EMI trouble and rebuilding the interior

Post date: Sep 1, 2015 8:44:29 PM

During the summer, we spent a lot of time cleaning up the wiring in the engine bay. Also, access to the motor controller was very difficult, and required a complex sequence of unbolting various things. Now we have created a plate that holds the motor controller on one side, and a contactor box on the opposite side. We also accidently burned a hole in a battery box with just 36V of lithium cells.

Motor controller interference

However, a previously unnoticed problem popped up: when enabling the motor controller, all BMS communication would fail. Turning off the motor controller restored it. Obviously an EMI issue, as the 10kHz switching frequency of the Curtis controller was visible on every wire in the car. Although our battery boxes are aluminium all around, there is still a rubber seal on top, that could prevent proper grounding. We solved that first, but to no avail.

Next we suspected that the long communication wires, running from the front batteries to the batteries in the centre, absorb too much EMI. Thus we switched to shielded ethernet cable wire and then even coax cable. This all made no difference. We even wrapped the motor controller in aluminium foil, but it seems the noise is injected into the battery cables themselves.

Fortunately the Emus BMS system allows the grouping of cell modules into CAN group modules (CGM), that can contain uneven and unequal number of cells. So the solution could be to divide our front pack into 3 separate groups, each with its own CGM. This is illustrated below.

The required changes led us having to take out all batteries in the rear to reach the bottom boxes next to the differential:

Eventually the hard work paid off and now the BMS keeps working! For a brief moment, the problem appeared again under heavy regeneration, but this was due to the rubber seals isolating the battery box covers from the chassis ground... EMI, tricky stuff to debug!

Heater core installation

Our heating system was also ready to be installed into the air-box:

On the first picture above, you can see that the flap that allows mixing of cold and hot air is removed, since the temperature is now controlled purely by a PI-loop running on an Arduino nano.

Below you can see the connections to the two ceramic heaters, in parallel, and the wires to the PT100 temperature sensor.

Interior installation

Next up was the cleaning of the carpets, which smelled rather funny after being outside for almost two years. We rubbed them with a solution of BioTex and now they smell totally fresh and were ready to be installed:

Electric power windows

The power windows in the car were very, very slow. After one year they even seized completely. Some google-fu showed that this is likely due dried-out grease in the rails in which the glass move. Thus we took them apart according to these instructions, degreased and regreased the rails, and voila, working power windows!

Now the car is getting very close to finishing, and we are ready to bring it to a professional garage to realign the wheels and lights, maybe check the brakes... and do the final adjustments to get the car approved and road-legal.