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November 23, 2011

Retro Rechargeable USB Booster


This project started when I found a 7805 voltage regulator when I was searching through old circuit board for useful parts to scavenge.  Since these chips are often used in DIY USB chargers, I decided to build such a charger, but with some major improvements over the typical 9V battery powered chargers housed in Altoids tins.


Retro Rechargeable USB Booster

The two main things I wanted to improve upon were:


  • Aesthetics.  There is nothing wrong with an Altoids  tin, but there is also a lot of room for improvement as far as looks are concerned.


  • Batteries:  The vast majority of DIY portable USB chargers use alkaline batteries, which means that they must be replaced when they run out.  Also, their capacity is not especially impressive.
My goal was to fix both of these problems, while using only parts I had lying around.  Every single component of this charger I either already had, or I pulled out of some broken electronic device.  Because I only used what was available, the charging circuit uses a 7805 voltage regulator, meaning it is not especially efficient.  On average, it will still be more efficient than a 9V charger, because the peak voltage of the Li-Ion battery pack is around 7.5-7.8V.  Had I built a Mintyboost type circuit, it would no doubt have been more efficient.  However, as the battery pack I used is significantly larger than AA batteries or a 9V (it is 1/3 of a 15" Macbook Pro battery, in fact), this device should be able to power any iPod, phone, or other USB powered device for hours at a time before it must be recharged.


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


Retro Rechargeable USB Booster


So, how did I make it?  First off, here's what I used:


Electronics:
  • 7805 Voltage regulator
  • Resistors: 2x 49.7K, 1x 43K, 1x 74.9K (values do not need to be exact, and are taken from this instructable)
  • 2X Lithium Ion Cells (I got mine from a "dead" Macbook Pro battery)
  • DPDTslide switch
  • Barrel jack
  • Thin gauge wire
  • Female USB connector
  • Heatsink (for the 7805)
  • iPod cable
  • 13cm ribbon
Case and Structure:
  • Hot Glue - All the internal bits are glued together and insulated with this stuff
  • Aluminum flashing (approximately 12cm x 16cm)
  • 1/4" plywood, preferably good looking (I used marine mahogany)
  • 2x small wood screws
  • Epoxy
  • 3mm Stainless Steel rod
  • Black paint
  • 2x small neodymium magnets
  • Tung Oil
  • Satin spray-on acrylic
Tools
  • Soldering iron and solder
  • Dremel/rotary tool with sanding wheel
  • Needle files - square and circular
  • Scissors
  • Philips head screwdriver
  • Multimeter
  • Drill and small drill bit
Here's most of the Macbook battery I started with.  The other cells appear to be dead, as they read under 1V.  The cells on the right seemed to be fine though:

Tools and Materials

To get an iPod to recognize the charger, I followed the guide from this Instructable.  I did not have the exact resistor values, so I improvised and created the correct resistances by soldering resistors of about double or half the required values in series or parallel.  The result of this circuit is that the iPod gets 2.8V over both data lines, which signals the iPod to draw 1A from the charger.  Many devices will charge without the added resistors, so if you do not own an iPod/iPhone do not bother with them.


After soldering the resistors together and to the voltage regulator, I connected a female USB connector to the appropriate parts of the circuit.  When testing the circuit, be careful not to run it for too long, as the voltage regulator does not yet have a heatsink and will get hot.

Here's the (mostly) assembled circuit:

Charging Circuit

Working:
Charging Circuit

When building the charger, the most serious electronics problem I faced was that I only had a Li-Ion charger that could charge 1 cell, but in order to use the 7805 voltage regulator, I needed well over 5V, meaning that I had to use 2 cells in a series.  To get around this problem, I designed a circuit using a DPDT switch.  When the switch is flipped one direction, the two cells are wired in parallel, and are connected to a barrel connector for charging.  When the switch is flipped the other direction, the cells are wired in a series, and output to the voltage regulator.  This lets me charge the cells at 3.7V but discharge them at 7.4V.

