# EV Conversion on a BMW Z3



## Yabert (Feb 7, 2010)

Hi

The 0-60 mph isn't a problem, but not with tight budget and long range. I think you will need to choose between 90 miles range and explosed budget or 40-50 miles and tight budget.

I think you can't choose AC because your budget is tight and you need good performance.

To have performance with a 1300 kg car, your DC motor will need to be supply by at least a 1000A controller. The Soliton 1 have good reputation and functionality (I have one..).
High voltage will be need if you need high power and it's why a Kostov K11 (or dual K9) or a Warp 11 HV will be good. 

But without a powerful battery pack, those powerful parts can't do anything. And all that will cost more than 10K$

The only way to reduce budget is by reduce performance.

An example here: http://www.diyelectriccar.com/forums/showthread.php/bmw-z4-conversion-kostov-ac-dci-60127.html


Good luck


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## mizlplix (May 1, 2011)

I might be wrong but:

Lithium batteries=8,000.00-10,000.00USD

Adapter plate/drive coupler=1,200.00USD

motor-controller-other small stuff=6,000USD

*Just a rough guess*....15,000-18,000USD total

To get the performance you wanted.

Miz


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## theFREElaker (Jan 17, 2012)

Yabert said:


> Hi
> 
> The 0-60 mph isn't a problem, but not with tight budget and long range. I think you will need to choose between 90 miles range and explosed budget or 40-50 miles and tight budget.
> 
> ...


 This all very helpful! Just for comparison's sake, do you know of any solid AC motor/controller combos that could deliver the performance i am looking for? I mainly want to compare price and performance just to get a grasp of what i really want. 
I was afraid that my budget was a bit low for my expectations but maybe that will give me some time to raise a bit more cash and double my research. 
Also, what brand and voltage/amp rating batteries am i looking at?


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## theFREElaker (Jan 17, 2012)

mizlplix said:


> I might be wrong but:
> 
> Lithium batteries=8,000.00-10,000.00USD
> 
> ...


 I thought that i would have to scrounge up some more cash  I assume that adapter plate/drive coupler cost is the combination of materials and pay for a mechanist? Is it better to go with a machinist so as not to risk screwing up the plate and messing up your motor? Or is it not that big of a deal, that i could have an experienced friend help me with the its fabrication?


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## DJBecker (Nov 3, 2010)

For estimation you should look at CALB cells.

One way to estimate the size of the battery pack is to look at your required performance, not the range.

The "standard" discharge rate is typically 0.3C. That means you need enough battery capacity for over 3 hours of driving if you want the advertised cycle life. Unless your expectation is a top speed 20MPH, that's a whole bunch of batteries.

The "maximum continuous rating" is 3C or 4C. This is how much current you can withdraw during a typical acceleration event e.g. from 0-60MPH. You'll need a pack large enough to provide the total horsepower you want. Despite "continuous" in the phrase, you can't count on extracting that much power for more than a minute. Using the cells close to this limit will significantly shorten their cycle life, but it's a tradeoff you'll need to make.

There is also a higher "burst rating" of 10C or 12C. That's the drag racing current. You can extract that much for a few seconds without structural damage, but it will dramatically reduce the cycle life of the cells. People drag racing might sell the pack after a 100 runs or so. You should probably stay away from batteries "almost new, used only a few cycles" available a slight discount.

Right now battery pricing is almost exactly proportional to the capacity. A 100Ah cell costs exactly 2.5x a 40Ah cell. So we can ignore the pack voltage when calculating the capacity and cost.

1KWh of battery costs about $400. That gives us 1KW at a 1C rate.

The motor and controller combination will have about an efficiency of about 75% for either AC or DC. We can estimate that it takes 1KW of battery power to get 1HP out.

So if the car takes 20HP to cruise at highway speed, we need a 20*$400 = $8K battery pack. That gives us a limit of 60HP for normal acceleration and climbing hills. That's (barely) acceptable, but a bit sad.

The good news is that you can briefly use the 10C rate, 200HP, and give an impressive show. Which is why every electric car demo always includes an acceleration, followed by a bit of talking to allow everything to cool down.


