# Which EV Powertrain?



## gtwilliams (Apr 3, 2018)

Hi, if I wanted to convert a 600-700kg road car to be fully electric, is there an off-the-shelf powertrain that I could consider other than using Tesla components? A previous suggestion focussed on:

1 x Tesla Rear SDU (Small Drive Unit)
12 x Tesla Battery Modules
1 x Tesla DCDC
1 x Orion BMS
1 x Tesla Gen 2 Charger
1 x Junction Box

This would produce around 300bhp and a top speed of ~150mph, apparently...

Any help or advice would be gratefully received!


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## jbman (Oct 26, 2017)

gtwilliams said:


> Hi, if I wanted to convert a 600-700kg road car to be fully electric, is there an off-the-shelf powertrain that I could consider other than using Tesla components? A previous suggestion focussed on:
> 
> 
> 
> ...


What is your goal? Those components would be both very expensive and way overkill, most likely...

That's almost 700lbs of lithium batteries in a car that weighs almost 1,600lbs. 64 kWh is a big pack, too.

Let's work backwards from your requirements to design a system instead. You'll get a better car. Are you building a drag car? Daily driver? Etc.

Sent from my SM-N960U using Tapatalk


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## gtwilliams (Apr 3, 2018)

jbman said:


> gtwilliams said:
> 
> 
> > Hi, if I wanted to convert a 600-700kg road car to be fully electric, is there an off-the-shelf powertrain that I could consider other than using Tesla components? A previous suggestion focussed on:
> ...


Hi jbman, thank you for your reply. I thought as much regarding weight, cost and power. So, I am basically looking to convert a small mid-engined kit car from ICE to EV. The objective is to build a unique hillclimb/track car for personal use. However, this does not mean that I’m happy to compromise on quality. So, I’m looking to keep the vehicle under 800kg (ideally), top speed of around 150mph, 0-60mph of 3-4 seconds and to have a range of 100-150 miles. I’d also like the charging system to be onboard...

Does this sound possible or more like fantasy?!?


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## brian_ (Feb 7, 2017)

gtwilliams said:


> So, I am basically looking to convert a small mid-engined kit car from ICE to EV.


Since the car is mid-engined, it already has the engine and transaxle together, so they could be replaced by a typical EV "drive unit" (consisting of motor and transaxle) without having to adapt a motor to a transmission. The Tesla drive unit is an example of this.

The big problem is also fitting in a huge and massive battery pack.

If you take this approach, when selecting between the many EV drive units, here are some factors to consider:

most EVs are front wheel drive, but their drive units could be placed at the rear
essentially all drive units place the motor transversely, so they are configured with the transaxle much like a common transverse engine configuration in a front wheel drive car (and some mid-engine cars); however, the motor can be in different positions (ahead of, on, or behind the axle line), which changes how the unit packages into the car
the shape and position of the drive unit will affect how it fits with the car's rear suspension... and so whether you can keep that suspension or change it
the peak power output of a production EV motor could be much higher than the stock value if a modified or alternative controller is used

What engine, transaxle, and rear suspension does this car use? The small details don't matter - I'm just wondering about the size and position of the components. A "small mid-engined kit car" could use a transverse 4-cylinder engine from a production car, or a longitudinal engine on a transaxle that extends rearward (like classic formula cars and most mid-engine exotic road cars), or even some other unusual arrangement.



gtwilliams said:


> The objective is to build a unique hillclimb/track car for personal use.
> ...
> I’d also like the charging system to be onboard...


Essentially all EVs include an on-board charger, which can be salvaged from a production EV, such as the Tesla charger that you listed. On the other hand, if this is a competition car, is it also intended to roadworthy? If it must be transported to events on a trailer anyway, I wouldn't want to carry the charger in the car, especially when targeting very low weight; it can just go with all the rest of the tools and supplies.


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## brian_ (Feb 7, 2017)

gtwilliams said:


> ... I’m looking to keep the vehicle under 800kg (ideally), top speed of around 150mph, 0-60mph of 3-4 seconds and to have a range of 100-150 miles. I’d also like the charging system to be onboard...
> 
> Does this sound possible or more like fantasy?!?


