The Mazda MX-5 is a great EV conversion candidate for the same reasons it’s a great gas car- it’s light, has a great chassis, and is great to drive. It’s not such a great conversion candidate because it has an incredibly small amount of interior space, which makes positioning batteries and building racks complex. My plan to fit the comparitively small 12 x Group34 battery pack was to build three seperate racks:
The front rack holds six batteries in the engine compartment above the electric motor and transmission. It includes a shelf at the front for the motor controller, contactor and fuses. The DC/DC converter is bolted to its underside. The rack is sloped at an angle to fit under the hood and over the top of the transmission. It is offset slightly to the passenger side to clear the brake master cylinder, in order to be as close as possible to the firewall. I flux-core wire welded the rack together out of hot-rolled steel angle stock. The rack has mounting ears which are bolted to nut-plates I welded to the body sheetmetal “seam” around the edges of the engine compartment. The batteries are secured to the rack using nylon ratchet-straps. They are easy and quick to set and release, and are very strong.
The “Mid positioned” battery rack holds three batteries and is placed just behind the car seats- where the fuel tank was originally located, sitting atop the rear sub-chassis and differential. This rack was stick welded out of steel angle. It is bolted to the sub-frame underneath. The clear acrylic cover for the rack holds the fans for the battery regulators.
In the original layout the muffler was situated under the floor of the trunk- without that it’s possible to use that space for three more batteries. This rack has mounting ears bolted to the chassis rails on the bottom side of the trunk. The main challenge involved in the mid and rear racks lay in sealing them against dirt and moisture intrusion from the road under the car. I used pieces of ABS plate on the bottom of the racks for the batteries to sit on. Pieces of 1/4-20 all-thread poke up between the batteries for the top hold-down bar. The walls are covered with corrugated plastic. Cor-plast is also used around the racks to join up with the original sheet metal. The cor-plast is attached using pop-rivets with washers to spread the load on the plastic and reduce the chance of having the rivets rip through. Copious amounts of silicone caulk provides a weather seal. This solution is obviously not as good as the original sheet metal, and not as good as custom fiberglass lay-up- but it has held up well and is easy and cheap.