Peter VanDerWal wrote: > 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. 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.) It might be as simple as replacing your spare tire well with a rectangular box. Or not. Think before you cut. > 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. > Remember this box will probably be holding over 1/2 ton of > batteries, do > you really want to risk having them come loose at speed when > you hit a > bump or have an accident? > > Welding is best and it's realitively cheap. Around here > welders charge > about $45 and hour in their shop or about $60 if they come to you. I > don't know how long it would take to weld in your box, but > I'd bet less > than an hour if you do all the prep work and have it ready to weld. There are some very conscientious welders out there. Unfortunately, I've seen way too many who think if they melt two pieces of metal together their job is a success. Unibody sheet metal is sometimes less than 0.030" thick. Welders typically prep the weld area with a disc grinder or sander, which can reduce the thickness at the weld to under 0.015" in a heartbeat. That can be critical. Also keep in mind that the weld heat will destroy any rustproofing near the weld, frequently in places you can't easily get to. You're putting a lot of effort and cash into your car. Make sure it lasts. I'm not saying welding is necessarily a bad idea. I bought a cheap wire welder to do parts of my LeSled. But I also spent nearly as much on structural rivets for most of my sheet metal work, and I will be bolting through sheet metal in some areas. Every technique has its proper application. 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." Chris
