As the functions of cell phones increased astronomically, so their power requirements. Nowadays a clever :) phone which is purchased new can hardly stand working for 1-2 days and their endurance even decreases as the battery inside wears down as it gets older. So many people are buying and using battery power packs.
I've also bought one from ebay, it has 4x4200 mAh Li-ion battery power inside and even a led ligh to be used as a torch. It is able to charge my phone 4 times from zero to full. I'm using it especially in our 3-4 days bicycle tours, it is very useful.
Then my girlfriend saw the thing and wanted one for herself for daily use :)
I've thought of ordering one more from ebay but it takes 2 months for ebay orders to arrive via slow chinese post. And the customer asked for a much smaller one. So I thought making one by using a single Li-ion battery could be a much better and faster way. I had batteries, charging and usb power supply modules lying around which I'd bough on ebay some time ago so no new purchase was necessary.
So, lets start
Step 1: Design Research
I started with researching the market for available products as inspiration. There are many products of similar kind on the market, on the internet you can find hundreds, maybe thousands of different products.
So i've looked at the ones already designed and built, being sold on ebay. Saw that lots of them are very similar to each other. When the quick search is complete, I did some sketches and decided on a boxy rectangular shape, with rounded corners. I've planned that my charger will have two main body parts that will lock-shut on eachother without the need of screws.
Step 2: Parts Used
I've had all the parts lying around as I always purchase 10 electronic parts (sometimes more) when I need one. That makes future projects much easier. And here are they and their ebay links.
Usb power regulator module (I've used the 0.9-5v to 5v 600mA type)
I don't have a link for the switch but I've added two close-up photo of it with its dimensions, one similar in size and shape should do the job.
Also ripped off the battery contacts of an old electronic toy and used in my product.
Step 3: Electrical Connections and Testing
As the usb power regulator draws around 15ma current even while not supplying any current, it became necessary to use an on-off switch. I've also used the switch as a commutator between the charger and power regulator. While charging, the power output module will be disconnected and while outputting power, the charging module will be disconnected. As the charging module doesn'r draw any power from the battery, it will remain connected in power off mode.
Step 4: Industrial Design Engineering: Internal Placement of the Parts
For this step, I've modeled all internal parts and electronic modules as solidsorks parts.
I did the internal placement to find the optimum case shape and dimensions before continuing the 3d modeling of my design. I did some modifications to the design according to the needs arised during this placement process. I've used solidworks' assembly mode for this purpose.
Step 5: Industrial Design Engineering: the 3d Modeling
The modeling of the product case is straightforward, in summary it starts with a rectangular prism. Turns into required form step by step, then it is cut into required parts, added internal details and thats it. I've just selected several of the modeling steps on which a visible difference is done, in fact there are a little bir more than this :D
There are 3 parts at the final work, upper body, lower body and the internal support part.
No screwing is required internally or externally including the electronic cards. The parts locks on each other securing themselves very firmly. The internal support part divides the main interior space into two; battery space and the electronics space. While it counters the mechanic force applied by the battery & spring, it also applies support to the power&charging modules, holding them in place when the plugs are being inserted.
As i said, the case locks up itself, I mean really locks up. So the builder should be sure the device works properly before closing the case or it might be a little difficult (:) to open it back up.
Step 6: 3D Printing
I did the printing with an UP Printer.
it took around 5 hours and used up 40grams of ABS filament.
I've used a semi transparent filament for the leds on electronic modules to be seen from the outside, I didn't open holes for the leds.
Step 7: Assembly
The assembly is not difficult, I first inserted the modules to their places and first cut several wires into required lengths; 3 pieces of wire are cut in approx 3-4cm length and one is cut in approx 7-8cm length. Then followerd the steps below.
These steps are in fact just the translation of the circuit schematic above, if you can already read it, then you may skip the steps and continue building the circuit by using the schematic.
-> solder the 3 wires to the terminals of the switch.
-> solder the other end of the wire on the mid pin of the switch to the + pole of the battery.
-> negative pole of the battery, negative input of the power regulator circuit, negative output of the battery charging circuit are all connected to each other by the long wire. ( see pics)
-> connect the remaining pins of the switch to the positive terminals of the two circuit boards via the remaining two 3cm long wires.
I did the last step in a way that when the switch also shows the direction of power transfer. For instance if it is pushed towards the inside of the product-battery, that means the product is in charge mode, you can charge it by using any usb adapter or a pc usb port. When the switch direction is to the outside of the product, namely to usb sockets' direction, that means the product is in power output mode and you can charge your phone.
in power output mode, a red light turns on and stays on as long as the battery stands.
in charge store mode, there are two lights, a blue and a red led. Red means charging, blue means charging is complete.
Step 8: Testing
After connecting everything up, I loaded it with an usb adapter to full and tested charging with two phones. It charged one to full and the next to %47 percent. Not bad. you can use a higher capacity battery if you like to charge both of the cellphones to full. :)
Step 9: Happy Customer
I've given it to my girlfriend. She doesn't seem much impressed and asked if it is possible to paint it, then asked whether that thing has a light too :D
I plan to make an additional led light part which will be inserted to the usb port when necessary and I guess there is also a small paintjob is waiting in the near future. Maybe I should leave the painting to her.
Comments are welcome.