Extremely informal schematic.  The two top rectangles are the battery cells, and the two middle ones are SPDT switches.  When I actually built the thing, I used 1 DPDT switch:

Wiring the Battery Pack

Wired switch.  From left to right, top row then bottom row:  Cell 1 +, cell 1 -, cell 2 +, cell 2 -, 7.4V out +, 7.4V ground, 3.7V ground, 3.7V out +:

Wiring the Battery Pack

Here's the circuit attached to the pair of battery cells, with a barrel connector soldered on to the charging input:

Wiring the Battery Pack

The only Li-Ion charger I had available was a camera battery charger, so I had to do some modifications to it so that it could charge this project.  I opened up the charger, and soldered two wires connected to a barrel connector to the positive and negative terminals inside the charger.  I then cut a small hole through the plastic wall of the charger, and routed the new wires out of the whole.  Now, to charge the batteries, I simply flip the switch to the "charge" position, and plug the barrel connector coming out of the charger into the socket I added in the previous step.

Modified charger:

Modifying the Charger

Modifying the Charger

I decided it would be easier to build a good looking case if the charger had an internal structure holding it together.  Then the case could be entirely aesthetic, rather than structurally important.  To secure all the components, I simply hot glued them all to the battery cells, as compactly as possible.  The downside of using lots of hot glue to hold everything together is that it is nearly impossible to fix any electrical problems that may arise.  However, since the circuit used is very simple, I am hoping that nothing will go wrong any time soon.  During this step, I added a heatsink to the voltage regulator as well.  I used a thin segment of a heatsink pulled from a dead ATX power supply, and I cut and filed it to fit withing the dimensions of the charger.  It already had a tapped hole in it, so I simply screwed it onto the 7805 with a little bit of thermal paste between the two.  Before gluing everything together, make sure to test the circuit to see that nothing has gone wrong.  You would not want to have to fix it once all the components are covered in glue.

Mostly glued together:

Internal Structure

Heatsink:

Internal Structure

Internal Structure

All glued:

Internal Structure

Internal Structure

Internal Structure

Internal Structure

Internal Structure

Internal Structure

To eliminate the need for a cable when charging iPods or iPhone, I made a compact right-angle USB to 30 pin iPod adapter.  To do this, I first cut both ends of an iPod cable.  I removed as much plastic casing on both sides as possible, and on the Male USB end, I removed all the metal housing from the USB connector.  I cut and stripped the four wires on both sides, and soldered the two ends back together with about 1-2 cm of wire connecting them.  I then glued the two pieces together at a right angle, so that when the USB end was plugged into the battery pack, the iPod end would be in a plane parallel to the batteries.  This way, when the iPod was charging, it could rest against the battery pack.

Stripped iPod plug:

USB to iPod adapter

USB to iPod adapter

Glued in position:

USB to iPod adapter

USB to iPod adapter

Plugged into the battery pack:

USB to iPod adapter

USB to iPod adapter

I made most of the case out of aluminum flashing.  It is very thin, so it is very easy to bend and work with, but it also looks nice when finished properly.  The casing fits very tightly around the internal components, so the insides are only held in position by friction.  To bend the aluminum to the proper shape, I first cut a long strip about 1 cm longer than the length of the battery pack, and about 3 times as wide.  I bent smooth curves by bending the aluminum around a 1 cm diameter dowel.  I then put the electronics inside the rough aluminum case, and marked the locations of all the ports that needed to be cut: the USB port in the front, and the switch and charging ports along the side.  To cut the holes for these ports, I first drilled small pilot holes and then used needle files to file the holes to shape.


When the aluminum was satisfactorily cut, I placed the electronics inside the aluminum, and plugged in a USB cable into the USB port and the charger into the charging port, to keep the enclosure properly aligned about the electronics.  I then glued the seam in the metal with epoxy, and wrapped the assembly in electrical tape to hold the seam together while the glue dried

Flashing:

Making the Case

Roughly bent into shape:

Making the Case

Hole for charging filed:

Making the Case

Making the Case

Making the Case

I plugged things into the ports to hold everything in place while the epoxy was drying:

Making the Case

To give it a bit more strength and make it look better, I enclosed the USB to iPod adapter in aluminum as well.  To do this, I bent a small piece of aluminum to fit the right-angle bend in the adapter.  I then glued it in place, and filled out the rest of the adapter with glue, to give it an nice shape.  To hide the color of the glue, I painted it all  black.


