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My friend Theo is making a film about converting his Toyota Sera. Part one is now finished, check it out.

I made a little load tester with some stove elements. They draw 27A at 260V. The camera is sensitive to near infrared -- they don't look as bright in real life. I think I will have to improve the cooling system before running it at higher voltage. The 3rd element away from the fan runs hottest, probably because the 4th element radiates heat away on it's outside and heats the 3rd element with the other.

Connecting this thing is not entirely straightforward. At low currents, you can use an Anderson disconnect with moderate safety, but things go badly at 27A and 260V. When I connected all 4 elements for the first time, the pins hit end on and the plug didn't go together. I don't know if disconnecting would have gone better with the small run-up that a fully mated connector offers, but I do know that separating from half connected went badly. There was a pop and a ball of white a big bigger than a hand span. When the after-image started to fade I could see the outline of the connector with a jet of white exiting the connector at 45 degrees on each side.

Safe disconnection is easily achieved with the right contactor. A small flash is visible inside the arc chamber during disconnection.

One of the weakest parts of my motor mounting system is the bush which absorbs the torque generated by the motor. This mount was made very quickly from stuff I had lieing around and it turns out I applied force to the bush in different direction to that which it was designed for. I'm now working on a new design involving at least two more mounts which will better control the front-rear position of the motor in addition to it's torque.

The first mount is nearly done and sits between the gearbox and the front rail of the subframe, you can just see the top bolt and the hole for the bottom bolt in the middle left of this picture:

Revenge of the Electric Car is on at the Documentary Edge Festival in Auckland and Wellington. The director, Chris Paine will be speaking at the opening night (tomorrow! 26th April!) and on the 4th of May. I'm going along to the 4th of May. Unfortunately it doesn't look like he'll be attending the Wellington showings.

Ed came over and helped me make a temporary battery box for the rear seat. This lets me evaluate performance with 40 more cells, for a total of 76. Knowing how well the car performs at higher voltage with a larger battery lets me decide how hard I need to work to squeeze cells under the bonnet. The intention is still to retain 4 seats in the car, this box is just an experiment.

Building this battery box was harder than it sounds. The seat base is full of curves so the bottom of the box needs a strong base, and holding the cells down with their dangerous high voltage terminals very close to the edges is not trivial. I'll post a picture of the lid which was key to holding the cells down shortly. The box is made of wood which is more flammable than I would like, restraint will be achieved with ratchet tied downs attached to the seat belt anchors.

In other news, the new cable connecting the inverter to the motor has resolved my inverter instability. I'll blog more about this cable soon.

Previously, I reported that my Simovert motor controller was happy in the rear of the car with the motor in the front of the car. It turns out this is not the case. While going up and down the driveway did not uncover any problems, going up and down the road has. The inverter shuts down with a range of errors:

• GateDriveUnit
• LCA Err Latch
• Overcurrent
• VC_Over_Voltage

I am hoping that this is caused by a combination of poor motor phase cable routing and poor motor-inverter grounding. It turns out that the Siemens supplied motor cables have a shield which is grounded in the cable glands, effectively joining and extending the casing of the motor and the inverter to envelope the motor cables. Such a shield will do a lot to control noise radiated by the motor cables. My motor cables had none of this and worse the motor was not well grounded -- I'm told that non-trivial current can flow between the motor and inverter through the ground due to "induction effects". Regardless of how real this is, properly bonding the inverter ground to the motor ground seems reasonable.

I am solving this problem with a 50mm² 3 phase neutral screen cable and appropriate glands. The very stiff underground rated cable I have isn't really appropriate and in hindsight, I should have found a supplier of the right cable, but that story is for my next post.

In 2008 I bought a battery. At the time, I knew that I was buying a product with a shelf and cycle life (it wears out even if you aren't using it). I didn't expect the battery to sit around for as long as it has, but here we are 3.5 years later. I did a capacity test of the 36 cells installed in the car and found a usable capacity of 33.5Ah: The nameplate rating is 40Ah which is substantially more. There are several possible causes of this discrepancy:

• Calendar Life
• Cycle Life
• High current abuse
• High temperature abuse
• Differing test methodology
• Low capacity when delivered

