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Discussion Starter #1 (Edited)
Thought we would share our progress converting a 2003 Mini-Cooper S to an EV. My sons and I started this effort in April 2009 with purchase of the donor car followed by the VFD, Batteries, and AC motor. We are still in the prototyping phase. We recently drove the car and have learned the limitations of our Industrial VFD.

Donor Car: 2003 Mini Cooper S w/o Engine and Drive Tran
Car.jpg

Motor: Ford F8Y8-14B280-AC (Siemens PV5133-4WS20 W11)
AC Motor.jpg

Motor Control: BENSHAW 100 HP VFD
VFD.jpg

Battery: Two custom packs made of 42 Prius Battery Modules
Battery Pack.jpg

Motor and Transmission Mounted
Motor_Trans_Mounted.jpg


Manual Charging of Battery Stack
Charging.jpg
 

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it look good ^^
did you manage to make some wheel spin?
 

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Discussion Starter #5 (Edited)
it look good ^^
did you manage to make some wheel spin?

If you mean a burn out, then no. We threw it together to try it before winter hits and did not torque the coupler properly yet. We need to disassemble to change out the non-lubricated bearings in the motor, wanted to make sure we could get it off. We did manage to spin the tires pulling up our drive way because of its angle. We have a video of that, but I was not able to upload to anywhere yet -- I am not that knowledgeable in that area. I hope to put a link to the video of Mini on road with some help from my son.
 
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Are you running the prius pack as one high voltage pack or two parallel packs? I am working on the same type of thing. Experimenting right now. My pack is a low voltage pack. Much harder to do. How do you like the Prius batteries? How's the charging? BMS? What is your running voltage?

Pete :)
 

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Discussion Starter #7 (Edited)
Awesome! Whats was the cost of all that?
I have not added all the costs up. Here is a breakdown of the major components. We don’t have a battery charger yet. I plan to modify a power supply for this.

Mini $3,400 + $700 shipping
Motor: $1,590
VFD: $ 990
Transmission: $1,700
Three Prius Battery Packs: $1,467
Misc. est. $1,400
 

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Discussion Starter #8
That looks great!
Where's the build thread? It would be good to see how you did it.:)
Thanks !! . I don't have a thread or a web page. I hope to get some help from my sons getting something setup over the Chrismas Holidays, when we have some time.
 

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Discussion Starter #9
Are you running the prius pack as one high voltage pack or two parallel packs? I am working on the same type of thing. Experimenting right now. My pack is a low voltage pack. Much harder to do. How do you like the Prius batteries? How's the charging? BMS? What is your running voltage?

Pete :)
We are running two battery packs of 42 series modules in parallel (best case 13 amp-hr). I hope just enough to get me to work and back daily. I wanted to run all in series so we would not need to modify the controller we have -- not sure what effect the modifications have had on its overall performance. I was not able to get any answers on the dielectric operating voltage of the motor, so we went with the lower voltage.

For test runs we are not fully charging or discharging (we think) the battery pack. Only charging the battery pack at 5 amps for now. We don’t have a battery fan or BMS setup yet. Have been charging the pack to 357 volts (42 x 8.5).

The Prius battery modules are nice to work with from a packaging and flexibility point of view. You must keep a close eye on the temperature of the battery modules when charging to get a full charge. We put one pack in what looked like thermal runaway before we got smarter about charging. It took two large fans more than an hour to get it back to room temperature.
 

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Discussion Starter #11
Posted these videos on youtube:

Home grown Mini-EV spins wheel first time
http://www.youtube.com/watch?v=pSs0aYbaRo0


Home grown Mini-EV slow but almost smooth start
http://www.youtube.com/watch?v=9bxt0E2ezGg

Home grown Mini-EV driving first time in second gear
http://www.youtube.com/watch?v=FduVqLQpz14

We have put up a web site http://www.bmpenterprises.net/ to caputure this and possible future projects. Below is the post on how we made the Mini-EV version of a Tischer style coupler. I could not include all the pictures here so if you want to see more please look at the web site.

