November 11, 2001

Building the battery connectors:

Our test pack will be made up of 180 2 volt Cyclon batteries. These sealed lead acid batteries should be able to deliver the 700 amp currents that the motors will demand. To connect the batteries, we will need to fabricate cables capable of surviving 700 amps. We want to use copper which is highly conductive. We are going to use cable rather than copper plate to minimize vibration and shock transmitted from battery terminal to battery terminal. And finally, we are going to use a braided strap rather than a round wire to maximize passive cooling.
A search on the Internet shows that

http://thewireman.com/wire.html#tcb offers one inch by .090 braided strap. This is the equivalent of between 0 gauge and 00 gauge wire.

Copper braided strap
To connect the copper strap to the batteries, we need to form 360 lugs. Home Depot supplies us with ½ inch copper pipes. 1/2 inch copper pipes

These have to be cut into ¾ inch sections. A pipe cutter gets the job done fairly quickly.

cutting pipes to 3/4 inch sections
Next we improvise a quick strap measuring device … measuring the strap
And cut 180 2 inch straps. cutting the straps
A battery pack is normally only as good as it's weakest battery. To get the maximum out of our battery pack, we need to be able to easily check individually, the state of each battery. To allow this, we are going to include signal wires from each battery. To minimize wiring, we will use a wire from each positive terminal only. By measuring voltage from the positive wire of the first battery to the positive of the second battery, we will get the voltage of the first battery and it's connectors. Since this wire will be used for low amperage, we can use a very fine gauge wire.
For $10, Home depot supplies a surplus roll of 1000 feet of Cat 3 Network wire. This is 3 sets of 24 gauge twisted pair wires.
1000' roll Cat 3 Network wire
We cut 35 15 foot lengths. Strip approximately a foot of the external coating, and then 2 inches of each individual insulation. stripping the network wire
Now, all the parts are ready. It is time to start production. Step 1, Insert strap in tube… Inserting strap into tube
Then use a drill press to crush the tube onto the strap. Half crush, adjust strap, finish crush so copper pipe does not move easily.
crushing tube
Insert the other end of the strap into another bit of tubing (this is why we need 360 tube pieces and only 180 straps). inserting other end
Half crush tubing, adjust and insert signal wire fully (blue and white wire on right). Some signal wire will stick out the back. Crush the rest of the way. Signal wire should be secure for a gentle tug. Crushing other end
Repeat this six times until you have used all the signal wires in a bundle. Next carefully lay out the six connectors on a metal block in a press. None of the signal wires should cross another connector or even the tube part of it's own connector. Otherwise the signal wire or it's coating can be damaged. Laying out connectors
Using another block of metal and a 20 ton Press, crush the copper tubing onto the strapping. The goal is to "cold weld" the tubing to the strapping. "Cold welding connectors"
The result are some very flat pieces. The signal wire does not pull out. Ready for drilling
Using a drill press vice, we drilled six at a time (with a sacrificial piece below to ensure a clean hole on the bottom lug). Stacked in drill press
The drill bit is 8 mm for the positive terminal. 8mm

Turn the six around and use a 6 mm bit to drill the negative lug holes.

Simple, Huh?

6mm

 

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