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


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:


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?


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

Tree House Layout Diagram

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

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    \$\begingroup\$ Tell us ALL of the REAL specifications. Dry cells usually mean non rechargeable. I assume this is not te case. What size are they (AAA?). What mAh. What brans? What model if known. Do you have PV (Solar ) cell specs. If not - place ONE in bright sun. What is Voc(open circuit voltage). What is Isc (short circuit current). What current do the LED lights draw at 4.5V. At 3V? At 3.6V? | If your batteries are NimH or (just maybe NiCd) they will have Vmax about 1.2V eac h cell and Vmin V cell so battery = 3 to 3.6V. | If batteries measure 1.6V+ each they are Alkaline. If 1.4 to 1.5V .... \$\endgroup\$
    – Russell McMahon
    Jan 28, 2015 at 8:37
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    \$\begingroup\$ .... they are probably "zinc" and not rechargeable. Please answer ALL questions above. \$\endgroup\$
    – Russell McMahon
    Jan 28, 2015 at 8:38
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    \$\begingroup\$ "please critique my design" is not a specific question. \$\endgroup\$
    – Phil Frost
    Jan 28, 2015 at 13:25
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    \$\begingroup\$ Usually you want to switch the high side not ground. Agreed with Dan Laks on the diode issues. Is the mA on the batteries supposed to be mAH? amp hours are not the same thing as mA. \$\endgroup\$
    – I. Wolfe
    Jan 28, 2015 at 14:05
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    \$\begingroup\$ Good job on the question. You have a somewhat detailed plan, you know in some sense what you are trying to accomplish and you decided to come here prior to building it. I do agree with Russel that we can't really comment unless we understand more about the specifications of the various components. And this forum discourages broad and open-ended questions. So perhaps you could focus on one aspect at a time. For example, "do you see any safety hazards?" Once that is resolved, you could move on to "will this likely function for at least 6 months or a year, and if not, how can I improve it?" \$\endgroup\$
    – user57037
    Jan 28, 2015 at 18:03

1 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.


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