Coupling, make it right the third time.

This is one of the most, if not the most important and tricky mechanical manipulations you have to do when converting a vehicle into electric. Connecting the electric motor to the existing transmission is a big debate, as you can just connect both axis together with some sort a coupler or do it using a clutch.



Usually, both axis have different diameter, splines or are in C-fase (as they say in America), so you will need two different couplers, one for each shaft (motor and gear-box).



Now, those two couplers can be connected directly or with the original clutch (there is a big debate around this subject). In our case, we will follow the clutch design. The main reason is efficiency, as having the ability of changing gears, will give you more efficiency in all cases of the driving, such short, medium and long gears. Although this approach is a bit more complicated in implementing, as the flywheel needs to be adapted to the motor shaft, the driving of the car will be as similar as with the combustion engine.

The first part of this transformation is to have the adapter plate mounted in the motor so the flywheel attached keeps in the same position in relation to the gearbox.





Then, we need to attach the flywheel to the motor with an adapter. You can use a steel coupler from Lovejoy or Rotex, machined exactly for the electric motor shaft. It is also very important to measure all the components including the clutch that will go inside the gearbox, so they all fit perfectly.

Once the flywheel machined and attached to the motor, it is time to screw the clutch to the flywheel. From that point on, the operation it is just a standard clutch installation.




Now, in the 1st attempt to install the clutch, it all went smooth a part from a little periodic noise from inside the gearbox. So, we had to dismantle the clutch again to see what happened. Our surprise was that the flywheel was touching very lightly inside the gearbox. That was the 1st problem easily solved by reducing the flywheel or by carving a bit the specific gearbox area where the flywheel was touching.



Another and second problem was the flywheel, even that was correctly inserted into the splined motor shaft; it wasn’t properly screwed, so that centrifuge force could cause the flywheel to move forwards touching the gearbox shaft. So apart from soldering a coupler in the centre of the flywheel, we asked for a whole too to be able to screw and stop the flywheel.
Now this modification caused to move the block flywheel-clutch forwards 6 mm, so we had to cut the gearbox shaft 7 mm.



Also we discovered that the flywheel wasn’t properly turning flat respect the axis, so we sent it to a machinist to rectify that tiny difference and also to reduce the diameter of the flywheel, with that we solve 2 issues. Removing mass of it, so it would had less inertia and also avoid touching the gearbox inside.



The final result was this 3rd attempt, where the flywheel was turning flat against the clutch disk, was fitted to the motor shaft, the diameter was much smaller, so it wouldn’t touch inside the gearbox and had less mass, so less inertia and better performance. It needed to be balanced (to have the same mass radially so it wouldn’t vibrate at high rpm) , but as the flywheel was already balanced when manufactured, we trust it would still be balanced after the rectification. The gearbox shaft was also cut 7 mm to receive the motor block. And once all modified it all fitted as a glove.





The final result fitted quite well. Tested at high rpm and ahd no vibrations at all.



Batteries, The big deal.

The batteries world is in constant change nowadays with the electric vehicles take off , the new and improved power storage, super capacitors, and the new kid on the block, graphene.

Lead batteries and AGM or gel are a thing of the past. We are now having the Li-ion present going to the new Li-air future.

The necessity of longer trips, fast charging times a better performance are a must in electric vehicles, and more and more, those demands are the big deal in EV.

Fresh air, still to come.

Till now, the obvious technology in the batteries department has been lithium-ion. But since some time ago, a new technology based in air is the real interest for manufacturers and EV developers. The new Li-air promises up to 10 times the energy density of their cousins li-ion. IBM´s project 500 has the aim of driving 500 miles in one single charge  in a family car using those new batteries. Although this has been achieved already by the Metron Institute (Slovenia) with LiFePo4 technology.

Li-air cells

The way it works is, a Li-air cell uses cheap carbon as a cathode (instead of cobalt), a molecule of a oxygen pivots through the cathode and gives the battery its name. But it has remained theoretical because of its big challenges. Among them: the other electrode in such batteries—the anode—is pure lithium metal, which provides a lot of energy but also ignites when exposed to water, carbon dioxide, or other contaminants.

