>> If you cut a hole in a unibody vehicle it is now weaker. >> Bolt a box in >> and it's still weak, weld it in and it will be as strong (or >> stronger) >> as it used to be. > >While this certainly can be true, I don't think it's a good idea to >accept it as a general truism. You need to look at your sheet metal and >determine what loads it is carrying. Then decide where you'll cut the >hole, and how your added structure (angle iron, sheet metal, whatever) >will support the original loads in addition to the batteries. One >approach is to make it way stronger than it needs to be. That can add >unnecessary weight, and can also add point loads or stress risers to >your original sheet metal, something it's not good at dealing with. >
Ok, perhaps I should have been a bit more verbose. My answered was directed at Matt, clearly he has some mechanical aptitude but he doesn't understand structural engineering (if he did he wouldn't have asked the question). Obviously he is trying to save money (commendable) by doing as much of the conversion as possible by himself. So either I tell him to press on and bolt it in himself (bad idea judging by his posts) or I tell him to have it welded by a profession who probably has a fair understanding of structural integrity. The way I see it he has a better chance ending up with a safe and sound vehicle by having a professional weld it in rather than bolting it together himself, especially when there is no way I can teach him structural engineering in a simple post (not that I'm an expert mind you). >You can also make it too strong. If your battery box is so solid it >refuses to crumple in an accident, who gets hurt? (And how does the >battery box cover keep the acid out of the passenger compartment even >when it's attached to crumpled sheet metal? Consider a flexible cover >of reinforced rubber sheet.) The batteries inside won't crumple much anyway, I think it's preferable to have a strong box that will contain the batteries than one designed to crumple/split/loose containment. >> While it might be possible to nuild/attach battery boxes to a unibody >> vehicle using nuts&bolts, it won't be as strong as a welded >> box. And it >> will probably cost more in materials to build one that won't fall out. > >Depends on how it's done. If you're attaching a piece of angle iron to >a firewall to support racks, bolts could be just fine. You're far >better off with six 1/4" bolts rather than two 3/8" bolts because you >*must* spread the load when attaching to sheet metal. No exceptions. >Use big washers so the bolts can't pull through in an accident. So now Matt thinks he can attach his battery box containing 600 lbs of batteries with six 1/4" bolts (see what I mean about not being able to teach engineering in one post). Again I was talking about a box built by Matt, not an expert. An expert might use a combination of welding, bonding and bolting depending on any number of factors. There is no "best" choice, I was just trying to recommend the best "simple" choice that I thought would apply to Matt. I.e. get some professional help. >I'm often bedazzled by the the discussions between electrical wizards on >philosophical differences concerning fusing, controller design, hardware >vs. software safeguards, etc. It's a little disconcerting to hear the >same wizards say, "Yeah, just get it welded. You'll be fine." Like I said, my answer was directed at Matt and my feelings about his general abilities. P.S. Matt, it hasn't been my intention here to insult you. Nobody can be an expert at everything. My posts are based on my feelings about your knowledge and abilities and if I've misjudged you I apologize. I've been told that I have a tendency to come off heavy handed and if I've done that again...that was not my intention.
