# Planning '86 BMW 325e (e30) conversion



## breadly (Apr 11, 2012)

Hi guys,
I'm in the early stages of planning a conversion of my beloved e30. Wanted to get your take on my plan as detailed.

About me:
I'm a mechanical engineer. I have some electronics / mechatronics experience (microcontrollers etc). I have free access to a machine shop with CNC milling capability as well as welding equipment. I worked on a hybrid car project in university (Ford's "Future Truck" competition), so i have a little bit of EV experience as well.

Goals for the project:
Range: My one-way commute is <5miles. This includes 1-2 miles at freeway speeds, but the highway can be avoided if i like. I'll probably have opportunity charging at work. I have an occasional need to drive ~ 30 miles round trip with a 2hr opportunity charge at the 1/2 way point. I have another gasoline vehicle for long trips, so range is not a crucial issue. My ideal vehicle would make the 30mile round trip @ 70-80% DOD.

Performance: My 325e is a little tired after 25+ years of service, but it still does 0-60 in ~ 9.5s. I'd really like the conversion to match or better this. Curb weight of the vehicle is ~ 2500lb stock according to the interweb.

Tentative Plan: 
Motor: I'm expecting a 9" DC motor will fit my budget. Need to decide if this matches my performance goal.

Transmission: I'd really like to go direct-drive to the differential. The Diff on the 325e is ~ 2.89:1 ratio. I've seen other DD e30 conversions in the "garage" and on evalbums but I've not gotten a clear picture of what the performance would be like with this diff and a 9" motor. My transmission has problems with the main bearings as well as worn synchros, so if it can be scrapped, I'd really like to. I think ditching this weight will help towards my performance goal, while going DirectDrive is going to counter it. Any thoughts on this?

Controller: I expect that to get the performance I want, I'll need 500+ Amps to the motor. Probably more like 750? I'm leaning heavily towards building an OpenReVolt, but the 1000A version is still in "beta". I have no issue with assembling the controller from a kit, I'm less enthusiastic about etching my own boards etc.

Batterie$: This is the tricky part. I'm not looking for a dramatic range, but I would like the car to be pretty zippy. Other e30 conversions list their power usage at ~ 300wh/mi, so I expect my once-a-week 30mi drive to only need ~12kWh pack capacity. This would put me into a cheap PbA pack, but I'm not liking the weight/ lifetime prospects. Not sure if it makes sense to do LiFePo4 in my budget, but with this light capacity, it may be OK. Would love to build the system to be "expandable" and add a second pack in parallel to increase range after initial build has been driven for a while. I'm planning on 144V.

Instrumentation: I have an Arduino that I've not used for anything else yet, so I may build / program my own SOC panel to save some $$ and learn something new. Any tips on this?

Timing: I'm in no hurry. Expect I'll acquire components slowly over the next 6-10mo and do the conversion after the kit is compiled. Want to have fun building it and definitely want the car to be a "fun" drive when it is completed. I drive the e30 every day, but i have another car to drive while the conversion is underway.

What do you all think of my plan so far?

-b


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## somanywelps (Jan 25, 2012)

1x 9" is probably not suitable for direct drive. Certainly not 0-60 in 10s (and certainly not with lead-acid).

I would do 1x 11" (or 2x 9" to keep up the RPM).

You do not want to use lead acid.


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## breadly (Apr 11, 2012)

somanywelps said:


> 1x 9" is probably not suitable for direct drive. Certainly not 0-60 in 10s (and certainly not with lead-acid).
> 
> I would do 1x 11" (or 2x 9" to keep up the RPM).
> 
> You do not want to use lead acid.


Agreed. No PbA. I'll be trading the cost vs range on a LiFePo4 pack, but I don't see that as a problem given my needs.

The thing I'm having trouble with is finding the real performance specs to compare these 9" and 11" motors. For example, all of the NetGain data is published at a 72V test range. This doesn't help me when I'm planning a 144V conversion. Anyone have ideas where to get good Apples-to-Apples data for motors?

-b


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## mora (Nov 11, 2009)

72V data gives you idea how that motor will behave at 144V. At given load your rpm will double if you use 144V instead of 72V (might not actually double but should be somewhat close). Torque is held longer to higher rpms. Increasing voltage will not give low end torque, unless you go for 300V pack and limit motor voltage.

You don't have to etch any pcbs for any OpenRevolt project. That would be hardcore but doable. You can buy all the pcbs needed directly from Paul. You can source components and other hardware elsewhere. But I agree, waiting until beta is over and 1000A unit is stable sounds good.

