After weighing the wagon of Cor I made an estimate of a wagon with and without the internal combustion engine components. It was still not very accurate and as well for 3 battery modules in the front and 5 in the back and for 6 in the back and 2 in the front were good arguments. Via the Volvo Amazon Facebook group I received a document for the Amazon wagon indicating a maximum total weight of 1800 kg (750 kg front and 1050 kg rear) and 1190 kg own weight and thus 610 kg maximum load. Very convenient for the test to getting the car registered in the end.
Will 6 battery modules it in the back?
First I explored whether 6 modules would even fit in the back. I created a dummy battery box.
Would become quite low.
Too low for entering a parking garage. There is some spare room above the axle since I won’t have an exhaust anymore.
Disadvantage is that a support beam needs to be modified and I am introducing a third battery box. This increases the complexity of the cooling and wiring infrastructure.
A friend suggested to install them in there in the length. A case to slide them in from the back would be an option.
That would allow me to add two below and two in the back. In that case it remains one battery box. Constructing it won’t be easy since both a support and chassis beam are in the way.
The case could compensate that, but it becomes quite complex.
Calculating weight distribution, center of gravity and axle pressures
On the website van de Nederlandse Kampeerauto Club (NKC) I found a nice spreadsheet for calculating the center of gravity.
They indicate a minimum front axle load of 30% and a center of gravity between 1,17 and 1,25 m in front of the rear axle (at a wheel basis of 2,60 m).
According to BMW the ideal weight distribution between front and rear is 50:50 for an optimal handling.
| Weight | % on the front axle | Center of gravity | |
|---|---|---|---|
| Maximum load according to the documentation | 750 + 1050 = 1800 kg | 41% | 1,08 m in front of the rear axle |
| Regular Amazon wagon | 557 + 737 = 1294 kg | 43% | 1,12 m in front of the rear axle |
| EV Wagon, batteries 5/3 | 607 + 782 = 1389 kg | 44% | 1,14 m in front of the rear axle |
| EV Wagon, batteries 6/2 | 582 + 807 = 1389 kg | 42% | 1,09 m in front of the rear axle |
All quite close together. I decided to continue weighing.
Another weighing
My father had a wagon that was apart partly.
I installed a rear door.
And the doors and front wings.
I took out the spare wheel but left in the fuel tank for convenience as well as the heaterbox and the exhaust. Next I could weigh the car.
Front axle = 350 kg
Rear axle = 550 kg
Total = 900 kg
This is quite close to the weight I measured a while ago using my own car (333 + 595 = 918 kg).
Furthermore I weighted some parts individually.
M40 gearbox with bellhouse = 22 kg
B20E engine with M40 gearbox, clutch, starter, generator and ignition = 200 kg.
Spare wheel 16 kg
Fuel tank 11 kg
Reference: a drivable wagon
Next step was to determine the weight and weight distribution of a complete and drivable wagon.
This car has both the original gasoline fuel tank as well as LPG and drives very nice despite the additional weight.
Weighted it using the same approach.
Front axle = 558 kg
Rear axle = 715 kg
Total = 1273 kg
Which aligns well with the own weight of 1190 kg from the documentation plus a LPG tank. 43,8% of the weight is on the front axle and the center of gravity lies 1,14 meter in front of the rear axle. Now the differences.
| Empty | Drivable | Delta | |
|---|---|---|---|
| Front axle | 350 kg | 558 kg | 208 kg |
| Rear axle | 550 kg | 715 kg | 165 kg |
| Total | 900 kg | 1273 kg | 373 kg |
The motor, controller and M400 gearbox together are 140 kg. I assume 90% of this weight is carried by the front axle (which is 126 kg front and 14 kg rear). That results in the following overview:
| Empty | Batteries 3/5 | Batteries 2/6 | Reference | |
|---|---|---|---|---|
| Front axle | 350 kg | 551 kg | 526 kg | 558 kg |
| Rear axle | 550 kg | 689 kg | 714 kg | 715 kg |
| Total | 900 kg | 1240 kg | 1240 kg | 1273 kg |
| % on the front axle (norm 45 to 48%) | 44,4% | 42,4% | 44% | |
| Center of gravity (norm 1,17 to 1,25 m) | 1,16 m | 1,10 m | 1,14 m |
Some more weight will be added to the EV, for example for the DC-DC converter, heat exchanger, pumps, fluids, radiators, etcetera. In the end I expect the overall weight to be similar to the reference wagon.
Conclusion battery distribution
Looking at the data, the best option is 3 battery modules in the front and 5 in the back.
In that case I will be adding 201 kg in the front while taking 208 kg out. In the back I am taking 165 kg out and am adding 139 kg. Using this layout the weight on the front axle remains more or less the same.
So: 3 battery modules in the front and 5 in the back.
Do you agree on this conclusion based in the data?
An additional advantage is that it is much easier to build than the 2/6 option. A disadvantage is that the center of gravity becomes higher.
Higher center of gravity?
The height of the center of gravity can be calculated. I got this old technical book (Johan thanks, also for thinking along).
So I also tilted the car 6,3 degrees and measured the front axle pressure again.
It turned out to be 578 kg (compared to 558 kg). I am going to try and do some calculations on that.
With some help from the people on wetenschapsforum.nl and the book I calculated the center of gravity then lies at 70 cm above the ground.
For fun I can repeat this once my own car has been converted.
