Configuring panel meters

I wanted the Corolla to have simple yet informative metering to be shown to the driver at all times. Three digital panel meters will be mounted below the original speed and rpm meter to monitor the 72V battery pack voltage, 72V battery pack current and motor current. CX-102-B digital led panel meters were chosen for the job and they were ordered from www.circuitspecialists.eu.

These panel meters are easy to configure by external resistors to give a desired reading from a measured dc input. The battery voltage meter was configured to show the voltage with a 100mV resolution. The battery pack current is measured using a 400A 75mV shunt resistor. Therefore the meter showing the battery pack current was configured to give a reading of 400 when the input voltage is 75mV.

The motor current will be measured from the current meter output of the Kelly Controls motor controller. I contacted the Kelly Controls support to get more information about their controllers current meter output and learned that it is generated with a 5V 8-bit pwm output which should be readable using any 5V panel meter. I configured the panel meter to give a reading of 400 when 5V is applied to its input. An isolated power supply is needed for the motor current metering as the panel meter connected to Kelly Controls current meter output is intented to be connected between +5V and the current meter output. Once the meters are installed it will be interesting to see how accurate current metering the Kelly motor controller can give.

12V battery pack initial charging

Before buying the LiFePO4 cells for the 72V battery pack I wanted to make sure that the cells for the 12V battery pack were ok. Each of the cells were measured to have a voltage of exactly 3,30V after shipping which indicates that the cells would be in good condition. 

The cell balancing modules were connected parallel to each cell and a laboratory power supply was used to charge the battery pack. The cell balancing modules will be located in a separate enclosure and the connection to the cells is made by 1,5mm^2 wires. Each of the wires have a fuseholder that is located as close to the cell terminal as possible. The fuses will act in case a short circuit occurs and they are also helpful when connecting electronics to the balancing circuits and protection circuit module. The connections can be made safely first and after the connections are ready the fuses can then be placed in the fuse holders.

After two days of charging with a current of about 0,8A the battery pack was fully charged up to 14,4V and the balancing circuits seemed to work as expected. I will not make any deeper tests to the batteries at this point. They look to be in good shape and I am ready to order the cells for the 72V battery pack.

Electric brake vacuum booster testing

The brake booster used to get its needed vacuum from the manifold of the original gasoline engine. Now that it is removed vacuum needs to be generated using electricity as it is the only energy source that will be used. I bought a dismantled electric vacuum pump from some model of VW Golf MK4. The pump was measured to reach a vacuum of 0.8 bar while drawing a current of 8 amps.

A simple vacuum switch is used to control the pump so that it will only be turned on when more vacuum is needed. The vacuum switch was made many years ago by my father who used a vacuum advance unit of a ignition distributor and a microswitch. The working principle of the vacuum switch is very simple. The vacuum advance unit pulls a lever according to the vacuum applied to it. Once enough vacuum is applied the lever operates the microswitch. The operating point of the vacuum switch can be easily adjusted just by positioning the microswitch to be operated on a desired level of vacuum. Using the vacuum gauge shown in the picture a vacuum level of 0.57 bar was adjusted as the operating point of the vacuum switch. Once it is reached the microswitch cuts the power off from the vacuum pump. A power diode was placed parallel to the vacuum pump motor to increase the lifetime of the microswitch.

When the vacuum pump motor is stopped it leaks vacuum through it so a check valve is needed between the brake booster and the vacuum pump. The vacuum level to be adjusted by the vacuum switch needs to be taken from the brake booster side of the check valve. In this case the original Corolla's check valve was able to be used as it was working well without any leak and it was easy to mount an additional pipe to connect the vacuum switch between the check valve and the brake booster.

The test setup worked well. Pressing the brake pedal all the way down caused the vacuum to drop to a level of ~0.44bar and it took one second for the pump to reach the 0.57bar vacuum again. As the tests looked ok, this setup will be assembled to boost Corolla's brakes. Further braking experiences will have to wait for the first road test drives.

Corolla eFX circuit diagram

During the last weeks I have spent hours and hours in studying different batteries, chargers, LiFePO4 protection modules, cell balancing modules and battery management systems. I'm pleased to finally have made up my mind about the solutions that will be used in this electric Corolla. I'm even more pleased about the circuit diagram that turned out to be quite simple and low cost yet providing all the features I wanted.

LiFePO4 Protection Circuit Modules (PCM) will be used in both 12,8V and 76,8V battery packs to monitor that each cell's voltage is kept between 2,0V and 3,9V. If the voltage of any cell goes outside of this range the PCM disconnects the P- terminal from the battery packs negative terminal. If that happens in either of the battery packs, the Corolla will stop immediately. This feature is only the last resort to protect the LiFePO4 cells from severe over- or undervoltage. In normal conditions the driver is responsible to maintain acceptable charge level by charging the batteries often enough and not trying to drive too far.

