Friday, June 3. 2016
I've added remote climate control support in the Nissan Leaf OVMS firmware. This is relatively straightforward because Nissan built this feature into the Leaf's CARWINGS package. In New Zealand CARWINGS wasn't sold with the Leaf and Japanese import Leaves have a Japanese cell phone which doesn't work in New Zealand. Making it work here means emulating the function of the TCU module. On a Gen 2 Leaf this is simple, send a CAN bus frame to wake the car up and another frame to tell it to turn on or off the climate control, or start charging.
The Gen 1 Leaf is a little more complicated. The TCU wakes up the car by applying 12v to a wire, telling the VCU to wake up. After the VCU wakes up, the TCU sends the same command message as on the Gen 2 car. The OVMS hardware doesn't have an external 12V GPIO so I had to make something. I had a small relay lying around and using that was easier than building a 12v protected output. I glued a drive transistor on one side of the expansion port and the relay to the cell phone module. The LED catches the relay's turn off spike but any diode would do.
OVMS Module with modification to wake up Gen 1 Nissan Leaf
I used the previously unconnected Ring Indicate pin on the DIAG serial port to get the 12V signal out of the OVMS. RI is a good pin because it's an output from the OVMS and it is intended to tell the host the phone is ringing which matches up well with the "hey something important is happening, pay attention" use here. RS232 uses +12v signaling so a normal serial device will still be ok to plug into the port. The wire from the relay goes through one of the mounting holes for the serial port to access the pins on the back side of the circuit board, this avoids fouling the case which is pretty tight on all sides of the circuit board.
I've disconnected Nissan's TCU and stuffed a wire into it's plug to connect the OVMS to the Leaf's wiring loom. Nothing has complained about the disconnected TCU that I can see.
I'll post a schematic shortly.
Remote climate control is great, you can press a button on the OVMS cell phone app to get the car headed to toasty warm or cooled down before you get to it. If it's not plugged in then you get 15 minutes of cooling or heating, and more if it is plugged in. You can't control what the climate control does, Nissan have hard coded it to target 25C which is likely to cool the cabin in the summer and certainly heats it in the winter. Nissan have programmed the remote climate control to use recirculated air so in winter the windows are usually fogged up. I don't think there is anything I can do about that but the windscreen button once you're in the car doesn't take long to clear it.
Sunday, August 11. 2013
Many high voltage DC contactors, switches and circuit breakers are only able to perform to their specifications if the current is flowing in the expected direction. This is because they include magnets which push the arc away from the switching element and into an arc chute or other plasma management device. A wire carrying a current through a magnetic field experiences a force (this is how motors work!) and this is particularly effective in the case of an arc because the "wire" is actually made of ionized gas. The problem comes when you reverse the direction of the current -- the "blow out" magnets suddenly become "blow in" magnets and the switch catches fire.
RISE did some testing of polarized DC circuit breakers intended for solar power and the results were quite spectacular. Do wait for the 40A tests towards the end!
Consult the manufacturer's datasheet to ensure your switches are correctly installed!
Friday, August 9. 2013
I tested a few circuit breakers rated for AC using my car's 250V DC battery. I used my load tester to limit the current to about 27A. I found that with a resistive load, the breakers successfully interrupted the current but failed safely after 5 or 10 switching cycles. Since I didn't have the equipment to limit the current to 50 or 100A, I used one of the windings in an isolation transformer to make the load more inductive and sort-of simulate a higher fault current situation. With this additional resistance, the current dropped to 23A. The results were quite scary:
It's important to note these tests represent abuse of the circuit breakers, if you ask them to switch AC they will likely give years of trouble free operation. The key is that 50Hz AC current falls to zero for long enough that the plasma cools, when the voltage rises during the next cycle, the arc can't re-establish without the plasma. With DC, the current doesn't stop and the arc just keeps burning.
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:
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.
Saturday, February 7. 2009
When I installed my EVision, I removed my fuel gauge. I'm using a fixed gear ratio, so motor speed isn't particularly interesting. The EVision has an output to drive a fuel gauge, but it needs reprogramming to drive a tachometer. Victor suggested that I bypass the tachometer's circuit and drive the movement directly. This is made especially easy because the tachometer comes out of the instrument cluster on it's own, and the movement is connected to it's circuit board with wires. I simply reconnected the movement to the input of the rev counter circuit and connected the EVision to the existing plug. Unfortunately the EVision's driver wasn't powerful enough to drive the movement beyond 2000 rpm, so I added a small transistor to amplify the signal. Power for the amplifier was already available on the circuit board so this was easy.
One of the great things about an electric car is it can be totally silent when you're not moving. Unfortunately the PWM frequency is about 3kHz and while the tachometer makes a fairly bad speaker, it's quite audible. I'm going to soften the switching with some kind of capacitor, which will hopefully make it silent. I'm also planning to make a circuit to turn off my water pump when the car isn't moving.
Wednesday, February 4. 2009
If Google Maps is correct in measuring my trip, I'm doing
I still only have only 1/3 of my final battery installed and it's getting quite hot. (this is why I'm limiting my power to 10 or 11kW, about 3C). It's 25℃ at night here and the battery isn't even getting down to ambiant overnight. The trip started at 27℃ in the middle of the battery and ended at 33℃. My record battery temperature is 43℃ (after charging 20Ah at 30A right after discharging about 10Ah at 50-100A right after baking in the sun). This isn't very good for the battery. I need to install more cells so each one doesn't work so hard.
I'm charging without a BMS, I have my charge voltage set very low so it slows down as soon as the first few cells start to come up. Luckily none of the cells have come up by themselves, it's always a group which is enough to slow the charger down and stop it. I last balanced my cells back in September and October. Today I went round with my 3A bench supply and topped up the low ones. Of the low cells, most required only a few minutes of charging at 3A to come up above 3.6V (at 3A). 3 or 4 took about an hour each. I guess these cells have higher self-discharge.
Less than a 10% variance in absolute self-discharge over 4 months or so is really quite good. I've put very few cycles on the battery so I figure self-discharge dominates any other effect that would push them out of balance.
Monday, February 25. 2008
For your entertainment I present the crappiest aluminium welding I've ever seen (well, almost). I've put the centering ring on a couple of times and even mounted the motor and so far it hasn't fallen off.
While I don't claim to be the greatest welder, I feel I must point the finger at low argon flow for the very poor finish. I didn't want to attempt a continuous bead because the argon pressure is OK but the flow rate is very low, so you get a burst of gas when you pull the trigger and then very little. I'm not sure if I'm low on gas or the regulator is faulty (for argon I use very small disposable cylinders and my small regulator doesn't have pressure gauges).
The break profile allowed reasonably good relocation, so there is a chance I got the back into the right place. If the shaft runs smoothly after everything is assembled then I'll be very tempted to use this case instead of spending a few hours getting another one from the wrecker.
I'm using a 175A MIG welder, 1mm aluminium wire, argon shield gas, wire feed 5, power 6 and this is the second time I've tried to weld aluminium. I chose not to practice on scrap aluminium in case I ran out of gas completely -- I'm a little surprised that the weld is as good as it is.
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