[boznz]

I will attempt to document my EV Conversion of my 1998 BMW 528i E39 in this thread over the coming year.

The actual car is below. I also purchased a second identical vehicle (year,make,color,engine,transmission etc) in case I require parts and to compare systems after I have removed the old engine. The cars were NZ$1900 and NZ$1600, ie about US$1000 each, both are in test, clean, mechanically sound, and, aside from a few minor wear and trim issues run great.

http://rodyne.com/wp-content/uploads/2018/10/872337940.jpg

My intention is to keep the total budget for whole project (including the buying of all donor cars) to under NZ$20K. I have now bought most of the hardware and tools I need to do the conversion and I still have approximately $5K left for other tools, engineering work etc. I intend to finance the build by no longer buying the Tesla Model 3 I reserved and I will be putting the remainder of my "Tesla Money" in to building a new garage/workshop where I also intend to do the actual conversion.

The Current Plan (which is close but still keep changing as I get more information and advice), is to directly replace the engine, engine management system, transmission and transmission control system, cooling, exhaust and fuel systems with a 55KW permanent magnet AC Motor directly driving the rear axle using the existing prop shaft. This wont be a performance build, I just want to learn the process and at the end have something for my daily 50KM flat commute. I will be using a motor controller based on Paul Holmes open source design, and a battery unit, charger and as much else as I can salvage from a collision damaged 2015 Nissan Leaf I recently purchased at auction. It is likely other BMW peripheral systems such as the ignition system (key/immobiliser) A/C, heating and some of the hydraulic systems for brake and steering will need to be changed to get the system to work, also a lot of signal-faking to let the BMW dashboard know all is still well despite most of its bits being at the local scrapyard! As an Electronics Engineer and Programmer and look forward to these bits the most.

The major work wont start until I get my workshop built, possibly after Christmas, the things I will be doing before then is stripping down the Nissan Leaf and assembling most of the EV components on the bench to check they will work. I intend to update this thread as I progress and also parallel document the build at my company web site.

I expect the conversion to realistically take 6 to 12 months as it will need to fit around my work commitments (plus, lets face it, I am a total newbie!).

A Lot of friends and colleagues have expressed support and interest and if all goes well I plan to help other people and businesses in my area do the same.

 

[brian_]

175 Nm of torque, multiplied by the 4.1:1 final drive ratio, divided by the 0.324 m tire radius, means 2215 N of drive force. With a 1320 kg curb weight, that's about 0.17 g acceleration. "Sedate" would be a generous term for this.

The stock engine puts out up to about 280 Nm of torque, and is multiplied by the lower transmission gears, so this is a small fraction of the stock performance.

The motor can run up to 8000 rpm and can't produce its full rated power until 3000 rpm, but that gearing means those correspond to 238 km/h (@8000 rpm) and 89 km/h (@3000 rpm). So in normal driving, the motor is rarely given a chance to perform properly. The motor is just not well suited to driving the final drive directly, without an extreme final drive ratio. If you could get an 8.22:1 final drive (and you can't), you could get twice the acceleration up to 45 km/h, without losing any performance above that; you would have a 120 km/h top speed due to the motor speed limit, but you won't be able to reach that in a reasonable time anyway.

A typical production EV with a motor of similar speed specs (and usually much higher power) runs at least 6:1 overall reduction.

 

[boznz]

Thanks for the feedback,

This is about the same as the 0-100KM in 18 seconds I calculated, slow, but faster than the 24 seconds I've been timing myself at up to that speed. My commute is a flat/quiet country road with some small town driving and I barely see another vehicle until town. I also based the choice of direct drive on the fact that a lot of the EV conversions's of similar weight and power seem to happily start off in 3rd gear with no apparent issues and I really would like to do a direct drive if possible.

You are right however in one sense, that is most people who do ride in an EV now expect much better performance than the ICE equivalent, and I may not be up-selling the idea to many people if I run a snooze-mobile. So I will have a think on this, I have a few months before the car goes under the butchers knife.

Food for thought as they say.