The PCM's that will be used have integrated balancing circuits but the balancing current is typically only less than 100mA. I think it is quite low for 60Ah batteries and a 10A charger so I decided that 1,7A Cell Balancing Modules (CBM) will be installed parallel with each cell to help the situation.

Now that the plan is done it's time to purchase the rest of the components and complete the project. Let's see how many changes will be needed along the way!

First batteries arrived

I have recently spent hours of time searching for suitable batteries, chargers and battery management systems to be used in this project. I decided that the Corolla would be powered by Winston made LYP60AHA LiFeYPO4 cells. They are 3.2V 60Ah cells capable of 3C (180A) continuous discharge rate. Four of these cells will be used to make a 12V battery pack for lights and heating etc. 24 of these same cells will be used to form a 72V battery pack for moving the car.

The first four cells shown in the picture were purchased from www.ev-power.eu that is located in Czech Republic. Purchasing was easy and I was well informed at all times during the order process. After finishing up my plans for the 72V pack battery management and chargers I will most likely purchase the rest of the batteries from the same place.

www.ev-power.eu has also a very informative blog: gwl-power.tumblr.com that gives us readers interesting posts related to solar energy, batteries and everything around them.

Weekend test driving

Some more test driving was done on a beautiful winter saturday. A couple of visitors also made a short test drive with the Corolla eFX and we learned together that it is extremely silent. It was  sometimes hard to notice its movement because the wheels are the only thing making noticeable noise. On the video most of the noise is made by the train that goes by far away.

Some simple performance tests were also made. We learned that the corolla could climb the slope on our yard on its first and second gear, but on third gear it did not accelerate anymore uphill. On even road it started rather easily with third gear. We still had no voltage or current meters installed on the car so we did not learn about the used motor current or battery power.

I just received a pair of 400A shunt resistors bought through ebay that will soon be installed to measure battery and motor currents. With the shunt resistors and a battery voltage meter installed it will be much easier to evaluate the performance of the car.

The second test drive

A temporary ~72V battery pack was created using four 12V 12Ah lead acid motorcycle starter batteries and two 13,2V 6,9Ah LiFePo4 battery packs in series. The two LiFePo4 packs are the same ones used in my electric lawn mover introduced in my other blog.

The power on/off switch was also a temporary solution. A switch was brought into the cabinet through the driver side window.

After charging the batteries the controller was tested and the motor rotating direction was verified. The last job before driving out from the garage was to change winter tires to the front as our yard has a steep and icy slope that could not be climbed with summer tires.

It was about -10 degrees celcius when the Corolla eFX was reversed out of the garage for the first time. I had never driven an electric car before and it felt great to accelerate from 0 rpm just using the throttle pedal. I took the risk to reverse all the way down of the icy slope in our yard unsure if the corolla would make it back to the garage on its own. On the bottom of the slope I changed to the 1st gear and gave some throttle. The Corolla moved up the slope easily and silently! It was so fun that I drove back to the bottom once more before driving back to the garage.

On this second test drive I did not have any voltage or current meters installed so I do not know what kind of motor and battery currents were used. Once I have installed some meters I'll drive up and down the same slope many times to learn about the current levels used and if the regenerative braking works correctly or not.

Motor controller power connections

I had some 50mm^2 welding cable available and it was used for the motor power connections and for the shorter wirings inside the controller's enclosure. While connecting the power cables on the controller I noticed that the motor output connectors are very close to the round control signal connectors. I had to lower the head of one of the M8 bolts to prevent it from making a short with the signal connector body. The clearance between the connectors are now just 2mm. I will use some additional insulation between them for peace of mind.

Fitting the motor controller

A L-shaped steel rod was bolted between the original engine mounting and the gearbox. The motor controller enclosure was placed on top of the steel rod. In this position the enclosure can be accessed easily and the throttle cable reaches the modified hall throttle pedal.

Motor controller programming

The motor controller was carefully powered up for the first time using a laboratory power supply. Only the power cables and the serial cable was attached to the controller to program it. About 20Vdc was given to the controller and it drew less than 100mA current when turned on.

A RS-232 cable was provided with the controller. Luckily my laptop has a serial port which is getting rare on newer laptops. The laptop used for the programming runs Windows XP so there should be no problems.

I installed the programming software that is available from Kelly Controls web page. Then after powering up the controller and having the serial cable connected between the PC and controller the Kelly Controls software found the motor controller by itself!

The programming software was easy to use and the available options were quite well explained. Most of the default setting were accepted at this time but some were altered. I am preparing for the second test drive where I would use 6 small lead acid batteries is series. For these weak batteries I wanted to set the battery current limit to as low as possible (80A). I also adjusted the throttle voltage range to be 1.2V to 3.8V after testing the throttle pedal output with a multimeter. With 5V power supply the hall throttle signal range was measured very closely from 1V to 4V so I will start with about 0,2V margin on both ends.

