Posts tagged: parts - Kraln's RX-8 Blog

Winter Arrivals, Next Steps

I've been a busy bee, flitting around to various places to source pieces for building up the battery packs. I managed to gather quite a few of the important pieces before 2023 came to a close, but didn't manage to find the time to post an update. In no particular order:

High-current connectors

These snap-on connectors are perfect for connecting power through the various battery packs and to the end devices. They're vibration and water-proof, and can handle quite some current. Both the connector and the socket are coming from JNIcon in China. JNICon Connectors

High-current fuses and DC Contactors

This is a massive fuse: Main Fuse

Which is good, as it is one of the main fuses for the system, needing to be capable of interrupting >550A at >400V in the case of a dead short of the traction battery.

The other HV fuses are a bit smaller, protecting various subsystems like HVAC and the OBC. The main contactors (think like a relay, but for DC) are even bigger than the fuse! The big issue with switching DC is, in contrast with AC, there is no "zero" crossover point, so attempting to disconnect the circuit under load has the potential to start a spark which will self-sustain and cause big issues. These contactors are responsible for connecting and/or disconnecting loads to the traction battery. Fuses and Contactors

Copper/Nickel Hybrid Collector Plates

I originally was planning to build the battery packs up with nickel strips, with the cells being connected to the grid of strip with small fuse wires. After running the numbers, however, it was clear that not even the thickest, widest strips of nickel metal had the required ampacity to carry all the current I was asking without getting really quite hot. I will probably do a dedicated post for the design of the battery pack at some point, but for now know that I designed a custom hybrid copper/nickel plate for the battery packs which combines ease-of-welding with a high ampacity. Bonus, each cell has a small nickel fuse which limits things to <20A and should prevent a fire in the case of a single-cell short. Collector Plate Closeup

Onboard Charger and DC/DC

I will definitely have a whole post about this OBC from Kanchan. It's an onboard charger with a maximum of 6.6kW (single-phase) from AC, as well as a 2kW DC/DC to provide the 12V from the traction battery. It's liquid cooled and smol OBC

Next Steps

The biggest next step will be automating the harvest of the raw cells from the donor packs... hopefully a big update on that coming soon. Also looking into the motor control concept, which will be a roadtrip, and a few other bits and bobs outstanding... The RX-E will drive in 2024!

These tail lights are gorgeous

These aftermarket tail lights from Valenti are gorgeous. Maybe I can use some of the money saved from not paying for fuel to swap them out in the future?

Roughing out the motor location

I spent some time today figuring out where the electric motor is going to go. This is unfortunately a prerequisite before I can figure out where and how big the battery can be--it doesn't make sense to plan batteries only to find out that the motor is occupying your entire volume!

I'd like to, as much as it is possible, put the electric motor directly where the differential of the RX-8 was, which may involve some rear subframe stuff. I have the part drawings and some measurements, but what I really need to bring everything together is a detailed 3d model of the subframe. Someone has scanned their NC (gen-3) MX-5 subframes and put them online, and I was hoping that they'd be equivalent (there are various forum postings for and against). I did some digging, and while the rear subframe is /extremely/ similar, to the point of being bolt-on compatible, it's not 100% identical to the RX-8 rear subframe.

Spot the differences...

Thankfully, Andrew from Keisler Automation is super friendly, and sent me a copy of his 3d scanned RX-8 rear. Keisler sells bits and complete kits to swap a GM LFX V6 into an RX-8, and I noticed on their web store front for their rear differential kit something that looked like a 3d scan, so I asked nicely :)

It looks like the Tesla Small Drive unit wouldn't fit without quite a lot of modification, both to the subframe and the bodywork of the car. It'd also stick out the bottom, which is no bueno. The model 3 rear drive unit, however, seems to be possible and even reasonable.

NeRF or Nothing

I took the opportunity today to record video walking around the car in its current state. Using the cloud tool Luma AI, I was able to convert it into a NeRF, or neural radiance field. You can check it out here. I'll be able to pull a skinned mesh out of this and use it for other things, I think. If not, it's cool at least!

Donor Batteries Collected

I picked up the last of the batteries from the recyling bin today. In total, I have 77 Ninebot NEE1009-W packs, all with various levels of malfunctioning BMSes. They are being stored in a steel container in an industrial area away from any buildings in the case they decide to self-immolate.