emini

Auxiliary battery mounted next to inverter

Conduit more secure under the car

Rear suspension renovated and assembled

Accelerator pedal more securely mounted (also visible is the red brake pedal sensor)

There are a couple of people posting on the Tesla Motors Club forum about the Wayland Invitational on this weekend. It looks like Scotty Pollacheck (the KillaCycle rider) took a 2010 Tesla out and did 12.643 and 12.715 quarter miles for a new record. It sounds like all the other Tesla drivers were doing mid 13s at worst (those with no training).

The Mini has independent rear suspension comprising of a radius arm, shock & conical rubber spring. A shaft passes through the bearing at the front (left) end and is bolted to the rear subframe. The photo above is taken from the inboard side looking out, the wheel bolts to the other side of the drum brake. When the wheel moves up, the arm rotates around the shaft pushing the rod to the rear of the car, compressing the rubber spring. The bearing is in two parts, a needle roller bearing on the inboard side, and a bronze bush on the outboard side. In my case, the shaft at least is worn where both of these bearings run, leading to a small amount of play, so it's off to Lee at Minibitz for a new shaft and bearings.

I'm preparing the car for a motorkhana organised by the Mini Car Club of Auckland on the August 1, so I have to deal with a few loose things. I've also got to tie down the auxiliary battery, improve the throttle pedal mount, and improve the torque arm on the motor. The electric system ought to be a big advantage in motorkhana as it can go from forwards to reverse at the flip of a switch, and there's no faffing about with the clutch.

The Manzanita Micro PFC series chargers are renown for being noisy. The graph above shows just how noisy. Charging at about 10A starts at 50 seconds and continues for about 180 seconds. Charging resumes briefly at 40A. We can see about 50mV of noise while charging at 10A, and 200mV at 40A. Currently the EVD5 firmware does not average voltage readings, I had similar noise problems using a LabJack with the PFC-30 charger and averaging was very helpful.

The good news is that the BMS didn't crash. The LabJack crashed if I charged at more than 7A, while the EVD5 BMS, even with floating current sensors (I've only hooked up the voltage sense wires, the bypass circuit will come later) was happy at 40A, at least for a short time. I'll test high current more thoroughly when I've packaged enough BMS boards for the whole battery.

See evd5-pfc30.tar.bz2 for the raw data.

Today I finished the software addressing functions in my BMS firmware. I had previously been working with just one cell, getting the basic commands to work. Now I send a cell address and only that cell responds. Without this, all the cells respond at the same time and make a terrible din such that you can't understand any of them. My protocol isn't exactly fancy, but is a pain to type manually, so I wrote a very primitive monitor in C. With a computer sending commands, I found that the slave processors are too slow to keep up while they are actively monitoring the cell voltage, so I had to implement interrupt driven receive and a buffer to store the incoming command until the the slave has finished looking after it's cell.

The above graph shows 4 cells (my power supply only does 15V, which isn't enough for the 5th cell). All 4 cells are being charged at 350mA, and after 1000 seconds, cell 2's voltage hits 3550mV and the BMS starts to discharge that cell (i2 on the graph). The current lines appear to bifurcate because the current control is oscillating. The hardware isn't really designed to control current, I'm running a software control loop to make it do that, and it's a bit finicky. The software tries to keep the current within 50mV of it's target current, but the current control knob doesn't easily give it fine enough control to do that. Basically the program turns up the current, overshoots, turns it down, undershoots and repeats. I'll try a 100mV target next time.

The graph stops because my primitive monitor program detected a protocol error and stopped. The next change with be error recovery.

I expect to be hooking this up to the car and seeing what happens with the PFC30 charger in the next couple of days. Last year I made a simple BMS with a Labjack & a laptop which worked really well with my power supply but freaked out when I connected the big charger. The Manzanita PFC series is renown for injecting a lot of electrical noise into the battery.

See evd5-first-charge.tar.bz2 for the raw data.