I believe you need 1000A capable battery pack to accomplish your acceleration goal. 200Ah bricks will do 1000A (5C). Even 100Ah prismatics might do it but voltage sag will be horrible. Batteries with higher C-rating might solve amp issue but costs will go up too.


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## drgrieve (Apr 14, 2011)

Hi - for a while I researched doing a E30 conversion. I changed my mind and are now looking at a E46 conversion (also direct drive).

The 325E was on my list as a good candidate if keeping the transmission as stock the engine is very low RPM and matches very well to a DC motor.

For direct drive not so good. You want a diff in the high 3 to low 4 range. You could source one (maybe even LSD!) or buy a different donor. But I guess no harm in trying your current ratio as you can swap it out later.

See here for the ratios available (http://e30world.com/specifications/BMW-E30-specs-table

I use this site for determining RPMs with different ratios http://www.bokchoys.com/differential/e46_gear_ratio_calculator.htm. Remembering your power will start to drop off (depending on how high your voltage is) between 3000 and 3500 RPM.


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## CrunchTime (Feb 13, 2009)

breadly said:


> Instrumentation: I have an Arduino that I've not used for anything else yet, so I may build / program my own SOC panel to save some $$ and learn something new. Any tips on this?


If you;d like to keep the stock instrument cluster, you could check out the EVWorks Fuel Gauge Driver+ - it is known (by EVWorks) to work with the E30 fuel gauge, and I like the ability to display Amps on the Rev counter as well - I upgraded from the FGD to the FGD+ just to get that ability 

Although mine is an E36, and not on the road yet, although I've had it all working on the bench...


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## drgrieve (Apr 14, 2011)

Now for determining required torque and power.

As a guesstimate for required power to match or better stock you need battery peak power to be close to stock. Your 325E is 121hp which is ~ 90 kw.

For a calb 180ah that sags 25% at 5.5C (1000 amps) you would need 90/5.5*1.25 = 20.5 kwH pack. Which is only 36 cells. The pack voltage (115v) would be too low for RPMs.

For a Calb 100ah that sags 25% at 8C (800 amps) you would need 90/8*1.25 = 14kwH pack. This would be 44 cells. But I think that the pack voltage would still be too low. I would be more comfortable recommending 60 cells. For 192v and 19KwH and 120Kw peak battery output.

If you use a forced air blower a single warp 9 should be ok, but if you live in a steep area maybe a warp 11 would be better (still with forced air due to extra motor amps requirement for direct drive).

Torque - peak torque from stock is 127 ft-lbs. For adequate performance I compare to second gear. This would be 2.20. So you need around 280 ft-lbs. 

As it happens at 1000 motor amps a warp 9 will make around 270 ft-lbs. See here http://jackrickard.blogspot.com.au/2011/04/graphs-is-always-greener.html

To make 1000 motors amps I would recommend a Soliton 1 using liquid cooling (due to extra motor amps needed for direct drive)

So $$$. 20 kwH pack of Calb = 20000/3.2*1.20 = $7500. Soliton 1 and Warp9 = ~$5000.

This would work and give your the performance you want and last. You can save money with other alternatives but I would question the long term reliability.

Good luck!


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## breadly (Apr 11, 2012)

I'm in agreement about the battery pack power requirements (~ 90kW) but will probably down-scale a bit from your recommendations in the interest of cost.

I'm thinking of the following:
144V pack (45Cells at 3.2V ea), 100Ah LiFePO4. Try for some 10C cells for when I really stomp on it (1000A) probably use them at 6C most of the time (600A).

This gives: 
115V(sag)*1000A = 115kW
OR
115V(sag)*600A= 70kW (not as peppy as I'd like, but usable)

Range wise, I'd expect 144V*100Ah= 14,400 Wh. At 80%DOD, this gives ~11.5kWhr. With an expected consumption of ~ 300 Wh/mile i should be on the order of ~ 35-40 miles of range on a single charge.

w/ 45cells @ 100Ah ea *$1.25/Ah = ~ $5,400 (palatable for me).

