range

Step 28:  Figure efficiency.  

I can go 45 to 55 miles on a charge.  


I found the bad connection that was not allowing my BMS current sensor to work.  With the new current sensor operating I logged a run around the block.

get legal

Step 27:  Get legal.  I got an inspection on my lunch break.  So there you go, it takes 27 steps to convert a BMW 2002 to electric drive.  

I believe step 8 can be skipped.  A 9" motor is so huge for this little car I do not think it will need a fan.  Driving around it's apparent that the motor controller is the weak point heat-wise, and it has a fan and heat sink (step 25).

I also would skip step 13.  The ammeters chosen were of poor quality and do not work correctly.  I do not think you need to be looking at a gauge anyway.  As a driver you can tell when you're sacking the battery and when you're not.  

I drove it to work and lunch then to an Irish session in the evening, 42 miles total!  It then took (very roughly, to be refined) 137Ah to reach full charge.  Saving 20% capacity for long life this means my range driving like an excited kid is about 45 miles.  Half of that was flying down highways.  I suspect keeping under 45mph would greatly increase the range. 

test drive

Step 26:  Go for a test drive.  The new controller is faster and quieter.  With the muggy rain I was able to test the AC's ability to defog the windshield.  With two vents pointed up the fog quickly evaporated.

better, faster, ...

Step 25:  Work out the kinks.  Smoke escaped from the old PMC controller.  5 of its 8 power transistors are blown.  I suspect some had blown early in test driving.  It still operates the remaining 3 switches, but alone they can't provide enough current to push the car.  I will try to repair it but in the interest of getting on the road it will be replaced with a Curtis 1231c.  This has a higher current limit of 500A and a silent switching frequency.  

The Curtis 1231c is widely used and requires a heatsink.  I found one online and bolted it to the bottom using thermal grease.  I borrowed the fan from the old PMC and mounted it on the back.  There is good airflow out the end.

charge

Step 24: Charge batteries. The cells came around half full and I've driven some laps in the neighborhood. This charger, along with my motor controller, are from a 1981 Jet Electra. The charger is dual output, charging the 12V battery while powering the BMS. The BMS turns the charger off when the battery is full using a relay.  This charger could be put in the trunk and used at charging stations around town with the help of an adapter.  But the charge voltage profile combined with the number of cells I chose only allows for a trickle charge, a C/20 rate. Saving 20% capacity for long life a full charge will take 14 and a half hours. I don't expect to use a full charge everyday. 

I put the charger outlet behind the drivers front wheel, with a fuse at the battery. The location was partially chosen based on body damage in the vicinity.  Creepage and clearance was gained in the 7-pin connector by leaving an empty pin next to the high voltage pins.

After what seemed like forever she reached full charge. The BMS terminated the charge.

test drive

Step 23:  Go for a test drive.  Everything seems to work.  The next step is working out the charging system.

first ride goes to helper

wire batteries up

Step 22:  Wire batteries up.  These being expensive batteries I want to make sure they are protected from damage.  A battery management system (BMS) is employed.  A gracious EV-cohort donated an Elithion BMS needing only minimal additional components.  This BMS monitors voltage and temperature and disables the drive if a cell is in danger of being damaged.  It does the same during charge.  This BMS uses a small circuit board that attaches to each cell, these are daisy chained together and relay data to the BMS controller.  I've installed the BMS controller tucked up under the dash.  I will be able to view the status of the battery pack with my iPhone and a rs232 dongle.

front bank

rear bank, tucked into the back of the
trunk for good weight distribution

BMS controller, rat nests allowed