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## drgrieve (Apr 14, 2011)

I don't think that pushing a cell dramatically damages cycle life as long as you keep the temperature of the electrolyte under 60 degrees.

If you are building a track car instead of a commuter car then you should consider ways to cool the pack while driving or monitor temperature along with motor and controller temperature and limit the amps when any of these heat up near manufactures ratings.

I think most folks have the opposite problem. Batteries are too cold in winter and sag excessively and need to warm / insulate the pack.


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## tomofreno (Mar 3, 2009)

theFREElaker said:


> *BMW Z3*
> 
> My Expectations:
> -Range: about* 90 miles*
> -Acceleration: 0-60mph in about *6-7 seconds*


At what speed you want to go 90 miles? A $10k pack might get you that far in a 3000 lb car at 35 mph or less. An AC motor/controller package that will give the acceleration you desire will cost $15k or more I think - if you can get one. The 11" DC packages Yabert recommended would be around $ 6-7k I think, and are readily available. If you look around here a bit you will see almost everyone who wants the kind of acceleration you do uses DC for that reason. 

The (considerable) advantage of the higher voltage DC controllers is you can use a high pack voltage so that battery current is less than motor current, reducing the required Ah capacity of your cells. You can limit battery current in the controller software (and max controller output voltage so you don't burn up your motor). Power into the controller minus losses equals power out. So if you want say 150kW out and pack voltage is 300V (Soliton1 goes to 340V/1000A) you only need 500A from the battery pack, but can have the full 1000A output of the controller going through the motor at up to almost 150V input. This would be less than 3C for a pack of 180Ah CALB cells. 

Without such a higher voltage controller you are forced to use much smaller Ah cylindrical cells than can tolerate much higher discharge current as a fraction of cell capacity (like 10C rather than 3 or 4C). They are more costly per Wh energy storage and you will require a truckload of them to go 90 miles.


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## theFREElaker (Jan 17, 2012)

Well Ideally i would use this car to commute to college and back which is 40 miles one way with a speed limit of 70mph. I realize that the specifications that I had previously mentioned are quite intense, but i wanted an idea of what it would take (financially and electronically) to meet those. So basically what i am trying to figure of is:
a. How much would it cost to get a system that meets those specifications.
b. What kind of specs will $8-10k get me?
I also have a bit of time so i was looking for pointers so that i could research products and technical data to get a better grasp on the idea. So any info you guys have, throw it at me, cause im loving this


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## Bowser330 (Jun 15, 2008)

theFREElaker said:


> Well Ideally i would use this car to commute to college and back which is 40 miles one way with a speed limit of 70mph. I realize that the specifications that I had previously mentioned are quite intense, but i wanted an idea of what it would take (financially and electronically) to meet those. So basically what i am trying to figure of is:
> a. How much would it cost to get a system that meets those specifications.
> b. What kind of specs will $8-10k get me?
> I also have a bit of time so i was looking for pointers so that i could research products and technical data to get a better grasp on the idea. So any info you guys have, throw it at me, cause im loving this


Even an aerodynamic lightweight car will consume ~20kw @ 70mph....so assuming you will be consuming a bit more conservatively of 25kw @ 70mph =~ 350wh/mile, meaning for 50 mile range you will need a pack with 18kwh and for 100mile range 36kwh

The 180AH batteries others have been mentioning are you best bet, they are the cheapest per kwh. 200V * 180AH = 36kwh, so 200V, 63 cells @ 3.2V each =202V, 63 cells @ ~200$ each = 12,600$

Thats the cheapest price for 100mile range with a lithium chemistry (you should only really use 80%, so 80 miles range, after 80% depth you will be hurting the battery life)

DC is the best for performance per dollar, 6-7 seconds shouldn't be THAT hard to accomplish with a Warp11 & Soliton1 or Netgain Warp Drive....
http://www.evsource.com/tls_warp11.php
Motor: 
Warp11 3000$ (non HV)
Controllers:
Soliton1 3000$ (1000A peak & cont. ~ 320ftlbs**)
WarpDrive 4000$ (1400A peak ~ 460ftlbs**)
Zilla2KHV 5000$ (2000A peak ~ 550+ftlbs**)
** w/Warp11 motor

