Introduction: Safety Cage for a Recycled Nissan Leaf Battery (Power Racing Series Build)
This Safety Cage is designed to use 4 cells from a Nissan Leaf. Assuming you have access to the four Leaf cells, get those together. If you're buying from a re-seller or salvage see if they'll include the spacer hardware created for the cells by Nissan. If not you'll have to make your own for safety and spacing.
The primary purpose of this safety pack is to keep the cells compressed during all charging and discharging activity, and in the unlikely but terrifying event of a Lithium fire this box will direct the heat away from the driver of the PRS racer. Never built for the Power Racing Series?! Oh wow, here check this out: http://www.powerracingseries.org/ and come play with us!
Step 1: Gather Your Materials!
You'll need a sheet of 1/8” aluminum, minimum dimension: 35x10”
Two smaller sheet of 1/8” alum, 14.5x8” each
3/8” Threaded rod
3/8” Hardware, 16 washers and nuts (12 minimum)
G10 Fiberglass OR a sheet of Fiberglass/Phenolic sandwich (order online or check for scrap)
3D Printed ABS for the Terminal Protector
Access to a MIG welder and/or Spool Gun
3/8” Drill Bit
Sheet Metal Brake
Sheet Metal Shear
Plasma cutter if no Shear
Bandsaw – Preferably a big one
1: These sizes are used to give clearance around the full pack for out gassing and protection from impact. You can modify this for a smaller overall size as needed: Trim from the outer dimensions and leave the hole distances the same.
2: When measuring, always choose one corner to start and base all measurements off that datum point. Measuring between holes or from other locations will reduce the accuracy.
3: In Baltimore MD I used Access Metals and pulled cheap stainless and aluminum from their off cut (scrap) pile for a fraction of the retail price. In Oakland, CA Gorilla Metals will give you the same deal, so check around for your best metal price!
4: Note: I strongly recommend keeping ALL terminals covered with plastic or electrical tape at ALL TIMES while measuring, parting, separating, wiring, or in any other way working with the battery packs. Any metal that crosses multiple terminals can cause arcing which will injure the fabricator (burn/shock/blinding) and may destroy the battery’s internal structure. In a worst case scenario stray metal, even tools like wrenches or screwdrivers, can be accidentally arc welded across the terminals killing the battery entirely and creating a substantial risk of fire and explosion.
Please DO NOT WORK WITH THESE BATTERIES WITHOUT A SAFE-HANDLING PRIMER.
Step 2: Cutting the Sheet Metal to Size
Cut your sheet(s) to size. The best and easiest tool to make this happen is the Sheet Metal Shear (pictured). If you've never used this tool ask for help! The Shear is non-discriminate in what it cuts through and the average pedal-push shear is plenty powerful enough to take off the end of your finger. Never fear though, we've been safely using these tools for decades. It's all a matter of training and confidence, particularly in where your hand does (and does not) belong.
If you don't have access to a shear, a Plasma Cutter will do nicely. Remember that if you're using a straight edge for a guide, the tip of the Plasma Cutter will be 1/8” to 1/4” offset from your line, check your tool's guidelines during setup.
Step 3: Mark and Bend!
The best tool for a sheet metal bend is a Sheet Metal Brake. These are old & heavy, and usually require a bit a strength or leverage on long or thick pieces. In my case, being about a 5'5” human, I will sometimes use a pipe on my shoulder for leverage. This is another case where you shouldn't be afraid to ask for help. Even larger fabricators need a hand from time to time, and you should never operate a tool in a way that feels strenuous or unsafe.
If you don't have access to a brake (check your local hacker/makerspace!) you can also achieve the bend by clamping your sheet VERY tightly to a strong table, such as a steel welding table, and using a straight edge such as a few feet of square tube to make a nice clean line by clamping it down on the fold line. Apply even downward force across the entire sheet.
Adding heat, such as a torch, is an option but I'd recommend against it if you can avoid it as uneven heat application can cause warping, particularly with thinner sheet metal.
Step 4: Measuring and Punching
Measure out the spacing for the holes. I use the bottom left corner for my datum, or origin, and measure twice on the top and bottom to make sure I'm symmetric and properly aligned. Once you're all measured up, grab a punch. Hammer a little divet into the center of your marked hole with the punch, this will help guide the drill bit to the center and give you a cleaner, round hole.
Step 5: The Drill Press
Take your bent sheet to the Drill Press. You'll need something inside to push against and drill into; a block of scrap wood works perfectly. Take your time lining your work piece up and securing it with clamps or hold down hardware. Items improperly secured to the press can swing out and injure the user.
Step 6: Cutting a Sandwich!