As far as the motor is concerned, I like what i'm seeing from the forced air cooled Warp9. In my instance, probably a "TransWarP" so i don't have to muck too much with the drive-line interface. Mounts etc can be fabricated, so i'll be on my own there. I see from the link you provided that driving the W9 at ~ 1000A and 200V gives a monstrous 270 ft-lbs of torque. This easily gives the "2nd gear" feel I'd want with a direct drive application. Not sure how a de-rated system at 144V and 600-1000A will feel. Worst case scenario is a differential swap. If i don't like the performance with my (relatively low) 2.93 final gearing, e30 diffs are available all the way up to 4.10 as a swap-in replacement. This should let me re-claim the off-the-line performance I might lose with a lower voltage and possibly reduced current limit.

As far as the controller goes, I love the looks of the Soliton, but am not sure if i can stand paying the $3295 MSRP for this baby. The zilla 1k is only (ha!) $1975 by comparison. Any reason I want my 1000A to cost another 1.3 kilodollars? On the low end of the spectrum is the Open ReVolt at ~ $600 for the kit. Still not sure if I'd rather get the experience and savings of a DIY, or get the reliability of an off-the-shelf...

This is fun!


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## drgrieve (Apr 14, 2011)

Reducing pack voltage won't affect your off the line performance - it will reduce the effective RPM range. Instead of power dropping off at 3500 RPM at 115 volts it would drop off at 2500 RPM (not accurate just an example).

Perhaps look at going with a 60ah cell (Calb or maybe Sinopoly [which on manufacturer specs looks better than Calb for the 60ah]) so you can keep voltage higher if you need to be able to accelerate decently (safely!) at highway speeds.

Running at 600 amps (motor amps not battery amps) would approximately cut ft-lbs 270 * 0.6 = 160. This would be like 3rd gear. Doable but you won't do your stock time.

You won't be able to use a large format cell at 10C for more than a second. 8C is hammering the Calb 100ah cell pretty hard. You'd need to look at headway cells or A123 for high performance (and difficult assembly) in a small pack.

In regards to controllers - well you get what you pay for. The Soliton1 at 300kw continuous is future proof if you decide to add more cells or put in a psycho pack later on . The Zilla 1LV is a bit low voltage look at the Zilla1k HV. Not sure what it's continuous rating is.

I haven't heard anything bad about the Zilla in reliability terms (you should check on that) just the design is old (not sure of the implications of that) and it doesn't come with inbuilt pre-charge (so you need to buy contactors and build that yourself) and I'm fairly sure it doesn't have the option of water cooling - so you might having trouble with overheating (again you'll need to check to see if that would be a problem for you) in a direct drive (read high motor amps) build

Perhaps the cheaper option for a lower budget is to replace the transmission. Then you can use something like the Soliton Jr and a Kostov K9 220v in combination with Sinopoly 60ah cells using a smaller budget pack for now and then extending it later for some EV performance.


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## breadly (Apr 11, 2012)

With a 2.93 differential and 195/65-14 tires on my e30, The motor will only spin ~ 2500 rpm at 60mph. 3000rpm pushes me up about 73mph.

Is there any reason to expect that i won't be able to get 2500-3000 RPM out of a Warp9 with 144V (or ~ 120V sagged)? Can anyone point me to a reference?

If I can push 1000A at 120-144V, I expect that this setup will give me something like the performance I want. I'm open to discussion to the contrary...


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## breadly (Apr 11, 2012)

Digging through this a second time, i see that drgrieve and i made a bit of a mistake. The stock torque of a 325e is ~170 lb-ft, not 127. This means that for 2nd gear (2.2 ratio) performance, I need a peak torque of 374 lb-ft into my differential. This is probably not achievable with a Warp9.

Options: leave the transmission in (yuck), swap the differential for a 4.11 (hmmm) or find a motor with 374 ft-lbs of torque (unlikely) ...

I think the diff swap is my favourite of the options. the investigation continues...


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## shoup (Feb 10, 2009)

I would recommend keeping the transmission just to give yourself more flexibility. I picked up a good used Getrag 260 for one of my cars for $150. I don't shift much in my E30, but when I do I'm glad I can. The higher ratio LSDs tend to cost a bit more than a used transmission. 

I have lead acid in my car and it feels heavy when stopping and cornering. I could not commit to the costs of a LiFePo4 pack when I didn't even have a running car. When my PbA batteries wear out I will make the switch.


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## Yabert (Feb 7, 2010)

breadly said:


> I need a peak torque of 374 lb-ft into my differential. This is probably not achievable with a Warp9.


Maybe not with a Warp 9, but with an 11'' motor and 1200A controller, 380-390 lbs-ft of torque is achievable.
And seriously, do you really apply full throttle in second gear when you accelerating?

Direct drive it's not a bad alternative if you don't need really high top speed.


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