An Electric Car

Lots of things have changed since I last updated this site. The biggest change is my criteria for electric vehicle design. Firstly, I'm not going to carry on commuting long distances, so my personal need for an electric vehicle has dropped. But also it is apparent that if peak oil hasn't already passed, it will soon, and I live in a country where the bulk of transport infrastructure relies on road based freight.

My priority now is to produce a design for an electric tractor unit conversion. I'm going to electrify my Quantum, and produce a from-scratch electric Dutton Amphijeep, but these are for my own use and to learn about EVs.

My Quantum's ICE is now dead, so it's a priority.

Design Requirements

I expect the following features from an electric truck:-
1) Range: 500 miles at 60mph
2) Acceleration: ...would be nice
3) Top Speed: 60mph
4) Carrying Capacity: 40 tons on a 1:10 slope
5) Safety: at least as good as the petrol equivalent
6) Ease of use: as simple as the petrol equivalent
and, for an electric car
7) Charging:from 220-240v 3phase 125A

My Project Design


To make an electric car, you need to choose a car, some batteries, some motors, and some control electronics and auxiliaries

First my project design was intended to use a kit car. This has a GRP body, which should save weight. The reason for using GRP in kit cars is to build ground rockets, but saving weight helps to make it go further and faster. I bought a Quantum Mk2 coupe, which is based on the Mark2 XR2.

I also have a Suzuki Samurai which is planned to be a donor car for a Dutton Amphijeep, but that's going to be petrol for a while yet.

The Car

Obviously, the first thing to do is to measure the drag and rolling resistance of the chosen car. This determines battery and motor sizes, and enables us to predict range. Drag measurements and calculations are described on a separate page.

I was aiming to take as much as possible out of the ICE car, and then replace it with a big pile of batteries and a motor at each driven wheel. For an electric truck, that would be four motors, one on each side of each of the two differentials. But I don't have time to build those motors right now, and one of those 130hp monsters on each wheel of a plastic kitcar would be madness. So I'm going to go to the conventional arrangement and replace the engine with an electric motor.

A surprising amount of information is available concerning weights of car components. Real figures are linked to their sources:-

  Quantum Mk2 Coupe Duttom Amphijeep
Original empty weight 800kg 1000kg
Original max weight 1175kg 1500kg
ICE components 218kg 200kg
Weight without ICE components 582kg 600kg
Available weight to original 218kg 200kg
Available weight to max 593kg 700kg

The Drivetrain

The plan was to use a motor for each drivewheel, so saving the weight of the gearbox and diff. That's not normal EV practice, but there are new motors that weigh as little as 11kg for a 20kW motor. Unfortunately, plans have changed, and so I'm going to use a pair of motors coupled straight into the gearbox: the pair of motors weighs 22kg, the gearbox (and clutch/bellhousing assembly) probably weighs 40kg. That's silly, but it's quicker.

I may end up taking the gearbox apart and linking straight to the diff. That'll mean mucking about with oil seals and similar nonsense, but it might save some weight.

There is a motors page that describes the motors I've found. I want the Lynch motor, initially, and a homebrew motor one day.

The Batteries

Batteries are selected on the basis of three things: weight, cost per kWh, and safety. Cost is the most complex of these variables, since the others are all well quantified.

Batteries in an EV are a consumable item. It is probably best to think of the battery pack as part of the fuel, rather than part of the vehicle. The key question is how many kWh they'll deliver in their useful life; a figure I've tabulated as price per kWh per cycle. This figure, divided by the number of miles per kWh, gives an expected cost-per-mile of the batteries. The cost of the electricity to charge them must be added to this.

In the UK, that figure wants to be something less than £0.10 for the Fiesta kit, or less than about £0.12 for the Sierra.

Batteries are discussed on a separate batteries page.

I've chosen the Exide Marathon batteries, because someone was ebaying them at £12 each. At that price I couldn't say no, and I didn't.

One day I will work on battery chemistry. But today I'm using lead acid AGM, like everyone else.

Control and Metering

Initially it's going to have a pair of motors, each connected to a 60v battery via a current controller; a double headed charger running off a 32A 55v-0-55v isolation transformer, using triacs and capable of charging the battery when running; a pair of 60v 500w heaters for the windscreen; a vacuum pump for the brake servo; and a 60v -> 12v DC-DC convertor for the auxiliaries.

There might be more one day, but that's the minimum I can get away with.

The intention is to move the electronics into the appropriate place to make modules. So the battery would include chargers, battery condition monitors and contactors; the motor would include the motor controller; and the instrumentation would include a charger for the auxiliaries, as well as control for the other modules.

One day the "rev-counter" should show power; the "fuel gauge" should show fuel, and the ignition warning light should show "low fuel"; and the temperature gauge should show battery temperature. One day ... but for now, it's not going to happen.


If servo brakes are fitted to the original car, a vacuum pump will need to be fitted to run the servo brakes. This must operate all the time the ignition is on.

If power assisted steering is fitted to the original car, a hydraulic pump must be fitted to provide hydraulic pressure for the steering. This must operate all the time the ignition is on.

A DC-DC convertor will be needed to recharge a motorcycle battery to operate the 12v system. The battery will need to run the sidelights overnight: that's 6x6w bulbs, or 3A, for 12 hours. So a 36Ah battery will do fine. Driving at night with the headlights on (add 10A), the wipers going (add 5A) and the rear window defrost going (add 15A) suggests that we need the DC-DC convertor to deliver at least 33A. A 40A system would be good. The system must be isolated.

The cabin heat exchanger must be replaced with some sort of electric heater. Running a series of say 10 chains of 5 resistors each of 8.2Ω and 20W would give just under 900W, which should be enough to heat the windows fine. Ten switches on the heat control could connect 0 to 5 strings to each of the two batteries.

The charger would either run off an isolating transformer suitable for running outdoor tools, providing 32A and 55v-0-55v. These transformers can be bought at tool shops. Also at tool shops they sell generators that provide 32A 55v-0-55v, and one of these could be used to extend range and give recharging for long journeys.

This page is part of an Open Source Electric Car Project, and is written and maintained by Simon. At this stage these pages are constantly under revision. Thoughts and comments are