If you don't have access to Fiberglass or a Fiberglass/Phenolic sandwich, you can use hardwood in a pinch, but I specifically chose fiberglass for heat/flame resistance as this is a safety item. The fiberglass/phenolic structure is REALLY resistant to crush! I had the good fortune of pulling mine from an Air Force Base scrap pile and using a water jet to cut the shape from a .dxf file (included here). If you don't have that kind of access you can use a router HOWEVER please use the appropriate bit. A solid carbide composite end bit can work for your CNC router. Amana Tools also offers a solid carbide spiral bit for your router. You must use eye, ear, respiratory, and skin protection any time you are cutting fiberglass. An enclosure is even better!
The action of the water jet piercing the fiberglass layer into the phenolic caused a small amount of delamination. I took a tip and filled the edges and through holes with Bondo, then sanded down these areas and recreated the through holes with a 3/8” drill bit. 3/8” is the maximum hardware size that can fit the battery pack through holes without modifying the pack.
Two of these are used for this build, one for top and one for bottom. The Top is the critical part though, we're using this object to avoid "edge crush" in which the lips of the metal housing are compressed causing connections to form where they should not. Remember back when the lithium batteries in phones were exploding? Edge Crush. This spacer sits within the edge to prevent it.
This is also why the Terminal Protector (featured later) has been modified to allow the curled lips to sit undisturbed behind the 3D print.
Step 7: Cutting the Hardware
Cut your Threaded Rod to size. I believe I cut 4 pieces to 8” each, then later trimmed them to fit. It's OK to cut them larger than needed and trim later.
Pro Tip: During cutting on say, a band saw or with a portaband or cutoff disc, the threads will warp and bend a little. Same for the threads in a clamp. Wrap your threaded rod in a few shop rags before clamping it and put a nut or two on either side of the cut line. After cutting, you can trim off the area of the thread that is the thinnest and use the nut to reform the threads to keep.
Step 8: Assembly Part One
With your sheet cut and bent, holes drilled, fiberglass spacer, and hardware cut to size—it's assembly time! This is actually tricky because the height of the box is meant for the cells under compression and, well, they are not compressed yet. I recommend getting the cells and their spacers into a reasonable position to secure one corner at a time, starting front (opening) to back. Place one nut and one washer on the end of each rod, you can even tack weld the nut in place.
Take your time, this can be a real pain in the buns as the internal spacers may move while you apply increasing pressure. Make sure your threaded rod goes through ALL of the holes and ALL of the spacers.
Make sure you slide a washer onto the other end of the rod before adding the nut and tightening the whole package down.
That's /basically/ it!
Ha, not really.
Step 9: The Side Caps
I'd like to provide you with the perfect measurements for the side caps here but as I assembled and disassembled the pack I found that the best measurement came not from my math but from measuring against the actual width. So, measure your pack! After that take your remaining aluminum sheet and cut it to size leaving a half inch on three sides to bend up with the Brake. You'll need to notch out the corner on the Band Saw to get a clean bend and a nice seam to weld.
Step 10: Putting a Corner on the Caps
TIG Welding is a great skill I recommend trying out, but you don't need it here if you have access to a Spool Gun.
When using a MIG Welder for steel you have Mixed Inert Gas (or Flux shielding) to shield wire fed through through a lead to the tip where electricity is used to arc weld your wire and material. Aluminum is too soft to be run the length of a MIG Welder's line, but a Spool Gun brings an aluminum spool very close to the tip and otherwise operates in the same way; using an inert gas (CO2, Argon) to flood the weld pool and prevent oxidation as the arc welds your wire and material.
Lacking a Spool Gun you can TIG Weld using a non-consumable tungsten rod and consumable aluminum alloy rod to arc weld the corners.
If you have no access to this kind of welding gear try a hardware solution such as pipe strap.
Step 11: Secure the Caps
Align your new caps with your case and drill a 1/8” hole through each to accommodate a sheet metal screw being EXTREMELY CAREFUL to avoid nicking or puncturing the cells.
Step 12: 3D Print the Terminal Protector
Find yourself a 3D printer to make the terminal protector. Again I'd recommend checking out your local Hackerspace or Makerspace, or Fab Lab, or make a friend on the Internet. There are 3D printing services you can hire online as well. The up-to-date .stl file is available by request (I'm happy to send) or can be downloaded from the Powerwheels Racers for Adults Facebook page.
Step 13: All Together Now!
3D printer terminal protector only fits when the pack is assembled and properly compressed, but if you have it all together it'll snap into place and be held tight by Nissan's own hardware. TA DA!
I needed custom C Channel for the frame and a slide for the pack, so I made them. The shop’s MIG welder was the perfect tool for the job. I used four feet of 1” angle steel, thickness 1/8”, and four feet of 1” flat stock, also 1/8” thickness. Clamping the angle and flat together, using another stretch of 1/4" thick flat aluminum stock as a spacer, I welded 4” segments at a time moving back and forth across the full length to prevent warping. One long straight bead would have very likely warped, by way of heat, the entire length to the point that it would not be usable in a stable vertical frame. The vertical frame also supports the steering column, doing double-duty.