A while ago I already did some work on designing the contactor box and ended up using a Rittal enclosure.
At the sides a solid busbar for HV plus and minus. Two CHAdeMO contactors and some small components. Next step was to check the actual fitment on which I did have some help from my son.
It all worked out nicely, even under the hood.
Next I stopped by at Mischa from Garage71, engineering partner of my project to discuss some design choices.
In his workshop there is a Morris EV conversion that was almost ready and also featured CHAdeMO fastcharge. I discussed my design choices with him and got lots of new input and ideas. For example to weld the frame of the front box to the outer skin and adding some flanges for improved stability during the welding. So I opened Onshape again.
New idea: swapping the battery modules
So far, the primary driver for the layout of the batteries was the ease of connecting the high voltage wiring in the box. Therefore I had chosen to have the cascading poles at the front. However, in terms of routing of coolant tubes and highvoltage layout it was inconvenient. Suddenly I realised, why don’t I just rotate the modules? The I have the cooling connection in the front and high voltage in the back, right where I need them.
Works out pretty well. However having the maintenance switch in the plus circuit became quite tricky.
And I like it’s position at the driver side just above the pedal box.
So I changed the layout and decided to implement the maintenance switch in the – circuit.
So I implemented all changes triggered by the rotated modules in the drawings. Every module has it’s own entry and exit for the cooling tube having the distribution blocks outside the box.
Furthermore I positioned the contactors and moved the shunt since it needs to be directly at the main -.
Added the blow off valves too.
And thus the front box started to become quite complete.
I fully redesigned the outer skin of the rear box to reduce another weld.
Furthermore I modified the design so the box will be installed against the chassis rail of the car instead of in between together with the frame.
Battery management system layout
Next questions was how to distribute the circuit boards of the battery management system (BMS). Every battery module has it’s own board that measures individual cell voltages and module temperatures. Via CAN-BUS that information is being send to a central master board. Main question was: do I add that master in the front or rear battery box?
Most obvious would be to put it in the rear box because the EVCC and many other components that need to be connected are in the back too. The only thing is that the shunt is located in the front. After consulting Celso from New Electric it became clear that is is no problem to have longer wiring between the master BMS board and the shunt as long as it is a high quality and shielded cable.
As a result, the layout of the BMS boards was final with three Cell Monitoring Units (CMU’s) in the front. So I designed a mount that could be installed into the battery box.
To protect the bare printed circuit boards I added a cover made from 0,8 mm stainless steel.
In the back therefore will be five Cell Monitoring Units (CMU’s), the Master Control Unit (MCU) and an AUX-PCB. The latter is a component that is developed by New Electric and allows me to easily connect the BMS, EVCC and other components and also takes care of the precharge circuit. Designing a mount that would fit in the car and on top of the battery module was quite a puzzle.
To be sure that it all fits I used the actual board to check the routing of the wiring.
Finalising the design
Once more I went to Mischa to discuss my designs before I was going to submit my order. As a coincidence I passed a 24/7 Tailorsteel truck and a Volvo Amazon in front of it.
Battery box design finalised
In the end this is the final battery box design.
And the front box is ready too.
The I placed my order at 24/7 Tailorsteel to have them lasercut and bend.
Unfortunately after reviewing my order it turned out I violated some of the manufacturability constraints and would cause a tool collision as a result.
So I modified the design a bit to prevent that.
I’ll have to bend this last bit at home on my own bending machine. Now the order was accepted and was added to the production queue.