72V battery pack mounted

The finished 72V battery pack base plate was painted first with zink- paint and then with black paint to slow down corrosion. It was then mounted on its place where the radiator used to be. Next the battery pack was mounted on it cell by cell. The easy to reach location of the 72V battery pack will be handy while making the electrical connections on the cell's terminals.

Mounting the cells on the base plate

All of the cells of the 72V battery pack found their place on the base plate. The cells are sitting tightly on their places as the cells do nothave room to move in any direction on the base plate. The cells are tied togheter using bent washers that are shown in the close up photo below the wing nut and the rubber washer. When the wing nut is tightened, the bent washer presses both cells towards the base plate and also makes sure that the cells can not escape sideways.

Battery base plate under construction

The base plate for the 72V battery pack is being built from different steel materials that I had available. Most of the base plate is done using 25 x 25 mm steel square tube that is cut and welded. A tight place is made for each of the cells and the cells are fixed on their placed by pressing them against the base plate with a threaded rod and a wing nut.

The cells are slightly separated from each other to allow a better airflow which improves cooling. While the maximum continuous current of 160A is drawn from the battery pack every cell dissipates approximately 20W of power according to my interpretion of the datas given by the cell manufacturer Winston. If the cells would be tightly packed next to each other I would be worried that the ones in the middle of the pack would overheat. After getting the Corolla on the road it will be necessary to learn how the batteries, motor and the motor controller heat up so that any unpleasant suprises due to overheating could be avoided.

Heater assembly

A simple heater system was built from 5pcs of 2.7ohm 100W aluminum case resistors and 5pcs of temperature switches, bought from China through ebay. The resistors and temperature switches were mounted on a 1m long aluminum plate that will be mounted on top of the air vent that blows air to the windshield. The idea is to have just enough heat to keep fog out of the windshield.

Temperature switches were mounted next to each of the 2.7ohm resistors. Their job is to cut the power off from the resistor next to it if it reaches the temperature switches temperature limit. The temperature switches that were ordered have a limit of 55 celsius.

The heater will be powered from the 13,2V 60Ah LiFePo4 battery pack and all of the 2.7ohm resistors are connected parallel. This gives an initial heating power of about 320W.
If the heating power of the heater turns out to be too low I'll need to either improve the heat sink, install more resistors, or install temperature switches with a higher temperature limit. Practise will tell what will need to be changed.

In addition to the windshield heater, seat heaters will be placed on front seats. Anyway while travelling in this car during cold days, some extra clothing will definitely be needed as only a fraction of the original Corolla's heating power will be available.

72V Battery pack test fitting

The batteries for the 72V battery pack arrived today! They were nicely packed in a wooden box with a good amount of padding.

While waiting for the batteries to arrive, I had welded a frame for the batteries to be mounted on. The frame is attached to Corolla's chassis under the same bolts that attach the Corolla's front bumber. I was eager to see how the batteries would fit on their frame and made a test fitting for them right away. After trying different possible layout alternatives, the solution shown in the picture above felt like the way to go. Now that the place for each cell has been decided, next thing to do is to fix them securely into their places.

To make room for the batteries the motor controller was decided to be moved slightly. There seems to be enough room for the battery chargers to be mounted right next to the motor controller. The 12V battery pack is planned to be mounted on the same place where Corolla had its original 12V battery.