Electric Vehicle - How to build an electric car 04

Anybody who has been looking at building their own electric vehicle has come across the advertised electric vehicle conversion kits. What are they and why would you bother with one?  

From 0-100 in 4 seconds, or from oil to electricity in one conversion?


When doing a conversion from scratch there are a lot of issues you need to be aware off and take into account with your design, also check out my other posts under thistag, they provide details on the sizings of the motor and the battery. The electric vehicle conversion kits are generally designed with a specific type or model of a car in mind and are tailored made for it.


A conversion kit, it has all the parts you need for a conversion - Link


The advantage is that in the case you happen to have such a car (or can get one in an easy and convenient matter), the kit provides you a one-stop solution to converting the car. The size of the electric motor and the battery have been thought out. There is a small and easy to understand manual with it that describes what to do, including on how to take out the internal combustion engine and the associated parts you no longer need. The parts that are supplied with the package also help installing the electric vehicle parts. It can contain mounting brackets for the electric motor or the battery pack for example. Great stuff to get you started and you no longer have to worry about what to look for and purchase.




Electric vehicle conversion kits are generally designed for one specific type of vehicle (with a few exceptions ofcourse). If you have a vehicle that is ‘like’ a type or model of the vehicle a conversion kit it designed for, you might still want to purchase the conversion kit, or at least consider it. Contact the supplier upfront to be sure that the kit can be fitted to your specific vehicle, but often the engine supplied with the package can do perfectly ok for similar cars of the same weight, etc. You might run into some trouble with mounting the various parts into your soon-to-be electric vehicle, but if you know your tools and like to create the mounting pieces yourself (or know somebody who does), this might still be a viable and cheap solution for you.




Convert your car and become part of this wonderful comunity - Link


Again, as with every step in the conversion process of getting rid of the oil addiction, planning is key. If you know the car model you have or want to drive, you can shop around for a compatible conversion kit. Just hold off the purchase until you are absolutely sure you have a match between the two, both the car and the kit are the most expensive parts in your project so you really don’t want to buy the wrong stuff. Go look around and compare what is out there, in case you have questions, leave a message or comment here.




Electric Vehicle - How to build an electric car 03

Selecting the electric motor and battery when building your own electric car can be quite a challenge. There are a few approaches here that can be followed in this post I’ll just touch on the easiest of all, a good look at the alternatives and some educated guessing. This approach is to see what the others are doing and check what power the engines are that are used in similar vehicles. If you plan to convert a sedan like vehicle that is roughly the same size/weight as a Nissan Leaf, check the power that those engines are specified for. (the Nissan Leaf has a motor which is rated at 80kW btw, also check Wikipedia).


The Nissan Leaf, you can learn a lot from the current EVs already out there.


The idea behind it is simple, they did the math, and it works good (they are selling the product). If you want something that can go quicker or accelerate quicker, you’ll want to look for a little bigger engine, but you get a feel of the industry at least and know what you should be aiming for.

Always make sure that the vehicle you are working on and the vehicle you are looking at for the engine specification are reasonably the same. In other words, don’t look at the Tesla Roadster if you want to convert a heavy SUV, the weights are far off, but also the aerodynamics of the two are not comparable.


For the battery a similar approach is viable, check what comparable vehicles have for the battery capacity (the kWh figure!) and ensure that the battery/motor are compatible. An electric motor that runs on 48V will be no good using a single 12V battery. You can check again what the size of for example the Nissan Leaf is (24kWh) and use it as a guideline. The Nissan Leaf can travel around 100 miles / 160 km. If you have a comparable vehicle as the Leaf and put in a 12 kWh battery pack, you will likely get around half the range of the Leaf. This is not entirely a linear scale, but ok for some educated guessing as long as you don’t use a factor 10 bigger or smaller batteries.


Another nice guideline that might help is that the average passenger cars use between 20-30 kWh per 100 miles / 160 km. If you have a relatively light vehicle, you’re bound to be on the low end, if you have a heavier, you’re on the high end of this range (or even higher if it is a really heavy vehicle).


You can save a lot of fuel by converting this one to electric, just don't put in a Leaf-like drive train.


Assume you have a light vehicle, and want to be able to drive 300 miles with it. Assuming a 20 kWh consumption per 100 miles / 160 km, you would need a battery that supplies 60 kWh. Batteries are preferably not fully discharged, and are operated generally in a safe range, so it is more likely you will need 70-80 kWh pack to ensure you have 60 kWh available to drive. The problem that arises is that with battery packs of this size, the weight plays a big factor. If you have to add a battery pack that weighs half that of the original light weight vehicle, your consumption will go up more. This makes for an iterative process where you have to balance the motor and the battery pack versus what you want and what vehicle you have.


Not an easy process and one that can be quite time consuming as well. Luckily there are various companies around, mostly US or Australia based, that offer so called electric car conversion kits. As the name implies, it allows you to convert your petrol vehicle to an electric one. There are even some that are tailored to specific models. The biggest advantage of this: you get a fully matching system that is suitable for your vehicle. Why do the guesswork if they found out and likely the hard way. They know what works and what not.

Electric Vehicle - How to build an electric car - 02

This guide is part two on how to build an electric car, continuing on the previous post. The drive train of a pure electric vehicle is the easiest configuration, the main components are the electric motor and the battery. True enough there are some other (vital) components that are required, such as a convertor between the electric motor and the battery.  

The rather simple configuration of an electric vehicle drive train.


The electric motor is there to move the vehicle forward, the battery is there to store the power. The convertor in the middle is used to control the amount of power that moves from the battery to the motor and ensure the voltages on each side remain within a specified range. For a more easier understanding of what the converter does, compare it with a valve in a water line; where the valve is turned more open when the a consumer wants to increase the flow of water. Similar, when a driver wants to increase speed, he/she pushes down the accelerator pedal which controls the converter. The converter then knows how much power to allow from the battery to the motor.

The electric motor is also used during the process that is called regenerative braking. This process allows to recoup the energy from braking or decelerating the car. Basically what happens is that the vehicle slows down on the friction of the motor, which acts as a generator. Power then flows from the motor through the converter and into the battery to be used at a later time. During this process the converter’s job is to ensure that the voltages on both end remain within the specifications and try to balance out between what amount of power is available and allowed at that time into the battery. The goal in this case for the converter is to recoup as much energy as possible, but protect the battery and ensure it stays in good condition. In case the power that is generated becomes too much for the converter or the battery to handle, mechanical brakes can be used to take out the excess energy.

With regards to what the specified conditions the converter has to keep the voltages; that really depends on the battery and the motor that are chosen in the configuration. Better is to first check what motor and battery are required/desired for the application and then check the specifications of the available models before looking at the converter.

To determine which type of electric motor to pick the two most important factors to consider are the total mass of the vehicle and the driving characteristic that is required or desired. The heavier a vehicle, the bigger the motor will have to be. Also include the added mass for the batteries and the optional large cargo loads that you want to take along with it. The method to determine the size of your motor/battery will be discussed in a next post.