Such is the challenge, that IBM and JCESR (Joint Center for Energy Storage Research) have decided to step back from the LI-air project, and IBM has turned his favour to a Lithium Sodium technology.

Li-Na cells

But with all these changes, a new development continues, and metal chemistries are also under development, in particular Aluminium-Air. An Israeli company (Phinergy), has claimed to solved corrosion, and recharging issues with a silver based catalyst. A prototype EV claimed to have 1600km range with Al-air batteries. However those cells cannot be electrically re-charged having to re-load them mechanically and topped up with water.

It smells sulphur.

Lithium Sulphur cells are another energy dense technology that could solve the needs for the EV in a near future. This new chemistry tends to solve issues like life cycle and stability. Based around a carbon based electrode, those cells are said they could go ahead Li-air technology.

Li-S cells

Many studies and research from Imperial College (London)  to German company BASF are putting their efforts into Li-S. They said this could be the 4th generation of batteries, expecting ranges of 400Kms in the next decade. Scientists at Lawrence Berkeley Labs (California) have introduced graphene oxide into Li-S cells that are said to deliver 1,500 charge cycles without deterioration.

Other researchers from ETH Zurich are working with Sodium-ion cells, stating that are much cheaper than Li-ion. But they have two major problems; they are three times heavier than lithium and tend to lose capacity when not in use.

Lithium Ion are here to stay.

Despite all the development in the power storage field, one thing is clear, most of EV at the moment go for Li-ion, and the fact that manufacturer are offering cheaper prices and even Tesla is building a new Lithium batteries plant, makes you think that in the long term this technology is here to stay.

Li-ion cells

Li-Ion developers, Bosch, GS Yuasa and Mitsubishi, claim that the could reduce the prices to half in the Li-ion filed, and double the capacity, that would make EV much more approachable to normal consumers.

There are also many new promising developments with carbon, but the gap between the lab and the factories is too big to stop producing Li-ion for EVs.

graphene cells

The magazine “Electric & Hybrid Vehicle Technology International” writes in their July 2014 issue about the carbon:

“The real deal?. A new type of dual-carbon battery technology that could potentially be a game changer for EVs has been launched by a Japanese R&D company. Called Ryden, the new battery is said to offer energy density that’s comparable to Li-ion products, but over a much longer functional lifetime with far improved safety and cradle-tocradle sustainability, says Power Japan Plus, which will begin production of the cells later this year at its manufacturing facility in Okinawa, Japan. The Ryden battery makes use of a completely unique chemistry, with both the anode and the cathode made of carbon. “Power Japan Plus is a materials engineer for a new class of carbon material that balances economics, performance and sustainability in a world of constrained resources,” says CEO Dou Kani. “The Ryden dual-carbon battery is the energy storage breakthrough needed to bring green technology such as electric vehicles to mass market.” Kani says that the Ryden battery balances a breadth of consumer demands previously unattainable by a single battery chemistry. In terms of performance, the new battery is not only energy dense and operates at above four volts, but also offers a charge time that’s 20 times faster than that of current Li-ion designs.

dual carbon cellsThe Ryden technology has been created so that it can slot directly into existing manufacturing processes, requiring no change to existing manufacturing lines. Furthermore, the battery enables consolidation of the supply chain, with carbon being the only active material used. As a result, manufacture of the Ryden battery is under no threat of supply disruption or price spikes from rare earth materials, rare metals or heavy metals. According to Power Japan Plus, its technology is the first high-performance battery that meets consumer cycle-life demands, being rated for more than 3,000 charge/discharge cycles. The breakthrough also eliminates the unstable active material used in other high-performance batteries, thus greatly reducing fire and explosion hazard. Furthermore, the new battery experiences minimal thermal change during operation, eliminating the threat of a thermal runaway. Finally, it can be 100% charged and discharged with no damage. Adding to the sense that the Ryden battery could be a key moment for EVs is that it is 100% recyclable, vastly improving the cradle-to-cradle sustainability of battery technology. As an add-on to this, Power Japan Plus is testing the battery with its organic carbon complex material, working toward the goal of producing the battery with all-organic carbon in the future. Made of naturally grown organic cotton, the carbon complex exhibits properties not seen in other carbon materials. By controlling the size of the carbon crystals during production, Power Japan Plus can engineer the carbon complex for a variety of applications.”

