Concerns About Solar Charging Tree House Lights

Question

I'm Building a lighting system for my tree house with 4 LED work lights I picked up at the hardware store. I want it to have solar charging and be operable via one switch. Theres alot of background so skip to the end for just the question.

^{simulate this circuit – Schematic created using CircuitLab}

Here is my plan so far; I have made a schematic. The LED Lights are made to run on three AAA batteries in series. I wanted to be able to turn them on with one switch so I have them hooked up to 12 AAA batteries in series/parallel as shown. The ends of the battery holder(s) will run up to the celling where the lights will be hooked up in paralell.

For the solar aspect I found some cheep 4.5V 80mA Solar cells online and put 5 of them in parallel to give me 400mA charging, staying under/at a 10% recharge rate (1000mAh on per battery X 4 parallel groups of batteries). Add a diode to prevent backdraw from the solar cells and a switch to turn the lights on and off and thats about it.

Heres as much specs as i can get from each component and a link to each.

Solar Cells-4.5V 80mA

Batterys-1.5v,1000mAh,NiMH

Lights-Run off 3 AAA batteries usually, 27 LEDs in parallel with a 0.25Ohm? Resistor(red,green,gold,gold). I know theres a way to calc. the current draw but I'm having real trouble with that.

Here's my two main questions that I'm concerned about:

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1: Will the batteries charge and discharge correctly? Elaborations:Are the solar panels hooked up so that they will correctly charge the batteries? Can the batteries actually charge and discharge in series/parallel like that?

2: Will the lights being powered With the correct current and voltage? Elaborations: If each light is supposed to be powered with three AAA Batteries, will they each get about the same amount of current and volts in this setup?

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Also here is a diagram of the Layout to solve any confusion (And cause diagrams are just cool).

This is an update from my previous question witch I left open ended without any specific questions. After a little more digging, I was able to ask the right questions and find out what I needed: Lesson Learned

Answer 1

There are a number of issues here. In no particular order:

• The solar panels should each have their own series blocking diode. If one solar panel is covered and getting partial shade, its output will be less than the other panels and will be a power sink instead of a power source.

• The solar panels deliver 4.5V at 80mA at full sun. Under partial sun they won't deliver enough voltage to charge the batteries.

• The rechargeable batteries have a voltage of 1.2V, not 1.5V. This means your battery bank has a 3.6V output, not a 4.5V. This works to your advantage as the LEDs will still work (typically from 3V - 5V), and the solar panels minus the diode voltage drop is still enough to charge the batteries under full sun.

• Rechargeable batteries like this need to charge at a rate of 10% of the aH rating for 16 hours, for a total of 160% energy in to get 100% energy out. You may need to let this charge for 2 full days to get the batteries to full charge, under full sun.

Given that, will the system charge and discharge correctly? Under full sun, yes, your system will work as expected. The light output may be a little lower than if you were running off of non-rechargeable batteries, but not enough to notice.

Will the lights be powered with the correct voltage and current? Yes. These types of LED lights are designed to work with 4.5V of non-rechargeable batteries and will provide light down to about 3V. By staying just under the engineered voltage for the LED lamps, you are not likely to overdrive them and still achieve an acceptable amount of light.