21-07-2012, 12:53 PM
Solar Powered Battery Charger
[attachment=28323]
Objectives
Operate in various sunlight conditions
Sunny and cloudy days
Operate for a wide variety of input voltages
6.8V to 13.5V
Charge both lithium and nickel chemistries
Charging Lithium Batteries
Very Strict Regulation of Current vs. Voltage
Charge Voltage at 4.2V or 4.1V most common
Our batteries charge at 4.1V to prolong lifetime
Many Built-in safety precautions
Temperature, low voltage
Charge time ~3 hours at 500ma
Fast chargers skip stage 2 in next slide
70% charged
Charging NiCd Batteries
Three types of charging
Slow(.1C->14 to 16hrs)
70% efficient
Quick(.5C->3 to 6hrs)
Fast(Full charge with topping->1hr)
90% efficient
Pressure and Temperature increase
Full Charge detected by:
Voltage Drop
Rate of temperature increase
Timeout timers
Charging Unit
MAX1501 linear charger
Charges both Ni and Li chemistries
Low minimum input voltage
4.5 Volts Li
5.25 Volts NiCd
High maximum input voltage
13.5 Volts
Low current drain (5-8 mA)
Safety Features
Circuit Performance
GLED on for fully charged battery
Vbatt=4.1 V
RLED on for discharged battery
Steady voltage increase across battery
Drew about 450mA from supply at 7V
Within boundary of solar cell operation
Low output ripple voltage~20mVpp
Power Recommendations
Use buck converter that needs less current
Then, smaller solar panel can be used
Decrease power used by LEDs
Find lower-power PIC, or implement in different fashion
[attachment=28323]
Objectives
Operate in various sunlight conditions
Sunny and cloudy days
Operate for a wide variety of input voltages
6.8V to 13.5V
Charge both lithium and nickel chemistries
Charging Lithium Batteries
Very Strict Regulation of Current vs. Voltage
Charge Voltage at 4.2V or 4.1V most common
Our batteries charge at 4.1V to prolong lifetime
Many Built-in safety precautions
Temperature, low voltage
Charge time ~3 hours at 500ma
Fast chargers skip stage 2 in next slide
70% charged
Charging NiCd Batteries
Three types of charging
Slow(.1C->14 to 16hrs)
70% efficient
Quick(.5C->3 to 6hrs)
Fast(Full charge with topping->1hr)
90% efficient
Pressure and Temperature increase
Full Charge detected by:
Voltage Drop
Rate of temperature increase
Timeout timers
Charging Unit
MAX1501 linear charger
Charges both Ni and Li chemistries
Low minimum input voltage
4.5 Volts Li
5.25 Volts NiCd
High maximum input voltage
13.5 Volts
Low current drain (5-8 mA)
Safety Features
Circuit Performance
GLED on for fully charged battery
Vbatt=4.1 V
RLED on for discharged battery
Steady voltage increase across battery
Drew about 450mA from supply at 7V
Within boundary of solar cell operation
Low output ripple voltage~20mVpp
Power Recommendations
Use buck converter that needs less current
Then, smaller solar panel can be used
Decrease power used by LEDs
Find lower-power PIC, or implement in different fashion