Which vehicles are best to convert to electric.

There are hundreds of thousands of cars out there waiting to be converted. The best cars to be converted to electric are small old cars. The older is de car, the less electronic components it has and the easier will be the conversion.

As the batteries are still the big issue in a conversion project, regarding the weight and the price, the only way to minimize this aspect is by installing the less battery modules possible, and this can only be achieve nowadays by using a donor car that needs little electric power to drive, therefore it will need few batteries to run.

Another advantage in this philosophy is financial cost in the project. An old car will always cost you less than the equivalent two years old car. The Mini may be the exception in this case, but hey, it is a Mini.

Here are some examples or perfect old cars easily convertible, and examples of their prices in the second hand market.

o    Renault twingo


o    Fiat Punto


o    Citroën AX



o    Ford Ka


o    Mini


o    Nissan Micra



o    Open Corsa


o    Peugeot 205


o    Seat Ibiza


o    Volkswagen Polo



The adapter plate

One of the key aspects of a conversion is how to connect the existing gearbox to the new electric motor. This is normally done by an adapter plate that fits in both sides, the old gear box and the new motor.

This has to be designed and fabricated with high precision, as the geometry of the whole transmission is under jeopardy if there are errors. There are already manufacturers with already made adapter plates designed and proven to be working perfect. The other option, will cost more time, but it may be cheaper, is to design yourself. That was my case, as so far none did a conversion for a Renault Twingo yet.

So, I decided to design it myself, and give the machinist an sketch of the actual plate.

The plate needs to be made out of a material that needs to be strong, light and cheap. The perfect balance between those 3 variables is aluminium, that is why 99% of the adapter plates are done in such material.

The thickness for the adapter plate depends on the torque and power for the electric motor. For a 14 Kw motor I was recommended a 17mm plate, but my local supplier only had 10mm or 20mm (a paradox working next to Alcoa), so I went for 20mm, that would not add much more weight and it would improve how strong the joint would be.

I started to disassemble the gearbox, and making a template based on a front picture.


After having a proper front picture, I edited with a photo manipulation software (The Gimp) to have just the shape of it.


Once I have a shape of it, I started taking measurements from the centre to the screw holes, between them, and so on, to have a real measurements of it. As in this procedure, error needs to be near zero, I recommend to use a good calibre.


Once all measure have been done (double check and triple check), I draw that template into a 2D CAD software (LibreCAD), and draw many references within the same distances, all the centre points of the pin holes and the actual centre.


Then, when I finished drawing all the circles and, I measured within the 2D CAD software all lines and compare with the real measurements. Surprise, surprise..I had some minor errors.

After double checking the real measurements and the positions in the 2D draw, I printed out in paper 100% sized, and I could see all the wholes were in the exact position, so I gave the design pre- green light.

I took the final design to the machinist as ask him to fabricate a 1mm cheap copy just to try all the screws. They have a super-sized kind of plotter/cutter that can cut  2 cms aluminium as it was butter.


I tried the 1mm template and I fitted like a glove. Just one small 8mm was a bit miss-aligned (about 0.5 mm), the rest all fitted perfect. So I gave the 100% green light and I asked the machinist to cut it in a 20 mm aluminium plate. Even though it took some time as the were out of stock, finally I had it and connect both, gearbox and motor like a charm.


The vacuum pump and the brakes.

Mostly all cars use a braking system with power brakes and this system needs to be left as it is in a electric converted vehicle. If the weight is bigger after the conversion because of the batteries, then the brake system should have at least the same braking capacity or even more.

Working brakes are very important with an EV since one way of emergency braking (engine compression, the one experienced when you downshift) is gone with an EV, you get no such thing from an electric motor, unless you have a regenerative braking system.

The difference between the braking system in a electric converted car and a petrol car is not the actual brakes, but the system on how the vacuum is generated to the brake booster. In a converted car this has to be done with a vacuum pump.

