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Last active September 14, 2023 12:16
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RX-E Project Notes
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RX-E.md

RX-E Electrification Project

Purpose and Goal

I bought an RX-8 with the intention of converting it to run on Hydrogen. Conveniently, the hydrogen fueling network was shutdown shorly after purchase. After driving the car around for much longer than I originally intended to with the Renesis engine, it started to lose significant power at 145k km. Rather than exchanging the existing (fun, but unreliable) motor with another (fun, but unreliable) motor, or a different (boring, but more reliable) motor, I'd like to return to the original goal of making the RX-8 zero-emissions.

The goal is an RX-8 that, from the outside and inside, will be nearly indistinguishable from stock. All safety and comfort features should still work, and the car shouldn't gain too much additional weight. The original structure should stay as intact as possible, and the handling and dynamics should be as close to as-delivered. But, the whole thing will be electric; none of the original drive train will be there.

Considerations

  • TÜV certification is required for the car to be street legal in Germany. I need a place to work on the car for the duration of the exchange until the car is re-certified, as I can't park it on the street while it's "not street legal". https://bauplan-elektroauto.de/umruestung-tuev/ -- basically, R100 rules, CE stuff.
  • LVD 2014/35/EU
  • EMC 2014/30/EU
  • EN 60335-1:2012
  • EN55014-1:2006
  • EN50498:2010

  • To keep the stock instrument cluster, ABS/DSC, and HVAC/Radio working, some CAN-bus hacking is required, but this is mostly figured out already: https://www.chamberofunderstanding.co.uk/2021/03/14/rx8-project-part-20-canbus-5-rx8-odometer/ https://www.chamberofunderstanding.co.uk/2021/06/11/rx8-project-part-21-canbus-6-working-code/

  • The car should have sufficient range to reach as far as the borders of Brandenburg and back without having to charge from full--Humbolthain to Medewitz is 111km one-way, so 250km should be sufficient for all-weather conditions.

  • The car needs to be able to charge fully from nearly drained within four hours, which is the charge time limit for public stations.

  • The original car weighs approximately 1350kg empty. The Drivetrain weighs approximately 450kg. The total weight of the battery plus drivetrain plus battery frames, etc. should not put the car outside of its suspension design, so much stay under 1800kg (max gross weight) + 695kg (max load, unbraked)

Required Equipment / Resources

Anything missing??? Liquid cooling stuff??? Regen braking stuff???

Helpful Links

Budget

The original motor exchange would cost in the neighborhood of ~6000 euro plus labor, total probably 10k euro. So.. let's keep it under that

  • Motor/Inverter: 3000 euro lightly used from ebay

  • Motor/Inverter/Controller: EV Controls T-2C would be ~ 2500 euro. from seller

The above together can be had for lots of money: https://www.evwest.com/catalog/product_info.php?products_id=570

Misc stuff?

Battery Pack

  • 137.8 Wh/km is average
  • The motor wants 280-400VDC
  • The motor can take up to 800A
  • The motor can regen up to 65kw
  • The charger will charge at 6.5 or 11kw
  • The BMS can fast DC charge (CHAdeMO)
  • The batteries are 3.6 nom (4.2v max) INR18650-32E from Samsung. 1C is 3.2A
  • The battery cells should charge at a max of 0.5C, or 1,600mA per cell
  • The donor packaging is 10S09P yielding 1004Wh, and weighing 7.5kg
    • -> 1kWh = 7.5kg, 60kWh = 450kg battery ;)

Potential topology:

  • 80 cells in series, 60 series in parallel (80S60P)
  • 320V and 576A max, approximately 53.5kWh
  • 4800 individual cells (approx 54 donor packs)
  • Expected range with average drain: 385km

Sanity check:

  • Nissan Leaf is 96S2P
  • Tesla Model S is 96S74P
  • Internet says (Most EV battery packs use 96 cells in series, regardless of the number in parallel, because each cell is always 3.7 volts nominal and 4.2 volts fully charged, resulting in a total of around 350 to 400 volts, which is the voltage range that most EV motors are designed to run on. To increase the capacity of the pack, more cells are added in parallel, while the number of series cells stays the same.)

With 320V and 192A at 1C, sustained output will be 60kw or about 80hp. The batteries can support short bursts of 2C discharge, which would boost that to 160hp for a short time, or even 3C at peak which would be 240hp (bringing the total current to 575A for a short amount of time) nearly exactly the 231hp of the RX8 motor.

Pack Construction Ideas

(old, bad ideas below)

Cooling Concept

Water mixing with HV is a bad idea, and copper/steel/aluminum junctions can cause galvanic rusting. the body of the RX8 is already aluminum, and some mounting concept for the batteries will be needed anyway.

Perhaps an extruded aluminum plate could be used? https://www.isel-us.com/aluminum-extrusion-t-slot-table-plate/pr-30 T-slots to hold the battery modules in place, and coolant can be run through the extrusion. https://www.cncshop.at/T-Nutenplatte / https://www.cncshop.at/T-Nutenplatte-PR-350-Laenge-frei-waehlbar

If the aluminum plate should be exposed to the bottom of the car, it will need protection against stones and sticks and stuff. Some combination of fiberglass, steel, or potentially the "lackschutz" PVC foil will be neccesary

The best outcome for attaching the battery is that it can be attached from the bottom

HVAC thoughts

https://www.amazon.com/-/de/dp/B0BLKSY5N5/ref=m_pd_aw_sbs_sccl_2/261-6406954-4078249?pd_rd_w=bzWd7&content-id=amzn1.sym.bc45384a-cf15-479c-b874-e31c5245d34e&pf_rd_p=bc45384a-cf15-479c-b874-e31c5245d34e&pf_rd_r=1RAJEKY485S60715PVP0&pd_rd_wg=QCE90&pd_rd_r=536490c6-f63b-4115-bfb9-4e8a9833dd19&pd_rd_i=B0BLKSY5N5&psc=1

Some sort of electric compressor will be needed for cooling--the battery pack probably needs the cooling more than the passenger cabin. Heating is 100% required by law.

Considerations for Drivability

  • If the weight distribution changes more than a little bit, the springs on the suspension will need to be readjusted
  • Ride height changes
  • Stiffness changes to the chassis
  • How to mount the battery pack? Firmly (urethane?) or loosely?
  • Additional mounting points may be needed to carry the pack

Battery Storage during Development

I've secured place at MotionLab to work on the battery pack and store the cells while under development

Next Steps

Measure available space on chassis Design battery pack physical dimensions

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