 

[Emyr]

Have you watched @jackbauer's YouTube vids about his 5-series conversion?

 

[brian_]

175 Nm of torque, multiplied by the 4.1:1 final drive ratio, divided by the 0.324 m tire radius, means 2215 N of drive force. With a 1320 kg curb weight, that's about 0.17 g acceleration...

This is about the same as the 0-100KM in 18 seconds I calculated, slow, but faster than the 24 seconds I've been timing myself at up to that speed.

Accelerating at 0.17 g for 18 seconds would result in 100 km/h, but that rate of acceleration is only at the instant of starting from a standstill. As soon as the car is moving it has drag, which will take some of the power (and more as it speeds up) resulting in significantly lower acceleration, so even 24 seconds to 100 km/h seems very optimistic to me.

 

[brian_]

You are right however in one sense, that is most people who do ride in an EV now expect much better performance than the ICE equivalent, and I may not be up-selling the idea to many people if I run a snooze-mobile.

I don't think it's realistic expectation to expect "much better" performance from an EV. Tesla cars are quick, but so are all $100,000 cars; the rest of the worlds available EVs have modest performance, not better overall (and often slower) than engine-driven cars of similar size and type. Single-speed EVs respond quickly to the accelerator pedal (no need to shift to a lower gear), and usually have good low-speed acceleration, but they usually lag before highway speeds; they just don't have enough power. The pre-2018 Leaf is a good example: everyone likes the low-speed acceleration, but 80 kW (107 hp) just can't keep up with lighter (due to the lack of the big battery) cars with at least 50% more power.

The performance likely with this planned project isn't just not "much better" than the gas engine car... it's much, much worse.

On the other hand, most cars have far better performance than they need, and much more than people use. I'm sure that most drivers have never used the full power of the car they are driving.

 

[boznz]

Hi Brian

So I would need something like this ? http://rodyne.com/wp-content/uploads/2018/10/ev-reduction-gear.jpg

 

[boznz]

Have you watched @jackbauer's YouTube vids about his 5-series conversion?

Been ploughing through some of Damien's videos over the past few weeks, the guy makes it all look so easy, however he didn't have much success with auto boxes, I would have liked to see him try the auto box without the torque converter, everyone says its unnecessary but I cant find any reference to anyone who has done it! Manual is not an option as the wife and daughter cannot drive them and refuse to learn and as you can see from my first post I'm no speed demon.

 

[brian_]

So I would need something like this ? http://rodyne.com/wp-content/uploads/2018/10/ev-reduction-gear.jpg

Yes, a reduction gearbox like that would match the motor to the required operating speed range. One challenge with that design is that it offsets the motor, so it can be hard to fit in a limited space (such as the transmission tunnel). It does appear to meet the torque and speed requirements.

Another option is the ev-TorqueBox, which is well suited to this vehicle configuration, but has more capacity than required (it was designed for pickup trucks) and is expensive.

 

[brian_]

... he didn't have much success with auto boxes, I would have liked to see him try the auto box without the torque converter, everyone says its unnecessary but I cant find any reference to anyone who has done it!

There have been lots of ancient Powerglide transmissions converted for EV use, including some without the torque converter. They are commercially available... but they're also expensive and massive: Powerglide 2 Speed Direct Drive Transmission for EV Motors - EVGlide. Removing the torque converter and keeping the transmission functional might be more difficult with more complex transmissions.

 

[boznz]

Another option is the ev-TorqueBox, which is well suited to this vehicle configuration, but has more capacity than required (it was designed for pickup trucks) and is expensive.

Thanks, the torqueBox looks bullet proof and may be preferable to the Chinese copy or "welding out" the torque converter. I got in touch with the company in China anyway just to see the price.

On a brighter note, my Salvaged Leaf turned up this morning, I put the charger on the 12V battery and lots of red lights but it drives! Battery says its low so I need a mains charger then going to have to source an older ODB2 bluetooth adaptor to get leaf spy and some diagnostics going to see how the battery is, but looking good so far. Lots of learning to do!

