I feel a little out of depth in this project. I am the kind of guy who can design and build a computer but the last time I worked on cars was 20 years ago, and usually resulted in towing the mess to a mechanic who would shake his head, sigh, and then fix it for me.
Electrically, I am OK with digital logic and low level analog but death to anything over 5V and 1A. Electric cars run on something like 144V and over 300A.
So here I am doing an Electric Vehicle (EV) conversion!
The idea is to take a regular car, pull out the petrol engine and fuel system, exhaust etc, and replace it with a electric motor and lots of batteries. I will focus on my conversion, and talk about a few things that I have discovered as an EV learner that might be useful to others. As well as a rant or two and the usual digressions. But I digress (already)……
Details of my EV Conversion
I am converting a 1991 Daihatsu Charade. A similar car was the first (and probably last) new car that my wife and I ever bought, and we were rather attached to it until we sold it a few years back. They are popular targets for EV conversion in Australia, so it was an easy choice for us. The Charade weighs 780 kg in ICE (Internal Combustion Engine) configuration, I figure it will be around 1000 kg as an EV. I am estimating a range of 50 km.
Most of our driving is home-shop-daycare-home so we will be able to charge at home during the day between trips. Our trips are rarely longer than 10km, mostly 1.5 persons (adult plus toddler), and where I live in Adelaide is very flat. Overall an ideal scenario for an EV.
Anyway, back to the conversion. Many years ago, George and Michael from Electric Vehicle Motors converted a Charade just like mine:
So I am roughly following their template (similar batteries and motor). George and Michael have been very helpful with advice and bringing me up to speed on EV conversions. Thanks guys!
- Car: I looked for a good clean car with a nice straight body but was unconcerned about the ICE condition. I want this to be a car that I will be happy to drive for the next 10 years. Bought a 1991 Daihatsu Charade as it was small, light, and my wife and I owned one a few years ago and really liked it. ($2,000)
- Electric Motor: Advanced DC X91-4001 6.7 inch motor. ($1,900)
- Controller: Curtis 1231C-860196-144v 500A. ($2,100)
- Batteries: Much dithering here. Looked into various combinations including the new Lithiums but eventually settled on 12 Optima Group 31 Yellow Tops ($5,300). I figured Lithiums were going to cost me > $12,000 with a special BMS (Battery Management System), charger, and on balance I felt there is still some risk. Will consider Lithiums in a few years time when the technology has matured. George has had nearly 10 years from his yellow tops with a simple BMS which is kinda remarkable for lead acid batteries. There batteries are only USD$220 in the US, but I paid AUD$440 which sucks but what can I do? You can’t easily air freight 300kg worth of batteries. Sigh. A nice feature of the Yellow Tops is that they are sealed, so I think I can mount them inside the car without the special ventilation systems required by wet cells. I think I can also mount them sideways, which will help squeezing them into the car.
- Adapter Plate: Nathan from Convert Ur Car is handling the machining involved in getting my gearbox to interface with the electric motor. Nathan has also been very helpful with advice and tips for my conversion – thanks Nathan. ($1,500)
- Charger: I am taking the adventurous step of designing my own charger. This is a little scary due to the power involved – common EV chargers are rated at 2kW. That’s around 15A at 144V. My idea is to develop a low cost open hardware charger design that anyone is free to copy. To avoid battery damage, charging systems must take care not to over (or under) charge any batteries in the pack. The design I am working on will be powered off a relatively low voltage supply (like 2-3 rewound microwave oven or arc welding transformers delivering 48VDC at around 50A) to reduce the risks posed by high voltages. I will then build 12 little chargers that will charge each battery separately. These will use floating-output microcontroller-based DC-DC converters to efficiently charge each battery at around 14V at 10-15A. More on this in a later blog post.
There are also a bunch of smaller components like a contactor, cable, vacuum pump, uprated springs etc. Still working on them.
- Range: I have 12 x 12V Yellow Tops which are rated at 75AH each. However from the data sheet the 1 hour rating is 60AH. This gives me 144 x 60 = 8.64 kWh of energy. George’s Charade gets 8 km/kWh, so I can expect a range of 8.64 x 8 = 69 km. However it’s not a good idea to completely discharge the batteries, so at say 80% depth-of-discharge (DOD) I can expect 0.8 x 69 = 55km range.