Calendar life and differing test methodology will certainly have an effect. I am charging to 3.55V at 1A which is substantially lower than thunder sky's recommendation. My pack is moderately closely top balanced and at the end of discharge, the highest cell was just below 3.1V while the lowest cell was at about 2.8V at 10A discharge. This suggests the cells have varying capacity or are not properly balanced. I also tested 10 cells which have not been cycled or abused with high current or high temperature. The pack in the car has had perhaps 10 cycles, a lot of it discharging at 3C for 5 or 10 minutes at a time. I limited my maximum current to 200A or 5C and kept currents above 120A to short 5 or 10 second bursts. This is not too far from Thunder Sky's specs but does cause significant battery heating. In the summer I have measured over 40C at the battery terminals. The 10 cell pack that sat on the bench has not been subjected to high current or high temperature, probably never getting higher than 25C. This pack achieved 34.3Ah and showed less spread in capacity, with the hightest cell at 3.0V while the lowest was at 2.85V: That these two packs show very similar capacity suggests the high temperature and high current and cycling had little effect on the battery in the car. Cell voltages were measured with the EVD5 BMS, discharge current and Ah counter performed by my EVision and recorded from it's CAN bus by the BMS data logger. The car's battery was discharged with two domestic 240V heaters and a kettle (which nearly boiled dry). The small 10 cell battery was discharged with a steel wire on a wood form in a large bucket of water. The 10 cell battery shows a larger spread of voltages under load because i did nothing to prepare the cell terminals before putting making the connections, the terminal connection resistance was all over the place.

On Thursday, Mike Duke & his Waikato University team's electric car will join Bochum University's solar car on a trip from Auckland to Bluff.

They're starting at the domain in the morning, but it's not exactly clear when they are leaving. I'll be there to see them off, if I get wind of the departure time I'll update this post.

I seem to have successfully moved my inverter to the rear of the car. This will allow me to put a much larger number of cells in the front of the car and improve the weight distribution (I'm currently rear heavy). I found connectors to extend the motor's encoder cable and Ed made one up using some special cable he had left over from a job. I replaced the terminal cover on the inverter with a mounting plate for the new Gigavac GX14 contactors (replacing the large Schaltbau 162 units that wouldn't really fit anywhere), precharge circuit and the EVision shunt. This has a number of drawbacks,

• quite a lot of effort is required to inspect the terminals under the cover
• the positive battery cable connection is partially obscured below the boot opening and is close to the body, working on it is a little scary
• a rear end crash could cause major problems
• I haven't worked out how to form a cover

I may yet move this contactors plate above the inverter or to the right of it.

Pictured is my current test implementation, there are a number of things that need fixing,

• there are some very thin copper bus bars that need to replaced with thicker bars
• the jumpers between the contactors and the inverter are much too thin
• the fuse should be much closer to the battery
• one of the phase cables is completely unsuitable (about 10mm2 total from all three conductors of a household electric oven supply cable (including the oven's on-off switch!)
• the low voltage wires need some tidying up
• putting everything on top of an insulator and standing some insulation between the various components might be a good idea
• I need to make a cover

This worked well for going up and down the driveway, well enough to make me feel confident the inverter will live in the rear of the car without being effected by noise escaping from the phase cables.

I did have one mishap while testing. I know you have to keep the loop area small in the phase cables (this is a clever way of saying "keep the phase cables close together"!) and Ed repeated this several times while I was fabricating, but when it came time to actually put it together, well, I forgot. The inverter was most unhappy to have one phase cable go over, one go under and one go around the side (the latter two going out the boot aperture). It refused to run the motor smoothly with no load and then it blew the 30A test fuse! I re-directed the cables to all go over the inverter and through the hole in the front of the boot and everything was smooth and happy. My testing so far is limited by the thin wires in both the battery and motor circuits but I think (and hope) I put enough current through the phase cables to prove it will work. The encoder cable runs down the side of the car while the phase cables run down the middle. Shortly additional battery cables will also run down the middle, hopefully this won't introduce problems.

This Sunday 8th May is the EV Builders Expo 2011 at TAPAC, 12 - 6 pm. I'll be there (possibly even with my car, I'm working through mounting the inverter in the boot). This should be a good show, my friend Phil explaining how he will go racing in his his electric Saker sports car, F40 Motorsport designed my adapter plate so it will be good to catch up with them, and the Formula E electric go karting guys are good value too.

Theo, the organiser is making an EV documentary which I'm keen to see (not least to find out how our interview went) and he's building an electric Toyota Sera. This is a fund raising event and there is a $20 cost which goes towards finishing the Sera.