The circuit which has been discussed here has most of the standard specifications included with it, the following data explains it more elaborately:
LED Lamp Specifications
Voltage: 12 volts (12V/26AH Battery)
Current Consumption: 1.4 Amps @13 volts, and 1.2 Amps @12V
Power Consumption: 1.2 * 12 = 14.4 watts, (equivalent to light emitted by 39 watt LED lamp)
Light Intensity: Approximately around 2000 lm(lumens)
Input: 32 volts from a solar panel specified with around 32 volts open circuit voltage, and short circuit current of 5 to 7 Amps.
Output: Max. 14.3 volts, current limited to 4.4 Amps
Battery Full – Cut OFF at 13.98 volts (set by P2).
Low Battery – Cut OFF at 11.04 volts (set by P1).
Battery charged at C/5 rate with float voltage restricted to 13.4 volts after “battery full cut OFF”.
Automatic Day/Night Switching with LDR Sensor (set by selecting R10 appropriately).
In this first part of the article we will study the solar charger/controller stage and the corresponding over/low voltage cut-off circuit, and also the automatic day/night cut-off section.
R1, R3,R4, R12 = 10k
R5 = 240 OHMS
P1,P2 =10K preset
P3 = 10k pot or preset
R10 = 470K,
R11 = 100K
R8=10 OHMS 2 WATT
T1—-T4 = BC547
A1/A2 = 1/2 IC324
ALL ZENER DIODES = 4.7V, 1/2 WATT
D1—D3,D6 = 1N4007
D4,D5 = 6AMP DIODES
IC2 = IC555
IC1 = LM338
RELAYS = 12V,400 OHMS, SPDT
BATTERY = 12V, 26AH
SOLAR PANEL = 21V OPEN CIRCUIT, 7AMP @SHORT CIRCUIT.
Solar Charger/Controller, High/Low Battery Cut OFF and Ambient Light Detector Circuit Stages:
Referring to the circuit diagram above, the panel voltage is regulated and stabilized to the required 14.4 volts by the IC LM 338.
P3 is used for setting the output voltage to exactly 14.3 volts or somewhere near to it.
R6 and R7 forms the current limiting components and must be calculated appropriately as discussed in this solar panel voltage regulator circuit.
The stabilized voltage is next applied to the voltage/charge control and the associated stages.
Two opamps A1 and A2 are wired with converse configurations, meaning the output of A1 becomes high when a predetermined over voltage value is detected, while the output of A2 goes high on detection of a predetermined low voltage threshold.
The above high and low voltage thresholds are appropriately set by the preset P2 and P1 respectively.
Transistors T1 and T2 respond accordingly to the above outputs from the opamps and activates the respective relay for controlling the charge levels of the connected battery with respect to the given parameters.
The relay connected to T1 specifically controls the overcharge limit of the battery.
The relay connected to T3 is responsible for holding the voltage to the LED lamp stage. As long as the battery voltage is above the low voltage threshold and as long as no ambient light is present around the system, this relay keeps the lamp switched ON, the LED module is instantly switched OFF in case the stipulated conditions are not fulfilled.
IC1 along with the associated parts forms the light detector circuit, its output goes high in the presence of ambient light and vice versa.
Assume it’s day time and a partially discharged battery at 11.8V is connected to the relevant points, also assume the high voltage cut off to be set at 14.4V. On power switch ON (either from the solar panel or an external DC source), the battery starts charging via the N/C contacts of the relay.
Since it’s day, the output of IC1 is high, which switches ON T3. The relay connected to T3 holds the battery voltage and inhibits it from reaching the LED module and the lamp remains switched OFF.
Once the battery gets fully charged, A1’s output goes high switching ON T1 and the associated relay.
This disconnects the battery from the charging voltage.
The above situation latches ON with the help of the feedback voltage from the N/O contacts of the above relay to the base of T1.
The latch persists until the low voltage condition is reached, when T2 switches ON, grounding T1’s base biasing and reverting the top relay into the charging mode.
In the NEXT ARTICLE we will discuss the PWM controlled, simple LED lamp module and find out how the above circuit is integrated with it.