Making of the «AC-Box»

One later goal of the E-Syncro project is the supply of mobile power. Therefore we organized an inverter to create 230V AC off the 400V DC battery. Nicely the company Power-One offered us a very good deal for their inverter. It is a product designed for the american grid (split-phase 2x120V) but it can be used as single phase 240V @ 50Hz. It works with exactly the required battery voltage from 240 up to 430 volts and supplies power up to 6kW. Here I present to you the first part of the making of. The reason why the box was built before finishing the bus is that we need the AC-Box for our yearly festival ‘Openair Hohen Rätien’ in the swiss alps! There we will power the bar, fridges and lights and amps with the AC-BOX!

A short technical explanation: The AC-Box should be portable ‘plug-and-play’ solution. So the idea was to put it into a standalone box and the only connection to the car (containing the battery) should be the high voltage connection. The water cooling, wiring, fuses and AC output plugs should all be put into that box. Therefore a water pump, heat exchanger and expansion volume needed to be put into that cooling circuit. Temporarily I used the expansion tank from the Syncro (the part with the blue lid).

Motor & Gear 2

Welcome back! Much time has passed since last update, much work also. Let us begin… When the custom shaft was finished, all parts were ready to mount the motor on the original gearbox. The hollow rotor inside of the electric motor needs to be filled with oil to lubricate the toothing to the adapter shaft when in operation.




When the motor and the gear were hooked together it was interesting to see the difference in weight compared to the gasoline motor. Before the conversion the motor weighed 120kg and the gear 60kg. Now the combined weight is only around 100 kilograms. The electric motor is 50kg, hence the gear weight was also reduced by 10kg when the unnecessary gears were taken out!


Right after I put the drive train under the car to see how much empty room remains around the motor in the rear end of the bus. We still need to place 36 battery cells in a third box in the back to get to the targeted capacity of 50kWh. The challenge will be to construct a box with as many cells as possible and still remain serviceable and mountable with not too much effort.





With cardboard I built a mockup of a possible box shape. The empty space looks big but the dimensions of the cells do not leave many degrees of freedom. With the shown box I am able to put 35 cells and the neccessary space for battery management system and contactors inside it. That is one cell to little, but hey, that results in 2.5km range difference, should be okay. I did not find a better solution.


Another thing that needs to be built now is the suspension of the motor and the battery box onto the chassis. We will use the original support of the motor. There we will ‘just’ need to design a rubber bearing for the motor and a fixed support for the battery box. Nothing easier than this… Update follows.



Motor & Gear

Finally everything was ready to combine motor and the customized gear! First some words to the gearbox: Electric motors in general do not need a gearbox with multiple gears like ‘old fashioned’ combustion engines. But when using a fast turning machine like the hybrid syncronous motor made by Brusa, a transmission is necessary. The motor has a maximum speed of 11’000rpm and maximum torque of 220Nm (up to 4000rpm). The gear will scale down the speed and scale up the torque as we learned in physics class. Together with the gear ratio of the differential gear we can calculate the scale factor between motor speed and wheel speed. Using the original 2nd gear of the Syncro-gearbox we get a top speed of about 120km/h which is even a bit more than what you really want to drive with this car. Together with Toni from Technikschmitte we decided to keep the original 1st gear as our ‘offroad gear’.

Battery work continued…

We are still working on the two battery packs that will go on the underside of the car. A little bit behind schedule! It was planned to finish this task in april, but the devil is in the details! These two boxes will each hold 42 cells (of 120 total) which leaves 36 cells to be packed somewhere in the back of the car. Challenging was to add spacing elements to get the cells to exactly the desired height. We put many rubber layers between the groups to absorb oscillations and shocks when the car is on the road. Time consuming as well is the mechanical fixation of the battery service disconnect plug and the dc power connector plug. Everything needs to be watertight as these boxes will be hanging below the car directly above the road!

But now they are almost finished! We are waiting for some more parts of the battery management system that read the measured cell voltages and communicate these to the master unit.

Battery work

Currently there are two big construction sites in the project. One is the finishing of the mechanical work at the drive train with gearbox, adapter flange and shaft. Concurrently we are also in the process of filling the battery boxes that will go under the car beneath the two axles. The two boxes will hold more than two thirds of all the battery cells but some will need to be placed in another box in the rear end of the car where the combustion engine was located. Here are some pictures of the cell packages all wired up and ready for mounting into the box. The attentive reader of this blog will realize that the boxes now are nicely powder coated to prevent corrosion of the aluminium in the harsh street climate.


How to get from …

The raw piece
The raw piece

to …

Turned shaft piece
Turned shaft piece

in ten steps is shown below. As I hardly know any of the technical terms in English used to describe this process, I rather let the pictures speak. Some examples would be Drehbank, Dreibackenfutter, Zentrierbohrer, Hartmetall, Einsatzstahl and so on… Now the piece is ready for getting some teeths! This will be the next step.

Drive train work

We are planning to use the original gearbox. This leads us to the question how to connect the new electric motor with the vintage Volkswagen gear? We will need two parts: A flange to screw the two parts together. Luckily Frank who did the inspiring and fantastic conversion of the E-Bulli (a Volkswagen Transporter T2), we could build up on technical drawings for the flange and gearbox. In this place a big thank you to Frankie, the very patient ‘technical consultant’ of this project!

And secondly we will need a shaft with proper toothing on both ends, one end with Brusa Motor toothing and the other with Volkswagen gear toothing. As cutting the toothing is a science by itself we will just prepare the raw shaft and give the piece to an expert. After teeth are cut the steel must additionally be hardened. More infos and photos on this later…

Welding, rasping and filing the battery boxes

After the two battery boxes were welded, some parts were still missing inside. We needed to add stabilisation tubes, through which the main suspension screws will go. Roman helped us welding the tubes to the boxes. Thanks a lot! Afterwards they were sealed with Sika to prevent water from running into the boxes.

Another action was to rasp the holes into the back walls of the boxes which will carry the plugs for signal and power connectors. The signal connector will carry CAN-communication lines, supply power for the battery management and an interlock line. Sweet! The power connector takes two shielded power cables carrying upto 350 amps!

Mobile electrical power