12V system testing

The 12V 60Ah LiFePO4 battery pack was mounted on its place with a simple sheet metal frame and a belt. I wanted to test if all the original electronics still work after the original motor was removed. It was great to notice that all lights worked and only the cabin fan did not work. After some research I found out that its power wire was in the motors cable harness and got the fan also working just by connecting it.

Current consumption was measured for the different utilities and the main consumers were found to be the cabin fan taking 16A on full power while the driving lights took 14A.  It's good to know these so I can rate the new fuses and relays correctly. Some changes have already been made on the circuit diagram that was posted earlier. I'll post its updates along the way.

The Corolla eFX is now in a driveable condition with its lights fully functional. The following steps will be wiring the 12V battery pack protection electronics, finishing the heater and mounting the electric brake booster and chargers. After that I'll show the car to the local authorities and hopefully get the car street legal!

Controller programming for full power and release throttle regeneration

The traction battery is now ready to be driven with full power so the motor controller needs to be programmed to give its maximum motor and battery current. I also wanted to try the "release throttle regen" mentioned in Kelly Controller's PM72401B features. I had to contact their support in order to get the release thottle regen to work as I could not find the parameters for it in the configuration program. I case some of you have the same problem "release throttle regen" can be activated by setting the desired regeneration value to the parameter described as "Tps Mode And Max Allowed Regen Current[3]" shown in the picture above. I do not know what "Tps" means, but setting a value to this parameter certainly started regeneration when the throttle was released.

The release throttle generation was set to an amount of 30% which in practice felt a bit too powerful for easy gear switching and too weak to actually stop the car by regenerating. Also there seems not to be any ramp when regeneration is started resulting in a fast torque change which can be felt as a distracting thump in such a light car as the Corolla.

I am thinking of testing a combination of perhaps 10% release throttle regeneration and maybe 40% of brake switch regeneration activated by a microswitch that would be installed on the brake pedal. I am happy over the ease of Kelly Controller's programming so testing different alternatives is only a matter of time and ideas.

First smoke - CBM overheating

 

 

It was a good thing to follow closely through the first charging of the traction battery pack. When the first cell voltages reached the balancing threshold I started to be worried of the CBMs possible overheating as I had only tested the CBMs in free air in a vertical orientation with a very small charging current. I consentrated for a while into other things and when I checked the charging situation again about 20 of the 24 CBMs were active and the whole enclosure was clearly too hot to survive. I stopped the charging but it was too late. The heat shrink tube used as insulation between the CBMs melted resulting in a short between two CBMs. Smoke started to rise and I started to remove the fuses to disconnect the batteries from the smoking CBMs. Finally all 24 fuses were removed and no flames were seen. The molten heat shrink tubing and smoked CBMs are shown in the first picture. This was a good reminder for me  about how easy it is to underrate cooling.

Luckily the PCM board was not harmed. As seen in the picture the CBMs were removed from the enclosure dropping the balancing current to just 60 mA provided by the PCM board only. While charging the battery pack with 10A the charging was now stopped into a cell over voltage as one of the cells reached a voltage of 3,9V. Some other cells were clearly not yet full so I made a manual balancing for the battery pack by sinking current from the fully charged cells and charging the ones with lower state of charge. After a while of manual balancing I got the cells balanced enough to make the charger to stop charging normally; the charging voltage was about 87,6V and the charging current was reduced into about 1A.

Now the first traction battery charging cycle is done. I am curious to see if 60mA top balancing current is enough to keep the cells balanced. Anyway I am so far very pleased with the PCM board!

Traction battery charger close up

The charger was purchased from www.kellycontroller.com. It is an engineered product made for customers specs. I ordered this charger with the following specs that were needed for the order:

Mains voltage: 230vac
Output voltage: 87,6V (24 cells x 3,65V)
Battery capacity: 60Ah

This charger is ment for indoor use only so I cannot place it under the hood where it would be exposed to moisture and dirt. Therefore I decided to mount it in corolla's trunk.

The chargers manual does not say anything about its leakage current (current drawn from the battery while the charger is unpowered) so I measured it to be 1,8mA with 80v battery voltage. This is lower than what I expected so its well suited for onboard use.

The chargers manual does also not mention the chargers power factor which is claimed to be 0,96 according to www.kellycontroller.com. I will measure its power factor to find out if it really has an active PFC or not. Anyway I'm a bit dissapointed with the chargers documentation.

First time traction battery charging

Before connecting the motor controller to the traction battery pack I wanted to test the connections made so far as well as the PCM board and the charger bought for the 72V battery pack.

I first inserted the mini blade fuses in their fuse holders at the battery terminals. The fuses were inserted starting from the cell closest to the pack's negative terminal and then proceeding to the next cell connected to it. This connecting procedure was adwised by some PCM's and I decided to follow it as the PCM I received did not come with any manuals.

Before inserting the last fuse I checked that the mosfets in the PCM board were turned off. Once the last fuse was inserted the PCM's mosfets were turned on which is correct as all cells had a voltage of about 3,3V.

The charger was plugged in and a charging current of 10A was measured. I was beforehand a bit worried about the PCM's mosfets heating, but the heat dissipation with 10A charging current was measured to be just 0,5W divided by two TO-220 packaged mosfets so they only warmed up barely noticeable. I do not know which mosfets have been installed on the PCM as all of their markings have been sanded off for some reason.

I did not make a full charge as I want to be around with my multimeter learning about how the top balancing behaves and how the CBMs and everything else heats up. So I'll continue charging while working in the garage ready to stop charging if something fails.

New meters behind Corolla's steering wheel

Three led panel meters were installed to be easily seen by the driver. The panel meters were earlier introduced in the post titled "Configuring panel meters".

The enclosure for the meters was made from a piece of white plastic 30x30mm cable trunking which was covered with black duct tape to better match with Corolla's dashboard.

These meters will be giving readings of the traction battery voltage and current as well as motor current. Only the speed meter will be left in use from the original meters, although rpm and motor temperature metering might also be nice in the future.

Battery pack connected to BMS

The next layer of wires connect the traction battery pack to its battery management circuits. The connections were made using 1,5mm^2 wire with a mini blade fuse holder as close to each cell terminal as possible. The mini blade fuse holders were soldered on each of the wires.