 

[Duncan]

Hi boznz

If I was you I would sell that motor on

You have a much better motor and final drive in the Leaf you just bought!

Fitting it in the front of the BMW would be easy but drive the wrong end - I would try and put it in the back

That would give the whole engine bay and transmission tunnel for your batteries

And some people are extracting 300 hp from that unit

On a different note
Have you contacted your certifier yet? - I have a feeling the only one on the Mainland is in Dunedin

Have you got a copy of the NZ Hobby Car Manual ? - AKA "The Bible"

 

[brian_]

I wondered why not use the Leaf motor, given the use of other salvage Leaf components. The Leaf motor has twice the continuous power rating of the proposed motor, although it would need the entire Leaf battery pack to reach the voltage required for full power over the full speed range.

The assembly of motor and transaxle (reduction gears and differential) is sometimes called a 'drive unit'. The problem with putting the entire Leaf (or similar from another EV) drive unit in the back of the car are that:

1. the small space for the suspension and final drive unit is far from large enough (in height) for the motor and transaxle, especially if you keep the inverter on top of the motor; and,
2. the E39 rear suspension is a multi-link design which is not designed to accommodate an engine or motor and does not have a lot of width available between the control arms, so the drive unit (which places the motor transversely) is probably too wide to fit in.

In this particular case, the rear suspension subframe is a massive aluminum structure - it doesn't look really friendly to massive DIY modification.

We've seen a few people try to put drive units in the back of cars which started as rear wheel drive, using the car's original suspension. There has been if any little success other than with Tesla drive units (which place the motor behind the axle, unlike the Leaf) and semi-trailing arm suspensions (like the E34, not the E39).

 

[MattsAwesomeStuff]

We've seen a few people try to put drive units in the back of cars which started as rear wheel drive, using the car's original suspension. There has been if any little success other than with Tesla drive units (which place the motor behind the axle, unlike the Leaf) and semi-trailing arm suspensions (like the E34, not the E39).

Is there a particular place that describes this thought process and the common constraints of motor mounting with respect for suspension types and OEM EV orientations?

I feel like it's sort of a common question people have been having and it doesn't seem to be something very well described anywhere so people keep describing things for their one situation.

In my head there's a little "I dunno I'll just make it work" placeholder that skips over this whole topic entirely, especially with respect to what kind of donor car I might look for and what different things might limit me to. RWD with a forklift motor up front is a pretty universal solution, but perhaps the least elegant especially with all the OEM options available nowadays.

Like, if I'm going to spend $5-10k on a conversion, I wonder if I'm going to regret "saving" $1000 on a cheap motor and the simplest solution rather than go with something fancier.

Anyway, it seems like the kind of thing that could be written thoroughly, once, and updated maybe once a year and get everyone 95% of the way to navigating this part of their build decision-making process.

 

[Duncan]

Hi boznz

My tuppence worth

Get the complete Leaf front subframe and suspension with the motor drive unit in it

Sit that down - chocked so it sits "right

Get the arse of the BMW high in the air
Unbolt EVERYTHING that unbolts -

You will be left with
some visible "hard points" that all the BMW bits bolt onto
Some structural "rails"

And a lot of sheet metal

get some cardboard boxes and mock up the Leaf drive unit

Try and convince yourself if it is a forlorn hope or if you have a chance of it fitting

Think of how much you love your BMW

At this point you can
Give up the Leaf idea
Bite the bullet and Cut the sheet metal - cutting away the rails and hard points only if necessary

Go and get another old BMW shell to experiment on and leave yours until after you have made most of the mistakes

The ideal situation is when you can cut away the sheet metal and get the Leaf unit in there then make a subframe (or several) to go from the Leaf Subframe to the hard points on the BMW

 

[brian_]

Is there a particular place that describes this thought process and the common constraints of motor mounting with respect for suspension types and OEM EV orientations?

I feel like it's sort of a common question people have been having and it doesn't seem to be something very well described anywhere so people keep describing things for their one situation.
...
Anyway, it seems like the kind of thing that could be written thoroughly, once, and updated maybe once a year and get everyone 95% of the way to navigating this part of their build decision-making process.

