# Planning my first build on a BMW



## mons2b (Nov 17, 2015)

Im always interested in someone looking at converting a BMW. Its the less frequent choice. Myself I snatched a e36 for my project. Its going slowly. I learn things as I go. 

If you want to make your life a bit easier I suggest you also go for the e36 generation as you will have less complication with getting the gauges to work and they are reasonably light. 

It looks like you might have a better budget than me but keep in touch as I would be happy to share what choices ive made and what my ideas are.


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## Roderick (Dec 8, 2013)

> I'd like to build something a bit future proof, and ultimately quick, that I can upgrade as battery tech improves, or I want more power/range.


I Have similar idea with my build



> For a chassis I want something comfortable and am thinking of a BMW 3 series (Today, I have the E46 in my head!) as it's a good size, and a nice chassis, but not fixed on that. I Know it's a bit heavy for a first car. (Though I am following Damien Maguire's drift car build with interest)


if you want to keep it for a long time, best choice is to always go for the car you love to drive. (that way you will take care of it and wont have a second thoughts)



> My biggest problem at the moment is that I've nowhere to work, so that's a problem I've to fix first. I may have to build that first!


I didnt have a place first but there should be local garage or even sublet garage that you can use to work on your car.



> For range, 100+ miles range would be nice. As for performance, I'd like something quick, roughly equivalent to 150-200hp internal combustion.


good choice, I'd say DC 11" motor. (you can always upgrade in future.)



> I'd really like peoples opinion on what would be a reasonable budget? or if you would get to this point differently?


with 100miles of range with BMW, I'd say spend 25k USD or more. 
Take a look at EV album, There, you should be able to find specs and components you desire for your build and if lucky, web site to go with it.

Best of luck!


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## Duncan (Dec 8, 2008)

Hi Gromit
Where are you?
Always useful to fill in your location

A guy in Kansas city is looking at picking up an 11 inch cheap - is that close?

(second to last page on this thread)

http://www.diyelectriccar.com/forum...orklift-motor-and-choosing-good-7598p217.html


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## Gromit (Mar 29, 2016)

Ah, thanks for the replies so far. I'm in Ireland. The car building centre of the world - not 

I've been reading up a bit more on a few builds (some great reading on this forum) and have probably been a bit over-optimistic on my performance requirements in terms of budget, but it'd be nice to get to those figures in the end, but for starters it will be more modest. I reckon the most important thing for a first build is to actually finish it!

Completely agree about building on a nice car to keep the enthusiasm up. (I once bought a very cheap Renault van and God did I hate every minute of sitting, driving and looking at that thing. I was never happier when it finally let a whole bunch of steam out its head  )

As the battery pack seems to be the most expensive, right now, I'm thinking to take some time and try and find a crashed Leaf locally and get the batteries. Shipping heaving things to Ireland is expensive.

If the right well-spec'd (with blown-engine or resellable-engine) BMW comes up for cheap I'll get that - or something similar. There are quite a few 10 - 15 year old e46s here for around the €1000 mark or less.

Once I've gotten that far, I might have learned enough to figure out motor/controller options?


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## Duncan (Dec 8, 2008)

Hi Gromit

If you find a crashed Leaf it may be a good idea to try and get the whole car,

Then you will have everything you need to convert to EV - and you may be able to sell on the bits you don't need


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## Gromit (Mar 29, 2016)

Duncan said:


> If you find a crashed Leaf it may be a good idea to try and get the whole car,
> 
> Then you will have everything you need to convert to EV ...


Interesting. OK, what else would be useful? BMS? Controller? Charger? Motor?

Do things like a BMS work if the pack is reorientated to a different voltage or if I have say 1 & 1/2 cars worth of Leaf batteries in the future?


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## Duncan (Dec 8, 2008)

Hi Gromit
There are two ways to go
You basically use the whole Leaf setup - and all of the electronics thinks it's still in a Leaf
Relatively easy - but less flexible
If you had two sets of kit you could have 4WD and a long range

The other way is to spoof the electronics - some of the guys on the forum are working on this sort of thing
Replace the relatively cheap "brain boards" and keep using the expensive power electronics
A guy on the forum called "eldis" in Switzerland is working on that


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## Gromit (Mar 29, 2016)

Duncan said:


> You basically use the whole Leaf setup - and all of the electronics thinks it's still in a Leaf
> Relatively easy - but less flexible
> If you had two sets of kit you could have 4WD and a long range
> 
> ...


Cheers for the info. I was reading up on it and saw the video of the entire Leaf functioning on a peg board. The lack of flexibility and upgrade route puts me off that slightly though. 

I saw however that the DC-DC converter is pretty easy to control over CAN, which is something I'd tackle. Cool, more to think about and read.


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## Gromit (Mar 29, 2016)

Hello All,

So, I've been trying to get my head around the most common routes of doing this conversion. I realise that D/C would give better performance, but am also considering the A/C numbers. I also like minimal wearing parts!

If I go with an AC-50 and the Curtis controller, I can run at 72, 96 or 144v.

So if I were to use a Leaf pack, 20 modules in series = 150V (which I assume is ok for 144v?) which is 10kWh, 2 of these in parallel = 150v 20kWh and I've 8 modules left over.

Could someone guestimate what sort of range and performance I could expect with a 1400kg (3000lbs) doner car with this setup?

Would I be better with 60 modules from 1.5 leaf packs?
Or a different motor or controller?

Many thanks for your help.


