Monday, October 31, 2011

Safety Issues

While at EVCCON, I spent a good deal of time looking at and admiring all the conversion, and trying to get ideas for how I might improve the Z3.  Among the things that made an impression on me was the fact that the constructors of virtually all the EVs had made a great deal of effort to make the car's motor bays "touch safe."  The Illuminati team mentioned that during the X-Prize contest, they were required to shows that all the compartments that held batteries and electronics were also "wrench safe."  Meaning that you could throw a wrench into any compartment or area in the car and there was no danger of a short or explosion. 

It became clear to me that I'd fallen short in this area.  I never really considered putting much effort into making the z3 "touch safe" or "wrench safe" figuring I was the only one in that area, and I know what's safe and what isn't so why does it matter?  But as I watched all these people milling around my car, I found myself with an unusually high level of anxiety worrying about someone hurting them self.  Several times people leaned over the motor and battery compartment to get a close look at something, only to have their EVCCON lanyard drag across the top of the cells.  In fact a local boy came in to look at the neat cars.  I explained to him not to touch anything for safety reasons, but then watched him like a hawk to be sure he was safe. 

I realized at that time that not only would making the whole motor compartment touch safe be a good idea, it was essential.  Here's the thing...  I never anticipated that the car would draw as much attention as it does.  I never envisioned that I'd be taking it to car shows and there would be strange people so interested in it and getting so close to it to inspect it.  Imagine what the news media (especially Fox News) would say if some hapless person were accidentally injured, or worse, by an electric car at some car show.  In one fell swoop, I'd be responsible for not only injuring or perhaps killing some poor soul, but the EV movement as well! 

At the public car show the last day of the conference, one of the attendees, David Hrivnak, made a point of pulling me aside and asking me what I intended to do about the safety issues.  Not "are you thinking about doing something?", but "what are you going to do?"  David clearly recognized the risks I was exposed to and the implications, and had the courage to bring it to me.  By that time I had already got it.  I was absolutely on the same page as David.  I understood what was at stake and the imperative to resolve the safety concerns he, and by that time, I had.  Thanks again David, I'm very grateful.

I had been looking at the other cars to see which ideas of theirs I could steal.  What I saw was basically two ways of covering the batteries,  terminal and high voltage connections, if they were in an area where they were exposed.  Either they were sealed in a custom built box, or they were simply covered with plastic.  For anyone who's seen the Z3 or the pictures of it, you know there is no room to redo things in order to incorporate battery boxes.  That meant I was going to need to figure out how to simply cover the terminals of the batteries.  In addition, I needed to figure out how to cover the electrics bay where the controller and contactor are.  That bay is the only placed where the positive terminal is exposed that has full pack voltage. 

After a little research I learned that the best material was probably Lexan, so I purchased some from the local hardware store and started measuring and cutting.  Cutting Lexan is not too difficult.  There are special blades available to cut it, or you can cut it with a thin blade, fine toothed saw.  When you cut it with a blade, you simply score the same line 15 or 20 times and then bend the plastic to kind of tear it through the rest of the way. 

I knew the front batteries were going to be the most difficult to cover.  It looks easy enough, but the clearance between the front corner of the batteries and the hood is as little as 1/2".  So to place a piece of Lexan on top of the terminals and run it straight to the edge of the batteries would certainly be hit by the hood once it was shut.  It would require careful cutting and measuring to make it fit.  Since you can't actually see the space once the hood is closed, I used Play Dough to figure out the clearances.  I simply shaped a chunk of it to the size I needed and laid it on the area where I thought the battery cover and the hood touch. Then I shut and opened the hood and inspected the Play Dough.  You can easily see where it's been crushed too thin, or even pierced.  That's where I needed to trim and do some more fitting.

Ultimately I found I needed to bend the front edges of the cover to clear the hood.  I found a piece of scrap Lexan, and sicked my heat gun on it.  I used the low setting thinking that I didn't want to heat it too fast and potentially over melt or set the piece on fire.  It worked pretty well but I found that when I tried to bend a longer edge, the plastic started to show bubbles inside by the time it finally started to wilt.  I tried the higher temperature and that turned out to work much better.  First, it was faster, but second since the plastic was exposed to the heat for a much shorter period of time, so there was no time for those bubbles to appear.  So, higher heat yielded a much cleaner looking bend.

In the detail shot you can see what I mean about the plastic bubbling under the heat gun.  Structurally, it seems fine, but cosmetically it's kind of ugly.  You can also see the slots that I cut into the plastic and the clips I'm using to hold the piece in place.  These clips are an assembly of two channel clips used to hold a mirror up to a wall.  This works fine, but admittedly it's ugly.  I'd love to have come up with a better way to hold this cover down, but this was the best thing I could think of.  I also drilled little 3/32" holes in the Lexan next to each of the positive terminals.  This way I can stick the probe of my multi-meter through the plastic to measure any one or group of batteries I want.

On the larger set of batteries I used D-hooks mounted to the aluminum frame and Velcro straps to hold the piece down in place. Again, not the best looking solution.  You can see that the plastic follows the curve of the batteries nicely.  In the detail shot, you can see that I was able to shape the plastic to accommodate the 2/0 cable coming off the pack, and turn the corner down just a bit to make it less lethal.  I used high heat to make these bends; notice the difference in the plastic from the first bends I made.  It looks much better.

The cover over the electrics bay took a lot more fiddling and cutting to get it just right.  It rests nicely in the grove just below the cushy part of the rubber that seals the area from the elements when the hood is closed.  I made a template out of cardboard and then trimmed the plastic to shape.  As it happened, I'd run out of Lexan and the only sheets at the store were either too small or way too big (and expensive).  So I used an acrylic sheet instead.  I can see why people said that Lexan is better.  Acrylic is much more prone to snapping, cracking and chipping.  I was able to get it done, but it would have been way easier with Lexan. 

There is still one more safety concern I need to address, and that's an emergency cut off switch.  You may remember that I had the big red slap switch under the hood, but there were two problems with that.  One, I had no way of actually slapping it in the event of an emergency, that is if I were in the car driving it, and two, it melted.  At some point, enough current went through it that one of the internal contact points melted.  You can see pictures of that from a couple posts ago if you wish.  To replace it, I got this unit:

This needs to be mounted either in the cabin so that the driver can reach it while moving, or I need to rig up some way of actuating it from in the cabin.  I'm thinking that a push/pull cable mounted to the handle should work well.  The questions remaining are, where do I mount the switch and where and how do I mount the cable?  As of now, I have no idea about either.

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