GarageConverter

The 25-unit annual production threshold is the right line to draw. Below that you're in hobbyist territory where individual responsibility and state inspection laws apply; above it you're a commercial operation where fleet customers reasonably expect standardized safety verification. The question of whether small conversion shops need a simplified pathway is a real one — NHTSA is right to specifically request comment on it.

The instructor pipeline lagging the student pipeline is the bottleneck that's hard to solve with money alone. You can fund equipment and curriculum at community colleges, but ASE L3-certified instructors with real-world EV diagnostic experience are in short supply precisely because they can earn more working at a dealership than teaching. That feedback loop takes time to resolve.

The section on defect rates from vetted importers versus spot market buys is the most actionable part of this guide. I learned the hard way in 2023 that saving $40 on cells from an unverified supplier is not worth the time spent testing every cell and returning the bad ones. The advice to budget for two spare cells per pack regardless of supplier is solid.

If it's a Hyundai Kona or Niro motor, you're in luck — those motors have been reverse-engineered by the Korean DIY community and there's a reasonable amount of CAN bus documentation floating around. The OEM inverter from a crashed Kona is a legitimate find — they're capable motors (150kW on the 64kWh version) and the inverter is well-integrated. Search "Kona EV motor conversion" on the EV conversion forums and you'll find people who've done it.

@batterynerd The plates are clean — these came from cars I pulled myself, all drivable at time of pull. I have photos of each car's engine bay (they kept their original plates so I never got water in the cabin). The port fittings are aluminum and look good. I'll send photos of a representative sample if you're serious about the lot.

I learned this lesson the hard way on my first build — a motorcycle conversion with a canned motor and a cheap 72V pack stuffed into the existing battery box with no airflow. First summer ride in Phoenix I watched the cell temperature climb to 52°C before I cut power and pulled over. The pack recovered but the cells were noticeably weaker after that season. My Beetle build has a temperature display as a primary instrument and I won't start a drive with cells above 35°C.

@packrat I'm in Arizona which is much simpler — I just went to MVD with the title, a bill of sale for the motor and pack, and photos of the engine bay. They stamped it "Electric" on the title and that was it. California is a completely different story. The BAR EV conversion regulations require specific components meet CARB certification, and many common DIY components (Warp motors, older controllers) don't have that certification. CA people: look at the BAR regulations carefully before starting a build, or plan to register it as an out-of-state vehicle.

@engineer I'm running a simplified loop — the Volt's original aluminum cooling plates are still on the modules (they're integral to the module housing). I replaced the OEM pump with a 12V Bosch brushless pump that I control with a PWM signal from my BMS temperature output. The loop goes: pump → modules → 4-row aluminum radiator (from a Chevy pickup truck, repurposed) → pump. No thermostat — just pump speed proportional to module temp. It's worked well; I've never seen module temps above 38°C even in Phoenix summer.

Running an Orion BMS 2 in my Beetle conversion. Overkill for the application, but I wanted the CAN bus integration with my BMS touch screen display. The configuration software is complex (took me a full weekend to get it right) but once set up it's rock solid. One thing I'd add on the MOSFET vs. contactor point the OP raised: make sure your BMS is rated for peak discharge current, not just average. I've seen people spec a 200A BMS on a pack that sees 400A peaks under hard acceleration. What happens is the MOSFETs take an overcurrent event they can't handle and fail shorted — the drain-to-source junction permanently conducts. The BMS tries to disconnect and can't. Current flows when it shouldn't; you've lost all protection. (You'll sometimes see this called "fails open" in forums, but that terminology is backwards — a MOSFET failing shorted means it's stuck closed, passing current. The practical result is the same: no disconnect capability.) Always size your BMS for peak current with real margin, and consider contactor-based architecture at high current levels where MOSFET reliability becomes an issue.

@packrat I bought 50 Grade B BYD Blade cells from a supplier in California last year. Of the 50, I got usable cells out of maybe 38 — the rest either had internal resistance too high for my application or showed early signs of swelling. The good ones tested great. My 75% yield was probably a better-than-average outcome — community reports on Second Life Storage and DIY Solar Forum describe more typical Grade B yields in the 50–65% range, with some batches delivering cells testing at barely 55% of rated capacity. One broader warning: genuinely new BYD Blade cells outside of OEM supply chains are reportedly nearly impossible to source; most "Grade B" cells available to DIY buyers are reject or used cells from vehicle packs, which is why variance is so high. Price accordingly, assume the lower yield range, and load test everything before you commit.