New Lithium Battery Pack for my EV

Eight years ago I installed a pack of 36 Lithium cells in my EV. After about 50,000km and several near-death battery pack experiences (over discharge) the range decreased beneath a useful level so I have just purchased a new pack.

Same sort of cells, CALB 100AH, 3.2V per cell (80km range). The pack was about AUD$6,000 delivered and took an afternoon to install. I’ve adjusted my Zivan NG3 to cut out at an average of 3.6 v/cell (129.6V), and still have the BMS system that will drop out the charger if any one cell exceeds 4.1V.

The original pack was rated at 10 years (3000 cycles) and given the abuse we subjected it to I’m quite pleased it lasted 8 years. I don’t have a fail-safe battery management system like a modern factory EV so we occasionally drove the car when dead flat. While I could normally pick this problem quickly from the instrumentation my teenage children tended to just blissfully drive on. Oh well, this is an experimental hobby, and mistakes will be made. The Wright brothers broke a few wings……

I just took the car with it’s new battery pack for a 25km test drive and all seems well. The battery voltage is about 118V at rest, and 114V when cruising at 60 km/hr. It’s not dropping beneath 110V during acceleration, much better than the old pack which would sag beneath 100V. I guess the internal resistance of the new cells is much lower.

I plan to keep driving my little home-brew EV until I can by a commercial EV with a > 200km range here in Australia for about $30k, which I estimate will happen around 2020.

It’s nice to have my little EV back on the road.

Torturing the Clutch in my EV

My 17 year old son recently been given a drivers license, and has, like his sister before him, taken over my EV. Free driving (Dad pays the electricity bills) is kind of irresistible. And also like his sister before him – I was full of fear and angst. You see my EV is something of a prototype, and likes to be babied by it’s Creator. Lots of traps for the unwary. If you want an EV fit for general consumption talk to Tesla.

Sure enough, just 4 weeks later, I get “the phone call” from my son. The EV has died. Motor running but making nasty sounds and won’t move. Fortunately, it stopped a few blocks from home. I attended the scene, and all I could hear was a grating sound from the front. We pushed it home and I consulted my motor vehicle brains trusts (friends Kyle and Scott) who pronounced a likely transmission failure.

I prepared to drop the motor and gearbox, something I haven’t done since I blew up the armature 6 years ago. Looking forward to the project, as doing something mechanical is a welcome change in my lifestyle. Feeling determined as well, my EV must be kept running!

I was talking about the problem on the local repeater when Gary, VK5FGRY popped up and said he might be able to help. Gary has a fully equipped workshop and years of experience with car repairs. He also has the most important resource of all – time. Gary came around this morning at 9:30am to assess the situation. He suggested we make a start, so we could at least work out what the problem was.

Within a few hours the gearbox was on the ground and the problem found – a stripped spline in the hub of the clutch plate. The noise I could hear was the stripped spline being filed away by the (somewhat harder) gearbox input shaft. Gary also discovered a few minor issues with stripped or missing gearbox mounting bolts. Note the filings on the inside of the hub, and splines mostly gone:

This was a lucky escape – I thought I was up for a new gearbox ($500 second hand). We guessed the torque of the electric motor (200Nm, about twice that of the original infernal combustion engine) had caused the fault. Well it’s been Electric for 8 years and 50,000km, so I guess I can’t complain.

We headed out and bought a new clutch plate ($100), some bolts, and transmission oil. After a nice lunch of home made bread and condiments, we picked up the tools again and by 6pm my little EV was on the road! Yayyyyyyy. Thank you so much Gary!

Here is the clutch (purple) re-assembled and attached to the electric motor, just before the gearbox was re-installed. Silver metal is the adapter plate. Lots of cables all over the place:

It was a great day. Nice change from my usual keyboard and laptop filled life. Lovely summer day, working outside with the tools, getting a bit dirty (but not oily – this is an electric car so no grease under my bonnet). So much nicer to do it with good company – especially someone as experienced as Gary.

I do live an interesting life. What did you do today Dad? “I worked with a friend to fix a home brew Electric Car!”

Links

My EV page

My EValbum page. Lots of pictures and technical stuff.

