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.
Tuesday, February 22. 2011
It seems improved Weight distribution can be had by putting the inverter in the boot and most of the battery in the front. This does introduce longer motor cable runs which will reduce efficiency but it is looking worth it -- with the inverter up front there isn't much room for cells and it's 70kg lighter on the front axle than when I started. I'll be mocking up the front to see exactly how many cells fit without the inverter before I commit to this move.
Monday, February 14. 2011
The contactors supplied with my Siemens electric drive system were large Schaltbau C160 series contactors with arc chutes and blowout magnets in an even larger box. This was quite inconvenient in the mini as the only place they would was in the boot. I'm planning on putting at least some cells in the front of the car, which would require some clever packaging to get the contactors to at the front. So I replaced them with two Gigavac GX14 sealed contactors. At the moment I've mounted them on a plastic base in same place the old contactor box lived. When I'm done, they will likely be split up, I'm expecting one in the boot at the negative end of the battery and and one at the front of the car at the positive end.
In the foreground you can see the precharge circuit, two small relays and 8 PTC resistors allow the controller's capacitors to charge in an orderly fashion before the main contactors close. If this isn't done the capacitors charge very suddenly. This huge inrush current is hard on the capacitors, battery and contactors. Such situations may even cause the contactors to weld closed. You can see this inrush on a small scale when you plug your laptop or cell phone charger into the mains. Sometimes there is a pop and (in a darkened room) quite a large flash as the circuit connects (it only happens sometimes because the AC might be in a low voltage part of the cycle when you connect, or it might be at a high voltage). Check out the ends of the pins, you'll see pitting and scorch marks on most laptop power cords. Charging an electric vehicle's capacitors involves perhaps 100 to 1000 times more energy than a laptop so there is a soft start circuit to avoid the bang and the flash.
I left the wires long and curly because I'll be moving the contactors. When they're in their final location, I'll cut the wires just right. Unless I keep them curly (never underestimate the aesthetics of curly wires).
I'll post a side-by-side comparison of the contactors some time. The GX14 appears to be safer in an accident.
Tuesday, January 18. 2011
Friday, November 19. 2010
I have been making slow progress on the EVD5 BMS. I fixed no less than 5 bad joints in my backplane arrangement (I specified the wrong size hole and ended up drilling them bigger and soldering the top and bottom, but not so well) and have the BMS behaving well on my 36 cell battery.
I haven't implemented the necessary code to deal with voltage drop in the wires while shunting because I'm going to get rid of the wires. The wires are a disaster from a safety and construction point of view. Constructing the wires out of ribbon cable with soldered in fuses takes a very long time and I've already had to replace two blown ones (don't know the cause). My earlier backplane design packs too many boards too close together and makes me nervous.
Removing the scary difficult wire while keeping the 5 cell EVD5 BMS is possible, if you make a backplane like Tritium's IQCell system. The squiggly bits in the circuit board will allow the cells to move as the car jiggles down the road. The problem with this is that the EVD5 has an awful lot of wires to each cell -- temperature, sense, shunt+ and shunt- and I'm having trouble getting them all through the squiggles. It's worse if I want to mount the shunt transistors away from the main EVD5 board. You'll note that Tritium's hardware is a lot simpler than the EVD5, this comes from more R&D, when Bob designed the hardware (in 2007!) it was much less clear what was needed, so he designed it to be very flexible.
Its fair to say that the EVD5 isn't really suitable for prismatic cells and while this is true, it isn't a really a fair criticism as it was never designed for this purpose. It was designed for Bob's particular cylindrical cell construction.
I've put together a schematic with only 3 wires to each cell and none of them carrying current by putting the shunt transistor at the cell and only passing it's gate back to the central EVD5 board. To control current, I abandon the current sensing system in the EVD5 and add a series resistor. I haven't yet done the layout and seen if this works better -- thinner and one fewer wires isn't all that compelling.
If you've been watching the commit log, you'll see I've made a fair amount of progress with the software, with a bunch of small improvements to the laptop based monitor and better use of the LEDs on the EVD5 board.
I also found another hardware bug, the reset line on U10, the 555 timer in the RS485 section is floating. This is a FET based part and it doesn't take very many electrons to reset the timer and stop communications. With this line tied high, I don't have problems with the software addressing any more.