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My childhood go-kart engine finally frustrated me enough.  The engine would run ok for a while, die, then be very difficult to restart.  After many attempts to rebuild the carburetor, replace spark plugs, etc, I finally gave up on internal combustion and decided to bring this thing into the 21st century with some good ol' fashioned electrification!

The motor I had on hand was a SEW Eurodrive 2HP 240/480VAC 3 phase induction motor.  I also had a Automation Direct 2HP 240V VFD.

The motor was easy enough to mount to the existing motor mounts with an adapter plate that I welded myself (yay learning to weld!).  The motor shaft was 12mm (metric) and the sprocket was meant for a 1/2" shaft so a small stainless steel shim was required to get a nice tight fit.

I picked a sprocket from McMaster that would yield about the same torque and max speed as the gas engine.

The battery is where things get interesting!

A 240VAC VFD expects (you guessed it) 240VAC at its input terminals.  It then rectifies the voltage to about 330VDC for its internal DC bus.  So I needed to bypass the rectifier circuit on the VFD and directly inject 300+VDC into the drive's DC bus and build a 300+V battery pack.  Using some Samsung 18650 cells from batteryjunction.com, I assembled a 80S1P pack for a nominal voltage of 296V and max voltage of 336V.

Charging at 336V is very difficult so I created a circuit to reconfigure the pack to two groups of 10S4P for a nominal 37V which is much more common and many chargers are available.  The two different configurations are selectable via a switch and some relays.

The Automation Direct drive kinda sucked.  It would frequently overload and shutdown because it only operates in V/Hz mode.

In the next iteration, I upped my game and used an Allen Bradley PowerFlex 525 drive which supports a mode called Sensorless Vector Control (SVC).  SVC allows the drive to take a guess at where the commutation should be based on back-EMF and gives much finer control over the motor current.  It's really just a much nicer drive overall.

The speed input to the drive is a linear potentiometer configured as a voltage divider and hooked into one of the 0-10V analog inputs.   By setting a few key parameters in the drive and a little work with the Connected Components Workbench (CCW), I was able to get this drive working really nicely.  But...

Lesson learned: never build a battery pack without a BMS, and get a good tab welder.

My battery failed in multiple ways.  Many of the tab welds broke loose due to the vibration.  My cheap Amazon tab welder was not up to the job.  Also, putting cells in series without balancing is a BAD IDEA!  Many cells caught fire during charging.

The next version will operate at a lower voltage and include a balancing BMS.