Self Driving Cars

I’m a believer in self driving car technology, and predict it will have enormous effects, for example:

  1. Our cars currently spend most of the time doing nothing. They could be out making money for us as taxis while we are at work.
  2. How much infrastructure and frustration (home garage, driveways, car parks, finding a park) do we devote to cars that are standing still? We could park them a few km away in a “car hive” and arrange to have them turn up only when we need them.
  3. I can make interstate trips laying down sleeping or working.
  4. Electric cars can recharge themselves.
  5. It throws personal car ownership into question. I can just summon a car on my smart phone then send the thing away when I’m finished. No need for parking, central maintenance. If they are electric, and driverless, then very low running costs.
  6. It will decimate the major cause of accidental deaths, saving untold misery. Imagine if your car knew the GPS coordinates of every car within 1000m, even if outside of visual range, like around a corner. No more t-boning, or even car doors opening in the path of my bike.
  7. Speeding and traffic fines go away, which will present a revenue problem for governments like mine that depend on the statistical likelihood of people accidentally speeding.
  8. My red wine consumption can set impressive new records as the car can drive me home and pour me into bed.

I think the time will come when computers do a lot better than we can at driving. The record of these cars in the US is impressive. The record for humans in car accidents dismal (a leading case of death).

We already have driverless planes (autopilot, anti-collision radar, autoland), that do a pretty good job with up to 500 lives at a time.

I can see a time (say 20 years) when there will be penalties (like a large insurance excess) if a human is at the wheel during an accident. Meat bags like me really shouldn’t be in control of 1000kg of steel hurtling along at 60 km/hr. Incidentally that’s 144.5 kJ of kinetic energy. A 9mm bullet exits a pistol with 0.519 kJ of energy. No wonder cars hurt people.

However many people are concerned about “blue screens of death”. I recently had an email exchange on a mailing list, here are some key points for and against:

  1. The cars might be hacked. My response is that computers and micro-controllers have been in cars for 30 years. Hacking of safety critical systems (ABS or EFI or cruise control) is unheard of. However unlike a 1980’s EFI system, self driving cars will have operating systems and connectivity, so this does need to be addressed. The technology will (initially at least) be closed source, increasing the security risk. Here is a recent example of a modern car being hacked.
  2. Planes are not really “driverless”, they have controls and pilots present. My response is that long distance commercial aircraft are under autonomous control for the majority of their flying hours, even if manual controls are present. Given the large number of people on board an aircraft it is of course prudent to have manual control/pilot back up, even if rarely used.
  3. The drivers of planes are sometimes a weak link. As we saw last year and on Sep 11 2001, there are issues when a malicious pilot gains control. Human error is also behind a large number of airplane incidents, and most car accidents. It was noted that software has been behind some airplane accidents too – a fair point.
  4. Compared to aircraft the scale is much different for cars (billions rather than 1000s). The passenger payload is also very different (1.5 people in a car on average?), and the safety record of cars much much worse – it’s crying out for improvement via automation. So I think automation of cars will eventually be a public safety issue (like vaccinations) and controls will disappear.
  5. Insurance companies may refuse a claim if the car is driverless. My response is that insurance companies will look at the actuarial data as that’s how they make money. So far all of the accidents involving Google driverless cars have been caused by meat bags, not silicon.

I have put my money where my mouth is and invested in a modest amount of Google shares based on my belief in this technology. This is also an ethical buy for me. I’d rather have some involvement in an exciting future that saves lives and makes the a world a better place than invest in banks and mining companies which don’t.

8 Mega Watts in your bare hands

I recently went on a nice road trip to Gippstech, an interstate Ham radio conference, with Andrew, VK5XFG. On the way, we were chatting about Electric Cars, and how much of infernal combustion technology is really just a nasty hack. Andrew made the point that if petrol cars had been developed now, we would have all sorts of Hazmat rules around using them.

Take refueling. Gasoline contains 42MJ of energy in every litre. On one of our stops we took 3 minutes to refuel 36 litres. That’s 42*36/180 or 8.4MJ/s. Now one watt is 1J/s, so that’s a “power” (the rate energy is moving) of 8.4MW. Would anyone be allowed to hold an electrical cable carrying 8.4MW? That’s like 8000V at 1000A. Based on an average household electricity consumption of 2kW, that’s like hanging onto the HT line supplying 4200 homes.

But it’s OK, as long as your don’t smoke or hold a mobile phone!

The irony is that while I was sitting on 60 litres of high explosive, spraying fumes along the Princes Highway and bitching about petrol cars I was enjoying the use of one. Oh well, bring on the Tesla charge stations and low cost EVs. Infrastructure, the forces of mass production and renewable power will defeat the evils of fossil fuels.

Reading Further

Energy Equivalents of a Krispy Kreme Factory.

Fuel Consumption of a Pedestrian Crossing

WTF Internal Combustion?

