Thursday, February 9. 2012
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.
Monday, January 30. 2012
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:
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.
Friday, January 20. 2012
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:
Tuesday, November 22. 2011
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.
Thursday, October 6. 2011
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,
Pictured is my current test implementation, there are a number of things that need fixing,
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.
Tuesday, May 3. 2011
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.
Tuesday, April 12. 2011
There is an electric truck for sale on trademe at the moment. It appears to be an industrial 3 phase motor with a 336V lead acid battery. 20km range and 45km/h top speed. The vendor isn't supplying too many other details, but it looks to be a bargain at the reserve price. If it was closer to home I'd go have a look, but Whakatane is a bit far.
Thursday, March 31. 2011
Last time I talked about the call for feedback on the LVV Standard 75‐00(00) Electric and Hybrid Vehicles Draft #5. You can read my feedback below, unfortunately it doesn't make a lot of sense without the questions so you might want to have them too.
In addition to answers to the numbered questions, I have the following comments:
Wednesday, March 23. 2011
In New Zealand, modified vehicles need to be signed off or "certified" by an engineer. In the 1990s an effort was made to create rules governing the certification of Electric Vehicles but it was never completed and the rules are now quite out of date. The Low Volume Vehicle Technical Association have been updating these rules over the last year or so, addressing a number of shortcomings with the old draft. They are now publicly requesting feedback.
I've already had a hand in the new draft document and I'll be posting my feedback here (and to the LVVTA) in the next few days. If you are building an electric vehicle or thinking of doing so, you should read the draft and submit feedback by the end of the month (8 days!).
Monday, March 21. 2011
There is room for another row of cells in front of the two shown, but this row will have to be slightly lower since the front of the car curves down. There is enough height in the middle to put cells above the motor where it protrudes through the plywood, higher than the rest.