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## Moltenmetal (Mar 20, 2014)

The Curtis 1238 controller which is rated 96V can actually handle a peak voltage up to 130 V.

A 3000 lb car will take about 300 Wh/mile driven. So take your range- say 50 miles- and work it out as follows: 50 miles x 300 Wh/mile /0.8 (you never want to take your pack below 80% depth of discharge- 70% is safer still) and you would get 18,750 Wh or 18.75 kWh- a little more than one Volt pack, or about 2/3 of a full Leaf pack, and just about spot on what I have in my E-Fire. Then you work the series/parallel connections possible with the type of cells or pack fragments you have available to you, to figure out what combination of cells will give you the capacity you need within the voltage you need. 

Any pack of that capacity is going to likely fall within the 650A limit of the Curtis 96V controller for bursts under 2 minutes duration. But if you go with the 144V 1239 controller, be aware of two things: 1) That controller is limited to 500 rather than 650 A so the low end torque isn't as good, and 2) If you go higher voltage, i.e. a larger number of smaller capacity cells in series, you may challenge the upper C rate limit of your cells because you won't have enough of them in parallel. That can be hard on them, causing some self-heating and of course a loss of voltage and hence power as well.


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## Gromit (Mar 29, 2016)

Moltenmetal said:


> The Curtis 1238 controller which is rated 96V can actually handle a peak voltage up to 130 V.
> <snip>


ok, thanks for all the info MM. Thanks makes sense. So the better route is to configure for a lower voltage. Pity I can only use 2/3 of a Leaf pack. (There aren't any Chevy Volts here) 

Any idea how to calculate the expected performance? I'm still debating the whole A/C D/C thing


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## Moltenmetal (Mar 20, 2014)

Do some research here and you'll find out about the DC performance. DC motors pulling 1000 A are no sweat. So you can do almost 40% more torque with a DC setup at the same voltage- if you want performance, DC is the way to go. But again it comes with compromises as I noted earlier.

For the AC units, the HPEVS curves for each motor and controller/voltage combination are posted. The data is reliable and should tell you all you need to know. For instance, I never use the clutch to take off- only to switch gears. When I step on the accelerator, I am rewarded with acceleration that my Spitfire never had before- not even with its 2.2L Celica engine. Sure that 2.2L could crank out the same torque as my AC50 can, but not until it was up above 3,000 rpm- the AC50 does it from 100 rpm! My top speed is higher than I would ever feel safe driving the car, and far faster than the law around here allows. How much more performance do you want or need? That's a personal question, and of course depends on the weight and Cd and rolling resistance of your selected donor vehicle.

I wouldn't conclude that you only need 2/3 of a Leaf pack: you need to work the series-parallel combinations of those cells that will give you both the voltage and Ah capacity you need. Leaf packs consist of nice separate modules which are already prewired in a 2S2P configuration, unless I misremember- unlike others here, I've never bought one. I don't recall how many Ah each module is- you can look it up in the Batteries forum easily enough. You may need to parallel these modules (going 2S4P or 2s6P by wiring 2 or 3 modules in parallel, then stringing those modules in series) to give you a pack with the capacity you need while staying under the voltage limit of the Curtis controller.

If you go DC, some of the controllers can handle higher voltages as well as higher currents. Current times voltage is power- assuming the motor you've selected can handle that power without melting. That makes transmissionless conversions an option for DC conversions, but doing that with a HPEVS/Curtis setup would be disappointing for most people.

Going lower voltage is something the OEMs don't like to do for many reasons- efficiency decreases and copper and semiconductor costs go up as you drop the voltage. But there are a few benefits to lower voltage for a DIY: one is safety or mental comfort for someone who has a rational fear of HV DC. Another is reduced BMS parts count- each group of paralleled cells only needs one BMS channel or celltop board because it's effectively one cell of larger capacity. Another is the absence of a high voltage boost stage in your charger. But you do need heavier wire and your ohmic losses will be worse irrespective of the wire you select.


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## mons2b (Nov 17, 2015)

Moltenmetal said:


> The Curtis 1238 controller which is rated 96V can actually handle a peak voltage up to 130 V.
> 
> A 3000 lb car will take about 300 Wh/mile driven. So take your range- say 50 miles- and work it out as follows: 50 miles x 300 Wh/mile /0.8 (you never want to take your pack below 80% depth of discharge- 70% is safer still) and you would get 18,750 Wh or 18.75 kWh- a little more than one Volt pack, or about 2/3 of a full Leaf pack, and just about spot on what I have in my E-Fire. Then you work the series/parallel connections possible with the type of cells or pack fragments you have available to you, to figure out what combination of cells will give you the capacity you need within the voltage you need.
> 
> Any pack of that capacity is going to likely fall within the 650A limit of the Curtis 96V controller for bursts under 2 minutes duration. But if you go with the 144V 1239 controller, be aware of two things: 1) That controller is limited to 500 rather than 650 A so the low end torque isn't as good, and 2) If you go higher voltage, i.e. a larger number of smaller capacity cells in series, you may challenge the upper C rate limit of your cells because you won't have enough of them in parallel. That can be hard on them, causing some self-heating and of course a loss of voltage and hence power as well.


Hi Molten

I want to use 144v with a AC motor that is 400amp max. I will be using 350amp fuses though as per the suppliers recommendation. With a 2012 Volt pack to get 144 I can do 3x48v modules then parallel another set of three. That will leave some modules I cant use. I want to achieve a comfortable 50KM per day weekly all year round. What are your thoughts please? My car is a older BMW than the one planned here for various reasons.


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