Why no, why Yes and hot to convert a car to electric propulsion…

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Joined: 06/04/2010
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Why no, why Yes and hot to convert a car to electric propulsion…

When will large car manufacturers really deliver electric cars?
When will price and performance of these cars match your expectations?
It might take longer than we are expected to wait…

Do you want to be independent and build an electric car that will meet your needs?
Maybe it makes sense to thinking of converting an existing fossil fuel car to electric propulsion?

First I will give you ten reasons why you should definitely not consider such an option (after that…)
1. Safety: do you really want do drive on road with something you have developed in your garage?
2. Homologation, certification: do you think your local authorities will approve your vehicle and give you all the required certification…
3. Details: Are you sure you will be able to make your car to look nice with all the required details that are so carefully designed…
4. Price: Do you really think that it is possible to convert a car for a reasonable price? We are talking about one or just a few units here, not million units mass production…
5. Durability: How can a home-made product achieve appropriate durability?
6. Time: do you really have all this time that has to be invested into converting a car to electric propulsion…
7. Well, maybe existing cars are not appropriate for conversions and it is better to build a completely new electric car… (but we could list 20 reasons why this really might not be a god idea…)
8. …
Well it is less than ten reasons why not to convert a car… maybe there is still hope… can someone please suggest some additional reasons not to be active...
…For those of you, who are still thinking about driving with electric car made in your garage I would just like to help and suggest few basic issues you might find interesting to consider during your conversion project….
1. Expected performance: Calculate what kind of electric motor you need to drive your car. It is not enough to know how powerful it is. You have to know at least approximate values of existing car motor torque, RPM range and gear ratio (both gearbox and differential ratios). What you need to know with how much torque or with what force your wheels will be able to pull the road and at what speed you will be able to drive. It is just primary school physics, but this is an important calculation. In case you are not replacing the central engine with direct drive motor that is without any gears, you also have to know detailed working points of this motor.
2. Expected range, selection of batteries and the resulting price: Be realistic about the required driving range. Most probably you will build a city car, not a car to drive 500km. Price of electric conversion will strongly depend on expected range. When you set a target range, add 10 to 20% more, just to make sure this will also be the range after few years when your batteries will lose some capacity. Do not select lead-acid batteries, since they are heavy, bad in cold weather and do not give the nominal capacity if used in fast discharge regime (as an electric car application inevitably is…). Make all calculations in few iterations and then purchase the batteries…
3. Compatibility: When selecting propulsion components such as motors and controllers, be sure to buy compatible items. This might be a challenging task… it is not just the same voltage, be sure also to have compatible position sensor and control interface.
4. Other components: make sure that you have a list of all items that are important for your electric car and don’t forget the battery charger, battery management system (BMS) (try to get them together with the battery), cabin heater (if you do not have the luxury of living in a warm climate…), gas pedal or compatible potentiometer, DC/DC converter (you will most probably want to keep the 12V battery and get rid of alternator…), high current fuse or relay… You will most likely also consider how electric conversion effect power steering and of course braking performance (which is a very important issue).

Of course I understand that many members are already experts in converting electric vehicles, but maybe let's go right from the beginning to hel everyone understand the challenge and the opportunity...
I would really appreciate some feedback and then we can go deeper in details…

Gorazd Lampic
6. January 2011


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