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  • Doug Cook

Recharging Smartphones During Multiday Scouting Events – Part 2: Renewable and Sustainable Sol

In part 1 of this series, I describe ideas on recharging USB rechargeable gadgets using a USB power port.  Section 1 deals with disposable batteries.

This section explores solar rechargeable options.

The workflow for this option involves setting out a solar panel to collect energy during the daytime storing the energy in a rechargeable batteries.  At night, you recharge your gadget using the power stored inside the solar-recharged battery.

This series offers build it yourself solutions to offer educational guidance about electronics projects.  For this section the complexity of the project increases compared to part 1’s Minty Boost project.  It’s still obtainable however for the do-it-yourself solution.  However it appears to cost a little more than a commercial product now available.

Commercial solar station option

Goal Zero Guide 10 Plus Adventure Kit (MRSP $159.95) (street price $105.00 +)


GZ1
GZ2

This may offer a workable solar solution.  Reviews show acceptable performance but I have not personally tested this device.  Get the Plus unit as it has more capacity than the standard unit for just a little extra cost.

The solar cells hook up to a 4 AA cell battery pack that seems to offer similar functions as the Tekkeon MP1580 Tekcharge.

The iPhone 5 has a 3.8V, 5.45 WH battery that should offer 1440 mAH of capacity. I recommend a rechargeable solar storage battery capacity twice that rated for your smartphone.   The Guide Plus seems to have that capacity.

However, since it uses 4 AA’s I worry that it may not be able to recharge a fully depleted smartphone if its battery unit behaves similar to the Tekkeon.

Recharging using batteries solely is not a one to one transfer of energy.  All batteries give off heat during recharging.  This means a recharger must be able to supply more than the rated capacity of the battery undergoing a recharge.  A rating double your smartphones battery rating acts as recharge insurance to insure a full recharge.  It also helps to insure against the gradual capacity reduction that develops over time with rechargeable batteries.

Jamboree Solar Minty Boost

This is a great build-it-yourself project that gives you a backpackable solar power solution for your smartphone or USB rechargeable gadget.

This project is a collection of two projects available from Adafruit.com.

Part one

First build the minty boost project.  Part one of my series covers this project.  It provides USB port power via disposable or rechargeable AA batteries.

From there…

Adafruit.com supplies solar components that can convert the energy of the sun into battery power.

The USB / DC / Solar Lithium Ion / Polymer charger is easy to assemble.


The circuit board is nearly complete with just a capacitor left to solder.  A solar cable connection and another cable connects the circuit board to a battery or your Minty Boost.


AdafruitSolar2

You can solder the capacitor so it’s straight up. I folded my over to keep a flatter profile in storage.


AdafruitSolar4

The circuit board has connectors that allow the attachment of (clockwise from top center): micro USB slot, solar panel, Load (leading to your minty boost) and a battery.


Three LED’s give information.  A red LED on the top left indicates if the solar panel has current incoming.  An amber LED between the two bottom connectors, closer to the battery outlet indicates charging status while a green LED adjacent to the Load for the Minty Boost indicates when charging is complete.

The battery I chose was a Lithium polymer 3.7V 6600 mAH – the largest.  Larger is better as well when it comes to solar panels.  The largest panel outputs 3.4 watts at 6 Volts.

Take your Minty Boost project and solder in the power connecter supplied in the solar kit to the Minty Boost power supply leads.


You will still be able to use your minty boost with disposable AA batteries.  I would not recommend attaching it to the circuit board as I haven’t tested to see if the circuit might drain the batteries in some way.

The usual configuration would be set up to store the collected solar energy in the Lithium polymer cell.  At night it recharges via the attached Minty Boost.  This allows you to use your smartphone during the day and recharge at night.  I should note that if the gadget can be attached directly during the daytime it would be more efficient to charge into the minty boost directly.  You lose the flexibility of using the smartphone so we store those converted photons into a battery.

The minty boost and a rechargeable separate battery can be attached simultaneously as shown in the illustration below.


The circuit sends priority current to the load (the minty boost).  When done the circuit then automatically switches to send the excess into the lithium polymer battery.  It’s smart and well designed this way.

Costs for the kits

Minty Boost Kit                                                                                                      $19.50 USB / DC / Solar   Lithium Ion /Polymer recharger                              $24.95 Medium 6 V 3.4 W solar panel                                                                         $25.00 Lithium Ion Polymer battery pack 3.7V / 6600 maH                            $39.50                                                                                                                                       $123.45

Note that the recharger circuit produces some heat that can get hot which is expected.

Advantages versus the Goal Zero solar product.

Jamboree Solar Minty Boost may have advantages of:

  1. Better solar panels

  2. Lithium polymer battery versus NiMH storage

  3. A project useable for Scouting Advancement

  4. Boy Scouting – Electronics merit badge

  5. Venturing – Arts & Hobbies bronze award & Outdoor bronze award


Other Advantages

  1. The cost of disposables eventually outweighs the cost of either the Goal Zero of the Jamboree Solar Minty Boost after about 20 days of use.

  2. These offer a lightweight energy source for backpacking

Disadvantages

  1. Bright sunny days are required else little to no power is generated.  Packing disposable batteries as an emergency source of power may be needed.

  2. Make sure to pack the Lithium ion battery in carry-on luggage if flying due to FAA rules.

In part 3 of this series I explore a larger scale solar energy station idea that has much more capacity but will cost 3 to 4 times more.

I also explore a solution unique to the BSA’s National Scout Jamboree where recharging stations are present during daytime hours.

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