There isn't a single location or a general treatment that I know of. There is the Wiki section of this forum, which is supposed to be reference material, but it isn't managed in a way that makes it useful... topics just dissolve into disorganized conversation.

I doubt a stable reference is a practical goal, and consensus is unlikely. If anyone wants to produce their own, host it elsewhere, and link to it when the topic comes up in discussion, that would be one way to maintain one point of view on the subject in a rational manner.

In my head there's a little "I dunno I'll just make it work" placeholder that skips over this whole topic entirely, especially with respect to what kind of donor car I might look for and what different things might limit me to.

I think a lot of people do that. There result is stalled projects, and projects that throw away the original components and get very different ones. There are also "interesting" results, such as the 8-series BMW downgraded from a modern multi-link suspension to semi-trailing arms to make the drive unit installation feasible.

It would help in planning if people just had the key dimensions of the drive units that they are considering, and access to the bottom of their potential donor while holding a tape measure. Some imagined installations are pretty clearly unworkable with just the basic dimensions considered.

 

[brian_]

Go and get another old BMW shell to experiment on and leave yours until after you have made most of the mistakes

I like that idea.

The ideal situation is when you can cut away the sheet metal and get the Leaf unit in there then make a subframe (or several) to go from the Leaf Subframe to the hard points on the BMW

That leads to either using the Leaf suspension (which might be feasible, but consider that it has McPherson struts to accommodate), or custom-building a suspension (hopefully with mostly parts original to the base vehicle).

It isn't a Leaf drive unit, or a BMW car, but an example of one extreme of this sort of adaptation is this project which inserted a Tesla drive unit and complete subframe with Tesla suspension into a Nissan Skyline:
Tesla Powered Nissan r32 skyline
The builder had been planning to use a Leaf drive unit in the rear of the car with the original Skyline suspension (which would be similar to putting a Leaf drive unit into the BMW with the original BMW suspension), but he decided that was not feasible so he used a lot more of the Tesla Model S. This involved building a tubular steel structure to connect the Tesla subframe to the Skyline body, and mounting the Tesla struts to the body as well.

 

[brian_]

boznz, if you are considering putting a whole Leaf drive unit in the back (rather than mounting a motor in the transmission tunnel), you might be interested in this project with a 1973 BMW 2002:
Mounting leaf motor gearbox ideas

That car is much older, and has the old semi-trailing arm suspension; your E39 has a very different suspension which is also a poor fit for the Leaf drive unit, but in a different way. They don't have much in common other than a BMW badge and rear wheel drive. The point of linking to it is mostly that the Leaf drive unit and subframe are shown, and the dimensions discussed.

One positive note is that, the E39 has four subframe mounting points which are much more like the Leaf subframe mounting points than the 2002.

 

[boznz]

Have you contacted your certifier yet? - I have a feeling the only one on the Mainland is in Dunedin

No, I was told he comes to Blenheim from Christchurch once a month, the certification is the reason I would like to keep the original BMW gross-weight/brakes/steering/suspension and avoid welding, I will contact him before I execute whatever plan I decide on.

Have you got a copy of the NZ Hobby Car Manual ? - AKA "The Bible"

No, I will look out for it now I know about it.

Brian/Duncan. Thanks for the links and advice I must admit, using the leaf motor sounds a good option if I can get it to work, I do have a "spare" BMW and I will have access to some much better tools when I get my workshop built, bit early yet, but I will look at all these options when everything is dismantled and I can get some pictures and measurements to work on.

On another note Leaf is from August 2015 and has 12 bars showing but its displaying 2 bars of charge and a low bat warning, it is going to be idle for 2-3 months so what is better for the battery health, if I charge it up? or should I leave it as is? Would hate for its health to decay due to lack of action.

 

[Duncan]

Hi boznz

You are going to build yourself a shed first?

Have a look at getting a Two Post hoist - they are incredibly useful and nowadays they are dirt cheap - $2500NZ - for everything!

I'm well chuffed with mine