Electric

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.

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!

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:

A Vynckier Series E circuit breaker interrupted the current once and caught fire on the second attempt. The fire only went out because I used my (400V 250A DC rated) contactor to turn off the current, you can see the flash on the left when it switches off.

A People DZ47-63 circuit breaker interrupted the current but destroyed itself in the process. Inside you can see the switching element is significantly shortened and the casing burnt:

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.

• Q1 Yes.
• Q3 Yes, a plug such as an anderson disconnect should be allowed in place of a switch and such disconnects should be allowed in a battery compartment when non-venting batteries are used.
• Q5 Yes, Over current devices should be allowed within the battery compartment(s) Why would they be forbidden within the battery compartment? 2.2(1) (c) allows flame proof switches and relays within a battery compartment, fuses should not emit flames if they are of good quality and used within their ratings. 2.2(5) NOTE (d) recommends fuses near the electrical middle of the battery, but 2.2(5) (b) forbids fuses within the battery compartment, making this recommendation harder to follow in some cases.
• Q9 A manual ground fault detection system should be mandatory, with an automatic system preferred. I have not had time to find a suitable automatic system so would hesitate to mandate an automatic system.
• Q10 I agree that a simple single potentiometer design is not safe enough. This is a problem as some existing and in-progress conversions likely only use a single potentiometer throttle. I believe a single potentiometer with broken wire detection and a "pedal up" switch inhibiting the traction system is sufficient, with a dual potentiometer preferred. Would a single hall effect sensor be sufficient? My own vehicle has a single potentiometer with broken wire detection, which I am uncomfortable about. Is this sufficient? I will likely add a pedal up inhibitor, but the details of doing this are not trivial due to the design of my control electronics.
• Q12 No.
• Q13 Yes, with an explanation that a proper pre-charge circuit will protect the main contactors
• Q14 No, I think it sufficient to require cables be marked with the voltage ratings by the manufacturer or documentation provided to require this.
• Q15 Yes, but not to the same level as the FIA. The FIA's "insulation resistance to ground" test is equivalent to the ground fault detection requirement in 2.4(1)(f). 2.4(1) NOTE 3 suggests that a ground fault is permissible so long as it is "safe". The FIA's 250k or 500k Ohm requirement is not possible with a brushed motor or flooded lead acid batteries. A maximum ground fault current should be allowed, so higher voltage systems must maintain a larger resistance to the body. For example a 150V system with a 5k Ohm ground fault will have a maximum ground fault current of 30mA, while a 300V system with the same ground fault will have a maximum ground fault current of 60mA. I am unsure what is achievable in a flooded lead acid battery vehicle with a brushed DC motor without super-human maintenance. Note well that testing the insulation resistance should not be done with a multimeter set to the resistance scale -- a low resistance ground fault will likely destroy the meter.
• Q16 Yes. Live parts should be covered by strong materials.
• Q17 Yes, but 5 seconds is too fast and will cause the discharge resistor to run hot while the vehicle is in use. 1 Minute would be safe. Siemens placed a warning to wait 1 minute before servicing on my controller.
• Q18 No. This requirement has several parts. Most obviously inappropriate is the requirement that the battery cell manufacturer attest to the safety of the battery. Most lithium battery packs are assembled by the owner, so the manufacturer is unlikely to be available for comment on the battery pack. Note the preceding wording requires the cell manufacturer manufacture the cells, but does not comment on assembling the battery pack. A requirement that the cell manufacturer assemble the battery, or that the cell manufacturer attest to the safety of a customer assembled battery would prevent most or all electric conversions using lithium batteries. Requiring the battery management system monitor the temperature of the battery is a good thing, but it's not clear how many of the commercially available battery management systems do this. Requiring batteries that are prone to thermal runaway to retain the manufacturer's monitoring and safety system is a good idea but doesn't say anything about such cells that are supplied without any monitoring and safety system. The Battery Management System issue is highly contentious at the moment. It is clear that a bad Battery Management System is worse than no battery management system for Lithium Iron Phosphate based batteries. Mandating that there be a battery management system may or may not cause more problems than it solves with this chemistry.
• Q19 No. This is already covered in 2.4(1) (a). I don't believe any additional instrumentation is required to warn of danger during maintenance since the battery box already has a high voltage warning on it, and turning the car off does not make the battery safe.
• Q20 Yes, you already do in 2.2(1) (b).

In addition to answers to the numbered questions, I have the following comments:

• The Note in 2.2(2) suggests typical operating temperatures of -10 to 40 degrees C. This is incorrect. Most electric motors operate happily with internal temperatures well over 100 degrees C.
• 2.4(1) (c) requests a "handbrake on" indication to the driver. Why is this required? For cars that did not have this indicator as original equipment, this is a fairly complex requirement. Is the presence of a handbrake lever next to the driver in the "handbrake on" position sufficient to satisfy this requirement?
• The last sentence in 2.4(1) NOTE 4 should read "This should be done between the body and several electrical positions within the battery, for example at the most negative battery, the most positive battery somewhere in the middle of the battery. If the body is non-conductive, then ground fault detection testing should conducted between the battery and all metal structural members near the battery." We want to detect a ground between any potential within the battery and the body (which, if it's all-metal, is always at the same potential). My wording around non-conductive body issues is somewhat clumsy, sorry.
• Section 5 "Ground fault detector" definition is wrong. We are not looking for an "imbalance in current between the energised conductor and the return neutral conductor since:
  1. there is no such thing as a neutral conductor in an electric vehicle
  2. if current flows in the ground fault, we already have a potential fire
  What we are looking for is a connection between the battery and the body of the vehicle. No current flows through the first ground fault. I would word this section as "means a device that detects a connection between the battery and the body of the vehicle. Such a connection will allow a current to flow through the body of a person who is simultaneously touches the body of the vehicle and part of the battery during maintenance. A second connection between the body and different part of the battery will allow current to flow through the body, potentially causing a fire or damaging the battery."

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.

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.

If Google Maps is correct in measuring my trip, I'm doing 177109 Wh/km on a return journey with stopping and starting and hills. I was driving like a nanna, and I limited myself to 10 or 11 kW (for 60km/h uphill, >80km/h downhill (56% at this sort of speed, the rest slower)). My record is now >20Ah and 20km without charging.

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.

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.