25 Miles

A long test drive

Today was a day of test drives.  The first was a speed test.  While cleaning up some wiring I realized that the accelerator cable may not be pulling the controllers sensor fully, so I lowered the effective top of range to 70% of full scale.  Well it made a difference and the motor is now spinning near 4300 rpm in neutral.  Which is very close to the theoretical limit of 50 rpm/V with a 85V battery.  Given, this I wanted to see what Jane would do in 4th gear, so we headed to the one stretch of nearby road with a 45 mph speed-limit which is outside the city limits.  On the level straight-away, Jane hit 53 mph and was humming along.  There may have been a few more mph available, but at about 50 mph, I noticed that the front wheels are out-of-balance and started to shimmy a bit.

Well, after a top-off-charge, we headed out again, this time with a goal of testing range and the fuel gauge.

The image shown above is the screen shot from the GPS Essentials program which shows 25.2 miles covered with a max speed of 35 mph.   The max speed is only captured while the screen is on.  It looks like in 2nd gear, Jane will do about 37 mph, which for city driving is perfect. 

The fuel gauge showed 15% remaining which calculates out to 41 AH consumed (out of the 60 AH available in the battery).   Using the 80% available capacity, this works out to a range of 29.6 miles on a full tank (with a 10% reserve still there to protect the battery).  The batteries were not showing any signs of being depleted.  Only one near the end did the low-voltage alarm trigger during a very steep hill climb.  It cleared as soon as the load was reduced.

The other interesting calculation is 41 AH x 84V / 25.2 miles = 137 WH/mile or 7.2 miles/KWH.  This works out to about 250 miles/gallon (MPGe) using the conversion factor of 1 MPGE = 0.0292 miles/KWH.  This does not take into account the efficiency of the charger which would lower this by about 40%.  You wouldn't think the charger would have to be taken into account....  I have not done the math to see if spending more on an efficient charger would save enough electricity to justify the added cost.

To take this one more step... At $4.00/gallon, Jane with the gas engine hit about 42 mpg or about 9.5 cents per mile for gas.  Based on Oregon electricity prices at 11.5 cents/KWH... the electrical cost comes in at about $0.115/7.2 miles or 1.6 cents/mile.  Even factoring in 60% efficiency 2.25 cents/mile.  The battery pack adds about 4 cents per mile so this brings the total cost of the electric mile to about 6.25 cents (a 30% savings from the gas model of 9.5 cents/mile).

Finally, accurate current measurements

Getting to the "truth"

With a borrowed Fluke 600A DC amp meter, I now have accurate current measurements for the charging system.

1. The charger's current reading is within 0.1 amps of what the Fluke reports for current going into the batteries.
2. The charger pulls 10.1A @ 240V or close to 2,450W.  The fan adds another 0.4 amps.
3. The 12V battery charger pulls about 0.5A @ 240V
4. The 12V power supply draws approximately 0.1A but is probably in the noise.

Impact

1. The current monitor (fuel gauge) Arduino is calibrated to the charger.  This should be now less than 5% off.
2. The fuel gauge is set to never exceed 100%, so it should "zero-out to full" near the end of every charge cycle, as long as the cycle runs to completion.  By ignoring the charging efficiency of the LiFePO4 cells, the fuel gauge should hit 100% about 1%-2% before the batteries are full.
3. The charger's efficiency is about 55%-60% based on power-in (240V x 10.1A = 2425W) divided by power-out (~90V x 16A = 1440W; the charger is rated at 1500W).  The charger spec states that charging should take 1.41x the battery capacity / 16A.  Not a surprise this ties out to the 60% efficiency, though it is spec'ed at 85%-95% efficient.  Maybe at the higher voltages it can achieve this.
4. The best news is the overall energy efficiency of the car is coming in where predicted.
1. 4000 KWH of usable capacity (80% of the pack)
2. Today I drove close to 12 miles using 48% of the pack.  This included several hill climbs and normal traffic driving. 
3. This leads to about a 25 mile range with 20% reserve. or 160 KWH/mile.
5. At work, there is CharePoint charger which reports KWH used, so next I'll try to calibrate against that with the data above.  Mostly it is good just to have an accurate fuel gauge

The Non-Fan - Cooling the ME0913

The Fan or lack there of....

A local machine shop fabricated up a blank disk to replace the fan in the Motenergy ME0913 motor.

This is the original fan in the motor.  Note the blades spin fairly close to the motor housing, which works well when the rotates counterclockwise (CCW, to the left).  In Jane the motor spins clockwise (CW) from the fan-end and thus the blades move no air and only serve to frustrate (restrict) any air that is trying to be pulled through the motor, from the shaft end, which is the direction the original fan attempts to move air..