Making the Coupler

The following shows the basic steps used to fabricate the Motor to Transmisson Coupler. This coupler used concepts shown by Tischer.


Testing fit of B-lock on Centering Plug:

Not shown here but we clamped on the B-Lock and drilled pilot holes using B-Lock as guide by removing and replacing each B-Lock screws one by one to drill the holes shown:


Its tough, but Adam lets it know who’s the boss:

Transmission Spline Coupler is cut loose. Note, the circular step bushing on the back we can use to center this piece to the coupler.


Test fit of Transmission Spline Coupler to its centering hole:



Boring out motor shaft clearance hole:

Used previously drilled pilot holes to center and drill each hole through aluminum spacer. Then we bolted on the Transmission Spline Coupler to match drill the bolt and locating pin holes:


Looks like its going to work:


 

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Discussion Starter #12
These are the steps we used to create the adapter plate to attach and center properly the motor to the transmission.

We started with a 3/4" 6061 aluminum plate and made an acrylic template that showed the bolt holes from both transmission and motor as well as the outlines. This kept us on track and helped make decisions.

The next step was to drill holes for the alignment pins in the transmission. We marked the two spots using the transmission as a guide.


The use of transfer punches made sure the plate was marked properly.


Here are the finished holes with threads, looks like we selected the correct bolt lengths.


From there we needed to find the exact center of the transmission to later line up with the exact center of the motor. To do this we created a 'center punch' that we fitted onto the transmission shaft and used the clutch action to make our mark.


At this point we didn't have the capability for precise machining on a piece of this size. So we hired a machinist to cut our centering ring and the hole for the coupler. Here it is back from the machine shop.


And then the first complete fitting test between motor and transmission.


Then we began the process of marking the bolt holes for the motor using a transfer screw set, shown above.
http://bmpenterprises.net/blog/wp-content/uploads/2009/12/IMG_0600.jpg
After drilling and testing all the holes they needed to be countersunk so the transmission could sit flush against the plate.


This is the plate countersunk and bolted to the motor.

http://bmpenterprises.net/blog/wp-content/uploads/2009/12/IMG_03011.jpg

The last modification to the plate was to make room for the trans-axle on that side. So we cut a radius by drilling several holes and cutting out with a saw.



See additional pictures at [URL="http://bmpenterprises.net/blog/2010/01/02/making-the-transmission-adapter-plate/"]http://bmpenterprises.net/blog/2010/01/02/making-the-transmission-adapter-plate/[/URL]
 

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Discussion Starter #13 (Edited)
This post contains a breif overview of what we learned trying to use an Industrial VFD as the Motor Controller.

If any one has some ideas or experience on how to overcome the issues associated with the transition from Coast to Stop, to Run, and then to Flying Start discussed below I would appriciate the help.

We purchased two used Industrial Variable Frequency Drives on eBay. The first one was a 30 HP 460 AC Benshaw Sensorless Vector Drive RSi030SX4B which turned out not have enough current output to get the car rolling consistently from a dead stop without tripping the hardware over-current protection circuit (~80 Amp). We were able to drive the car, once the car started rolling. It just could not supply enough current to move the car without tripping the hardware protection limit. The second one which we are using now is a 100 HP 460VAC Benshaw Sensorless Vector Drive RSi100SG-4B (~150 Amp).

If you are planning to try to use an Industrial Motor Control in your electric vehicle project here are some lessons learned:

Most units above 30 HP are only available in the higher 460 VAC. Unless you plan to run a 600 VDC system you will need to modify the unit to operate at a lower voltage.

Make sure it has a sensorless vector torque producing mode of operation, or you will need an external shaft position sensor to get high torque at low speeds.

Make sure the maximum AC frequency output of the controller is known and is high enough to support the the max motor rpm desired. The 100 HP unit we have is limited to 120 hz which sets our max to 2500 rpms, 40 mph in second gear. To get more out of our motor, it should be more like 300 Hz.

