# Smart Fortwo EV conversion questions without answers??



## electriccooper928 (Oct 1, 2015)

Yes another one thinking of converting a Smart fortwo. 
I'm at the beginning and nothing done yet. I've been offered a motor, controler and else for cheap that I could use to convert a Smart. My goal is not to have a powerful EV to do 0-60 in a half of a sec. but just a practical commuter car with an autonomy as long as possible. Of course I should not measure 0 to 60 with a calendar but I just hope it has the same performance than the CDI (diesel).
I searched the web a lot but I did'nt find answers about why nobody keeps the car 6 speeds transmission. Is it because it's not possible to couple the electric motor to the tranny? Or is it because of keeping electronics alive without diesel engine in? or both? What I would like would be to keep the stock tranny and all electronics but is it thinkable?
I will appreciate any help.
Thank's


----------



## dougingraham (Jul 26, 2011)

You need a transmission with a lot of gears with a small ICE in order to match the torque band to the car. The low gear is needed just to get the car moving so that the ICE does not stall. Electric motors do not have that problem. An ICE might have its usable torque band from 2000 to 4000 RPM. On either side of that torque drops off quickly. An electric motor like the Leaf is flat from 0 to around 5000 RPM and gradually tapers off above that. The reduction ratio in a Leaf is 7.93 to 1 and since the RPM limit is 10390 this gives a top speed of 94 MPH. The Leaf Motor has 187 ft-lb and when you amplify the torque by 7.93 you see about 1483 ft-lb at the face of the tires (tires are about a foot in radius). From looking at dyno plots it appears that you get full torque up to about 30 mph and above that it tapers off up to the top speed. This means you can expect a little less than 1/2G acceleration up to 30 mph and a gradual reduction above that. A smart for two should be pretty easy to do with a Leaf power train so that you don't need any transmission. The reason to keep the transmission with an EV would be because it does not have a wide enough torque band and the transmission would allow you to match what you have with what you need. If you transplant a leaf power train from a salvage Leaf you should expect similar performance to that of a Leaf as the cars are similar in mass. The differences would be from tire size. Smaller diameter tires would give a fast er acceleration but a lower top speed.

In your case you were looking for why people don't keep the automatic transmission. The modern transmissions are controlled by the ECU. So if you want to keep it you will need to either trick the ECU into thinking it still has an ICE connected or replace it with a device to provide the control signals. Each approach has its own problems and advantages. Tricking the ECU might seem simple because the rest of the stuff in the car connected to the ECU will continue to work. But an Electric motor has a very different RPM range and torque curve so tricking it is not just mapping the RPM and airflow sensors and exhaust temps vs throttle position sensor. You need to make all these things make sense when driving an electric motor. Eliminating the problem by not keeping the transmission at all is probably the best solution.


----------



## electriccooper928 (Oct 1, 2015)

Thank's a lot dougingraham for generously taking of your time to answer me. I understand very well the effect of the torque to easily move the car from complete stop directly with the electric motor compare to the ICE.
That effect can't hurt if I keep in mind to keep the stock tranny. 
I think the major challenge is to couple the motor to the tranny and to simulate the running of the removed engine to use the transmission like if the ICE was still there or if it would be possible to command the transmission directly without the CPU it would be perfect 
I found a guy who I think kept the stock transmission : http://www.evalbum.com/821
I tried to contact him but no news yet  He wrote he used the Getrag tranny which is the Smart tranny. After all we can use the auto or manual mode when driving a Smart!!


----------



## Yabert (Feb 7, 2010)

You are lucky for two reasons:

1-Reach the same performance than the CDI engine will be easy. A simple 25-30Kw system can do that
2-The Smart transmission is a regular manual transmission.... but automated (so automatic). That mean you can modified the gear change system or simply engage one gear and leave it in this gear all day long (if your electric motor can go in reverse).

In my Smart, I changed the transmission because my motor produce over 170 lbs-ft of torque, but with your low performance expectation, keep the original is doable.
Some food for thought: http://www.diyelectriccar.com/forums/showthread.php/72v-systems-small-car-68596.html


----------



## electriccooper928 (Oct 1, 2015)

Thank's a lot Yabert, I followed your work on this forum and on Youtube. Great work by the way. I just made another post about the stuff I could use. A guy offered me that. Since I'm a rookie I'm not sure yet if it would be ok for my project.
Also We're in the same country and same province mon ami


----------



## Yabert (Feb 7, 2010)

The part you listed on your other thread are from another decade. They will work and with proper battery they will move your Smart well.
But before start to spend money, maybe ask you if you want to spend few thousand dollars in an illegal conversion that will work correctly, but not more.

Well, a project is fun, you can learn a lot, you can be proud of...., but it can't be as good than a used Leaf, Imiev or other electric car for the same price.
So, if your goal is to go cheap, find used forklift motor, a 72v controller, a slow charger on 120v
If your goal is to learn the parts you are looking at can be good.
If your goal is to have a useful car with 70-120 Km of range with fast charge capability, nice electronic feature... buy a use electric car.


----------



## electriccooper928 (Oct 1, 2015)

Yabert said:


> The part you listed on your other thread are from another decade. They will work and with proper battery they will move your Smart well.
> But before start to spend money, maybe ask you if you want to spend few thousand dollars in an illegal conversion that will work correctly, but not more.
> 
> Well, a project is fun, you can learn a lot, you can be proud of...., but it can't be as good than a used Leaf, Imiev or other electric car for the same price.
> ...


 What you wrote is very significative. It's full of wisdom and resumes what I found in the last days about conversion etc.
Thank's a lot Yabert


----------