An untuned BMW 335i has ~ 320ftlbs of torque at the crank and can pull off a 0-60 in ~5 seconds flat with some grip....So with a Warp11 and even the Soliton1 a 0-60 in 6-7 seconds sounds reasonable to assume....if you don't achieve that, you can sell the soliton1 and go to a different controller.
So you're looking at 6000$ for motor+controller


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## theFREElaker (Jan 17, 2012)

Bowser330 said:


> Even an aerodynamic lightweight car will consume ~20kw @ 70mph....so assuming you will be consuming a bit more conservatively of 25kw @ 70mph =~ 350wh/mile, meaning for 50 mile range you will need a pack with 18kwh and for 100mile range 36kwh
> 
> The 180AH batteries others have been mentioning are you best bet, they are the cheapest per kwh. 200V * 180AH = 36kwh, so 200V, 63 cells @ 3.2V each =202V, 63 cells @ ~200$ each = 12,600$
> 
> ...


Wow this info is just grand!! Thank you so much for all the great responses! 
63 cells at ~12x7x4inches, will that be tough to cram into that tiny car?
Also, how much would a charger cost and if you have one in mind would you mind giving me a model so I can do some research? 

A few other random questions:
1. Is power steering a good idea? Or manual best way to go?
2. I talked to USAA about insuring a salvaged car that is an ev, but they won't cover the cost of any of the electrical components that I will have installed. So how do you guys deal with insurance?
3. Is a temperature management system a good idea for the batteries? Cause here in Kansas, temps range from 0-100 degrees farenheight?


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## somanywelps (Jan 25, 2012)

You want power steering and brakes for safety reasons.


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## charliehorse55 (Sep 23, 2011)

DJBecker said:


> The motor and controller combination will have about an efficiency of about 75% for either AC or DC. We can estimate that it takes 1KW of battery power to get 1HP out.
> 
> So if the car takes 20HP to cruise at highway speed, we need a 20*$400 = $8K battery pack. That gives us a limit of 60HP for normal acceleration and climbing hills. That's (barely) acceptable, but a bit sad.


Where did you get this idea? From what I've read:

AC - 95-97% controller, 94-96% motor, *total = 89-93%*
DC - 98-99% controller, 85-90% motor, *total = 83-89%*

Not a hugely appreciable difference between the two, but they are both well above 75%. 


Anyways, for an AC setup he'd probably need something like an AFM-140 and the tritium Wave200 Controller. Cost of around $10k for the motor, and $6k for the controller. Of course, it comes with a few advantages:

100 HP continuous
50kg total weight of motor + controller - Warp11 is 100kg by itself
Regenerative braking

It's still most likely not worth the cost, but in a 1300kg car it would give him 0-60 in around 5.5 seconds.


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## Bowser330 (Jun 15, 2008)

theFREElaker said:


> Wow this info is just grand!! Thank you so much for all the great responses!
> 63 cells at ~12x7x4inches, will that be tough to cram into that tiny car?
> Also, how much would a charger cost and if you have one in mind would you mind giving me a model so I can do some research?
> 
> ...


I would look into a DIY charger I know a lot of other members are working on them, I think paul holmes is working on a 6kw one, and Valerie has a 10kw charger DIY kit for 850$ not sure how much it will cost to get it built...if you find out let me know...
http://www.emotorwerks.com/emw3/product/complete-charger-component-kit-no-enclosure/


1. electrical power steering pumps from MR2 can be found for cheap
2. not sure, but contact other insurance companies and inquire on the costs, then call USAA back and let them know...they may change their mind to keep your business, all they have to do is have an appraiser check your receipts and value the vehicle, its not rocket science, they are just being overly conservative.
3. many people install those small computer fans on their battery boxes to turn on via a temperature switch/thermistor to circulate some air to keep things a bit cooler.


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