intelligent battery charger

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Intelligent Battery Charger

Intelligent Battery ChargerAl-Motasem Aqel Ahmed dar hamdanSubmitted to :Falah Mohammed

Presentation OutlineIntroductionCircuit DesignPIC ControlSuccesses and DifficultiesFuture Work

Design RequirementsCharge AA NiMH, AAA NiCad, Li-Ion batteries according to charge algorithmsVoltage and temperature charge terminationLess than 5% battery voltage/current rippleLCD voltage display

Original DesignUse a different circuit for each batteryUtilize switches to switch between battery circuits, as well as different charging stagesProblems with circuit size and complexityNot a very intelligent design that utilized very little PIC control

Final DesignAdded a buck converterPWM output of PIC controlled duty cycle of buck converterControl of battery current/voltage by varying duty cycleDynamic control in place of the static circuit of original design

Circuit Overview

AC-DC Circuit4:1 Step-down transformerFull-wave bridge rectifierFilter Capacitor

AC-DC waveformsAfter transformer

After rectifier

After filter capacitor

+5V Supply Was needed to power logic-level components : PIC, LCD, OscillatorUsed a voltage divider on the rectified DC waveform to obtain 21V DCUsed 7805CT +5V regulator to step down voltage

+5V Supply

Buck Converter DesignInductor Design: L (Vin,max-Vout)x (Vout/Vin,max)x(1/fsw)x(1/(LIR x Iout,max)) For 1% ripple, Vin,max = 42 V , and Iout,max=3.5A, we obtain L 6.29 mHOutput capacitor Design:C L(Iomax + I/2)^2 / ((V + Vo)^2 Vo^2)For 1% voltage and current ripple, we obtain C 44mF

PIC/Buck Converter InterfaceVarying duty cycle from PIC directly correlates to the voltage/current provided by buck converterMOSFET driver was necessary to supply enough current to drive the gate20kHz PWM from PIC was consistent with switching limits of diode and was fast enough to keep ripple low

PIC Features16F877A40-PINBuilt in PWM6 Analog Pins10-bit ADC ConversionFOX 1100E for 20MHz external clockPowered using +5V DC

PIC PWM Output

PIC PWM outputMIC4424CN PWM output

ADC Conversion

Original Choice Low Side DriverPros: Low side driver was easier to use and more readily available in the power labCon: Had to ground drain side and therefore couldnt ground the negative terminal of battery.This made it much harder to measure battery voltage using PIC

Final Choice High Side DriverPros: Allowed us to measure battery voltage with PIC, which was crucial to the projectCons: High side driver had a 9.5 V threshold for the PWM signalRequired a low side driver acting as a voltage stepper to increase from 5 V to above 9.5 VRequired extra 12 V and 15 V power supplies for the low side and high side drivers, respectively

LCD PanelPHICO Panel16x2 LCD w/HD44780 Controller4 Push Buttons3 LEDs

Charging AlgorithmNi-MH:Constant 1C =2.3 A - Fast charge until V >1.1VConstant 0.1 C = 0.23 A for 30 minutesTrickle 1/30 C = 7mA indefinitelyNi-CdConstant 1C =0.35 A fast charge until V >1.0 VConstant 0.1 C = 3.5 mA for 30 minutesTrickle 1/30 C = 1mA indefinitelyLi-ionIf V