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  • Author Author: shabaz
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Building a Solar Charger

shabaz
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Introduction

There is lots of scope for outdoor electronics. A solar charger is useful for this : ) The 90-second video here describes it.

 

 

I wanted to have a general purpose outdoor solar charger that could be used for (say) powering outdoor speakers, or for evening lighting. I wanted something that could easily charge some tens of Watt-hours energy capacity batteries, so that there is lots of power available, but small enough that it doesn’t need a massive panel.

 

I have several compact solar panels and a few rechargeable batteries to test with for now, but I hope to find slightly larger panels and batteries too.

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A charge current of a few amps was the ballpark I was looking for, and the ability to charge a cell or 2- or 3-cell battery, perhaps up to 12V.

 

It needed to have some flexibility, so that I could try out different panels and batteries. I didn’t want a microcontroller to be mandatory, so I wanted to be able to set the solar panel MPPT (maximum peak power tracking) value using a resistor.

 

The perfect IC for this seemed to be the BQ24650BQ24650. It can accept a reasonably wide power range for small panels (5V to 28V) and can handle different battery types and different numbers of cells.

 

Schematic

The circuit is fairly straightforward; it is based on the datasheet, with some external control to be able to switch it on/off using an optional microcontroller. The two main connectors J1 and J2 are used for the solar panel input and the battery to be charged. There is a third connector which carries the same connections plus a few more that are useful for connecting up a microcontroller or LEDs for status information.

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PCB Layout

The CAD layout here shows the current state of the board; it still needs to be routed! It will be fairly compact, around 100x50mm.

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Circuit Calculations

In order to determine precise component values, there is an excellent BQ24650 spreadsheet. I used it to experiment with what values will be required. These will be selected once a battery is chosen. Initially I may use a couple of D sized NiMH batteries, to build an outdoor lamp or speaker : )

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Summary

There is still lots to do (PCB layout, battery selection, component value adjustment) but I’m happy that soon there could be a compact, general-purpose solar charger for small to mid-powered outdoor projects!

  • in reply to shabaz

    Interesting. Hope you keep this post updated with your progress Shabaz. I am sure there are a lot of people who will be interested and can find useful applications for it.

     

    - raymond

  • in reply to urkraft

    I wasn't planning on purchasing any solar panels either to be honest - instead I purchased individual cells, they are quite cheap, less than $2 each even in small quantities.

     

    They are not environmentally protected however. It was just going to be an experimental project, i.e. it could be an interesting approach to have only partial environmental protection, and replace cells if/when they died or cracked. Also I'd rather just experiment with cells and learn a bit more about the technology for now, see how long the cells can last, and if the output is worth it.

  • in reply to shabaz

    Thanks for the update, Shabaz. While i was waiting for your response i decided to check out the prices for solar panels and other relevant components to get a ballpark figure for a solution to fit my needs. I did not get past solar panels - turns out to be way to expensive for my circumstances. So i will only be following your progress based on academic interest.

  • in reply to urkraft

    Hi Raymond,

     

    Unfortunately I've had this project on a lower priority recently : ( but I should hurry up, because summer is approaching and it would be good to test it. I've made some slight changes to the schematic in response to the comments above by Ka (the screenshot below shows the modified portions of the original schematic - a few resistors were added), and I have started laying out the PCB. I still need to do some work on it : ( but hopefully can have it laid out in the next month or so.

     

    image

  • Hi Shabaz,

     

    Very interesting project, in my opinion. I had plans on exploring something of the same nature. Could be useful for many applications - for example for controlling an irrigation system in a remote garden without any electricity. Have you made any ny progress/developments with it since October last year?

     

    - raymond