Encountered an Interesting Problem

Today I was planning to take my first electric test drive. In preparation for that, I began final testing of everything as I powered up the system. At some point I realized that the battery pack voltage was somehow getting into the chassis of the vehicle. The battery pack is completely isolated from the car so that is not supposed to happen. I stopped the testing and went about trying to solve this problem.

After spending quite a bit of time disconnecting all of the likely suspects - battery charger, DC-DC converter etc. - I was still unable to discover how the battery pack voltage was getting to the chassis.

Finally I remembered something that I had read awhile back. Sometimes a light coating of electrolyte on the top of the batteries will provide a path for battery current to get to the automobile frame. I tried cleaning the top of the front battery pack with baking soda and water. Although that didn't solve the problem, I saw fluctuations in the wayward voltage. From that I correctly surmised that my battery restraints were the culprits. Because of the obstructions on the ends of the batteries, I had run the steel very close to the cells on the front batteries. Recently I had noticed some corrosion starting to occur, even though I had coated them with rubberized undercoating. This was enough to conduct electricity to the steel restraints.


I completely removed the restraints and the problem was solved. WELL ALMOST. When I reconnected the rear battery pack to the system, half of the voltage was again making it into the vehicle chassis. So it was coming from the rear battery pack as well as the front. The rear restraints were constructed in a completely different way and were nowhere close to the cell openings.

I couldn't figure out where the electricity was making it to the chassis, but it was nearly the full voltage of the rear pack. To isolate the problem I had to remove all of the cables and reinstall them one-by-one while testing the voltage to the car chassis. Finally, I traced the problem to just one battery. Upon close inspection I found a small area of corrosion on the restraint at that battery.

I hit that area with some water and baking soda, which altered the wayward voltage. This confirmed that it was the problem area. I removed the bolts securing the restraint and lifted it up off the battery. The voltage to the chassis went to zero. Problem solved.

So, even though the problem has been diagnosed and solved for the time being, it demonstrates that my battery restraints are going to be a problem. This will undoubtedly happen again, so I am going to have to figure out a better way to restrain the batteries to keep this issue from reoccurring.