Wednesday, December 3, 2008

Crimping the Battery Cables

One of the major tasks during construction of an EV is properly crimping all the heavy duty battery cables together. Here's the process that I used.

I measured the distance between the terminals that I needed to connect, subtracted 1/2" and then cut a piece of 2/0 gauge welding cable for that distance. Welding cable is much more flexible than typical 2/0 gauge wire, allowing it to snake around various car parts.

The picture here shows a piece of cable and a special cable stripping tool. In addition to just cutting the cable to proper length, I marked the proper orientation on the cable for the lug at each end with a permanent marker. Once the lugs are crimped on, it's very difficult to twist the cable to get the lugs to fit.

With the tool (you can use a sharp utility knife too), I stripped off 3/4" of insulation.

I then squirted a good dose of Noalox anti-corrosion compound into the 2/0 lug needed for the connection. Make sure to smear the compound with the tip of the bottle all around the inside of the lug to get good protection.

I also smeared a bunch of Noalox on the ends of each cable and worked the compound into the braids. It's a good idea to protect your multi-hundred-dollar investment of cable and lugs with a $7 bottle of Noalox. The Noalox will also make your connections better and last much longer in the harsh automotive environment.

On my previous electric vehicle, I missed putting Noalox on four battery cable connections. After about two months of driving, these connections developed a high resistance and sapped my power during acceleration. After cleaning them up and adding Noalox, the car performed better and it's been fine for several months now.

Okay, with the cable and lug all gooped up, I needed to hold it steady for the crimper. If you have a partner, they can do the job. I didn't at the time, so I used a large plastic clamp and a chair to hold the cable like this. Make sure the orientation of the lug lines up with the marks you put on the cable.

With the cable and lug steady, I can now crimp it into place. Fortunately our local EV group has a crimper, stripper and cable cutter set that we share for people building EVs. These crimpers are often $350 or more, but are well worth it if you can spread the expense around.

Once the lug is crimped on the cable, project the joint with heat-shrink tubing. I use 1 3/4" lengths of tubing for the cables.

Here's the heat-shrink tubing in place, filling in all the gaps to protect the cable from corroding.

Here's a picture of the rear battery compartment with several cables attached. I also added Noalox compound to the battery terminals to keep the connections protected.

Here's where the flexible welding cable really shines. I mounted the contactor just over the motor and near the controller and most-negative terminal of the battery pack. With the flexible cable, I'm able to bend things into place.

Note: I used 2/0 gauge lugs with 3/8" holes for everything except the two lugs on the contactor (closest to the viewer in the picture above). These had smaller (1/4" holes) due to the smaller holes on the contactor. If I had used the larger holed lugs, they would have slid into the contacts and caused a contactor failure.


Paul Rehrig said...

I have a question regarding the crimping direction. I would have thought to crimp along the lines on the lugs instead of 90ยบ to them (as shown in your picture). Does it matter? Also, where can one get those nice little black and red, presumably rubber, caps for the top of the battery terminals?


TimK said...

Hi Paul,

The hex crimper shown in the picture squeezes the lug down on six sides and works quite well. All the crimpers I've seen for welding cable are similar to this. If you find something else, post a comment.

Regarding the rubber caps, most EV supply places sell them in bulk. If you're desperate for a few of them, you can go to a boating supply store like West Marine, but it will cost you.


Paul Rehrig said...

Thanks for the info, I understand the crimping a lot better now. Sorry if it seemed ignorant.

For the rubber caps, I apologize, but I can't seem to find them on the few EV supply places that I normally shop at. Can you suggest a few good EV supply stores?

Thanks in advance.

TimK said...

Hi Paul, has some under "Wire and Terminals". Heck, you might just try a local auto-parts store like Schucks and look in their battery terminal department.