That sounds very optimistic to me. For the mass, I think it would make sense to do some simple calculations:

start with the current mass
subtract the mass of the engine, transmission, exhaust system, and fuel tank
add the mass of all of the EV components
motor
controller
transaxle
battery, with cables and housings
charger
other electrical devices (contactors, etc)

What do you get? You are wanting to do this with a mass increase of only 100- 200 kg, but with the very large battery planned I don't think that will be possible.

A major variable is the battery. You need it to be large enough to have the energy capacity required to reach the range (or endurance, in racing terms) target. Even if you needed minimal range, it needs to be large enough to deliver the power required for your performance target.

The target weight of the Tesla Powered Cobra Race Car in this forum was 1800 pounds (816 kg) with a 30 kWh Kia Soul EV battery; I didn't search the whole thread for the final weight with the original battery pack, or the later upgrade to a 40 kWh Nissan Leaf battery. This vehicle is very similar to this project, in size, construction, and intended use - even using a Tesla drive unit - but is carrying much less battery than 12 Tesla Model S/X modules.


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## Duncan (Dec 8, 2008)

Hi
The problem with your requirements is the range

My "device" is 800 kg with over 300 hp - but less than 40 miles range - quadrupling the range would add over 300 kg 

Do an analysis on your driving - I found that I either drove for less than 40 km OR over 150 km


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## gtwilliams (Apr 3, 2018)

Duncan said:


> Hi
> The problem with your requirements is the range
> 
> My "device" is 800 kg with over 300 hp - but less than 40 miles range - quadrupling the range would add over 300 kg
> ...


Hi Duncan, thank you for your reply. The car doesn't necessarily require 300bhp. I simply need enough power to deliver a top speed of 125mph+ and 0-60mph of 3-4 seconds, ideally. I guess a range of around 50km would suffice for hillclimbs and track days as you could recharge the batteries between runs. I'm just thinking about future-proofing the design in case I ever did wish to make it roadworthy. Does that help? I need to do a few calculations!


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## gtwilliams (Apr 3, 2018)

brian_ said:


> That sounds very optimistic to me. For the mass, I think it would make sense to do some simple calculations:
> 
> start with the current mass
> subtract the mass of the engine, transmission, exhaust system, and fuel tank
> ...


Hi Brian, thank you for your replies. The arrangement I've currently got in mind is locating 12 x Tesla Battery Modules directly behind the driver, with the DCDC, BMS and Junction Box mounted directly above this sizeable block. The Tesla SDU (Rear) would then be mounted behind the batteries in exactly the same way as it is in a Tesla Model S, driving the rear wheels via a Quaife LSD. Finally, the charge would sit above the SDU. This is the best arrangement I've managed to establish diagrammatically so far! As you say, however, the major issue is the huge mass of batteries. This is predominantly where I feel there's potential for improvement as I feel 12 x Tesla Battery Modules is potentially overkill. Yet, I guess I need this quantity if batteries to produce the power and range required!

I should mention that I'd envisaged fitting 255/40 R18s on the rear and 205/40 17s on the front...

The overall layout would be very similar to that of an F1 car, I suppose.


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## gtwilliams (Apr 3, 2018)

Actually, thinking about it, 200-250bhp would probably suffice in a car of this size and weight. The issue I'm having is fitting all the components within the chassis. Ideally whatever EV powertrain I end up using wouldn't necessarily be salvaged from scrapped vehicles. Rather bought off-the-shelf...


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## gtwilliams (Apr 3, 2018)

This “start-up” powertrain for electric cars, for example, has caught my eye...

https://www.bosch-presse.de/presspo...bosch-e-axle-offers-greater-range-121216.html


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## MattsAwesomeStuff (Aug 10, 2017)

> Ideally whatever EV powertrain I end up using wouldn't necessarily be salvaged from scrapped vehicles. Rather bought off-the-shelf...


That's not really a thing.

An EV powertrain doesn't ever really break, so, there's not really a market for that kind of thing.

There's hardly any market for DIY conversions, certainly not enough to justify a factor run of any components.

The cheapest place and best place to get an EV drivetrain is from an existing EV.


