[Stef]

Hi everyone,

I am a student studying electromechanical engineering. I am trying to convert a smart fortwo to an electrical vehical and writing my master thesis about it.

Fair warning: I'm new to converting cars and also very new to writing stuff on fora. So please be patient with me while I try to do a fair job at it.

I have the following things:

• Donor car which is the smart ForTwo
• Two electrical motors with the following specs: Link to the motors
  
  • Power supply voltage: 72 V
  • Motor diameter: 12 inches
  • Rated power: 7 kW
  • Maximum power: 11 kW
  • Speed: 1100-1340 RPM
  • Efficiency: 83.3%
  • Torque: up to 78.6 N.m
• Controller: KBL BLDC Motor Speed Controller with the following specs: Link to controller
  
  • Controller supply voltage range, PWR, 18V-90V.
  • Frequency of Operation: 16.6kHz.
  • Standby Battery Current: < 0.5mA.
  • 5V Sensor Supply Current: 40mA.
  • Configurable battery voltage range, B+,18V-90V.
  • Analog brake and throttle Input: 0-5 Volts. Producing 0-5V signal with 3-wire pot.
  • Reverse alarm, Main contactor coil driver, meter.
  • Full power operating temperature range: 0°C to 50°C (controller case temperature).
  • Operating temperature range:-30°C to 90°C, 100°C shutdown (controller case temperature).
  • Boost current, 10 seconds: 450A.
  • Motor current limit, 1 minute: 400A.
  • Motor current limit, continuous: 160A.
  • Max battery current is configurable.
• Batteries that we are going to use are recycled from a Prius. The problem that we need to get the voltage down to 72V for inspection and safety reasons.
• Accelerator is a standard foot throttle

Now I had the following questions for who ever is friendly enough to respond to this Thread:

• Is there anything that I need to take in to acount before I start stripping the car?
• The smart holds three computers, the Desk-computer, Central-computer and Engine-computer. Does someone have experience in "cheating" the Central-Computer so that he thinks everything is fine with the engine?
• The lowering of the voltage to 72V, use a transformer or actually try to change the build of the Prius batteries?
• Changing the build of the car will undoubtedly change the handling of the car but is there anyone with experience who can say anything about this? With this I mean, can I just keep using the existing supension and still drive it safely?

Any opinions about the conversion and tips are always welcome!! If you need more information before giving an opinion please feel free to ask!

Best regards,

Stef

 

[Ziggythewiz]

Check out Yabert's thread.

 

[tylerwatts]

Seconded! great thread!

What are your performance goals? those motors will be outside of the performance Yabert experiences, simply due to their output ratings. But there have been very successful low power conversions in the past. I can't remember the name of the company, it is eastern European, so might be near you. Will try find it.

 

[tylerwatts]

http://clubsmartcar.com/index.php?showtopic=23469

Found this while looking, started reading it.

 

[tylerwatts]

Found it! Been impressed with these guys' work too!

http://www.evalbum.com/3503

http://www.ad-pecjak.si/ECO/Smart/default.htm

 

[tylerwatts]

I've been thinking about converting a Smart using an Azure AC24LS drive from the recent auction with a Curtis 144V controller. Will be keen to follow your build!

 

[tylerwatts]

Stef do you have details of the Prius batteries? Pictures of junctions etc. What configuration are they connected? I would want to try reconnect them to give the correct voltage and avoid a transformer or something similar to change the voltage.

Also, why not use the Prius transaxle and motor controller to drive the Smart? It would give you ALOT more power and performance!

 

[tylerwatts]

PS, I'll shut up now and give others a chance...

 

[Stef]

Thanks for the fast replies! I can feel the enthousiasm Tyler

About the performance goals, we just wanna get out of it what we can. I'm doing this project at school and we're trying to do the conversion as economical as possible using the things I mentioned.

I don't have details about the batteries yet because they haven't arrived yet, I'll specs and pics as soon as I have them. I was thinking the same thing about just reconnecting them to give the wanted voltage.

You make a fair point about the Prius transaxle and motor controller to drive the smart but then they would have to be bought. I'll look in to the transaxle but the controller is already on it's way.

Thanks again for the fast replies! And I have some reading to do now

 

[Ziggythewiz]

PS, I'll shut up now and give others a chance...

FYI if you have more stuff to add and no one else has replied you can just edit your post to keep adding on. More content, less space

 

[tylerwatts]

Yes, thanks Ziggy. Was rapid firing at work...

