Rear battery pack ready for work

Installing the rear battery pack is finally done and it is connected parallel to the front battery pack as shown in the circuit diagram posted earlier. The rear battery pack is electrically a copy of the front battery pack, but mounting it in the trunk is a lot easier environment than the engine room. In the trunk no waterproof encolures were used for the electronics.

This picture shows how the rear pack cable feed through looks from inside the trunk.

The first attempts to make a full charge resulted in a state where the Signalab PCM board blinked two leds next to each other and on the same time it switched its charge protection fets on and off with a frequency of approximately 1Hz. In this state the PCM kept its discharge protection fets off not allowing me to drive. The only way I could find out how this state could be resetted was by disconnecting the PCM from the battery pack. At first I had no clue what was happening and if I could rely on the PCM or not. I could not find a manual or functional description of this Signalab PCM so I did not know if it was some error state or if the PCM was broken.

I decided to double check the wiring if I had done some mistake that would have caused this problem. While checking I noticed that I had missed to install one blade fuse which resulted in a situation that the PCM did not have a connection to one of the cells in the battery pack. To make sure that the problem was linked to this forgotten fuse I charged the battery pack to get the fault state back again. Once the fault was active I installed the missing fuse and the fault disappeared. What a relieve!

Looking back I realized that the fuse was missing between the two cells whose balancing leds were blinking on the PCM. Without any proper manual or schematic I do not know if this was a designed feature of the Signalab PCM or not, but its a good indicator in such cases where connection is lost between a cell and the PCM.

After assembling the missing fuse the Signalab PCM has worked just like the one in the front battery pack. This regained my trust in it and I am hoping for a lot more careless kilometers just like with front battery pack alone.

The rear battery pack cells were not balanced manually in any way before use. The cells had a very consistent 3,3V reading so I decided to give the balancing task to the Signalab PCM board and see if it could handle it without having to help it manually. In the picture above the lit leds tell which of the cells are being bleeded by the balancing circuity at the time when the charger decided that the battery is fully charged and stopped charging. At this same moment the highest cell voltage I measured with my multimeter was 3,8V. I think a few more full charge cycles will be enough to make a good top balancing for the rear battery pack, just like with the front pack where nearly all balancing leds are lit just before the charger ends charging.

Things seem to be working as they are planned and I can enjoy driving with increased power output and efficiency due to lower voltage sag of the cars doubled battery capacity! Next step will be to cover up the rear battery pack nicely.