Make sure the controller has the ability to turn off the phase loss detection. If not you will need to "fake out" the detection circuits.

Make sure that it has a control mode which lets you command an output torque not speed. Our present controller only lets us command a target motor speed with timed speed ramps which results in difficult operating conditions when stopping.

If the controller does not have a command torque mode, it needs to have someway to associate an external switch input to the "COAST TO STOP/RUN control input to turn off the drive output when coming to a stop if you do not have a clutch. This input is needed to circumvent the controller speed control loop which is trying to hold the rpm at the commanded speed.

If the controller does not have a commanded torque mode it needs a "flying start" mode which keeps the the Controller's output current low until the motor and commanded rpm are the same. Unfortunately our experience to date is that this does not work well in our electric vehicle application and is the only reason we cannot drive the car around town safely. If "flying start" mode does not work well, the only way to accelerate after a "COAST TO STOP/RUN" command is issued, is to come to a complete stop, and then accelerate. The alternative to a full stop and then start is a screaming controller and a bucking car while the controller tries to sync the speed. This does not work in traffic.
 

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I was a VFD Applications Specialist for Square D for a number of years. I’m new to the EV world and was wondering if someone had tried to adapt an AC VFD to the EV world. I’m assuming you bypassed the front-end AC/DC converter and tied into the DC/Capacitor part of the drive. Seems like one thing you discovered is that AC VFD’s, though are listed by H.P., are actually current rated devices. The Benshaw unit you listed is rated at 152A’s when set up in Variable Torque load. When set up in what Benshaw refers to as “Heavy Duty” ( other mfr’s label this as constant torque) this is reduced to 111A’s. What this really means is that VFD will allow the current draw to be 166-167 FLA’s for 1 minute before it kicks of on “Over-current”. This is all based on AC motor current draw of a 100 hp AC motor drawing about 124FLA’s @ 460V’s. One requirement of an AC VFD is to limit the current inrush associated with the AC motor. An across-the-line start can be 6-10 times the current full-load draw.

The first/most critical parameter to set/understand is the Ramp/Up Ramp down time. Sq. D’s out of box was set at 3 seconds. I’m not familiar with the Benshaw, but most/all VFD’s have different torque profile’s. Most common is a linear, but there are typically modes like “Torque Boost” which can be tried. The reason I bring this up is that it appears the biggest issue you seem to be having is with the “Flying Start” parameter….Also known as a “Catch-on-the-Fly” parameter by other Mfr’s. What actually happens is that in the sensorless flux vector setting the VFD is looking at FREQUENCY the motor is running at, then induce more Hz back into the motor to accelerate the motor back up to the desired/set speed. Speed control on the VFD is usually achieved by a potentiometer wired into the VFD. If you go 0-100% on the pot and the ramp-up/ramp-down will follow the ramp speed you have set. IE: if you “floor” your EV it will allow current to flow to 100% whatever the ramp time is…same with ramp down/decel. Now when you get back on the “gas” while the EV is coasting you are trying to utilize the “flying start” and “coast to stop” parameters, but with the ramp times being a part of the speed control loop algorithm you are starting and stopping faster then what the algorithm is set to run. Have you played with the ramp times?
 

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Discussion Starter #15 (Edited)
I was a VFD Applications Specialist for Square D for a number of years. I’m new to the EV world and was wondering if someone had tried to adapt an AC VFD to the EV world. I’m assuming you bypassed the front-end AC/DC converter and tied into the DC/Capacitor part of the drive. Seems like one thing you discovered is that AC VFD’s, though are listed by H.P., are actually current rated devices. The Benshaw unit you listed is rated at 152A’s when set up in Variable Torque load. When set up in what Benshaw refers to as “Heavy Duty” ( other mfr’s label this as constant torque) this is reduced to 111A’s. What this really means is that VFD will allow the current draw to be 166-167 FLA’s for 1 minute before it kicks of on “Over-current”. This is all based on AC motor current draw of a 100 hp AC motor drawing about 124FLA’s @ 460V’s. One requirement of an AC VFD is to limit the current inrush associated with the AC motor. An across-the-line start can be 6-10 times the current full-load draw.

