Introduction: Inexpensive AC Power Adapter for My Digital Camera
- 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
The regulator chip shown in the blister pack with the purple "Regulator" label is in a TO-220 case. The LM350 regulator comes in the TO-220 case and in the TO-3 case shown in the lower right of the photo. I had to special order my regulator chip. I thought I had ordered the TO-220 case, but when I went to pick it up, all they had was the TO-3 case. I was expecting to pay $2.43, but the bill was almost $11 for the sturdier case. I used a marker pen to write "ADJ" and "IN" on the regulator so I do not become confused later. Notice the diagram on the plastic envelope. The two terminal pins are closer to one end than to the other, and that is how the user knows which pin is which. The case, itself is the OUT terminal.
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
The wiring diagram for the '350' series regulators in the TO-220 case is the same as for the '317' series. One difference is that R1 on the '317' series is usually about 240 ohms, but on the '350' series regulators R1 is only about 120 ohms. Most hobbyists use a potentiometer to set the value on R2 for the desired output voltage. But, I want to use what I already have as much as possible, and I have a box full of resistors I bought for other projects or have salvaged from defective equipment. I will use two fixed resistances. Rather than merely depending on the color band coding, I use my digital multi-meter to determine the exact value of each resistor. Then I use the formula for determining the value of R2 for my desired output voltage. The formula from the data sheet is: Vout = 1.25 x (1 + [R2/R1]). If Vout and R1 are known, but R2 is not known and needs to be determined, the factored formula becomes: R2 = R1 x ([Vout/1.25] - 1) Or, you may use an on-line calculator for the '317' series regulators. On the calculator linked in the previous sentence you will enter the value of R1 and insert trial values for R2 until the desired output voltage shows in the appropriate window.
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
I will use my 6 or 12 volt automobile battery charger from a previous Instructable. It puts out 12 volts at 3 amperes. That is well within the range of what the LM350 can handle to put out just a little over 3 volts at 3 amperes. Its current is rectified, but not smoothed. I will add a 4000 µfd electrolytic capacitor rated at 16 volts* across the output leads of the battery charger. The capacitor is from my junk electronic parts box. The smoothing capacitor eliminates the need for a small capacitor between Vin and ADJ on the voltage regulator chip. (My auto battery charger as shown here is being used as a power supply to charge an LED mini-flashlight in yet another Instructable.)
*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
I had noticed the power plug receptacle on my camera appears to be tiny. I was not sure where I would get one. But, one day I discovered it is the same size as the power plug on my phone charger. I used an extra cigarette lighter phone charger left over from a previous phone in another Instructable (Step 12) and decided to cut the power plug not needed in that project off to use for this project.
Step 5: Layout and Connections for the Power Supply
I used a scrap piece of wood as a mount for voltage regulator circuitry. The connections for the alligator clips from the auto battery charger are cut from some scrap copper tubing. I marked them red and black to avoid confusion. I drilled holes and used screws to secure the pieces of copper tubing to the wood. I soldered connection wires to the copper tubing.
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
I cut a piece of scrap wood 3/4 inch thick to a square about 3 x 3 inches. We are preparing for a move to a different house, so I have only a few hand tools available. I marked the wood to make a trough for the copper tubing that will be the connection points to my auto battery charger. I used chisels and files to make the trough work as a nesting place for the tubing. First I made a square trough with a 1/4 inch chisel and a hammer. Then I used a 1/2 inch chisel to slope the sides. Then I used a couple of files to remove variations in the depth of cut made by the chisels. The pieces of copper tubing will rest in the finished trough and one screw in each will keep them from twisting out of place.
Step 7: Fasten the Tubing to the Wooden Base
I would have preferred smaller diameter tubing so my alligator clips would fit over them more easily, but this is what I had. I cut two pieces about 2 1/8 inch long each. I used some fine sandpaper to remove years of oxidation. I drilled a small diameter hole through both sides of each piece of tubing. Then I bored out one of the holes on each piece to pass a screwhead. Each piece of copper tubing is held very firmly in its trough with a #8 sheet metal screw 1/2 inch long.
Step 8: Add the Smoothing Capacitor
I tinned the copper tubing and soldered leads for the smoothing capacitor to the tubing. I salvaged this 4000 µfd electrolytic capacitor rated for 16 volts* from something. When the tubing had cooled from the soldering, I loosened the screws that hold the tubing to the wooden base and wrapped the pieces of tubing with red and black tape to indicate polarity. This will make it easy and error free when I attach my automotive battery charger.
*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
I cut about seven feet of a medium weight speaker cable for the connection cable to the camera. Here you see the male power plug from my surplus phone charger soldered to the speaker cable. The solder joints are staggered as much as possible without stripping away too much of the lead behind the power plug for the sake of strain relief. The solder joints are taped. A piece of heat shrink tubing is ready to slide into place and heat for shrinking. The red wire from the power plug goes to the center terminal.
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
If I had been able to get an LM350 in a TO-220 case, the heat sink would have been a simple piece of 20 gauge aluminum. But, I cut a heat sink from the bottom of an old aluminum frying pan. Here you can see all of the holes drilled to fit the TO-3 case of the LM350. I used a paper pattern to mark the position of the holes. First I pushed the ADJ and IN pin through the paper. Then I turned the LM350 over and marked the center of the mounting holes on the paper. The two holes at the bottom edge of the heat sink are for screws to mount it to the wooden base. I found a small tube of thermal grease in my junk parts box and smeared some between the heat sink and the surface of the LM350.
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!
This photo shows my camera with the battery removed and standing next to the camera. The power jack from my old phone charger is plugged into the camera. My home-built auto battery charger is powering my home-built power adapter for my camera. The display is the original picture that is my current profile picture at Instructables. When all was done, the actual output on my power adapter is 3.20 volts, which is quite close to my calculations. I rounded off the resistances, but both R1 and R2 registered an extra few tenths of a volt, which would account for the very slight difference between what was projected by the calculations and what I actually got. (A repeated warning: before connecting the power adapter to the camera, check the actual output voltage at the power plug. [Stick a common straight pin or the thin wire lead of a resistor into the center of the power plug to get a good connection point.] Failure to do this could destroy your camera if there is an error in connecting the components.)
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.
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