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## Duncan (Dec 8, 2008)

Hi

Have you looked at my device?

https://www.diyelectriccar.com/foru...dubious-device-44370p15.html?highlight=duncan

It's the old Caterham/Mallock type layout rather than your mid engined approach

I'm using a forklift motor and a Subaru LSD 

If I was starting again now I would use a power unit from an EV - something like a Leaf with a new "brain board" - should be able to get 300 hp easily

I'm using most of a Chevy Volt battery - it's in handy modules so it can be re-configured

For motorsport we normally overload stuff - the Volt uses a maximum of 100 kW - I'm maxing out at 400 kW - but only for a couple of seconds

You can buy bespoke power units - but expect to pay an arm both legs and at least one nut

My car cost less than 4000 pounds all up

Expect to pay in excess of 10,000 for one of the "off the self" motors at a LOWER power output

Best bet get hold of a lightly crashed EV and start there - a Leaf or one of those small BMW I3 

Are speeds really getting up to the 150 mph levels in hill climbs and sprints? - here the organisers keep the speeds lower by shortening the straights - this enables them to have lower requirements for safety equipment and driver licencing

I used to use a mini with a Lancia twin cam (170 hp) in sprints in the UK in the 80's - the highest speed I achieved was 130 mph on the back straight at Goodwood


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## gtwilliams (Apr 3, 2018)

Duncan said:


> Hi
> 
> Have you looked at my device?
> 
> ...


That’s very cool! Very similar to what I’m trying to achieve other than the layout, as you say. 

I guess a lot of my specifications above are focussed on future-proofing the car, if you will. I would ideally like to make this vehicle roadworthy eventually, even though I know this is extremely difficult. As it is clearly a sports car, I’m keen to give it more credibility by affording a higher top speed. It’s the holy grail isn’t it, even though we rarely reach those speeds on track.

I think I need to revise my specifications, starting lower and extracting more power/speed as the vehicle potentially develops over the years.


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## gtwilliams (Apr 3, 2018)

Keeping things simple, then, what setup could you envisage that would provide a little less power than the Tesla configuration I originally posted for less cash and smaller mass? Those Chevy Volt cells look like a good option. Is there an alternative to the Tesla SDU? I’d rather not bolt a motor onto a transmission or transaxle. I like the compactness of this unit and think that perhaps it’s my best bet right now. Correct?


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## Duncan (Dec 8, 2008)

Hi
How much is your Tesla unit going to cost?

For cost effectiveness I would try and get a complete car

The Tesla unit is better in it's actual designed home - under the car

The Leaf unit is more like a FWD IC unit - which makes it relatively easy to fit into a mid engined layout
The BMW unit looks like it could be easy as well

I started some 11 years ago - my car has been on the road for the last 6 years - the options have changed since then!

The mechanical work of building your chassis and sorting the suspension are all as an IC car

The actual mechanical parts of the power unit are also fairly simple 

Then you need to mount the batteries
In my car everything is on the floor - I have relatively low rate springs and no anti-roll bars and it does not roll at all

All of that is simple

Then you get to the electronics! - which is well beyond me! - having a complete car means that you can try and con the electronics that it is still in the Leaf or whatever

In your shoes I would be looking at what I can find as a crashed EV
Preferably one that is crashed but still drivable

Decades ago I put a Lancia unit in my mini - start off with a rusty Lancia - left the whole thing in my garden until I had it all working in the mini

See what you can find
Drive some options - we had a BMW I3 at our last 1/8th mile drags
They put it in with "European Sports cars" - in this instance an SLK 230 - the merc won - but by 1/10th of a second

Drive a Leaf 

Dunno what else is available these days

Remember the power unit in these cars is expected to last for 300,000 miles with almost no warranty failure

You CAN turn the wick up a LOT and still get respectable "motorsport" reliability


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## brian_ (Feb 7, 2017)

The two big fit issues currently appear to be:

the unreasonably large battery, which is being reconsidered
the unknown structure and suspension in the rear, which affect what drive units will fit well
Can you name the car design, or provide a photo of the engine/transaxle/suspension area?



gtwilliams said:


> Ideally whatever EV powertrain I end up using wouldn't necessarily be salvaged from scrapped vehicles. Rather bought off-the-shelf...





MattsAwesomeStuff said:


> That's not really a thing.
> 
> An EV powertrain doesn't ever really break, so, there's not really a market for that kind of thing.
> 
> ...


I generally agree with Matt's assessment, although Tesla proved for years that they can screw up simple gearboxes, so lots of them did fail. There are suitable components manufactured, but they are generally not available to end customers, only to manufacturers who will commit to some substantial quantity; if you find one, it will be very expensive. One problem is that there are so many configuration options that they are not built until ordered in a specific configuration, and that's not practical for small quantities.

