Freitag, 6. November 2015

Short Circuit

Ever heard these well intended hints :

  1. Wear eye protection when working with batteries!
  2. Wear gloves when working with batteries!
  3. Glasses with a metal frame dropped on battery terminals will turn into a ball of hot plasma flying in your direction.

How serious did you take these advices? Honestly? Well, I respected them partially. I've seen the spanner creating a short over the poles of one single cell (at 24:30). After 10-20 seconds it was glowing white from the heat. So I was really really careful when installing the batteries. Also when I took them out of their provisional enclosure last weekend. I held on every strap I loosened so it couldn't turn and create a short. I reminded myself at least 5 times during the first ten minutes: "Be careful! Concentrate!". And yet, I made a serious error: I removed one bolt from a strap completely and only then started loosening the second bolt. The strap slipped out of my hand and created a short with a cell in the next row - over about 15-20 cells in series. Oh my! I won't forget that crackling sound and the feeling. It' possible that I imagined it but it felt like I could feel the magnetic field. I believe it took me less than half a second to grab the strap again and break the short. The result can be seen on the pictures and the video. Fortunately just 2-3 minutes before, I put on gloves to protect my hands from physical injury (scratching those bolts can tear your skin). The copper on the straps melted immediately and sprayed around the trunk in little liquid drops. On one picture you can see them and their burn marks in the carpet of the trunk. Imagine these drops landing on the skin or worse into an eye. I was wearing only my glasses which cover only about 70% of the area. Also discovering drops of copper below the emergency vent caps of some cells and looking at the black trails on the battery casing, I consider myself extremely lucky not to have gotten injured.
Once the smoke cleared from the trunk and I was sure nothing would happen any more, I had to take a walk outside - with weak knees. Next to the car stands a wagon filled with hay - imagine sparks flying over. I also remembered mounting the cells under the car. It was all done over-head, no hat, no eye protection. Believe me, I'd never do it that way again! At least a chap and full eye protection are a must - like it is for over-head welding.

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