The first/most critical parameter to set/understand is the Ramp/Up Ramp down time. Sq. D’s out of box was set at 3 seconds. I’m not familiar with the Benshaw, but most/all VFD’s have different torque profile’s. Most common is a linear, but there are typically modes like “Torque Boost” which can be tried. The reason I bring this up is that it appears the biggest issue you seem to be having is with the “Flying Start” parameter….Also known as a “Catch-on-the-Fly” parameter by other Mfr’s. What actually happens is that in the sensorless flux vector setting the VFD is looking at FREQUENCY the motor is running at, then induce more Hz back into the motor to accelerate the motor back up to the desired/set speed. Speed control on the VFD is usually achieved by a potentiometer wired into the VFD. If you go 0-100% on the pot and the ramp-up/ramp-down will follow the ramp speed you have set. IE: if you “floor” your EV it will allow current to flow to 100% whatever the ramp time is…same with ramp down/decel. Now when you get back on the “gas” while the EV is coasting you are trying to utilize the “flying start” and “coast to stop” parameters, but with the ramp times being a part of the speed control loop algorithm you are starting and stopping faster then what the algorithm is set to run. Have you played with the ramp times?
Thanks !! for reading and trying to help. I had hoped to put more info up on how we modified the drive but other things are too demanding right now. To get the drive to operate at the lower voltage we shorted out and trimmed some of the input voltage sense resistors and startup resistors on the auxiliary power supplies.

You are correct, we bypassed the AC/DC front end and tied into the DC Capacitor bus. We are using a pre-charge resistor before applying battery to prevent inrush.

We learned quickly we had to set the ramp down time much longer than the ramp up time or our heads might come off when you let off the accelerator peddle. We learned the hard way how well Regen in an AC Induction motor can work. The drive I have unfortunately does not have a parameter to adjust Regen current level. In Regen, it only halts deceleration based on the sensed input voltage increase which is not useful because that is basically held fixed by the battery. Have thought about using the future battery current sense circuit to offset the input voltage sense.

Last time we drove the Mini we had the ramp up time set for 5 seconds and the ramp down at 15 seconds. The 15 seconds avoids the head snapping and helps keep the Regen current to battery low. I have not investigated the relationship between the ramp times and the “flying start”. I was wondering if the issue was related to my inability to hold the throttle peddle still while the drive tries to sync up the frequency. I would like to think the drive would quickly sync up and then apply power to ramp like normal to whatever the set point was. It seems the ramp times and power should be off until it has synchronized. It acts like its driving current while its searching. I wondered if it is turning on the boost current during this time or some brake current. There is another mode “Delta Freq” I have not investigated to see if it would help here. In the “Delta Freq” mode the Accel/Decel time is the time that takes to reach a target frequency from any frequency. I tried this mode early on to try to address accelerator response. I did not like the results at the time. Do you think this mode would help with this issue?
 

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Please keep in mind I’m new to the EV world, but do know the Industrial VFD world. Trust me; I’m learning more from you and the other members on this forum then I will ever be able to give back. Don’t know your background, but it sounds like you really understand the electronics’ part of the drive (board-level if you will) better then me. One thing that might help you is to remember what the original intent of the VFD mfr. was/is.
You’ve run into the regen braking capability built into even a sensorless flux vector drive. In your research you probably ran into full flux vector drives with encoder/resolver feed-backs. Suffice it to say a VFD can be used in indexing machine’s such as Hass CNC machines. The VFD will inject DC back into the motor to stop it as fast as you want…the one thing required is a (dynamic braking) resistor bank to allow the current to bleed off somewhere. These are available from a number of sources, but I have a feeling you know enough you might want to “roll your own”. This function, however, is utilized more in position control applications (CNC machines) and with my limited knowledge of EV’s I didn’t think this was something that would come into play in the EV world. On the decel side of things I would have thought that you would set the “Free-Wheel” stop parameter set which should effectively ignore the “ramp-down” time and not try to slow the motor down. Sounds like you tried this already, but maybe the motor on decel is generating enough current that is having a hard time trying to dissipate. Just a thought.

