charger incorporates a timer which stops fast charge after a set period (called time-out). This prevents overcharging should the end of charge detection methods fail. Normally, time-out is about 1.6 times the expected charge time of the battery, as Main Features   Fast charges Nicad, NiM H, LiION, SLA and Le ad-Acid batteries Suitable for 1.2V, 2.4V, 3.6V, 4.8V, 6V, 7.2V, 8.4 V, 9.6V, 12V & 14.4V ba from 1.2Ah to 4.2Ah plu tteries s LiION 3.6V, 7.2V & 14 .4V  Charges either 6V or 12V SLA batteries fro m 1.2Ah to 4Ah  Charges 6V or 12 V Lead-Acid batteries of an y capacity above 1.2Ah  Includes a discharg er for Nicad batteries  Top-off charging at end of fast charge plu s pulsed trickle charge  Voltage limited ch for Nicad & NiMH arge for SLA & Lead-A cid batteries  Voltage drop & tem perature rise (dT/dt) ful l charge detection for  Under and over-tem Nicad & NiMH perature cutout for batte ry  Over temperature cutout for charger  Short circuit batte ry protection  Time-out protectio n  Fuse protection  Multi-LED charge indicators June 2001  25 ns: Specificationt. ...........nominally 6A ....................................  Fast Charge Curre .......200mA H).................................. NiM & d ica (N nt rre cu  Top-off .......................62mA d & NiMH).................... ica (N nt rre cu le ck Tri  ..............2A .................................... .... .... d). ica (N nt rre cu  Refresh ................. 1V per cell end-point...................... e arg ch dis sh fre Re  0.3V per cell NiMH).......................... & d ica (N t tec de low  Battery............... 0.9V per cell (LiION)........................ t tec de low rytte Ba  5V per cell ad-Acid)................... 0.4 Le & LA (S t tec de low  Battery................. 2V per cell t (Nicad & NiMH)........... tec de h hig rytte Ba  6V per cell .................................... ..... N) IO (Li t tec de h  Battery-hig ........ 2.97V per cell LA & Lead-Acid).......... (S t tec de h hig rytte  Ba V per cell & Lead-Acid).......... 2.4 LA (S t oin d-p en ge lta  Charge vo ........... 4.1V per cell oint (LiION)................. d-p en ge lta vo e arg  Ch per cell (SLA & Lead-Acid)...2.2V t oin d-p en er aft ge lta  Recharge vo .......... 3V per cell end-point (LiION)......... er aft ge lta vo e arg ch  Re 25% drop in top value tion (Nicad & NiMH).0.  Voltage peak detec .............. 0.25% n level (Nicad & NiMH) tio tec de e rat e tur era C  Temp H)......................... 12° e cutout (Nicad & NiM C ° 50  Under-temperatur . ............ (Nicad & NiMH).............. t tou cu ure rat pe tem  Over...................... 80° C. rature cutout..................  Charge over-tempe tes (nominal) ......... 15, 30 or 60 minu .... .... . ut. e-o tim e arg ch s  Fast.........about 90 minute e (Nicad & NiMH)........  Top-off charge tim determined by the capacity and charge current. When charging Lead-Acid batteries, the timer is reset at regular intervals to prevent time-out. This is because Lead-Acid batteries have a large capacity and require a much longer time to charge than the timer can accommodate. Various indicating LEDs show the status of the Fast Charger: Refresh, Fast, Protect, 100% and No Battery. The REFRESH LED indicates when a Nicad battery is being discharged. The discharge function is initiated by pushing the adjacent Refresh pushbutton. Refresh is only available when the charger is set to charge Nicad or NiMH batteries although it is not necessary to refresh NiMH batteries since they do not exhibit memory effect. The FAST LED shows that the charger is delivering a maximum of 6A to the battery under charge. After the battery is charged, the 100% LED is turned on. While this LED is on, the Charger is in “Topoff” mode which delivers a slow charge at 0.15 of the full fast current. After Topoff, the LEDs are all off and the charger is in trickle mode for Nicad & NiMH batteries but there is no further charge current for LiION, SLA and Lead-Acid types. Fig.1: inside the Philips TEA1102 battery management IC. This versatile chip forms the heart of our fast charger. 26  Silicon Chip Fig.2: the various functional elements of the charger are shown in this block diagram. Full operation is explained in the text. The PROTECT LED shows when a battery is shorted or has low voltage after a certain period of charging. It also lights with over or under-temperature if the thermistor in a battery pack is connected. The NO BATTERY LED only lights when Nicad & NiMH battery types are selected and if the thermistor is not connected to the charger. It simply indicates that the battery is either not connected or has a high impedance. When using the battery charger it is important to select the correct setting on the front panel for the particular battery under charge. You will need to select the battery type (Nicad, NiMH, LiION, SLA or Lead-Acid) and