How to Convert Your Car to Electric

When the idea of converting my own car to electric came up, I had two goals in mind, to be able to drive a new car that would not make noise and that would cost little or nothing in fuel. The other was to once and for all stop contributing to the impoverishment and pollution of the environment in which I lived, and to be able to let others know that it is possible today to have an electric car as it was at the beginning of the 20th century in New York (See the documentary "Who killed the electric car?").

Little by little the idea became more tangible, asking around, researching on the internet and in other countries where this was already a reality, I started the project of building an electric car.

Choosing a car.

The first step, once everything was clearer, was to choose a car that was cheap and suitable for this purpose. The best cars are vintage or classic cars, the reason being that they are less sophisticated and the electronics are not essential for other functions of the car to remain operational. There is no need to panic here, nothing that cannot be overcome by reading a little about the chosen car.

Another important characteristic is that the car should be small and not weigh too much, less than 1000 kg is more than adequate, and 800 kg is ideal. The reason for this is that the heavier it is, the more resistance the car will put up due to friction with the road, and the more electrical energy it will need to drive.

Then there are elements that at high speeds also have a big influence, such as the aerodynamic coefficient, but that is a subject for the second course.

The old Renault Twingo is a light car, which does not rely much on electronics (no power steering, automatic gearbox, etc.). So I decided to buy a cheap second hand Twingo. I spent my first 500 € on this project.

And now, an engine.

The engine is also something you need to spend some time researching to make the right choice. When choosing a small car, the engine does not have to be extremely powerful, so a 7 to 15 kW engine may be perfect.
There are two types of motors, direct current (DC) and alternating current (AC). The former are cheaper, more accessible second hand from a scrap yard and less efficient, the latter are more expensive, less heavy and more efficient. Then there are those that are synchronous or asynchronous, and those with permanent magnets, which are apparently the top of the range. As examples there are Chinese motors of 7500 W that can cost less than 1000 €, and in Europe or America you can get motors of 15 to 25 KW between 2000 to 4000 €. I decided on a 14 kW Slovenian AC motor from Letrika. I got to know this supplier at the EVS27 electric vehicle fair in 2013.

We move on to the controller.

This is also one of the main components, it is one of the most expensive and goes hand in hand with the engine, for two reasons: One because it is the one that converts the electricity from the car's batteries to the voltage needed for the motor, so it has to be able to perform that function, and the other is that it is the one that regulates the speed of the motor, so it has to be designed for that motor. Like motors, there are controllers for direct current and others for alternating current. The good news is that most motor manufacturers already manufacture the controller as well, and those that do not is because more generic controllers can be used. Controllers are also measured by the maximum current they are capable of inducing into the motor, the more current and voltage they can apply, the more powerful and more expensive they are. There are many brands as in everything, Brusa, Curtis, SAGEM,...

I bought a mid-range Curtis that works with AC motors, Curtis 1236. Most of the controllers are programmable, so you can adapt it to your motor. As with everything else, you have to study the variety and features a bit.

And then we come to the drums, the queens of the mambo.

Batteries are the most important element today, as they will decide how much power and how far the electric car can go. Hopefully the day will come when this will be the least important component, but for now the technology is very varied and more complex than we think. The choice of batteries is not only conditioned by the maximum distance we want our car to travel on a single charge, but depending on the batteries we will have to choose a specific charger for those batteries, and in some cases a battery management system (BMS), as not all batteries can be charged or discharged in the same way, and if the manufacturer's guidelines are not followed, we go from 10 years to 3... for example.

There are many technologies today, but in practical terms we can narrow them down to 3 or 4. Let's start with the cheapest ones:

–       Lead-acid batteries. They are the cheapest, the least suitable by design, as they are not designed to provide a gradual current, but are designed to provide a lot of current all at once, which is not how an electric car controller would use it. Advantage, even when they are worn out, you can revive them and make them last for another 3 years. It's a bit of a delicate process, as there is sulphuric acid involved,

I therefore recommend that if you are not sure of what you are doing, don't do it. I did it, very carefully, following many guidelines, using protective measures such as gloves, goggles and mask (as the gases are toxic), of course at the end do not pour the excess acid into the sump, you have to neutralize it before so that it is not harmful to the environment. You can also buy them and avoid this mess. They are very heavy but you don't need a special charger.

- Gel or AGM batteries. They are deep cycle batteries, they are lead-acid but have a slightly more efficient gel-type electrolyte. They are a bit more expensive and their design is made for the use of an electric car. They are also very heavy, but they last longer, there are manufacturers that will give you up to 1000 charges before they start to lose capacity. The charger will have to be a bit special, as it should charge with special parameters for Gel or AGM. They are not very expensive. I bought 6 batteries of 12V and 100Ah for about 900€.

- Lithium batteries. These are a little more expensive, but weigh half as much and have twice the capacity. So they are usually the standard option in electric cars. They usually come in 3.7V cells, so you have to buy a lot of them until you get the desired voltage. Another VERY IMPORTANT issue is that these batteries have to be managed (charged and discharged) by a special battery management system for Lithium batteries. The reason for this is that they must not be discharged beyond a certain limit or charged beyond the voltage recommended by the manufacturer. For example for 18650 lithium cells, the maximum voltage is usually 4.1V and the minimum 2.5V. Although this depends on the battery and the manufacturer.

- Lithium-ferrophosphate (LiFePO4) batteries are the highest capacity commercial batteries, but they are also the most expensive.

Enough with the batteries...

Another important component, a high voltage to 12V current converter.

When we eliminate the petrol engine, one of the things we also eliminate is the alternator, which is responsible for constantly recharging the car's battery (in this case it can be called an auxiliary battery) to provide electricity for the lights, windows, radio, etc. Without an alternator, the battery would gradually wear out until it is completely empty. This is why we need a system to charge the battery, and this is a DC converter, for example from 72V to 12V. In this way the high voltage battery pack will constantly charge the auxiliary battery.

Well, that's it, isn't it? No, something very important is still missing. The brakes.

For the brakes, it is necessary to replace the vacuum that the combustion engine produced in the brake servo. For this purpose, a vacuum pump is fitted, which does exactly what it says: vacuum.

Then you need other electrical components like a potentiometer for the throttle, a contactor, which is a relay but for high voltage, a lot of cable...relays, fuses, etc.

The accessory components are equally or even more important than the main components, because for example, with the motor and controller already in place, without a cable to connect it is equally important. For example, it is necessary to look at the high voltage cable requirements of the motor or controller manufacturer for the cable. Thin signal cables also have certain characteristics, not only in terms of cross-section but also in terms of insulation.

The adventure begins now, when everything is in place and needs to be installed in the car.

If you are interested in converting your car to electric and you need more information, support, documents or just someone to share the hobby with you can contact us by clicking here.