This is the original fan out of the motor.  The central hub is riveted on and the timing (magnetic) ring is bolted on.  There are no markings on the timing ring, so I marked its position relative to the key slot on the hub.  It took a little persuasion to get the fan off the motor shaft.  There is a 2.5 mm set screw holding the key and hub in place.

The blank aluminum disk is now mounted to the hub using #8 bolts and the timing ring mounted to it with the original bolts.

The disks is now on the motor.  A little high temperature grease was put on the shaft which eased the mounting process and hopefully removal if that is ever necessary in the future.  You will see there is now a nice gap between the disk and the vent holes in the motor housing.  The theory is air will move more freely through the motor and around the spinning disk to the exhaust fan.  The exhaust fan was able to cool the motor quickly when the motor was not spinning but when it was operating, the cooling efficiency really seemed to drop.

Good Results

Hill driving is the best test since it forces the highest current through the motor for an extended time.  I took Jane over to the steepest hill in town and attempted a climb at 20 MPH in 3rd gear.   The motor was already warmed to about 60C.  In the past the temperature would rocket up to 120C about half-way up the hill.   This time under a good load (15KW) it only got to 105C about the time Jane crested the top.  The second test was whether the cooling fan would be able to cool the motor while moving.   This was something that did not happen in the past.  The next 3-4 minutes were driven at lower power (3KW) and the temperature dropped quickly to 85C.  Just the fact the temperature dropped is a vast improvement.  In the past, the only way to see a decrease in temperature was to stop and let the cooling fan run for a few minutes.  Tomorrow, I'll try a more extended run to see if there is a steady-state temperature under normal driving conditions.  Also, the next enhancement is to connect the Arduino that reports the temperature from the Kelly controller to the original Mini engine temperature gauge.  

Controller Supply Voltage and Fan Update

Surging

During the last few test drives, I noticed that the motor tends to have a slight periodic surge when approaching maximum rpm.  It is subtle when cruising at a constant speed, but a slight pulsing or surging could be felt.  This led the following investigation:

1. The Kelly KBH 72710 controller is rated for a supply voltage of 8V-30V.  This is the supply for the controller's functions, not the main drive power which is 85V in Jane, with the controller rated at 90V.
2. The system currently has an adjustable voltage booster to covert the 12V standard car supply upward.    TI LM2577 Link
3. Previously, the booster was set to output 18V to supply the controller.
4. I can't remember why I landed on this but there were  published reports that 12V was insufficient.
5. While reviewing the Kelly datasheet again for the controller, it says that 24V is "preferred".
6. So, a few small turns of the screwdriver and the booster is now set to output 24V.
7. During a test drive today, the surging seems to have stopped.  But it will take a bit more testing to confirm.

Not sure why this was not noted previously but it can only help.  

Cooling

In the next attempt to cool the motor, a local machine shop is fabricating a blank disc to replace the fan in the Motenergy ME0913.  John from Motenergy provided the mechanical drawing for the fan assembly.  The fan carries the hall phase magnets so it is a critical component of the motor and can just be simply removed.  The current theory is the fan, though running in reverse (CCW from the fan end)  from its designed direction (CW from the fan end), is frustrating (impeding) the air flow through the motor.  With the blank disc, there should be no interference or obstruction for the air.  Currently, the cooling system is just on the verge of being sufficient, so if by removing the fan, there can be a 10%-20% gain in flow, the results should provide sufficient headroom.

Dashboard

Work continues on the electronic dashboard.  Here is the latest design:

Boot Up Screen  (Yes, that is an image of Jane Austen)

Sitting Idle

After pulling out from a stop sign

A few highlights:

1. The graph shows power consumption and regeneration in half second intervals.  The bars are color coded to make for quick interpretation.  It will show about the last 30 seconds of data and continuously rotates
2. Watts appear to be the best indicator of system strain and is closest to RPMs for a gas engine.  Thus the real-time motor watt consumption is now shown with the large numerals.  They are set to change color based on the following:
1. Regeneration in effect = Green
2. Less than 12KW (Continuous power limit for the motor) = White
3. 12KW - 18KW =Yellow
4. >18KW = Red - The motor's 1 minute rating is 30KW
5. This is a computed value based on values reported by the controller - Motor Amps ( % of controller rating - 700A) x Battery voltage at the controller x PWM % (pulse width modulator duty cycle)
3. The other values are also color active to help the driver quickly spot an issue.  Much like gas cars, the driver is responsible for managing the system.  This is no different than red-lining a gas engine or ignoring a check-engine light.   The car will let you do it but should warn the driver of the situation.
4. The large "Forward" indicates whether the motor is in Forward or Reverse
5. Warnings and error messages are displayed across the bottom of the screen when needed.