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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.

image

 

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!

Parents

  • I seem to recall you posted what the panel was, but I'm not sure where (and you add so much content the search engine would die image  )

     

    I'm interested in what you've decided on, since I have several projects that could use a 10-20W panel, but sadly most are just way too expensive.

    Most of the mainstream solar regulators are simply that, a limiting device to stop cooking the batteries, but having a device to convert the energy into the appropriate voltage is good for efficiency.

     

    Looks like an interesting project ...

    Mark

  • in reply to mcb1

    Hi Mark,

     

    The current assembled panels I have are actually all under 2W, for instance the black framed on in the photo above is a BP Solar one (that company no longer exists - the parent company infamous for Deepwater Horizon closed it down). 

    However, at least for testing, it should be possible to DIY a panel using individual cells, at low cost. It might only survive a few years (less for you due to weather conditions) but it could be worth a try, and possibly cheap enough to DIY a repair perhaps. Each of the cells in the video is about 4W.

     

    I just don't know how to go about it in terms of materials for the base and the transparent top and so on, and heat/cold expansion during summer/winter etc.. needs some thinking. Also the individual naked cells are brittle they would crack if impacted or if fitted too rigidly perhaps.

  • in reply to shabaz

    I just don't know how to go about it in terms of materials for the base and the transparent top and so on, and heat/cold expansion during summer/winter etc.. needs some thinking

    I'll make some enquiries tomorrow night (if he turns up).

     

    I seem to recall India is making solar cells cheap, and the business model was to make them cheap so that they can be replaced often.

    Not sure how far that supply line has extended, since most panels we see are large and need to meet building regulations, etc.

     

     

    As you say cold weather and hail, isn't a nice combination, but luckily that weather tends to arrive from the rear onto a panel angled about 32 deg for summer, and 57 deg for winter (relative to the ground)

     

     

     

    Cheers

    Mark

  • in reply to shabaz

    So tonight I asked the man who imports solar panels, about adding a glass layer, etc.

    His comment was yes you can do it by obtaining low lead glass and the right glue, but it just wasn't worth it

     

    He mentioned that someone had done it by laying them down on a padded blanket in a plastic bag and sucking out the air to apply pressure onto the glass while the glue set.

    He also commented that the current price was less than NZD$1 per watt for the panels, BUT they were dealing in 240w panels, and he wasn't sure it translated downwards to 10/20w panels.

     

     

     

    Cheers

    Mark

  • in reply to mcb1

    Hi Mark,

     

    Thanks for investigating!

    Here in quantities of five or less, the price varies, but is typically 4-6 times that cost : ( This is for smaller panels than the typical ones on roofs, but even the larger ones are 2-3 times the cost compared to NZ it seems.

    I don't particularly want to assemble my own panel, but I might try a 'non-weatherproof' version with little sealing, just to have something to test the charger with for now.

Comment
  • in reply to mcb1

    Hi Mark,

     

    Thanks for investigating!

    Here in quantities of five or less, the price varies, but is typically 4-6 times that cost : ( This is for smaller panels than the typical ones on roofs, but even the larger ones are 2-3 times the cost compared to NZ it seems.

    I don't particularly want to assemble my own panel, but I might try a 'non-weatherproof' version with little sealing, just to have something to test the charger with for now.

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