the battery voltage. Also the timer must be set to give a suitable safety time-out for the capacity of battery connected. Battery management IC As noted above, all of the charging features are provided by a single battery management IC, the TEA1102 from Philips Components. Its block diagram is shown in Fig.1. It comprises analog and digital circuits which are divided into six separate sub-sections, as shown on the block diagram. The charge control and output driver section comprises a current source, battery selection, oscillator, comparators, amplifiers and a pulse width modulation (PWM) and analog control output. Battery voltage is monitored at the Vbat input (pin 19) and this is com- pared against the Vreg voltage which sets the end-point voltage for charging the selected battery type. Options are for Nicad & NiMH, LiION and SLA. Note that there is a different Vreg selection for each type of battery but these do not refer to the voltage to which each cell is charged. The V/Vstb (Vstb means Voltage at standby) for Nicad & NiMH batteries refers to an option of either voltage regulation at end of charge or trickle charge. The no-battery selection automatically switches in when the Vbat voltage is above 1.9V. The comparator monitoring Vbat and Vreg controls the constant current source transistor which is supplied with one of four currents: fast charge, top-off, standby and load. When power is first applied, the TEA1102 is reset and fast charge is selected. Fast charge is set by a resistor at Rref (pin 20) to select the current flow to the IB output at pin 2. The current from the IB output pin flows through an external resistor to develop a voltage monitored by the two internal op amps, A1 and A4. A1’s output is amplified by A3 to give an analog control output at pin 18. A1’s output is also compared in A2 against a triangle waveform generated by the oscillator at pin 14. A2’s output is applied via a flipflop to provide a pulse width modulated (PWM) output to drive external circuitry to control the charge current. Refresh (Nicad discharge) is initiated by momentarily connecting the RFSH output (pin 10) to ground. This turns off the current source and op amp A4 drives an external transistor connecting across the battery. The current is set by a series current detecting resistor and the 100mV source at the non-inverting input to A4. The DA/AD converter monitors battery voltage when charging Nicad & NiMH batteries. As the battery is charging, the voltage gradually increases and at a regular period, the AD converter samples the voltage and stores it as a digital value if the voltage has increased from the previous reading. When the voltage begins to fall, the lower voltage is not stored but compared with the analog voltage resulting from the digital stored value. A fall of 0.25% indicates that the battery is charged and the charger will then switch to trickle mode. The DA/AD converter also monitors the thermistor voltage via the NTC input at pin 8. If the thermistor is connected, the DA/AD converter switches off fast charge when there is a sudden rise in temperature of the battery which also indicates full charge. Note that the fast charge will be switched off if a low or high temperature is detected by the Tmin and Tmax comparators. By the way, NTC stands for the Negative Temperature Coefficient of the thermistors fitted into Nicad and NiMH battery packs. As the temperature rises, the resistance of the thermistor drops (ie, negative coefficient) and this is monitored by the circuit. The “NTC present” comparator detects the connection of the thermistor, while the T-cut-off comparator switches on for a 0.25% rate of rise in temperature. The MTV input (pin 9) can be used to calibrate the thermistor temperature at Tmax. The Control Logic section monitors and sets the operation of the various blocks within the IC. Voltage on the FCT input (pin 11) selects the type of battery to be charged. The Supply Block takes its supply at the Vp pin and produces a reference voltage at the Vs output (pin 16). This reference provides an accurate and stable source June 2001  27 With the exception of the power transformer, bridge rectifier, thermistor and the front panel controls, just about everything else mounts on a single PC board. The complete assembly and wiring detail will be presented next month. for the battery end-point voltages. The Vsl output is used to switch on power to external indicating LEDs. These LEDs are driven by pins which serve a dual purpose and are seen in the Timer and Charge Status Indication block. Pins 4, 6 and 7 are used both as programming pins for the timers and as LED drivers. These pins are initially monitored at power on to check what options are set before the LEDs are lit. directly (ie, essentially unfiltered) to the switchmode step-down converter comprising transistor