At the moment I’m teaching my son to drive in my Electric Car. Like my daughter before him it’s his first driving experience. Recently, he has started to drive his grandfathers pollution generator, which has a manual transmission. So I was trying to explain why the clutch is needed, and it occurred to me just how stupid internal combustion engines are.

Dad: So if you dump the clutch too early the engine stops.
Son: Why?
Dad: Well, a petrol engine needs a certain amount of energy to keep it running, for like compression for the next cycle. If you put too big a load on the engine, it doesn’t have enough power to move the car and keep the engine running.
Dad: Oh yeah and that involves a complex clutch that can be burnt out if you don’t use it right. Or an automatic transmission that requires a complex cooling system and means you use even more (irreplaceable) fossil fuel as it’s less efficient.
Dad: Oh, and petrol motors only work well in a very narrow range of RPM so we need complex gearboxes.
Dad thinks to himself: WTF internal combustion?

Electric motors aren’t like that. Mine works better at 0 RPM (more torque), not worse. When the car stops my electric motor stops. It’s got one moving part and one gear ratio. Why on earth would you keep using irreplaceable fossil fuels when stopped at the traffic lights? It just doesn’t make sense.

The reason of course is energy density. We need to store a couple of hundred km worth of energy in a reasonable amount of weight. Petrol has about 44 MJ/kg. Let see, one of my Lithium cells weighs 3.3kg, and is rated at 100AH at 3.2V. So thats (100AH)(3600 seconds/H)(3.2V)/(3kg)=0.386MJ/kg or about 100 times worse than petrol. However that’s not the whole story, an EV is about 85% efficient in converting that energy into movement while a dinosaur juice combuster is only about 15% efficient.

Anyhoo it’s now possible to make EVs with 500 km range (hello Tesla) so energy density has been nailed. The rest is a business problem, like establishing a market for smart phones. We’re quite good at solving business problems, as someone tends to get rich.

I mean, if we can make billions of internal combustion engines with 1000’s of moving parts, cooling systems, gearboxes, anti-pollution, fuel injection, engine management, controlled detonation of an explosive (they also make napalm out of petrol) and countless other ancillary systems I am sure human kind can make a usable battery!

Internal combustion is just a bad hack.

History is going to judge us as very stupid. We are chewing through every last drop of fossil fuel to keep driving to and from homes in the suburbs that we can’t afford, to buy stuff we don’t need, making plastic for gadgets we throw away, and flying 1000’s of km to exotic locations for holidays, and overheating the planet using our grandchildren’s legacy of hydrocarbons that took 75 million years to form.

Oh that’s right. It’s for the economy.

New Charger for my EV

On Sunday morning I returned home and plugged in my trusty EV to feed it some electrons. Hmm, something is wrong. No lights on one of the chargers. Oh, and the charger circuit breaker in the car has popped. Always out for adventure, and being totally incompetent at anything above 5V and 1 Amp, I connected it directly to the mains. The shed lights started to waver ominously. Humming sounds like a Mary Shelley novel. And still no lights on the charger.

Oh Oh. Since disposing of my nasty carbon burner a few years ago I only have one car and it’s the EV. So I needed a way to get on the road quickly.

But luck was with me. I scoured my local EV association web site, and found a 2nd hand Zivan NG3 charger, that was configured for a 120V lead acid pack. I have a 36 cell Lithium pack that is around 120V when charged. Different batteries have different charging profiles, for example the way current tapers. However all I really need is a bulk current source, my external Battery Management System will shut down the charger when the cells are charged.

Using some residual charge I EVed down the road where I met Richard, a nice man, fellow engineer, and member of our local EV association. I arranged to buy his surplus NG3, took it home and fired it up. Away it went, fairly hosing electrons into my EV at 20A. The old charger was just 10A so this is a bonus – my charging time will be halved. I started popping breakers again, as I was sucking 2.4kW out of the AC. So I re-arranged a few AC wires, ripped out the older chargers, rewired the BMS module loop a little and away I went with the new charger.

Here is the lash up for the initial test. The new Zivan NG3 is the black box on the left, the dud charger the yellow box on the right. The NG3 replaces the 96V dud charger and two 12V chargers (all wired in series) that I needed to charge the entire pack. My current clamp meter (so useful!) is reading 17A.

Old chargers removed and looking a bit neater. I still need to secure the NG3 somehow. My BMS controller is the black box behind the NG3. It shuts down the AC power to the chargers when the batteries signal they are full.

Pretty red lights in the early morning. Each Lithium cell has a BMS module across it, that monitors the cell voltage, The red light means “just about full”. When the first cell hits 4.1V, it signals the BMS controller to shut down the charger. Richard pointed out that the BMS modules are shunt regulators, so will discharge each cell back down to about 3.6V, ensuring they are all at about the same state of charge.

