esoteriic.com

They've been around for more than a hundred years but they haven't seen much development. In recent years we've seen the development and release of the Tesla electric vehicles but they carry a high price tag and so they are not an accessible option for most people. The new Model S starts at $49k which is almost a mass market car but not quite, their future plans to release something in $30k range might be the affordable option for a mass market appeal. Given the topic title I think it is obvious where this is going, there are cheaper alternatives to Tesla. Some of the alternatives include the professionally built vehicles from the manufacturing giants (see wiki for full list of EV vehicles), and then there is the very low-cost DIY option. Building one an electric can be done for less than $10k as I will show in this article. I've been gathering research material for writing the article and some priming for a future project (I hope).

Some inspiration

First let me provide some inspiration for you to consider why building an electric car could be a fun process and a fun car to drive. I stumbled upon a youtube video which provide the greatest inspiration to try such a project, in this video someone converted an old 1970s Datsun into an electric car. He said it cost around $10k and has some impressive stats: White Zombie EV.

There is also this article in Wired magazine: We’re Building an Electric Car!: "I’m a regular guy. I have no experience as a mechanic, I don’t have a lot of time and I don’t have a lot of money. So, why am I doing this? It’s on my list." "It’s an electric vehicle they claim will offer 70 percent of the performance of the Tesla Roadster at 25 percent the cost."

And perhaps it is worth looking at the Voltswagon by security consultant David Brown, he talked about the car at the Defcon hacker meeting this year. "Brown did it for about $6,000, not counting the cost of his car, tools, and about 100 hours of labor."

Running Costs

Why run an electric car instead of a petrol car? For some people it will be all about the emissions are zero for the vehicle and then whatever the usual emissions are in the rest of the manufacturing supply chain and electricity generation. Some may find the lack of noise to bonus but the biggest selling point should be the costs of actually running the vehicles. One of the biggest attractions should be performance, or performance-per-$.

Not including servicing costs, the running costs are currently about $0.02 - $0.04 per mile. The initial buying cost for electric cars is higher if you buy from one of the big car companies. This is obvious as the infrastructure isn't going to be optimal when most of the focus has been upon creating better petrol-driven cars. The initial cost for the Roadster is 109k while the Lead is $35k. Tesla claim their cars run at $0.02 per mile, while the Nissan Leaf costs around $0.035 per mile. From wiki:

"[As] of December 2011 the Nissan Leaf has an out-of-pocket operating cost of 3.5 cents per mile (2.19¢ per km). These costs are based on the U.S. national average electricity rate of 11 cents per kWh."

"According to Nissan, the operating cost of the Leaf in the U.K is 1.75 pence per mile (1.09p per km) when charging at an off-peak electricity rate, while a conventional gasoline-powered car costs more than 10 pence per mile (6.25p per km). "

Build costs

As you would expect the building costs vary depending on the chassis you use as well as the performance that you desire. The first stage is chose a chassis, the simplest method is to pick up an old second hand car and convert it from petrol to electric. This may limit customizability but it should be cheaper as well as simpler, this is why the old style Volkswagen Beetle is a popular choice because it's cheap and simple. It doesn't have a lot of weight and there isn't a whole lot that you have to strip out. In both articles that I listed above the VW Beetle was chosen as the donor car.

Once you have a list of potential chassis you will need to create a list of parts. The biggest limitation to chassis selection (I think) is to make sure the electric motor will physically fit into the chassis. Motors can be fairly large at 40-60 cm long, I can see it being a potential problem but it seems to work for a VW Beetle which is about as small as they get. It is the single heaviest part although the overall weight contribution from a bank of batteries is likely to be greater.

While some of the projects are under $5k this is pretty hard to do. It is possible that you can find some old second hand parts that are appropriate but if it isn't then you should budget for up to $10k for all parts excluding the donor car.

Some of the necessary key parts: Motor, Motor Adapter,  Controller,   Liquid cooling kit,  Throttle,  Speed sensor,  Main contactor,  Reversing contactor,  Fuse,  Battery charger, Battery management.