- Weight: The empty weight of the Charade in ICE configuration is 780kg. I estimate that the ICE motor and related components (exhaust, fuel system etc) weigh about 160kg. My batteries weigh 27kg each, and the electric motor 40 kg. Plus add 30kg for cables, controller, battery mounting hardware etc. So the estimated weight is 780 – 160 (12 x 27) 40 30 = 1014 kg. The GVM of the Charade is 1240kg, so I may lose 2-3 people from the cars rating when I get it “blessed” by the Department of Transport (in Australia we need to allow 82 kg per person). Most of our driving is one adult plus one toddler so we can live with that.
- Clutch: After much debate and discussion with my brains trust I decided to keep the clutch. I figure no harm in having it in, although it means the adapter plate machining costs a little more. EVs don’t really need a clutch (n.b. the motor is off at traffic lights), but I thought it would be useful as an extra safety feature and would make the car less strange to drive for my wife.
- Running Costs: We currently do around 300 km a week in our 6 cylinder family car, which costs us perhaps $65 per week in petrol, plus maybe $1,500 each year for servicing and repairs. The EV uses around 1 kWh per 8 km travelled, so that’s 300/8 = 37.5 kWh of electricity per week. If we assume the charger is 70% efficient, that is 53.6 kWh from the outlet. My electricity costs $0.15/kWh which means just $8 a week in “fuel”! To be fair, the battery replacement costs must be factored into the running costs, however battery life is an unknown for me at present. Servicing costs for EVs are virtually nil – just brakes and tyres every few years. Think about it – all your cars servicing revolves around the ICE: oil, spark plugs, most repairs. All gone with an EV!
Progress to Date
I started working on my EV project in September 2007, and have averaged a few hours a week in between other projects and some travel. Actually a lot of my time has been spent reading up on EVs, talking to knowledgeable EV people, and planning my conversion.
Progress so far:
- I have pulled out most of the ICE parts. This was an interesting puzzle, especially working out how to get the engine out. Like a puzzle with a zillion wires and connectors. I needed to tilt the engine to hoist it out from the top, to prevent it fouling with the side of the car.
- The adaptor plate/gearbox machining has been completed and is being shipped back to me. Next step is to install the gearbox and electric motor so I can work out where and how I will mount the batteries in the front.
- After some thought I now have a good idea how to mount the batteries in the rear, time to start making the brackets.
- All of the major parts have been ordered and delivered.
- I have a plan for the charger, and have started simulating the design using SPICE.
- I have contacted the Department of Transport to make sure I am on the right track to get my EV “blessed” by them and therefore street legal (and insurable) in South Australia.
Most of the EV parts have now arrived, here is a picture of a few:
Notice the difference in size between the old ICE and it’s replacement – the electric motor! The electric motor doesn’t put out quite as much peak HP, however all it’s torque is developed at stall, so I am expecting similar performance off the line.
All of those batteries weigh about 320kg and store about the same amount of energy as 5 litres (1 gallon) of petrol. Makes you wonder. We pump oil out of the ground and burn this precious precious resource just as fast as we can, without a thought as to how wonderful and irreplaceable it is. Pure, concentrated energy. What the hell are our grand kids going to say to us when it’s all gone?
Hmm oily foot prints leading from the garage. Who’s been stepping on my gearbox oil?
Ah HA – my assistant mechanic Mikey (age 2)!
Many people have been kindly helping me come up to speed on EVs. They have been very generous with their time and I really appreciate it. Thanks to Bruno (my local mechanic), Nathan from Convert Ur Car, Michael & George from Electric Vehicle Motors, Rod from Strath Steam, and Shaun who’s Electric Echo site has been a great resource for me.
In South Australia you need to read and comply with Information Bulletin 74. I obtained my copy by emailing the Department of Transport. I can’t find it on-line however I did find a very similar document called NCOP 14 from other Australian sites. So it looks like all the Australian states have similar requirements, which is a good thing.
Shaun’s Electric Echo conversion, one of the best journals of an EV conversion. Every time I get stuck on some detail – I check Shauns’s journal!
Strath Steam EV conversion, located about 80km from me in lovely Victor Harbour. Also a good resource, a couple of small car conversions discussed. A step down in size from my Charade (600kg ICE vehicles), using 72V systems, which makes them a little easier and cheaper to build. I am now thinking I should have perhaps gone this way for my first EV.
Electric Vehicle Motors have been very helpful with advice, and supply of a motor for my Charade.