This is the only reason I go to petrol stations. For air. There is so little servicing on EVs that I forget to check the air for a year, some tyres were a bit low.

The old charger lasted 7 years and was used almost every day (say 2000 times) so I can’t complain. The NG3 was $875 2nd hand. Since converting to the Lithium pack in 2009 I have replaced the electric motor armature (about $900) as I blew it up from overheating, 2 cells ($150 ea) as we over discharged them, a DC-DC converter ($200 ish) and now this charger. Also tyres and brakes last year, which are the only wearing mechanical parts left. In that time I’ve done 45,000 electric km.

Electric Car Running Costs

While enjoying a coffee with my 18.5 year old daughter the other day I mentioned a friend’s car was for sale. At only $3,000 it seemed like a good deal. However then we started adding up the costs of running a car. She uses my EV all the time, so we decided to compare.

It occurred to me that my daughter is a pioneer – a young person who has done the majority of her driving in an EVs. She is making history.

I have been driving my EV for 5 years and 40,000 km so we have some long term data. Now my car is a recycled 23 year old carbon-burner, not one of the new breed of factory EVs. However I think the year-year maintenance would be about the same.

Annual running costs:

Item Infernal Combustion Electric
Registration $700 $700
3rd party Insurance $130 $130
Servicing $700 $0
Repairs $300 $300
Fuel/Electricity for 15,000 km $1,800 $900
Total (annual) $3,630 $2,030
Total (weekly) $69.80 $39.04

Assuming Petrol is $1.5/litre, ICE car does 8l/100km, electricity is $0.3/kWh, EV does 0.2kWh/km. If you save up the $2k/year you save with your EV for 2 years you can install a PV array. Now it costs $0 for electricity and we are down to $1,130/year or about 25% of the ICE vehicle. You aren’t ever going to make petrol on your roof for free, and with depleting fossil fuel reserves it will be forever getting more expensive. It’s non-renewable so every litre you use means one less for your grandchildren.

The average income for my daughters peer group (most of them studying) is $200/week. They generally have old cars that need constant repairs. Nothing goes wrong with EVs. If it does, it’s trivial to fix. Only wearing parts are brakes and tyres. No servicing. They don’t pollute.

That’s why she loves my EV.

My Vacuum Pump Won’t Stop!

The brake pump in my EV has been acting up. In an EV the brake pump provides vacuum to run the power brakes, as the original source of vacuum (the internal combustion engine) has been removed. I have mine connected to a little vacuum switch (bottom of photo with screwdriver adjustment) that turns the pump on when the vacuum drops beneath a certain level. This usually makes the pump run for a few seconds when you brake. However it was turning on then staying on indefinitely. It took me a while to work out why.

I initially thought there was a leak in the power brake hoses. Or a dud vacuum switch or brake pump. One day the pump was stuck on and I measured the voltage across the pump. It was only 11.2V. Now the nominal voltage should be 13 and a bit volts. Two volts doesn’t sound like much but power is V-squared on R, so assuming the motor has a constant resistance it’s V squared equals 122 versus 169, a 50% difference in power. This might explain the inability of the vacuum pump to switch off – it just couldn’t drive the vacuum down with the reduced supply voltage.

I exposed the DC-DC converter wiring (it’s hidden under the front passenger seat), and tried to measure the output voltage at that point. The ground wire immediately fell out of it’s crimped (last year by me) connection! Oh dear, that explains it. I re-soldered the connection and immediately the vacuum pump voltage lifted to nearly 13V under load, switched off quickly, and I could hear the pump was running much faster.

This took me a few weeks to work out before I eventually fixed it. In the mean time we just put up with the pump running most of the time, and the brakes still felt fine. Like most of my EV problems it’s something due to my inexpert construction of a one-off prototype, and costs very little (just time in this case) to fix.

My daughter and I drive the EV every day. Actually it’s more precise to say she drives it every day and I use my push bike! We have now driven over 40,000 electric km in 5 years. It’s been two years since I sold my last infernal combustion car, although I still borrow/rent or travel in them occasionally.

Update

Well that fix didn’t last long! Despite a good strong 13+ volts the brake pump is still staying stuck on at times. As a temporary measure I have wired the brake light to the relay that controls the brake pump. Press pedal, brake pump comes on. Pedal feel good so I think there is sufficient vacuum. Meanwhile I’ll try to source a new vacuum switch….