The vacuum pump is the same device as an air compressor, but the air valves are reversed so instead or throwing air it sucks it. In a standard car. De level of vacuum pressure needed for the brake booster is around 16” Hg to 18”hg (inches of mercury), that is about 54000 Pa (Pascals) or N/m2 (Newton/ m2), so this level of vacuum pressure is the one the vacuum pump should maintain.

There are electric vacuum pumps in some diesel cars as Volvo or vans whose diesel engine do not vacuum enough pressure for the brake booster. Those electric pumps work with 12V and they consume around 6 or 7 amps. You shouldn’t use the vacuum pumps designed for the door locking systems, as those do not provide enough vacuum for the braking system.

11_reservoir_enSometimes a long braking push in the pedal ma use all vacuum pressure in the braking circuit, so the pump would need a few seconds to make the needed pressure level again. To avoid this situation a vacuum container (what a paradox, a container  that holds emptiness lol) can be installed between the pump and the brake booster to keep some more time this level of pressure. Note that the bigger the container, the longer the braking capacity, that means, you can brake more times till the pump started again to generate the level of vacuum again.


12_vacuum_switchNow, for the container to work, a vacuum switch needs to be installed to keep the vacuum pressure level above the given value, in our case around 15” Hg. Those sensors have a valve associated that opens or closes the brake circuit for the pump to maintain the vacuum.

13_vacuum_pumpThis pump and components are very popular in conversion in the USA (SSBC pump), and the Hella vacuum pumps. I did order one for about 200€ plus 60€ of delivery. The surprise was when I received the package after paying some additional 90€ for customs tax, and saw the pump was Made in Spain.


How to convert your car to electric?

quien mato el coche electricoWhen I had the idea of converting my own car to electric, I had two goals in mind. To be able to drive a novel car, that wouldn´t make any noise and the cost for the fuel be little or nothing.  The other goal was to stop once for all contributing to dirt our environment and be able to tell the rest of the people “Yes, we can”, now days you also can have an electric vehicle exactly as it was at the beginning of the 20th century in New York (See the documentary “Who killed the electric car?” ).

Little by little, this idea was more and more real, asking other people, researching on the net and other countries where this was already a reality, I started the project of building an electric car.

Choosing a donor car.

The first step, once everything is clear, was to choose a cheap car and appropriate for the project The best cars are old vehicles o classic cars. The reason for this is because they are not complex in their design and electronics are not playing an important role in the car functions.  There is no need to be afraid at this point, nothing anyone can overcome reading a bit about the chosen car.

01_renault_twingo_elelectricAnother important requirement is the car to be light in weight, less than 1000 Kg is more than adequate, and 800Kg is ideal.  The reason behind this is the resistance the car has because of the friction in the roads, the more resistance, the more electric energy it will need to drive.

There is also other elements that a high speed affects the performance as the Aerodynamic coefficient, but this will leave it for the time being.

The old Renault Twingo is a car that weights very little, it doesn’t depends much on electronics (it doesn’t come with power steering or automatic gearbox). So I decided to get a cheap second hand Twingo and I spent 500€.



And now, the motor.

The motor is something you need to spend some time researching on it to take the correct decision. By choosing a small car, the motor doesn’t have to be very powerful, so a 7 to 15 Kw motor can be just perfect. There are two kinds of motors:  DC motors (direct current) and AC motors (alternating current). The first ones are cheaper, more accessible in second hand markets or scrap yards, but they are less efficient. The second ones are more expensive; they weigh less and are more efficient. Then according to other technical aspects are synchronous motor and asynchronous, also other with permanent magnets, which supposed to be top of the list. As examples, there are 7 Kw motors from China that cost less that 1000€, while in Europe or USA you can have 15 to 25Kw motor between 2000 and 4000€. I decided to go for an Slovenian 14 Kw motor, branded Letrika. I knew this provider at the electric car fair EVS27 in 2013.

Motor electrico

Motor electrico

Lets go to the motor controller.

