Sunday, July 13, 2008

Battery Racks, Continued

I did some more work on the battery racks over the past few days. The biggest challenge is getting everything to fit properly without hitting any blockages. At this point, I think I have all of the metal pieces cut, but I don't have the bolt holes drilled.

Note: the following descriptions are a bit verbose because I'm trying to keep track of all the detailed measurements as I go.

Here is a closeup of the front battery rack on the driver side. For the moment, the racks are only held in by the two beefy bolts from the towing bracket in the lower-right corner of the picture. I added a piece of 2" angle iron and a 10" support piece (1.25" wide and 3/16" thick) on the left side of the picture to support the back edge of the rack. I've already drilled the top hole and put in a 3/8" bolt and nylock nut. I have the bottom end clamped so I can drill an accurate hole through both pieces to insert the bottom 3/8" bolt. Of course, I actually drilled two 3/8" holes in the 10" support piece first 1" from each end, and then used those holes as guides to drill the holes in the bracket that I attached to.

Here's the front battery rack again, but on the passenger side of the vehicle. I'm using an already existing 6mm bolt on the side of the chassis support to hold the top end of the 10" support strut. This picture doesn't show it, but I'll eventually drill a hole through the bottom end of the diagonal support strut into the horizontal 2" angle iron and add a 3/8" bolt with nylock nut.

Moving onto the firewall battery rack. I'm using the existing 6mm bolts on the side of the shock towers to hold up four 6"x1.25"x3/16" steel flat bars which will support the base of the battery rack. I drilled 15/64" holes into these bars 5/8" from the end for the 6mm bolts.

I have two pieces of 2" angle iron 14" long clamped to the vertical bars to support the longer 1.5"horizontal angle iron (31.25" long) for the batteries. It turns out that 14" wasn't long enough (you can see the front horizontal angle iron teetering on the front edge of the 2" angle iron).

Here is a zoomed out view of the firewall battery rack mockup that I've clamped together. Again, the two pieces of 2" angle iron on the left and right are just about 1/2" too short to properly support the horizontal pieces of 1.5" angle iron. After contemplating this further, I decided to make the right side of 2" angle iron 15" long and the left side 24" long. This extends the left side forward so that I can add more supports and put in a platform for the motor controller and charger/dc-dc converter above the transmission.

To keep the system stable, I wanted to utilize these 8mm threaded holes near the back of the engine compartment. By extending the 2" angle iron to towards the back of the car, I can use 8mm metric threaded rod to bolt into the angle iron for support. This is a picture just behind the passenger side shock tower in the engine compartment where the original 12V battery used to be bolted into. I purchased a piece of 8mm all-thread to bolt into this. I expect to drill an 8mm hole 1" from the end of the angle iron and 1/2" in from the side to allow the use of the all-thread.

One more important thing to consider is the interference with the driver-side engine mount. The 2" angle iron can't come forward too far or it will interfere with the mount. I put a piece of
wood under the engine mount to raise it into it's final position to properly see the clearance.

The power steering reservoir is still underneath. I haven't figured out a good way to mount this under the firewall battery rack yet and allow the fluids to flow in and out of it. That will be another engineering project.

Moving to the rear batter rack, I've just placed the pieces of 1.5" square tubing and 1.5" angle iron to make sure the batteries fit (with foam-core model). While this design puts the batteries at a higher center of gravity, it allows us to keep the spare tire and avoids having the installer cut through the trunk floor, possibly compromising frame integrity. Two pieces of 1.5" square steel tubing (1/8" walls) are 18" long. The 1.5" angle iron pieces (1/8" wall) are 36" long.

Just a quick note about drilling holes: After drilling larger holes (like the 15/64" and 3/8" holes needed here), there will probably be lots of burrs left on the exit hole where you drilled. I found that the largest drill in my set (1/2") can be used with a light touch with the drill to remove these burrs. You could also use a 1/2" countersink to take the burrs off.

In order to prove that I can do this project with simple hand tools, I'm cutting all the angle iron with a hacksaw and drilling the holes with a hand drill. Several colleagues have suggested that I get a miter saw (chop saw) with a grinder blade to cut all the steel pieces since it would go much faster. A drill press would also be helpful for all these holes. While I agree that it would be faster and more accurate, I still like knowing this project can be done with simple hand tools.



jsn said...

A suggestion for tying into those 8mm holes that are a couple inches away from the rack is to cut a piece of pipe just larger than the 8mm bolt, and then use that to span the gap, while running the bolt through it and tightening it all up with bolts. You could potentially use a all-thread stud if you can't find the right bolt.

This will give it a lot more side-to-side rigidity than just the all-thread - especially if you can weld the pipe to the rack, but this is a no-weld plan, so nevermind.

TimK said...

Hi Jsn,

Thanks for the suggestion. I think that will work better than the all-thread with extra bolts. I'll look into it.

Cheers, Tim

Unknown said...

For about $3 you can buy a metal cutting blade for a hand held 7.25" circular saw (a skill saw). Well worth it, and just about everybody has a circular saw.

Anonymous said...

I love the minimalist approach to tooling.

(hacksaw and 6volt recharge drill)