Q1, inductor L1 and diodes D1 and D2. In effect, the battery under charge is fed with chopped and unfiltered DC. This allows a considerable saving on electrolytic filter capacitors and reduces power losses in the main series pass transistor, Q1. Block diagram Fig.3 shows the full circuit for the Multipurpose Fast Battery Charger. Power for the circuit comes from T1, an 18V 6A transformer which feeds the bridge rectifier BR1 and two 10µF 100VW polyester capacitors. These supply the peak current to the switchmode supply comprising transistor Fig.2 shows how we have used the TEA1102 battery management IC in our charger circuit. Transformer T1 and bridge rectifier BR1 provide an 18V DC supply for the charger circuit. This is lightly filtered to provide DC for the control circuitry but is fed through 28  Silicon Chip Circuit description Q1, diode D1 and inductor L1. The Pulse Width Modulation output at pin 15 of IC1 drives transistor Q3 which operates as a pulsed “current sink” to provide 34mA base current to Q1. Q1 switches current through inductor L1 and diode D2 into the battery load. When Q1 switches off, diode D1 enables the energy stored in the inductor to flow into the battery. Diode D2 prevents battery current from flowing back into the switchmode circuit. The 100µF capacitor across the battery is there to filter the supply when no battery is connected so that the “no battery” detection will operate within IC1. Fig.3 (right): the complete circuit diagram of the fast charger. 2001 3.3F NP 12V Lead Acid B E 4 3 2 12V SLA 6V SLA LiION NiCad, NiMH Q5 BC337 1 3 4.7k 10F 16V + 33k 15m 60m 30m D4 1N914 K  A A K 33k S2 TIMER 680 C Q4 BC548 E 1000F 63V 2.2k D3 1N4004 2 x 10F 100V LED5 NO BATT 3 ZD1 12V 1W S4d C 2 BATTERY TYPE 7 14 10 1 10F 16V S3 POSITION IC2c 4093 2 1 _ BR1  K +VS  K  E B C 33k LED3 PROTECT K A LED4 100% LED A A  LED1 REFRESH K A 1k 1W LED2 FAST B 1k 1W E C B 68 Q3 BC337 1k E C B 27k 20 PTD R REF POD LED PSD BC337 BC548 7 6 5 4 15 PWM 13 V SL 12 V P Q1 TIP147 MULTI-PURPOSE FAST BATTERY CHARGER II 3 6V Lead Acid 2 4 NiCad, NiMH, LiION, SLA IC2b 4093 1 6 5 8 BATTERY TYPE 220k 11 ZD2 11V 2.2k 0.5W T1 18V/6A 2 IB K GND 3 14 FCT NTC 2 1 0.1 5W 0.1 5W 1M 10k S6 REFRESH Q2 TIP142 RT1 NTC VR1 250k 11 8 1 S4a 3 E C 100F 16V VS 16 VSTB OSC A D6 1N914 RFSH VBATT 19 10 B D2 MUR1550 MUR1550 17 LS IC1 TEA1102 3.3k D1 MUR1550 L1 S3a +VS 4 2 3 1 12k 30k 15k 82k 33k 220k 100k 100k 2 3 2 S4c 3 12V 6V 3 2 1 4 6 S3b 10 7 8.4V TIP142 TIP147 1 S5 1 1.2V 5 20k 6V 100k 3.6V 4 56k 82k 4.8V 27k 330k 100k 100F 25V TH1 80C 8 12V 9.6V 9 B 1 + C E 2 C 3 S4b 10k 100k 12k 150k 18k 68k 18k 220k _ OUTPUT (TO BATTERY) F2 7A .4 V SC  16 VCC 1F 16V 22k S4 POSITION D5 1N914 12 13 0.1F IC2a 4093 IC3 Q14 3 4020 MR GND CLK 11 CHASSIS 10 E N 240VAC INPUT F1 630mA V A 820pF 2.4 7.2V S1 POWER 250VAC  0.18F THERMISTOR 14 June 2001  29 Fig.4: these ’scope waveforms show the switchmode operation of the charger. The triangle waveform (blue trace) is the output of the oscillator at pin 14 of IC1 while the purple trace intersecting the triangle waveform is the DC output of IC1 at pin 17. These two voltages are compared internally by IC1 to produce the PWM output at pin 15 which is the upper trace (yellow). Note that there is some jitter in these traces; this is caused by the fact that the circuit constantly hunts back and forth as it maintains a set current into the battery. The charge current is monitored by the .05Ω resistance (two 0.1Ω 5W resistors in parallel) connected in the ground return path to the emitter of Q2. IC1 monitors this via the IB input at pin 2 which is tied to the same “ground” via a 3.3kΩ resistor. Its operation is as follows: the Rref output at pin 20 is 1.25V and this is applied to the external 27kΩ resistor to set the current flow from the IB output (pin 2). The PWM output from pin 15 of IC1 controls the charge current into the battery so that the drop across the .05Ω resistance equals the voltage across the IB resistor to ground. The 0.18µF capacitor at the LS output (pin 17) filters the current feedback waveform. The Rref resistance at pin 20 also sets the oscillator frequency in conjunction with the 820pF capacitor at pin 14. The frequency of oscillation is about 50kHz. The time-out period is determined by the oscillator frequency and the switch setting at pin 7. When pin 7 is pulled low via the 33kΩ resistor at switch S2, the timeout is about 15 minutes. An open setting of S2 increases the timeout by a factor of two and when S2 pulls pin 7 high, the time-out is increased by a further factor two. These last two settings give the 30-minute and 60-minute settings. Battery selection Fig.5: these ’scope waveforms show how the battery is charged with what is essentially switched unfiltered DC. The lower trace (blue) is the unfiltered DC input to the anode of diode D3 while the upper trace (yellow) is the