6VDC Dummy Battery for a Canon AE-1 Program Camera
For astronomers who enjoy astrophotography or even those of you thinking of getting into the fascinating hobby of taking night sky photographs and the only 35mm film camera you have is a Canon AE-1 Program SLR, you'll eventually discover (if you haven't already) that this camera has been designed with an electronic shutter. This electronic shutter requires battery power to be held open and the longer you keep the shutter open, the faster the battery drains. Under normal use this small 6 volt camera battery will last long enough to take numerous rolls of film. But when you start using your AE-1P to take long exposures, long exposures required for astrophotography, you'll find out that you'll be lucky if that brand new 6V battery lasts through one roll (24 frames) of film before it gives up the ghost. Canon at one point actually made a dummy 6V battery unit that replaces this small 6V battery but these are very hard if not impossible to find. So I decided to build one of my own and after giving it some serious thought, this is what I came up with.
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All the parts you see in the photo above are from the 6V battery except for the wooden dowel. Use a pair of diagonal pliers and carefully unwrap the outer metal case of an old depleted battery. All you need is the end contact (shown top left) that has the three cuts in it and the top contact from one of the 4 batteries. The contact on the upper right can not be used (in my case) because it can not be soldered, so you'll have to use your diagonal pliers to carefully open one of the batteries. Be careful because there is acid inside these batteries. After carefully opening the battery, I took a toothpick and paper towel, cleaned out the inside of the top contact of the opened battery (being careful not to come in contact with any of the acidic contents) and immediately washed it and my hands in cold water and soap. If you don't want to open a battery (and I suggest that you don't), just get another old 6V battery and use the same contact as the first one we salvaged.
Now cut a 22mm long piece from a 1/2" round wooden dowel rod and cut two grooves into it as shown in the picture above using a Dremel with a cut off wheel. Leave a small gap in the middle of your dummy battery and cut deep enough to reach the center of it on each end. I used a 3 foot piece of small gauge speaker wire and soldered one end of it to each of the contacts. Press the wires with contacts into the cut grooves of the wooden dowel and make sure the metal contacts are seated firmly against the ends of the wooden dowel. Then insert this into the battery compartment of your Canon AE-1P camera for a test fit. My first try wouldn't fit so I had to shorten the length of the wooden dowel just a tiny bit. When your battery correctly fits the battery compartment, use some epoxy or fast drying glue and carefully raise each metal contact up and away from the wooden dowel and apply the glue using a toothpick. Also make sure to fill the grooves up with glue. When you've finished applying the glue, apply enough pressure to both ends of the dummy battery to insure that the metal contacts remain firmly seated against the ends of the wooden dowel until the glue has set. Once the glue is dry, clean off any glue that may have adhered to the tops of the metal contacts. Then solder a female RCA connector to the opposite end of the 3 foot length of speaker wire.
Next, head off to Radio Shack and pick up one of their enclosed black plastic battery holders that will hold 4 AA sized batteries. Also pick up some RCA connectors (if you don't have some spares around the home) along with a pack of heat shrink tubing and some black electrical tape. This R/S battery holder also comes with an On/Off switch which is really nice. Fit a proper length of heat shrink tubing over the black and red wires of the battery holder and press the end of it into the square opening where the wires enter the battery holder. Then solder on the male RCA connector and carefully use a lighter (or heat gun) to heat up the shrink tubing to shrink it down around the wires. Use some black electrical tape to wrap around the end of the RCA connecter that meets the end of the heat shrink tubing and you're done.
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I connected the wiring so the negative side (black) is attached to the outside terminals of the RCA jacks and the positive side (red) to the center terminals. Install alkaline, Ni-Cads, or N-M Hydride batteries into the battery holder and plug the two RCA jacks together. If you have a volt meter, just turn the switch on the battery holder to the "On" position and measure across the two terminals of the dummy battery and determine which is positive and negative. Or, just simply plug the dummy battery into the camera, turn the camera on and press the battery check button. If it beeps, the dummy battery is correctly installed. If it doesn't beep, reverse the dummy battery and recheck. Once you get the camera to beep, use a black marker and mark one end of the dummy battery (+) and the other end (-) so you know how to insert it into the camera correctly.
The only problem you might have is keeping the dummy battery from falling out during use. I used a rubber band that wraps around the battery door, around the right side of the camera to the back side hooked to the top left edge of the film label holder. If you happen to come up with a better solution for keeping the dummy battery in place, please feel free to let me know so I can post it for everyone.
I wish you all dark night skies and successful astrophotography!