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Step 2Building the Battery Pack - Plugs and Springs
Layout Overview
We have 10 C batteries, each running at 1.2v for a total of 12v. Each battery is approximately 1" in diameter. We will use a 1" PVC Electrical Conduit pipe to make two pipes of five batteries each. Note that while a C battery is outer diameter 1", a 1" PVC pipe has "give room", making it slightly larger than 1" inner diameter. White plumbing PVC pipe has even more give room (thinner walls).
A plug will be inserted on each end, containing a spring which will push into the batteries on both ends and terminals protrude out of back of each plug. Clumps of copper wire will go between each spring and it's battery terminal, since springs get crushed and bend with repeating impact (riding). The two pipes will be hot-glued together for strength and minimal space, and connected in series with a short, 1" wire. The full 12v will be accessed by soldering a 9v Snap-On Connector to the protruding terminals on the opposite pipes. Hot glue will hold everything together, along with sealing the pipes to be waterproof. As much tension as possible on the batteries is preferred, since mountain bikes take a lot of shock force than can cause batteries to bounce, and lights to annoyingly blink in the short gap of electricity.
Filing Plugs
The 3/4" PVC Plugs do not fit into the 1" PVC Electrical Conduit Pipe. They are about 1/16" too wide, which is essentially nothing. Because of this small size, we will use a file to grind the entire side of the plug until it does fit. It took me about 90 seconds of filing per plug to make it fit. A vice would be preferable to hold the plug, I don't have one, so I used a pair of pliers. I suggest holding your file with a cloth.
Extracting Springs
There are four large springs inside the Radioshack battery pack. Try to take as much wire off as you can get, if you don't, you can always stretch the spring for more distance. For the springs without excess wire to clip, I simply destroyed the case with scissors to remove as much metal as possible.
Mounting Springs in Plugs
With your needle-nose pliers, stretch out the back end of the spring through the hole in the plug. With about 1/8" protruding, grab and twist it with the needle-nose pliers to keep it from falling out, along with making a terminal to solder to.
Distance past the plugs is very important. We want as much tension on the batteries as possible, so the farther out the spring protrudes, the more force it will hold on the batteries for our limited distance of pipe.
With your hot-glue gun, fill the plug with hot glue, and allow it to dry. Try to have the spring as centered as possible.
Wire Cushions
In an ideal world, cheapy springs would withstand the weight of repeatedly being smashed by the 5x C batteries indefinitely. Sadly however, the springs become crunched and bend due to the forces of riding. As a result, we are going to perform a dirty, but very effective hack to always maintain a connection between our springs and the battery terminals.
I took a 1 1/2 foot piece of 16 AWG speaker wire to make each wire cushion. It doesn't have to be that specific thickness of wire, but we need a fairly thick blob of squishy metal (1/2" tall, 1" wide) to act as a conducting cushion. I use an X-Acto knife razor blade to cut down the length of the wire, and pull out the speaker wire, which is much easier and faster than how wires are normally stripped by cutting around the sheathing and sliding it off. Another good source of raw metal wire is old computer cables with a ton of pins in them, like the metal shielding in SCSI cables, I'm sure you can find something. I have pictures illustrating how I did it.
We have 10 C batteries, each running at 1.2v for a total of 12v. Each battery is approximately 1" in diameter. We will use a 1" PVC Electrical Conduit pipe to make two pipes of five batteries each. Note that while a C battery is outer diameter 1", a 1" PVC pipe has "give room", making it slightly larger than 1" inner diameter. White plumbing PVC pipe has even more give room (thinner walls).
A plug will be inserted on each end, containing a spring which will push into the batteries on both ends and terminals protrude out of back of each plug. Clumps of copper wire will go between each spring and it's battery terminal, since springs get crushed and bend with repeating impact (riding). The two pipes will be hot-glued together for strength and minimal space, and connected in series with a short, 1" wire. The full 12v will be accessed by soldering a 9v Snap-On Connector to the protruding terminals on the opposite pipes. Hot glue will hold everything together, along with sealing the pipes to be waterproof. As much tension as possible on the batteries is preferred, since mountain bikes take a lot of shock force than can cause batteries to bounce, and lights to annoyingly blink in the short gap of electricity.
Filing Plugs
The 3/4" PVC Plugs do not fit into the 1" PVC Electrical Conduit Pipe. They are about 1/16" too wide, which is essentially nothing. Because of this small size, we will use a file to grind the entire side of the plug until it does fit. It took me about 90 seconds of filing per plug to make it fit. A vice would be preferable to hold the plug, I don't have one, so I used a pair of pliers. I suggest holding your file with a cloth.
Extracting Springs
There are four large springs inside the Radioshack battery pack. Try to take as much wire off as you can get, if you don't, you can always stretch the spring for more distance. For the springs without excess wire to clip, I simply destroyed the case with scissors to remove as much metal as possible.
Mounting Springs in Plugs
With your needle-nose pliers, stretch out the back end of the spring through the hole in the plug. With about 1/8" protruding, grab and twist it with the needle-nose pliers to keep it from falling out, along with making a terminal to solder to.
Distance past the plugs is very important. We want as much tension on the batteries as possible, so the farther out the spring protrudes, the more force it will hold on the batteries for our limited distance of pipe.
With your hot-glue gun, fill the plug with hot glue, and allow it to dry. Try to have the spring as centered as possible.
Wire Cushions
In an ideal world, cheapy springs would withstand the weight of repeatedly being smashed by the 5x C batteries indefinitely. Sadly however, the springs become crunched and bend due to the forces of riding. As a result, we are going to perform a dirty, but very effective hack to always maintain a connection between our springs and the battery terminals.
I took a 1 1/2 foot piece of 16 AWG speaker wire to make each wire cushion. It doesn't have to be that specific thickness of wire, but we need a fairly thick blob of squishy metal (1/2" tall, 1" wide) to act as a conducting cushion. I use an X-Acto knife razor blade to cut down the length of the wire, and pull out the speaker wire, which is much easier and faster than how wires are normally stripped by cutting around the sheathing and sliding it off. Another good source of raw metal wire is old computer cables with a ton of pins in them, like the metal shielding in SCSI cables, I'm sure you can find something. I have pictures illustrating how I did it.
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