In my previous blogpost “3D CAD drawings of the battery boxes” I made quite some progress in designing the front battery box. It seemed just a matter of ‘just’ adding the cooling and rivet nuts and widening the box a bit. How wrong could I be. Many hours of moving around, puzzling and changing followed.
For example to make sure the rivet nuts for the front cover would not interfere with the modules I had to extend the box.
Furthermore I took detailed and exact measurements of the Tesla battery modules to be able to test fit them digitally properly.
In particular the width to be able to design the supporting rails in order to make it a tight fit.
The coolant distribution block just fitted in the room that was already there just behind the modules.
But no matter how much I moved around with the shunt, fuse holder, ampseal and cable routing I was not able to squeeze it into the space that was available.
Again Bas helped me out with improving my CAD skills, in particular for working with assemblies.
Design decisions
Drawing is also the process of getting into even more details and thus making choices. Where do the cooling connectors need to be and the high voltage cables, etcetera.
Flowtest thermostatic mixer
One of these details is related to the cooling system and therefore I conducted a flow test. A while ago I bought a EBSE thermostatic mixer. By design it is intended to limit the temperature of outflowing hot water by mixing in cold water for example to be used in hotels. I want to achieve the opposite: add warm water to a cold water flow up to a certain maximum. In my case it is crucial that the valve also allows water to pass it the incoming cold water flow temperature is above the setpoint. In that case it should not block the entire flow. I hooked the thermostatic mixing valve up to a shower mixing tap and a hot water tap and did some tests.
The results:
- 2x cold in = good flow
- cold in at cold and nothing at warm = no flow!
- hot in at cold and nothing at warm = no flow!
- cold in at hot and hot in at cold = good flow
- 2x hot in = good flow
He indeed uses the hot water input to add that to the cold water flow to achieve the setpoint temperature. As soon as the temperature at the cold input is higher than the setpoint he does allow that through as long as there is pressure on the hot inlet (which is then fully blocked).
Conclusion: it is usable as long as I make sure in my cooling circuit design that there is always pressure on the hot water inlet. This is the case in the anticipated design. More details about that later.
Some help from Ben
In the process it starts to become more important to reduce the number of degrees of freedom. Having everything open and undecided keeps me searching for the best and perfect layout.
Ben (from Tinustuning) wanted to think along. Thanks to his questions and input the design of the cooling system as well as the circuit have improved. The outcomes were:
- I will add contactors to the battery boxes to be able to switch of the whole system including the high voltage cables.
- The cooling system will be ‘closed’ with bleeding possibilities instead of overflow tanks.
- Check whether the pump has enough pressure to trigger the thermostatic mixer on the hot side.
- The battery boxes will be in parallel for a more uniform temperature distribution. Possibly using a valve to add a pressure drop towards the front box since that one will only have 3 modules and in the back one 5.
More 3D drawing
These insights resulted in some more evenings of drawing. It just did not fit all the time so I decided to use the maximum amount of space available instead of incrementally increasing the size. This triggered the idea to position the fuse holder next to the maintenance switch. Then everything easily fell into place. Only adding the cooling connector at the highest point was a challenge.
This resulted in a version 10 of the front battery box with all components in place and room for cooling hoses and high voltage cables.
Using you left mouse button you can rotate the model and using the scroll wheel you can zoom.
Next stap is to further design the high voltage circuit and the cooling system.
