- wood block
- copper tubing
- assorted 1/4 watt carbon resistors*
- electrical tape
- electrolytic smoothing capacitor
- LM350 variable voltage regulator
- aluminum for a heat sink
- 2.1mm power plug from a surplus cell phone charger
- wood files
- drill and bits
- Dremel tool and cutting discs
- low wattage soldering iron, solder, heat sink
- digital multi-meter
- automotive battery charger capable of at least 3 amperes in output current
- hot glue gun
Step 1: The Voltage Regulator
Numerous Instructables already show how to configure a very common LM317 variable voltage regulator. These regulator chips are very handy for using an old AC power converter from some device you no longer use so it can power some device you do use. The LM317 regulator chip allows you to change the output voltage of a converter that uses a transformer rather than a switch mode power supply from (for example) 9 volts DC to 6.3 volts DC or any other voltage you choose that is at minimum a couple of volts lower than the input voltage and with an output voltage at least 1.25 volts or larger. The LM317 has a total output capacity of 1.5 amperes with a heat sink, or 1 ampere without a heat sink. (A heat sink is a piece of metal that absorbs heat from an electronic device and dissipates the heat into the air to protect the device from destruction by overheating. The device is attached to the metal with a rivet or a screw. A thermal grease is usually smeared between the mating surfaces.).
My camera requires an AC adapter that puts out 3 volts at a minimum of about 2.5 amperes, which is beyond the range of the LM317. I will use an LM350 variable voltage regulator. It has the same voltage range of the LM317, but can handle twice the current or up to 3 amperes. Radio Shack does not stock the LM350 regulators in their stores. Amazon has them, but shipping charges are expensive unless you have an Amazon Prime membership. Here is one on-line supplier for the TO-220 case regulator, but I am not sure about the cost of shipping.
Step 2: The Wiring Diagram
My box of surplus resistors contains resistors I ganged together in series for an actual 117 ohms. I will use this array for R1. I have other resistors I linked together in series for a total actual resistance of 178 ohms. These will be R2. I calculated the output voltage with both the formula I factored and the on-line calculator. Both agree the output will be 3.16 volts. This voltage compares very well with the voltage of a new battery. When the battery falls to 3 volts or just a little below, the camera signals a low battery.
Only the two resistances are essential for this project. The capacitors and diodes often used are not necessary according to the data sheet for the LM350. The first graphic combines a wiring diagram with the pin diagram for the TO-220 case. The view in the graphic is from the front of the regulator chip. The metal tab at the top is a second output terminal. The neutral (-) on both the input and the output connect to the end of R2 as shown by the ground symbol. The second graphic gives the same information (pin diagram and wiring diagram) for the TO-3 case regulator. There is a need to be very careful of static electricity discharges from your body, lest the regulator chip be destroyed before it is even used the first time. I sat very near to an electrical outlet and stuck a Phillips screwdriver into the grounding terminal of a 120 volt wall outlet such as is used in the USA. I touched the metal shank of the screwdriver before touching the regulator chip.
I planned to use a piece of 20 to 22 gauge aluminum for a heat sink on the TO-220 case. To be safe, I will cut some aluminum from an old Teflon coated frying pan and use it for a heat sink.
Step 3: My Power Supply
*As phred2 commented below, with a 12 volt input, the capacitor should be rated at 25 volts or higher due to characteristics of rectified AC current. My battery charger also has a 6 volt setting, and I can use that to get around the problem.
Step 4: The Power Plug
Step 5: Layout and Connections for the Power Supply
The power plug on the camera needs to be connected to the output from the LM350 so it is center point positive (+).
The wire connected to the OUT terminal (case) of the LM350 uses a crimp-on connector soldered for assurance and held in place by one of the mounting screws for the LM350. I used two #6 screws 1/2 inch long each with nuts and lockwashers.
I made text boxes on the photo for a couple of things, but they do not show up properly in some browsers. The resistances are each a string of resistors soldered together in series to get as close as possible to the desired resistances. I folded them in a zig-zag arrangement and encased them in hot glue to keep the leads from shorting and altering the resistance value of each. Look closely and you can see them well.
I made the cable between the LM350 and the camera long enough to have some freedom of movement, and I added a good strain relief.
Do check the actual voltage output at the power plug that connects to the camera. If you make a mistake in wiring the LM350, the output will likely be the full voltage produced by the auto battery charger, which would likely be enough to destroy your camera. It is very easy to make a mistake.
This step is the end of the general overview that will be sufficient for many readers. Some loose pieces and exposed connections will be placed more neatly and better insulated. As shown I was able to test and make certain my power adapter for my camera works, and it does. For those who wish them, the next steps show detailed construction steps I used, but which you are free to adjust and modify.
Step 6: Making the Base
Step 7: Fasten the Tubing to the Wooden Base
Step 8: Add the Smoothing Capacitor
*A capacitor rated at 25 volts would be much better and less likely to fail. I will use the 6 volt setting on my battery charger.
Step 9: Camera Connection
Seven feet of length should give plenty of movement freedom when using the camera and, yet, the moderately heavy speaker wire should avoid enough resistance to drop the voltage. The short original wires from the power plug are considerably smaller. If I find they are too small, I could pare away the covering around the power plug, solder the heavier speaker cable directly to the power plug, and cover it with hot glue.
Step 10: The Heat Sink
The second photo shows the LM350 (TO-3 case) mounted on the heat sink. Notice the two screws at the bottom that attach it to the end of the wooden base. You can also see the crimp-on connector with a wire (red) that connects to R1 and the speaker wire that is the positive (+) lead to the camera.
Step 11: Sweet Success!
Notice I covered all bare wires and components with more hot glue. I even embedded some of the cable to the camera in hot glue for a very functional strain relief.
I had hopes of claiming I built my camera power adapter for less than $3 US, and I would have been able to claim that. But, my LM350 in a TO-3 case cost about four times what I expected. Whenever possible, photos for my future instructables will be made with power from this home-built adapter.