Finally I altered the regenerative braking settings a little. I would like to have the "release throttle regenerative braking" feature enabled, but this braking mode was not as well explained as the other two available braking modes. The second test drive will show if I had understood the braking parameters correctly or not.

Motor controller assembly

The motor controller components were installed in a 2U rack enclosure. It is not a watertight box but it can be sealed if needed. The heatsink was mounted on the bottom of the motor controller so that it sticks out from the enclosure.

The rack enclosure will be mounted close to the batteries and the motor to keep the power wirings short. The hall throttle can be seen next to the motor controller.

Electric gas pedal

The hall throttle pedal was modified so that corolla's original gas pedal and throttle cable could be used to actuate it. The hall throttle will be mounted in the same enclosure with the motor controller.

Main components for the motor control

The motor controller chosen for this project is Kelly Controls PM72401B. It's a 72V 160A continuous rated four quadrant dc motor controller capable of providing 400A current for short terms. In addition to the motor controller a 400A contactor with 72V coil voltage and a hall throttle pedal were bought from Kelly Controls. The fuse holder with 400A fuses were bought earlier from ebay.

Finished motor plate

Small pieces of 1,5mm steel was welded on the motor plate to fill the holes where splashing water could enter the clutch assembly. A small hole was left into the bottom of the motor plate similarly as with the original gasoline engine. The motor plate was then painted first with zinc containing paint and then with thick metal paint. This was ment to slow down corrosion.

After the paint work the motor was assembled back on its place. The corolla was given a second test drive and it could be noticed that the flywheel balancing had improved. It's not sure if the balancing is still good enough for the planned 3000rpm, but for 500rpm the balancing is now acceptable.

Flywheel balancing

The flywheel was mounted on a lathe using a rod with the same diameter as the motor shaft. It was then aligned using a dial gauge and the outer edge of the flywheel was machined to balance the flywheel better.

The motor plate will be given a finishing touch and then the motor will be mounted again to see if vibrations are now on an acceptable level.

Corolla's first test drive

The first test drive was performed without motor controller since it has not been purchased yet. Using start cables a 12V lead acid battery was connected to the motor while making sure that the gearbox was on neutral. The ME1003 runs approximately 500rpm unloaded with the 12V battery. The motor took about 14 amps while rotating the gearbox on neutral.

Moving the corolla forth and back was as easy as with any manual car. The clutch worked well and silently. A small vibration was noticed and the flywheel was decided to be balanced to fix the vibration.

From now on the tasks in the project should be more electric than mechanic. As shown in the picture there is a lot of room under corolla's hood. The motor controller, on-board charger and LiFePo4 batteries are planned to be installed next to the electric motor.

Installing the new motor

The motor assembly was lifted on its place by hand. After fixing the assembly with bolts into the gearbox one of the front wheels was rotated to find out how well the shafts had been aligned. It turned out that the shaft alignment had succeeded well and the motor assembly did not add much friction in addition to the gearbox internal friction. The clutch operation was also tested and it seemed to work nicely although the clutch fluid was found to be in a bad condition and must be replaced. The Corolla is now ready for a test drive and to meet its first electric driven meters!

Motor assembly ready to be fitted

Once the motor plate was carefully aligned with the gearbox shaft it was then welded on its place. The motor plate was then removed and welded from the other side to secure the flat bar pieces in their correct places. Now the ME1003 motor could be mounted into the motor plate and the flywheel assembly into the motor shaft. Two guide pins were mounted on the motor plate to get it installed back on the same position it was just removed from. Similar guide pins were used to position the original gasoline engine as well. The guide pins were made from M12 bolts using a lathe. One of the pins can be seen on the right side of the motor plate in the picture.

Alignin the motor plate

The motor plate is now on its place, but still unaligned. It will be aligned with the gearbox shaft with a simple method that one of my workmates suggested. An iron nail is attached to the gearbox shaft using strong magnets. The gearbox shaft is then rotated by rotating one of the front wheels with a gear selected from the gearbox. The distance between the motor shaft hole wall and the iron nail is then adjusted to be equal in every rotary position of the gearbox shaft. This measuring method should make the alignment accurate enough. Once the gearbox shaft is centered with the motor shaft hole, the motor plate will be secured in its place by welding. After this, the motor itself can be mounted with the flywheel assembly.

Fixing plate for ME1003

ME1003 motor fits tightly on the built fixing plate. The motor will be bolted on it with four 5/16-18 bolts that were bought from germany through ebay.

The next thing to do will be to align the plate accurately with the gearbox shaft. I will soon know whether it is a tricky or a simple task.