原创 LED Home Lighting Experimentation Part 2

I apologize for not been able to write part 2 sooner.  I am back.

so 10W of LED lighting, 12V, 6AH lead acid battery, Panel size depending on the time within which you want your battery charged.

Solar Panel output is say 15W/Sq. Ft. 14.4 V * 6 A = 86.4W. Consider you get an average of 10W/Sq. Ft throughout the day out of a panel. So 10W or 1 Sq.FT of panel will charge your battery in approximately 8.64 or 9 Hours. 15 Watts in panel output will do it in 6 hours and so on. 

Let us start with Lead Acid Battery Charging Part. The 12V Lead Acid Battery, not considering temperature compensated charging, will have to be charged to 14.4V. Six 2V cells in series will be charged to 2.4V per cell.
Consider you have a 15W worth of solar panel. This panel can charge your battery in 6 hours at the rate of 15WH, or 1A charge current. For better charge efficiency we can use switched mode charger designed for 1/6 (one sixth) the charge rate.

14.4V is the float voltage for the battery and it is good to have 20% head room at the switched mode charger input voltage. So let's plan to have the solar panels connected in such a way that the output is 17.5V. we may have to connect the panel cells in such a way that 17 to 17.5V is available at the panel loading of 1A. This gives the unconditional head room. There is no harm if this voltage goes below 17V but I prefer that there is some head room so the switched mode charger doesn't go into linear charge mode as head room voltage gets close to the float voltage of the battery. Each designer will have certain comfort zone parameters for headroom voltages based on the switcher design
It would be good to have a switched mode battery charger that can charge the battery in the recommended fashion. Trickle, Bulk, Equalize and Float are the four states the battery would charge in and are programmed into the state machine inside the charger. please let me know if you have any interest in looking at a charger circuitry in detail and I can post schematics for LA battery Charger.

Let's look into lighting the LEDs using the LA battery.

LEDs need  to be driven by current sources. Good stiff current sources are created from well regulated voltage sources. between the LA battery and the series/parallel combination of LEDs we will have an LED driver or a well regulated voltage/current source.

In our application we are looking at a 3W LED lamp. We can have 8, 100 mA LEDs in series. At 4V forward drop per LED, we will need 32V to drive these LEDs.
32V has to be generated fromthe 12V battery. This battery depending on the state of charge and age can vary between 10-14.4V. So we will need a boost converter that can generate a 32V @ 100mA source from this battery irrespective of the input voltage variations.

LEDs are connected in series and a current sense resistor in series with the LEDs referenced to ground is used for current feedback.

Most important in LED home lighting is "Light Diffuser". The light coming from LEDs have to be diffused or softened to be usable. Also we need residential lighting to be 360 Degrees. This is accomplished through the use of diffuser in the LED lamps.

Controlling LEDs using electronics has its advantages. Motion sensed lighting, dimming based on ambient light, sector lighting in case of Lanterns so we can get more hours out of the LA battery are some of the advanatges that electronic control offers.

Lastly a 60W Incandescent is equivalent to 11W CFL and is equivalent to 5W of LED lighting. Two points here:
1. Energy saved is energy not generated or diverted where it is more needed (industries/villages/Agriculture). This results in less green house gases.
2. The LED Power Consumption to Light Output actually matches well with the solar light to electricity conversion efficiencies. For what the solar panels are capable of generating today, LED Lighting offers the best use of that power.

END.