To keep the adapter secured in place while connected to the battery pack, I embedded neodymium magnets into both the adapter and the charger.  These magnets attract each other, and pull the adapter into place.

Enclosing the iPod Adapter

Way too much glue:

Enclosing the iPod Adapter

Enclosing the iPod Adapter

Enclosing the iPod Adapter

Enclosing the iPod Adapter

Painted black:

Enclosing the iPod Adapter

Magnet embedded:

Enclosing the iPod Adapter

Magnet glued just above the USB jack:

Enclosing the iPod Adapter

Enclosing the iPod Adapter

As I built the case, the switch that changes the battery pack from charging mode to discharging mode did not extend past the aluminum casing, and therefore could not be switched.  To fix this, and make the switch look nicer, I made an extension for the switch out of a thin rod of stainless steel I had lying around.  I drilled a small hole in the plastic sliding bit of the DPDT switch, and inserted a short length of the stainless steel rod into it.  The bit of stainless steel extends past the aluminum housing, and lets the user actuate the switch.

Metal bit:

Extending the Switch

Plugged into the switch:

Extending the Switch

Extending the Switch

Extending the Switch

The aluminum enclosure is not covered at the ends, so I made wood endcaps to hold all the parts inside the aluminum.  I chose to used some 1/4" mahogany marine plywood I had lying around, left over fromthe boat I built.  I cut the basic shape using a coping saw, and then filed the pieces to shape.  The final shaping was done with a very fine sanding wheel on my Dremel tool.  I also ground out a lip that extends half way into each endcap, so that they can only push half way into the aluminum casing.  I did this by using a routing attachment for my Dremel to keep the sanding wheel at exactly half the depth of the wood.  


The electronic internals slide into the metal casing only from one direction, as the insides are thicker on the bottom than on the top.  To fix the endcaps in place, I simply glued in the top one, since it never needs to be removed.  To secure the bottom one, I added tabs out of glue, to artificially extend the depth of the cap.  I then poke two very small holes into the sides of the aluminum casing, and screwed very small wood screws through them and into the glue tabs.  This way, if I need to remove the insides of the charger, I can unscrew the bottom cap and just slide the insides out.


I also made wood caps for the the USB to iPod adapter, using the same method as before.  These were just glued in place


I finished the wood by sanding it with 1500 grit paper, and then giving it a few coats of Tung oil.

Top end:

Woodwork

Woodwork

Woodwork

Bottom:

Woodwork

Woodwork

Finished with tung oil:

Woodwork

Woodwork

Woodwork

Woodwork

Woodwork

iPod adapter:

Woodwork

Woodwork

Screw hole:

Woodwork

Glue tabs on the bottom plate:

Woodwork

Screwed in:

Woodwork

By the time I had finished shaping the aluminum enclosure, it was quite scratched, and had an ugly seam down it where I glued it.  To fix the seam, I filed down the edge of the seam so that the top layer of aluminum tapers down into the bottom layer.  To fix the scratches, I brushed the aluminum with about 600 grit sandpaper, making sure to only sand in one direction.  After sanding, the aluminum was much too shiny for my liking, so I sprayed it with two coats of satin acrylic spray.  This evens out the color, makes it much less shiny, and also makes the metal feel nicer to the touch.

Surface before:

Finishing the Metal

Surface after:

Finishing the Metal

Finishing the Metal

Finishing the Metal

Since I wanted to be able to take it apart, I glued a ribbon onto the battery pack, which extends past the edge of the enclosure, and lets me pull out all the components.  To assemble everything, you just push the glued together electronics into the case as far as they will go.  Then you insert the bottom endcap, and screw it in place.  Finally, you push the stainless steel switch extender into place  through the slot for the switch.

Ribbon:

Assembly

Assembly

All put together:

Assembly

Assembly

Assembly

Assembly

Assembly

Assembly

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