voltage waveform across the two paralleled 0.1Ω sensing resistors. The RMS value of the voltage is 349mV so the resultant current is 6.98A. The mean value (that would be obtained on a standard multimeter) is only 229mV which would indicate an average current of 4.58A. 30  Silicon Chip Detection of battery type is done with using the (Fast Charge Termination) input at pin 11. When pin 11 is grounded via switches S4a and S3a, the SLA battery charge procedure is selected. When S4a is in positions 2 & 3, it ensures that pin 11 is grounded, regardless of the position of S3a. This prevents Lead-Acid batteries being charged as Nicad or NiMH types which would result in over-charging. LiION charging occurs when the FCT pin is at about 1.2V, as set by the 30kΩ and 12kΩ resistors. Similarly, Nicad and NiMH battery types are selected when pin 11 is connected via S3 to the 4.25V reference at pin 16. The Vstb (pin 1) input selects trickle charging after Nicad or NiMH batteries are charged rather than the voltage regulation option when pin 1 is open circuit. Voltage selection The Vbat input, pin 19, monitors the battery voltage via a filter network consisting of a 10kΩ resistor and 100µF capacitor, and via a resistive divider network switched by S5 and S3b. For Nicad, NiMH and LiION batteries, the division ratio is such that pin 19 sees only the single cell voltage. For example, with the 6V (5-cell) setting we divide the battery voltage by five to produce the equivalent single-cell voltage. The single cell setting at position 1 of S5 thus provides no resistive division of the voltage. The voltage divider for SLA and Lead-Acid batteries is selected when S3b is in position 3 or 4. The division ratio for 6V and 12V takes into account that the regulation voltage for SLA types is 1.63V at the Vbat input. For example, with a 12V battery, we want to charge it up to 14.4V or 2.4V per cell, so the division must be 14.4/1.63 or 8.83. Pin 8, the NTC input, detects if there is a thermistor in the battery pack. The 1MΩ resistor and VR1 at pin 8 pull the voltage up to 4.25V if no thermistor is present and to about 2V if one is connected, at normal room temperature. The thermistor is heated by the cells under charge and any sudden rise in temperature will produce a voltage drop at the NTC input. The charger will sense this as full charge and cease charging. If a sudden change is not detected before the thermistor voltage reaches 1V, the fast charge will cease because of over temperature. LED indication is provided on the LED, POD, PTD and PSD pins and controlled via the Vsl output. At power up, all LEDs are off and the IC looks at the POD, PTD and PSD pins to check the division ratio programming set on these pins. After this, the LEDs can be lit when Vsl goes high to turn on transistor Q4 via the 680Ω resistor. Refresh cycle Transistor Q2 turns on to discharge Nicad batteries when the pin 10 output of IC1 is momentarily shorted to ground via S6. Note that the switchmode circuit is disconnected while Q2 is turned on. In other words, the discharge current is continuous, not pulsed. Current flow through Q2 and the battery is also via the .05Ω resistance and is detected at the IB input at pin 2. This discharge current is regulated to 100mV/.05Ω or 2A. Power Power for IC1 comes from the positive side of bridge rectifier BR1 which charges a 1000µF capacitor via diode D3. D3 reduces the ripple on the capacitor and also prevents charging current for the battery being drawn from this capacitor. A 500Ω resistance comprising two 1kΩ resistors in parallel supplies current to pin 12 which has an internal 12V zener diode regulator. A 10µF capacitor decouples this supply rail. A 2.2kΩ resistor feeds the D3 supply to 12V zener diode ZD1, to power IC2 and IC3. These two ICs form the reset timer. The AC side of bridge rectifier BR1 feeds the 11V zener diode ZD2 via a 2.2kΩ resistor. ZD2 limits the voltage to 11V when the AC goes positive and to -0.7V when the voltage goes negative. The 1µF capacitor across the zener diode smoothes the resulting 50Hz waveform and this is again filtered with a 22kΩ resistor and 0.1µF capacitor and fed to IC2a. This squares up the 50Hz waveform which then clocks IC3. IC3 is a binary counter with the Q14 output producing a high output every 5.5 minutes. The high output is fed to inverter IC2b via a 3.3µF capacitor and the signal is inverted again by IC2c. IC2c drives transistor Q5 which momentarily pulls pin 12 (the 12V supply of IC1) to ground via a 10Ω resistor. This resets the internal timer of IC1. Next month, we will present the full construction details and the parts list for the Fast Charger. SC The rear panel of the charger isn’t particularly inspiring. Power in, fuse and a heasink are the only obvious bits. The four screws hold the power transformer in place against the rear panel. June 2001  31