Many of us have surplus 5 volt AC/DC chargers for cell phones we no longer use. Those chargers could be useful for a variety of power sources if there were a way to attach a female USB connector to the cord and do it for little or no cost. But, stores like Radio Shack do not list a female USB connector in their on-line inventory. USB cords with a female end are expensive unless you happen to have a non-working USB cord with a good female end. Improvising one's own female connector becomes an attractive option and others have done that. But, the base material for a connector needs to be quite sturdy, thin enough, and there needs to be a way to attach thin circuit traces. This Instructable is an approach I attempted. It worked with some devices, but not with others.
The photo shows the female USB connector on a car charger for a USB device.
Step 1: Tools and Materials
- An old circuit board
- Low wattage soldering iron
- Dremel with a cutting wheel
- Drill and bit
Step 2: Safety Concerns
The photo shows one of four 220 volt 820 micro-farad capacitors inside my old computer power supply. These capacitors hold a charge long after AC power was last applied to the power supply. PC guru Scott Mueller (Upgrading and Repairing PCs) tells his readers never to open a computer power supply because of the lethal charge of electricity stored by these capacitors. I cautiously opened the power supply case and visually located the capacitors. I determined which pins on the circuit board were connected to these capacitors. Then I shorted the pins on each capacitor with a screwdriver as shown in the photo. The screwdriver has an insulated plastic handle. Shorting the capacitors removes the charge they hold. In my experience it is good to short each capacitor three or more times to be certain the capacitors are fully discharged. Then it is safe to handle the circuit board and to desolder parts from the circuit board.
Step 3: Cut a Suitable Section of the Circuit Board
There are four circuit traces inside a USB connector, whether male or female. The two outermost traces in any USB connector are the power connections. On center these outermost circuit traces appear to be 7.2mm from one another. Look for traces on the power supply circuit board that are very close to that same dimension apart from one another. Failing that, it would be possible to use an area totally covered with one large circuit trace. Later the copper material could be ground away where it is not needed. This would make two circuit traces exactly where you need them.
I used a Dremel tool with a cutting wheel to cut away a portion of circuit board with two suitable circuit traces. I cut it larger than necessary so I can trim it more precisely later.
Step 4: Trim Component Sealant
This part of the circuit board held the large capacitors shown in step 2. A sealant was used on the board, perhaps to keep the capacitors from vibrating and making noise. Trim it away clean with a knife.
Step 5: Desolder Any Components
A small capacitor still needs to be removed from the section of circuit board I am using. I am using a 15 Watt soldering iron to desolder the remaining part.
Step 6: Other Preparations
The side of the circuit board with the traces also has a small surface mount diode that connects the two traces. I was not able to desolder it, so I used the cutting wheel on a Dremel tool to break the connection from the diode to one of the traces. Notice the tan color where there should be green.
I also used my soldering iron to smooth bumps in the solder on the traces.
Step 7: Trim the Circuit Board to Fit a Male USB Connector
Here you see the circuit board portion aligned with the opening on a male USB end. The red lines indicate the position of the traces in the male end. This picture gives an idea of how much of the circuit board needs to be removed on each side. (In use, the circuit board will be inverted.) I can use the face of a cutting wheel in a Dremel tool, but will need to be very careful and check my work often.
The photo shows a USB extension cable with a good male and female end. I want to save this for its original purpose and do not want to take an end from it.
Step 8: Preliminary Fit
I have a good preliminary fit. The circuit board portion fits nicely into the male USB end. In places, the solder presented too much thickness. I turned the circuit board face down on a piece of very fine sandpaper resting on tabletop and made a figure 8 motion to sand the solder to a uniform thickness that fit. Just to be safe, I want to remove whatever is necessary to prevent a short to the inner traces inside the USB connector.
Step 9: Raise the Traces for Better Connections
After some experimentation, I found I needed to make the traces a little elevated above the circuit board. The easiest way to do that was to lower the circuit board material by grinding it away with a cutting wheel on a Dremel. This also allowed me to narrow the traces for a better match with the traces in the male end. In the photo you can see the beige colored board material that appears when the green surface coating is ground away. You can also see the proper polarity for the male USB connector. The red (+) wire goes to the left side as shown and the black (-) wire goes to the right side.
And, I drilled two holes in the circuit board material to make a strain relief for the cable. The cable goes down through one of the holes and up through the other. Then the bare ends are soldered to the traces.
Step 10: Connecting the Ends
I inserted my new female end into a standard male USB end. The fit was a little loose so I used some folded paper to make it more firm and the contact more certain.
I wish I could say this works in every situation. It worked well with one USB device I have, but did not make adequate contact on another for which I really wanted to use it. Perhaps I need to make the traces more precisely fitted to match their counterparts in the male USB connector. Still, this may work on an application you need and may be worth a try.