Dead DC-DC converter in my EV

About a week ago I returned from LCA 2013 after being away from home for 1 month. My EV was parked at a house close to the airport. It burst into life and off I went. However about 1 km from home the front lights and dash went dim and the EV ground to halt. It looked like the 12V system was dead. With some kind help from my daughter and her friends we pushed the car home and the next morning I went to work.

As I suspected, the 12V battery was flat. I traced the problem to the DC-DC converter, which appeared to be dead. In an EV, the DC-DC converter works like the alternator in an internal combustion car. It converts the traction battery voltage (in my case about 120V) to 13.8V to power the 12V systems of the car and charge the 12V battery. In an EV only a small 12V battery is required. Just enough to power the 12V systems when the car is off and close the solid-state relay that switches power to the DC-DC converter when the car is “on”. Once the DC-DC converter is on it takes over, providing power to the 12V systems and charging the 12V battery.

The DC-DC converter must have died a few days before I left. The 12V battery by itself could supply the few amps required for a few days. Leaving the car for a month meant the 12V (lead acid) battery was further discharged. So there was just enough left in the 12V battery to run the car at night without the DC-DC converter for 10 minutes before it was completely discharged. No 12V power meant no power to close the contactor solenoid and the EV stopped – despite a nearly full traction battery.

I ordered a new DC-DC converter from EV-Works for $179 including shipping. To limp around until my new DC-DC converter arrived I manually charged the 12V battery each day. During day time driving the 12V system only draws a few amps to run the contactor, indicators, and brake lights. So I restricted my driving to day time to avoid the 14A load of the headlights.

A few days later the new DC-DC converter was installed in about 1 hour by crimping the connections to the existing wiring. The mounting holes fit the old DC-DC converter mounting holes under the passenger front seat. The new unit outputs 14.1V under light load, which delivered 13.8V to the 12V battery terminals. The 0.3V voltage drop is due to schottky diodes mounted on the battery terminals to prevent the battery discharging into the DC-DC converter when the car is off.

The DC-DC converter model I purchased was rated at 144V, with a minimum voltage of 115V. This was a concern, as my pack regularly drops beneath 115V under load. So I went for a driving test. With the headlights on high beam, and the car accelerating (bringing the traction pack voltage down to 110V) the DC-DC output voltage dropped to a minimum of 13.5V which is quite acceptable. Here is my clamp on ammeter next to teh new DC-DC converter measuring the “idle” current of the EV, I think it’s topping up the lead acid battery:

This new DC-DC converter doesn’t have a fan, the old one looked more like a PC power supply and had a fan that would stop and start as I drove. In fact it was noisiest thing inside my EV.

My EV is a one off prototype, so I expect occasional problems like this. Still 1 hours work and $179 in the 12 months since the last bug is not bad. My little EV has now done 33,000 electric km since conversion about 4 years ago.

Living Without a Petrol Car

About a year ago I sold my old ICE car, and have been experimenting with living with just the EV here at my home in Adelaide. It’s working out well.

The longest regular trip I make is to a friends country property, about 40km each way at 80-100 km/hr. I usually stay at his house for a few hours, charging while I am there to top up the pack. For an interstate road trip last year I rented an ICE car for 1 week, and some times I borrow my parents car when I need a 5 seater (my EV is limited to 4 seats).

I feel I am experimenting with different forms of car ownership. Rather than owning a long range ICE car and a short range EV, I am using an EV I own for 95% driving then temporarily using cars I don’t own for the rarer longer distance trips.

Intermittent EV

A few months ago I was cruising along and my EV suddenly lost power. It was like someone had pushed in the clutch. I lifted the bonnet but the problem seemed to have gone and off I went again. Then it happened again last week. I suspected the throttle pot, as I know they can wear or get dirty over time. The speed controller can sense if this pot is open circuit and will shut down for safety reasons. So I pulled off the connectors to the throttle pot and sprayed some circuit cleaner on them. This seemed to fix the problem for a days.

Then just today it became really bad. Stop-start, stop-start. I could hear the contactor clunking so I knew the 12V circuit was OK. Other possibilities were a loose connection in the battery pack or a bug in the (rather expensive) speed controller. So I popped the bonnet and started poking around. Then I noticed something. By moving one wire I could hear a small relay clicking on and off rapidly. This relay (I think, it’s been a while since I built the EV) supplies a “go” signal to the speed controller. As I moved the relay it would click on and off, and the motor power would cut off.

Then I wiggled the solder connections to the relay and sure enough one of them was loose. Ah-ha! A few minutes later the problem was solved. A bad solder joint is not bad for 3.5 years electric driving I guess. Shows how easy Electric Cars are to fix as well.