David Brown in the above wired article said he paid:

$1,200 for a motor, $1,000 for a controller, $800 for batteries, $600 for a charger, $500 for an adapter/charger, and $800 for miscellaneous.

If you follow the linked words above you can get prices from the EV Sources site, for example:

$1,700 - 4000 for a motor and $1,700 - 4,000 for a controller. These are perhaps the two most expensive single items, the amount you spend on batteries really depends on how many you need (performance vs price). They sell lithium batteries which are better (lighter/more powerful) than lead-acid but also more expensive, single batteries on that site cost $55 - 248. Don't be surprised if you need 20 - 40 batteries either!

If you can build a custom chassis then the sky is the limit. If you take a look at the Eliica car posted in the youtube link above then you will notice that it has 8 wheels. The reason is (afaik) that electric motors have a high amount of torque which enables rapid acceleration but they are not so good if you want a high speed. Note that many of the electric cars featured on this page have great acceleration but low top speed. The introduction of more motors, and also more wheels, allows for the each individual motor to contribute less to the speed. Therefore by adding more motors you can achieve a higher speed. Note that both the Tesla and the White Zombie (above) have two motors rather than just one (as seen in most EV projects), they are trying to get a higher top speed.

The White Zombie team also have an interesting piece of custom electronics that allows the batteries to switch from a series arrangement to a parallel arrangement. The idea here is that series provides a high current (low voltage) which enables a high acceleration but as you get faster then you want to have a lower current but higher voltage and hence a parallel arrangement. The amount of power is the same in both cases (power = current x voltage).

Example project

If you've followed the article this far then you should have a fair idea of the number of parts needed and the rough cost of the project. If you read the articles and watch the videos above then you can get a better how the parts will fit together. There are videos on youtube of how to assemble them, so all the knowledge you need to know is already online and freely available. So I shall direct towards yet another internet source for an example project, which was posted recently (29/10/2012): Kit Car 0-100km/h 2-3 sec. They are trying to build a car that accelerates to 60 mph in 3 seconds. To keep cost down then it needs to be light, if he uses a light (roofless) kit-car as a donor body then he might be able to keep the weight around 500kg. The original poster was estimating 230kW of battery power, which translates into a lot of batteries and a fairly ''high'' cost ($2k+ high relative to total cost of project).

He calculated the following costs: Kit car: $10k, Warp 11 (motor): $3k, Soliton 1 (controller): $3k, A123 90s2p (batteries): $2.7k. This is most of the major parts but it racks up a cost of around $19k and there are still quite a parts needed at this stage.

A couple posts later and you can see another user post another set of calculations that should allow the amount of power to be lower (lower number of batteries too):

100Kph = 28 meters per second. So 2 - 3 seconds means 1G acceleration (10m/sec/sec). Assume 500Kg car. Power = Force x Distance/time. At take off power = zero. As you accelerate you need more power, at 100 Kph need 500Kg x 10 x 28m/sec = 140Kw. So you need 140Kw - you won't be able to use all of it until 100Kph.

Sanity check
Kinetic energy = 1/2mass x velocity squared
1/2 x 500kg x 28 x 28 = 196Kjoules
Power from zero - 140Kw = average 70Kw
70Kw x 2.8 seconds = 196Kjoules
So you need 140Kw

These are the sort of necessary calculations that are needed for determining how many batteries are necessary to power your vehicle. You can copy this example and change the numbers to get an idea the amount of power (batteries) that is (are) needed. Weight is a huge factor and starting from a light shell will mean that you need less batteries. Ideally you will need to account for the driver's weight and you should properly account for the weight of the chassis plus all the components.

Edit: As a follow up exercise I did some power calculations in my new post, see here: power calculations. Also, I have a public Google document with my calculations. I think power is roughly correct but the number of batteries is probably wrong, I could do with someone fixing that. See here: Google Doc Power Calcs.

The final piece of inspiration I can offer is look at the projects on that forum or at EV Album, they have many projects which have been successfully completed.