Stef

I mentioned teh Prius drive as I assumed you had a whole car that was a donor or something. If not then no point wasting money on one. Seems like your drive components will do very well in the little smart if they perform as their spec suggests. The links I showed used a 15kW peak AC induction motor. I imagine yours has more torque than the AC. Do you have any decent specs or info on the motor and controller please?

Also, please check Yabert's thread for the maximum size motor you can fit in there. I seem to remember he had only an 11" motor then even went smaller. Hope that 12" motor of yours isn't going to be too big. Have you checked yet?

 

[tylerwatts]

http://www.evalbum.com/type/SMRT

FYI.

You've given me a little bug to see how easily I could source a suitable donor now! My only trouble is my commute involves 20mins of 80mph driving, about the max for any smart, including an electric one!

 

[Stef]

I have updated my text a bit so there is more info about the controller.

I have been reading Yabert's thread and you raise a valid point about the motors. They're most likely going to build up to be a problem but it are the motors that we're going to have so we're going to have to make it work...somehow. The motors themself haven't arrived yet but once they do I'll have more specs and info about them. (I know it should be the other way around but I'm working with what I get)

Reading the thread also kinda gave me a scare about the Kelly controller

I don't get your last post?

 

[tylerwatts]

May I ask what motors/ where from etc? regarding size, I vaguely recall Yabert teasing about hte possibility of going rediculous and sticking a 13" motor in, but I might be wrong. I think you'll be just about OK. Keen to know what you'll do about the transmission. I expect keeping it and overriding the gear select controls to set it up as automatic to the best gears for the given speed will be best. The motor's torque should be about right for the car.

I was saying that I have to travel for 20 minutes at average speed of 80mph, which is very fast for a smart, not top speed but high speed, and entering deminishin returns for needing to have lots of power and not enough batteries to give the range I need. I travel 50 miles to work and back (total) each day, plus any trips to shops or things, so need a substantial range and if having both that top speed and say 70mile range at 80% DOD I don't know if enough batteries can be fitted to a smart's chassis, or how much motor and controller I swoudl need. Might need a slightly bigger donor to fit that lot in... We'll see, I'm only scheming right now. At the other extreme I have 1,7tons of Volvo S60 I want to convert also! Much bigger task!

 

[Stef]

This are the motors: http://kellycontroller.com/car-hub-motor-72v-7kw-p-711.html

And yeah we should be fine but I don't think it's going to be straight forward with the largeness of the motors.

And about your problem...it does sound like a big task or an EV...especially if you wanna keep it all a bit economical. But I've seen some posts about calculators. But you've probably checked all of those out already?

The transmission is in fact another issue I have to study. I've put it up in the main text even. Like you said, I was thinking of 'recycling' the exhisting transmission but on the technique to be used there I'm not sure yet.

 

[Yabert]

Hi Stef

You bought a direct drive motor. Build to be mount inside the wheel (no transmission need). So you usually need two motor (one per drive wheel).
That can seem attractive to by-pass the transmission with two hub motors, but the power will be limited and the mounting on the original swing arm will be a bit complexe.

And about the Prius battery, rebuild it for 72v. But a Prius battery is small and don't contain a lot of energy, so your range will be small.

Good luck with your conversion.

 

[tylerwatts]

Stef, Yaberts is VERY right. Please tell me that link is correct. Otherwise reasile like Yabert says you will need 2 motors, either mounted to teh suspension frame, or better mounted in place of the engine/transmission using the existing drive shafts (likely shortened) to drive the wheels direct.

Are those the correct motors? Have yours been dispatched yet?

 

[Stef]

Yeah sorry about that guys I was confusing myself by reading about other peoples conversions (btw Yabert congrats on your conversion! Reading that thread was like reading a book, it had its ups and downs but the end was amazing!)

I indeed have two engines on it's way so like you Yabert pointed out...no transmission needed

 

[mk4gti]

It's going to be an interesting project since there aren't many wheel-motor swaps on here and the topic has come up many times.

 

[tylerwatts]

Yes very interesting prospects for your conversion Stef! Keen to see where you mount the motors personally. I was looking at this link earlier, look at the hub motors used here. They are rather large! I expect mounting those moors in teh smart will either increase the rear track or require significant modification to the rear suspension beam. Otherwise they could be mounted inboard with shortened drive shafts to the wheels and keep the stock brakes. Seems a simpler option, though it might cost more weight for the vehicle with the framework required to mount the motors like this...