Time for a re-design
In my previous post, I shared the excitement of unveiling my classic EV project at the Gardner Douglas open day. While I was still happy in my design, I couldn't help but have some reservations about certain choices I made in the first iteration.
The first area that gave me pause was the battery support frame. The battery pack is a critical component of the project, and I envisioned it as a unit that could be easily removed for servicing if required. This approach also aids in the assembly of the car. However, as I delved into fabricating the original
design of welded aluminum box section, doubts began to creep in. While it might have been structurally sound as a complete unit, I couldn't shake the feeling that it might not withstand uneven loads.
So, it was back to the drawing board, and I arrived at plan B. I designed a set of five bent steel support bars that would run under the battery pack. The batteries would bolt onto these bars, which, in turn, would attach to the chassis. Handling this new design left me much more satisfied with its rigidity. These support bars are constructed from 4mm thick steel with strategically placed bends for added strength. An added advantage is that this approach eliminates the need for welding; once delivered, they only require powder coating before being ready for installation.
It's worth noting that while this project is anything but budget-friendly, however I'm striving to ensure that it remains easily manufacturable. I anticipate that I'll be making more EV427 cars at some point, and keeping production straightforward and cost-effective is a priority.
Recalling the original plan, I had devised a three-layer cooling plate design. It consisted of a solid 2mm bottom plate, a 4mm middle layer with the cooling matrix, and another solid 2mm top plate. These layers were intended to be bonded together to form the cooling system.
However, I ran into a couple of issues with this design. The first and most critical problem was leaks. The initial version had a small leak due to insufficient clamping. I addressed this by constructing a clamping rig out of 22mm MDF for the second iteration, which proved leak-free. Nonetheless, a new issue emerged when I connected my Bosch pump—it struggled to circulate the water effectively. The likely culprits were the limited surface area and excessive bends in the complex matrix.
My new approach involves simplifying the cooling plate design. The cooling tracks now have a minimum cross-sectional area of 44x5mm, totaling 220mm². This corresponds to a pipe diameter of approximately 16.7mm, a significant improvement over the original Ø9mm cross section on V1. The less complicated matrix promises to enhance fluid flow significantly.
I've also been pondering the method of bonding the plates together. Several concerns kept me awake at night—how long will the gasket last, how will it handle vibration, and what about the heat cycles? A leak in the battery box could be catastrophic. As a contingency, I'm considering machining a step in the new cooling plates and welding in a plate, as shown in the cross-section example below. This approach ensures that the weld doesn't protrude above the surface, offering greater assurance against leaks and durability.
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