Recently I started designing the cooling system. I have now ordered some parts to do some tests. A heat exchanger and a ball valve with a 12V on/off actuator.
Furthermore an ESBE VTA322 mixer.
I do need to test whether it suits my needs since normally the hotwater input is leading and I want the cold inlet to be leading.
I also ordered a Watchdog timer circuit. My Arduino is controlling major supporting functions. If it crashed the cooling pumps will halt. The BMS and GEVCU will prevent anything to happen but it can be inconvenient..
The Watchdog timer checks whether there is a puls to the pumo and if not it forces the PWM signal to the pump to 100% and resets the Arduino.
Furthermore I’ve been playing around with a bigger LCD for Arduino. I used to have a 16×2 characters and now with 20×4 characters. This allows me to not only show temperature and PWM percentage but also the actual flow in a cooling loop. Tried different layouts.
I like the last on best. Without the units quite OK to interpret and I can add which column is which circuit by a sticker on top.
Picked up my first Tesla Model S battery modules
Recently I was able to testfit a Tesla battery module. However they were not ready yet. To have a nominal voltage of 355V with only 8 modules I am having them modified. Every module contains 444 individual 18650 cells.
Originally they are configured as 6s74p (so 6 sets of 74 cells in parallel) and thus a module is 22.2 V nominal. Like Tesla you need 16 modules to have 355 V. In my case that does not fit. Only the modules would already weigh 400 kg. Nevertheless I want 355 V. Having them modified to 12s37p will result in a nominal voltage of 44.4 V.
The capacity will drop from around 250 Ah to approximately 118 Ah. Building upon an allowed continuous load of 3C and 5 to 6 C peak, the max available current will be lower as well. However, I won’t even be near half of the current Tesla draws from a module (which is 900 Amps or even more).
Since transporting a module is quite different from grocery shopping I made wooden boxes.
The module will be supported by the original mounting brackets. I build one for two modules and two for individual modules.
Now I can get started with the batteryboxes. I noticed that the boxes can be smaller even keeping into account the space required for connecting the cooling hoses.
That is convenient for positioning them in the front. To be continued.