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Step 1: Bill of Materials
PVC pipe, 1 1/4" x 60cm in length
1 1/4" PVC pipe caps
1 1/4" test plugs
6 D-cell batteries
wire (~20 gauge)
battery contacts (negative ends I use for both, the spring I find has a better contact)
urethane sealant or another epoxy that will stick to pvc + metal + wood..
scroll saw or router
2x4 wood block, 1.5"
Step 2: Cut the pvc pipe
Step 3: Make a hole for the power and ground wires
-Drill a hole in this using a drill press. The hole should be just bigger than the thickness of your wire so that the wire can come through.
-You can take the caps off (if you need assistance pulling it off, slide a battery in the tube and bounce it up and down so it lands on the inside of the cap a few times. This should pop the cap off).
Step 4: Wire the tubes in series
-Hold the test plug next to the pvc tube as if it were fully in place. Mark a dot at the seam on the INSIDE of the pipes (ie the spots where they face each other). See the photo for reference.
-Drill a hole at each dot.
Step 5: Solder wire to 2 battery connects
Solder long wire onto two of the battery connect springs. This will be the power and ground wires that extend from your battery. If you like to use different color wire, ie red + black for power and ground, do one red and one black.
Step 6: Glue on the battery connects
-Bend the four corners of the square mount slightly upwards, attached to the springs from the battery connects. This will help it sit in place in the bottom of the inside of the cap.
-Glue the battery connects in the bottom of the cap by applying epoxy to the inside of the cap and to the back of the battery connect.
-Put the connect down into the bottom of the cap and press firmly.
-Let it dry.
Step 7: Put the caps on
-First, feed the wire coming off the battery connects into the holes that you cut at the seam of the cap / pipe. Feed them from inside outwards.
-For a permanent seal, sand the outside of the PVC pipe where the cap will touch when put on the pipe. Apply PVC cement onto both surfaces of the inside of the cap and the outside of the pipe.
-Slide the cap on firmly all the way.
-Let it dry.
Step 8: Wire it up
-In the holes that you cut where the test plug sits, thread it from the inside of one tube to the outside, then through the outside of the other tube extending out through the inside.
-Solder the battery connects onto the end of one wire.
-Adjust the length so that the connect that you just soldered comes out through the battery tube about half an inch.
-With the tubes parallel, and the caps flush against each other, The unsoldered wire end coming out the other pipe hole, cut this at about 3 inches from where it comes out of the hole, so it sticks out of the pipe a little bit.
-Solder on the final battery connect here.
-Now your two pipes are sort of joined as one unit.
Step 9: Prepare the batteries
Step 10: Attach a rubber piece to the connects
-Epoxy this to the battery connect.
-Let it dry. Once finished, put batteries in the tubes. Put them in series, so that towards the red (positive) wire you insert three batteries with the nub (+) facing down, towards the pvc cap, and the opposite in the other tube. Put in the spring + rubber to touch the batteries. Put the test plugs and test the voltage of the power and ground wires that are protruding. You should see about 7.2 volts.
NOTE: I used the flat connectors for the battery's positive side, but I found the spring ones work much better.
Step 11: Cut a piece of wood as a stabilizer for the two torpedo like battery tubes
-Hold the spare PVC piece flush against the edge of the 2x4, so the low point hits the edge of your 3/8" marking and comes into the corner of the wood. Trace this.
-Do the same thing on the bottom half of the edge of the 2x4.
-Use a scroll saw or a router to cut away the round part you just traced, leaving you with an hourglass shaped piece of wood.
-When you try to fit this flush against the pipe, if it has air space, try to sand this down with a rounded file.
Step 12: Glue your pipes flush together and caulk the holes
-Apply epoxy sealant to each surface where the pipes are flush, adhering them together. Clamp them in place.
-Apply caulk to the holes where the wires protrude.
NOTE: I am using three pipes because my application is as ballast in the bottom of a boat, and I filled one with ballast.
Let it dry.
Now you have a tubular torpedo 7.2V D-cell battery pack.