The controller has it’s mount so I continued working on the design of the battery boxes. More and more do the details matter such as layout of the components and connectors.
In the front battery box I will put the controller boards of the individual battery modules, the main battery management system (BMS) controller, a high voltage fuse, the shunt (to measure currents) and the high voltage maintenance switch.
Designing the wiring diagram
To know exactly which wire goes where and what kind of connectors need to be on the battery box I continued designing the wiring diagram. The wiring diagram design I created earlier needs to be redesigned since I have adopted a BMS since I am working with Tesla batteries.
That sometimes is quite a puzzle. I dropped by at New Electric to ask some questions. Many interesting projects are going on there at the moment. Among others a Jaguar is being converted using a dual! Siemens motor.
More and more people are using Leaf packs, not only in the DIY scene, but also beyond.
Parts
Furthermore I gathered some more parts. A Spal-008-A100-93D-3SP blower
Two original 5,5J wide Lemmerz 1538 wheels with as good as new Vredestein Sprint Classic 185HR15 tires.
And a new old stock panel to be mounted below the rear door.
Revisiting the weight and weight distribution
On a Volvo Amazon wagon that was advertised for sale, I noticed the following type plate.
This was typically added in Germany. So far I only found max. allowable axle pressure for a sedan. Dit was typisch voor Duitsland. According to this plate a wagon has a maximum front axle pressure of 650 kg and 1060 kg on the rear axle. I did not expect that much of the total weight would be on the rear axle.
Moving weight backwards?
That triggers the question whether I should not put 6 battery modules in the back and only two on the front instead of 3. The third module is installed quite high. On the other hand I want to have enough weight in the front not to get too much understeer. On the other hand it is understeer which is relatively easy to feel and correct.
The initial weights that I took were not perfect. The interior was already out and there were some things lying around in the car randomly. I had to find a good reference example.
Weighing a complete wagon without its engine
A post on the VolvoKV forum brought me to Cor who had a wagon without just the engine. Perfect to see what the axle pressures then are.
Interestingly enough it as also Cor who bought my first Volvo Amazon convertible. Nice to see him and the car again after ten years.
Back to the wagon: After putting on the hood, we could start.
Using 4 scales we measured the front and rear axle sequentially.
Cor thanks for helping out!
The results:
Front axle = 407 kg
Rear axle = 737 kg
Now the question is: what does this say without comparing apples with pears?
Below the values of my ‘complete’ wagon, after removing the internal combustion enging (ICE) components and the one from Cor.
| Weighing | EV wagon | EV wagon (de-iced) | Wagon Cor |
|---|---|---|---|
| Front axle | 575 kg | 333 kg (also without M41) | 407 kg (incl. M40) |
| Rear axle | 644 kg | 585 kg | 737 kg |
| Total | 1219 kg | 918 kg | 1144 kg |
Given the fact that just a B20 engine weighs 125 kg and a complete wagon about 1270 to 1300 kg one could conclude that my car had 50 to 60 kg missing during the measurements.
My wagon did have a M41 and in the 125 kg for an engine no starter, generator, etc. are included. Perhaps a complete engine is 140 to 150 kg.
Building on that the revised table could become as follows.
| Estimate | EV wagon | EV wagon (de-iced) | Wagon Cor |
|---|---|---|---|
| Front axle | 575 kg | 333 kg | 407 kg (ex engine of 150 kg) |
| Rear axle | 694 kg | 635 kg | 737 kg |
| Total | 1269 kg | 968 kg | 1144 kg (incl. engine 1294) |
Estimate weight difference
Front = 150 kg
Rear = 100 kg
The motor + controller + weight M400 gearbox instead of M40
Motor = 86 kg
Controller = 28 kg
M400 instead of M40 = 11 kg
Total = 125 kg
That gives me a margin of another 25 kg in the front and 100 kg in the back. The options for distributing the batteries are:
| Options | Weight front | Weight rear |
|---|---|---|
| 3 modules front / 5 modules rear | 75 kg | 125 kg |
| 2 modules front / 6 modules rear | 50 kg | 150 kg |
I tend to prefer the option of 2 modules in the front and 6 in the back. Additional advantage is that the weight will be positioned lower in the car.
In the back, 5 modules fit better, in that case I can even keep the original long tow bar. However I will also be able to squeeze in 6. The lowest point of the battery box will then become 2 cm lower than the long tow bar. Towards the front the box stays within the line of the tow bar.
The remaining question is: are the estimates accurate enough to build my design choice on it? Any feedback is welcome.
Myself I tend to prefer to weigh another car complete and with the combustion engine taken out. It is quite a significant design choice to make.