I don’t think your inability to hold constant the throttle pedal constant but you didn’t mention what you are using to control the speed. Don’t have a Benshaw manual handy, but it typically is a 10K pot. If your ramp up time is set at 5 seconds and you crank the pot to 100% the current flow should be linear over the 5 second ramp. If the linear ramp doesn’t suit the application there is typically other parameters that allow for voltage boost or other high enertia start applications to boost torque to the motor. These all work a little different from mfr. to mfr. Heavy flywheel’s, loaded conveyor system’s, etc. (EV’s) are the sort of applications the mfr’s. had in mind and they consider these to be constant torque (heavy duty in Benshaw language). The (potential) problem with setting your specific Benshaw VFD to “heavy duty” is that it is going to drop the FLA’s it bases everything on from 151 amps to 111 amps…probably not the direction you want to go.

The “Delta Freq” parameter I’m not positive as this sounds like Benshaw vernacular, but I’m fairly certain that this is more for set-point applications. An example is on a machine tool where there is a cutting speed at a specific rpm/frequency and then needs to jump to a different specific rpm/frequency. Doesn’t seem to be a parameter applicable to what you are trying to accomplish.
 

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Wow, not sure how I missed this thread. You have accomplished alot in 9 months, and thanks for posting.

Sounds like you are going through the same learning process I went though with my conversion. I too started out in a v/hz speed mode. Is your inverter capable of Sensorless vector?
 

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Sorry...not trying to answer for zaxxon, but being the new excited guy, I just quickly went thru your build. The Benshaw VFD zaxxon is using is a current sensorless flux vector drive. Looks like you are utilizing a loop feed-back resolver/encoder approach. One of the suggestions I was going to make to zaxxon was to put his drive in a volts/hz mode to do the preliminary tuning and familiarization, then switch back to the flux vector control. I think you can do that with the Benshaw unit.You probably have very valuable input for that approach.
 

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Discussion Starter #19 (Edited)
Please keep in mind I’m new to the EV world, but do know the Industrial VFD world. Trust me; I’m learning more from you and the other members on this forum then I will ever be able to give back. Don’t know your background, but it sounds like you really understand the electronics’ part of the drive (board-level if you will) better then me. One thing that might help you is to remember what the original intent of the VFD mfr. was/is.
You’ve run into the regen braking capability built into even a sensorless flux vector drive. In your research you probably ran into full flux vector drives with encoder/resolver feed-backs. Suffice it to say a VFD can be used in indexing machine’s such as Hass CNC machines. The VFD will inject DC back into the motor to stop it as fast as you want…the one thing required is a (dynamic braking) resistor bank to allow the current to bleed off somewhere. These are available from a number of sources, but I have a feeling you know enough you might want to “roll your own”. This function, however, is utilized more in position control applications (CNC machines) and with my limited knowledge of EV’s I didn’t think this was something that would come into play in the EV world. On the decel side of things I would have thought that you would set the “Free-Wheel” stop parameter set which should effectively ignore the “ramp-down” time and not try to slow the motor down. Sounds like you tried this already, but maybe the motor on decel is generating enough current that is having a hard time trying to dissipate. Just a thought.

I don’t think your inability to hold constant the throttle pedal constant but you didn’t mention what you are using to control the speed. Don’t have a Benshaw manual handy, but it typically is a 10K pot. If your ramp up time is set at 5 seconds and you crank the pot to 100% the current flow should be linear over the 5 second ramp. If the linear ramp doesn’t suit the application there is typically other parameters that allow for voltage boost or other high enertia start applications to boost torque to the motor. These all work a little different from mfr. to mfr. Heavy flywheel’s, loaded conveyor system’s, etc. (EV’s) are the sort of applications the mfr’s. had in mind and they consider these to be constant torque (heavy duty in Benshaw language). The (potential) problem with setting your specific Benshaw VFD to “heavy duty” is that it is going to drop the FLA’s it bases everything on from 151 amps to 111 amps…probably not the direction you want to go.

