After the batteries went dead in the middle of a shot using my new camera with double the number of megapixels and features, I discovered there was no external power connector. Once a shot is lost, it may be lost forever, so an external source of power can be a critical option.
This Instructable will show you how to work around a proprietary or a non-existent power connector by making a battery substitute power connector that will allow an external power source to be used.
Step 1: The Power Supply
Combine or Not?
In many devices, such as a flashlight, the batteries are wired in series. In these devices you may be able to combine the voltages with a single battery substitute connector and power supply that provides only the total voltage, hence one AA = 1.5 votls, so 2 x AA = 3 volts..
In other, more sophisticated devices like cameras the batteries may be wired, or look like they are wired, in series but the series connection between them may be tapped or non-existent. If you are making a battery substitute power connector for one of these devices then you might have to make separate 1.5 volt battery substitute connectors and supplies for each battery the device will use.
External Power Sources
A portable external power supply can be made using a bank of external cells wired in parallel to keep your device going all day.
If you don't need portability as with studio type work a wall wort type power adapter with a minimum rating of 1 amp can be made using a transformer, bridge rectifier and a voltage regulator. Most regulators will handle a supply of up to 36 volts so a wide range of transformers can be used. A large micro farad capacitor with various other circuit refinements can be incorporated to provide power that is smooth. A circuit diagram based on the 78xx voltage regulator series is shown below.
The other options are to purchase a used 1.5 or 3 volts power adapter at a thrift store or a new one from Radio Shack or Wal-Mart for a little more cash. Multiple output voltage adapters, if they have a 1.5 or a 3 volt output, can be used as well but may be more expensive. Be sure you have one that is rated for at least 1 amp output. Otherwise your device will probably not operate or will at some point do the very thing you are trying to over come, which is to shutdown.
I opted for a wall wort type power supply from Radio Shack because one was sitting in my drawer. (Its only rated at .3 amps so I replaced it with a bigger one.)
Step 2: The Connector
If the adapter has long leads then they may be all that is needed when the plug is removed.Otherwise a 22 AWG or lower AWG set of leads should be acquired. Speaker wire works very well for this application.
A wood dowel with a 13mm to 14mm (1/2") diameter is needed and also several thumbtacks.
I found both the dowel (USP code: 041426027356) and brass thumbtacks (USP code: 027755015240) at Wal-Mart.
Step 3: The "contacks"
To make the "contacks" simply strip the end of the lead, wind it around the tack and solder.
You'll need at least two "contacks," one for the negative and one for the positive terminal.
Step 4: Add the "contacks" to the Connector
If you have a device where there may not be a series connection between the batteries then you'll need to cut each piece of dowel to the length of an AA battery minus the height of the thumbtack caps. My thumbtack caps are about 1.5mm.
An AA battery is about 50mm long so the pieces of dowel are cut to 47mm for individual battery substitution and to 97mm for an combined inline configuration. You can adjust this measurement for a tighter or looser fit. In practice 48mm and 98mm gives a little bit tighter fit.
Use a stick pin to start a hole in the center of each end of the dowel. After the holes are started place the point of the thumbtack in the hole and hammer the tack down until it is seated. Mark the end of the dowel with the correct polarity of the "contack."
Tape can be used to secure the wire to the dowel. You can get fancy and cut a channel for the leads along the length of the dowel if battery compartment space is at a premium.
Step 5: Remote Battery Packs
Shown is just one AA battery but if you cut the piece of inner tube wider you can parallel several batteries for more amperage and amp-hours.
(Hint: Use larger tubes or rubber bands for C and D cells)
Step 6: Test and Finish Up
Test the contacts with a voltmeter to be sure the polarity and voltage are correct and then test the fit of the connectors and the external power supply in an expendable device.
If there are no voltage anomalies and everything is working then cut a notch in the battery compartment cover in a place where the cover can be closed large enough for the leads to come through.
If everything is still working with the cover closed then you are good to go.