The implementation of Tesla battery modules is one step closer again. I have been able to test fit a module. In real life they are heavier and bigger then I expected even though I knew the characteristics in advance. Looks good on the car, doesn’t it? Although you won’t see a thing of it in the end.
Three modules stacked on top of each other is going to fit in the front but not in a square battery box. On top of the length of the modules there is some space required for the connections. I ordered some pieces of wood to be able to experiment with different shapes.
Putting them gradually on top of each order makes it easier to connect the modules in the box. At first glance it looks like it doesn’t fit, but the hood does actually close. In the right front end corner turned out not to be the best spot for the DC/DC converter. Below the batterybox is a possibility.
But perhaps not the best option since it leaves less room for airflow through the radiators. Perhaps where the old heater used to be.
The advantage is that it sits high and dry with the 12V outlet close to the fuseboxes.
Designing the cooling system
Now I can dynamically control the pumps, the next step was to start thinking about the layout of the cooling system as a whole.
My idea was to use the waste heat from the controller to heat up the batteries when needed by mixing the two loops. Once you get down to the details it turned out to be a little more complicated. Thanks to some support at the Volvo club forum I made some progress in terms of insights. The current status is:
- Physically mixing the cooling loops is not a good idea. Synchronizing the pump speeds is doable but the pressure drop in the battery circuit is expected to be much higher than in the controller circuit.
- Building on an estimated power that is used most of the time of 10 to 20 kW and an efficiency of the controller of 97% only 300 to 600W waste heat is available. I estimated/calculated that to heat up the entire battery system with one degree, about 50 Wh is required. Therefore having 500W available would take 1 hour to warm up the system by only 10 degrees.
Building on those insights I tend to conclude that using a heat exchanger using the motor cooling loop is a better idea.
I do like the idea of adding a thermostatic mixing valve to ensure that the water coming from the heat exchanger cannot exceed for example 20 degrees.
I do need to check whether a standard thermostatic mixing valve is suitable. If that is the case I am going to apply the same to the 200V electric heater. I have found a test unit with cables.
Schematically my current idea can be summarized as follows.
A 3-way valve will make sure the coolant does not run through the heat exchanger as soon as the batteries are within their desired operating range.
Next I will look into hose diameters and do some more flow tests and calculations. Furthermore I will think more about the physical layout. I could use a double radiator for the motor and the controller and move the battery radiator to the back together with the 220V heater.