This is one of the main components, it is also one of the most expensive and it goes paired with the motor for two reasons: One, it is the one in charge to convert the batteries electric power to the correct voltage necessary for the motor, and the second, to regulate the speed of the motor, so the controller needs to be designed for it. As with the motor, there are DC controllers and AC controllers. The good news is that most of the motor manufacturer they also do the controllers, and if the don’t, normally the motor can be configured for generic configurable controllers.

Controllers are also classified according to the maximum current they can feed, the more current and voltage, the more powerful l the motor will be. There are several brands as Brusa, Curtis, Sagem, ..


03_curtis_controllerI got a Curtis controller, medium range for AC motor, the Curtis controller 1236. Most of the controllers are programmable, so you can adapt it to your own motor. You will have to study a bit about variety and features of the controller best suits you.



And we get to the batteries, the queens.

Batteries are the most important element in a electric vehicle, as they will define how much power and how much range the electric car will have. I hope one day this element will be the less important, but for the time being, this technology is more complex than we may think. The appropriate batteries bank is conditioned by the maximum distance the car will drive in one single char and also the charger and the BMS (Battery Management  System).  Not all kind of batteries can be charged or discharged in the same way, if you don’t follow the manufacturer requirements and limits, batteries can be affected and their life span be reduced.

There are several technologies in the market right now, but in practical terms we can talk about 3 or 4 types. Lets start by the cheap ones.

04_lead_batteryLead Batteries. They are the cheapest ones, but the least suitable  ones because its design, as they are not design to provide a constant current all the time, but to provide a very strong one in one go, and this is not what a controller for a electric motor needs. The good news for a budget car, is that even dead, you can re-acconditionate them or de-sulphate them. This is a delicate process as the content inside the batteries is sulphuric acid, so if you are a bit un-sure of what you are doing, better not to try. I have done it being very careful, and following all the security precautions and using protecting gloves, glasses and mask (in an open environment), at the end you need to neutralize the acid with sodium bicarbonate before wasting it to the sink. You can also buy them to avoid all this hassle. They are very heavy, but can be charged with any standard charger.


05_72V_agm_batteriesAGM or gel batteries.  Those are deep cycle batteries, they are lead batteries with more efficient electrolyte gel. They are a bit more expensive but they are designed for electric cars. They are very heavy too, and there are manufacturer that assure up to 1000 cycles before losing charge capacity. The charger has to be specially design for gel batteries to follow a correct charge parameters for gel or AGM. They are not very expensive, I bought 6 of them, 12V at 100Ah for about 900€.


06_lithium_battery Lithium batteries. This already more expensive, but they weight about half and they have double capacity. Those are the standard option for electric cars. They use to come in 3.7 cells, so you have to get many of them to achieve the desire voltage. Another VERY IMPORTANT issue is that lithium batteries need to be managed (charged and discharged) by a BMS (Battery Management System). The reason is that these batteries cannot be charged or discharged outside the recommended limits by the manufacturer. As an example, 18650 lithium cells can only be charged at a maximum of 4.1V and discharged at a minimum of 2.5V.
–    Pyrophosphate batteries (LiFePO4). They are the most expensive of all but also they have the more energy capacity.


Enough batteries for now..


07_dc_dc_converter_72vAnother very important component is a current converter for high voltage to 12V.
When we remove the IC engine (Internal combustion), one of the components that also disappears is the alternator, the one in charge of keep the battery always at the proper voltage (in this case we could call it the auxiliary battery) for lights, electric windows, radio, etc. So, as the alternator is missing, we need a system have it always charged, for example, a DC converter  72V to 12V.




Well, that´s it, isn’t ?. No, still something important, the brakes.

For the brakes, you need to supply the vacuum that the IC engine use to make for the brake booster. So we need to install a vacuum pump in order to replace the missing one in the IC engine.


Then you need other small components, but equally important as a pedal accelerator, a contactor, some relays, fuses, etc.


Those small components are as relevant as the big ones, because even with the motor and controller, with no cables, there is no use. Also, you need to see the high voltage requirements that the motor manufacturer recommends. Also the signal cables are also important in following no just the diameter but the isolation.

Now the adventure starts… just install everything in the car.



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