monitor

Step 29:  Monitor battery.  Add instrumentation to monitor battery.

I wired a plug-in clock to the BMS controlled charging relay (DPDT).  I set the clock at noon and start the charge.  The duration of the battery charge is recorded when the clock stops.  My charge is constant current so I can then calculate amp hours consumed since the last charge.  

The 12V output in the old charger is broken, I've replaced it with another 12V charger.

old school

I can communicate with the BMS using a terminal app on my iPhone.  The terminal app is what logged the run around the block in step 28.  If the BMS has a fault this is how I read it.

new school

The old school is producing a number around 315Wh/mile.  The new school 290Wh/mile.  I have more trust in the old school at this point.  While driving the new school appears to blank out under high current getting stuck for periods at 0A or 497A.  I need to rewire the current sensor using shielded cable.

new school current sensor

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.