The “Delta Freq” parameter I’m not positive as this sounds like Benshaw vernacular, but I’m fairly certain that this is more for set-point applications. An example is on a machine tool where there is a cutting speed at a specific rpm/frequency and then needs to jump to a different specific rpm/frequency. Doesn’t seem to be a parameter applicable to what you are trying to accomplish.
My background is electrical engineering, I graduated from Purdue in 1974. I am one of those old analog circuit type guys with some early career background in switch mode power converters. Back when 10KHz switching was fast and the first 1524 came out. Three of my four sons and I were members of a High School Solar car team which won the World Wide Winston Solar Car competition. So I can’t say I am a newbee to EVs, but I am to AC Induction Motors and especially VF AC Drives. One of the main purposes of this build project was to educate myself and my youngest son in this area and plug in cars. I can say I have learned a bunch the last few months, but I am not an expert and appreciate your help and suggestions.

I am using the Benshaw "COAST TO STOP/RUN control input to turn off the drive output when coming to a stop, I assume this is the same as “Free-Wheel” stop. I only want to use “Free-Wheel” stop when I use the mechanical brake. That way I can recover some energy back into the battery when slowing down before I put the brake on. The problem is under typical driving conditions one puts on the mechanical brake several times, like when someone slows quickly in front of you. Under this condition you don’t come to full stop and you want to go again. My issue is I have not found a configuration of functions where the motor smoothly recover to free wheeling motor rpm so I can reaccelerate. I think getting the “Flying Start” function to work is my last hope. I have not played extensity with the gain and integral setting provided for this function, but initial attempts did not seem to help. I have done my best to ensure the DC brake function and the like are off. But suggest anything that comes to your mind because again I am no expert either and I could have over looked something.


The Mini has what I think is a HALL position sensor on the throttle peddle that takes 5 volts and puts out a voltage proportional to the position. I added a regulator to the Benshaw sensor supply to provide 5 volts and ground and feed the signal into the A/D input and programmed the speed command to use the A/D channel and not key pad input. Then used program functions to set gain and offset to get full frequency range.


PS.
If you have an interest or think your High School would be interested in starting a Solar Car project go to this link http://www.winstonsolar.org/challenge/photos/2003/Day1/Originals/day1_12.jpg This was the last car we raced. The process to raise funds, plan, build and then race a car against your peers is a great learning experience for kids. Our car was called Solar Stealth. We raced 1997 to 2003.
 

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This is how I have my inverter programmed:

Foot off throttle: Speed set point = 0 rpm
Foot on throttle: Speed set point = 8500 rpm
accel & decel ramp = 0.1 seconds

Throttle position 0->100% = Torque set point 0->150%

Even though the speed set point is 8500 rpm, you are limiting torque, so the motor will only spin as fast as the torque demanded will allow it to spin. (you may need to disable speed error alarms)

If you want a bit of regen drag when off the throttle then
Throttle position 0->100% = Torque set point -10% -> 150%

When I hit the brake pedal, Torque set point goes to -50%

When braking, once battery voltage reaches 350 volts, for every volt above 350, I reduce regen torque limit by 5%. This gracefully prevents the bus voltage from going too high.

When I was running v/hz mode, I too tried to catch a spinning motor. On my inverter it was called "fly catching". I couldn't ever get it to work properly. I also tried ramping stop instead of coasting stop. I kept a speed pot on my lap to control the speed of the car. The major down side is the inverter wants to follow a ramp down which may significantly increase your stopping distance, and if you ramp down too fast you will either over current, over voltage, or loose synch and start bucking.

You really need to get torque control working to make the car drivable. Older drives may have a torque control mode, but often times at low rpm it is still using v/hz mode with dc boost. Does your inverter have an auto tune?
 
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