One option is to use the drive unit of a production EV, but buy it new. That's expensive, and unlikely to be even possible with a Tesla, but some of us have noticed that a lot of GM parts (including the entire battery pack of the Bolt) are available like any other replacement part, through dealers. I just don't see the value in buying - for instance - a complete new Bolt drive unit when the same thing from a wrecked Bolt will be perfectly reliable.

The advantage of something built for custom or conversion vehicles would be that it would presumably be sold with technical documentation and support; the challenge with motors and associated controllers from production EVs (with or without the stock transaxle) is that they can't be reprogrammed and will only operate by getting the computer network messages which would be expected in the production vehicle.


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## brian_ (Feb 7, 2017)

gtwilliams said:


> The Tesla SDU (Rear) would then be mounted behind the batteries in exactly the same way as it is in a Tesla Model S, driving the rear wheels via a Quaife LSD.


That really is the only way to use any of these complete drive units (with transaxle) - they typically can't be rotated to another orientation. That means a Tesla Model S/X motor will be behind the axle line, most others will be ahead of it, and the Chevrolet Spark EV and Bolt motors will be on the axle line.

The fact that someone else has already worked out the installation of a Quaife in the Tesla Model S/X drive units is valuable, since the car presumably wouldn't retain the brake-based traction control functionality of the production EV, and none of these EVs have a limited-slip differential from the factory. I'm sure a Quaife or similar could be installed in other drive units, but work would be required in disassembly, examination of dimensions and bearings, and searching of available parts... and it's not guaranteed that anything will fit.



gtwilliams said:


> Is there an alternative to the Tesla SDU? I’d rather not bolt a motor onto a transmission or transaxle. I like the compactness of this unit and think that perhaps it’s my best bet right now. Correct?


Any of the drive units from other EVs (the Leaf is most commonly used in or considered for conversions) have the same advantages as the Tesla units in compactness and inclusion of a suitable transaxle (reduction gearing and differential). There is the motor placement difference that I mentioned above, and of course the aftermarket support for ways to control them varies.


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## gtwilliams (Apr 3, 2018)

Duncan said:


> Hi
> How much is your Tesla unit going to cost?
> 
> For cost effectiveness I would try and get a complete car
> ...


Thank you for your help thus far. It's much appreciated!

My quote for the entire conversion kit was £33,500... That includes absolutely everything I'd need for the powertrain, apparently.

Unfortunately there's absolutely no chance of getting the battery modules under the car as the driver practically sits directly on the chassis floor and I don't want to increase the overall height of the vehicle. I'm actually quite happy with locating the battery box directly behind the driver as this means I can avoid issues with firewalls at motorsport events. The driver can be protected from potential battery fires more effectively with the configuration I have in mind. The battery box would actually form an integral part of the chassis itself, being mounted as low as possible with two banks of 6 modules side-by-side arranged longitudinally. I am happy this would provide a low enough centre of gravity.

I think I will take a look at the options you've suggested above. Namely the Leaf and Volt. Extracting components from lightly crashed examples does sound like a more cost effective option to the quote mentioned above.


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## Duncan (Dec 8, 2008)

gtwilliams said:


> Thank you for your help thus far. It's much appreciated!
> 
> My quote for the entire conversion kit was £33,500... That includes absolutely everything I'd need for the powertrain, apparently.
> 
> ...


33,000 is nearly ten times what I spent! - for the whole car! suspension brakes, body, chassis, certification, the electric car bits - the lot

Getting space for the batteries is one of the most difficult things - I am using the "engine bay" for batteries - the gearbox location for the motor and everything else as per usual

With a mid engined installation the driver is further forwards - 
The space between the driver and passenger is now free
Or you could move the driver and passenger closer together and give room for the batteries along the "sills"

I do fancy making another car - I'm thinking of a Jaguar C type look alike but with a leaf power unit in the back and running the batteries along the sills as well as in the "engine bay"

The Tesla modules are not well suited to this type of messing about - the Leaf modules would be easy to configure
Chevy Volt ones are bit larger and have water cooling


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## brian_ (Feb 7, 2017)

*Placing the battery modules*

If we knew the specific car design it would be easier to make helpful suggestions about configuration.

Regardless of the design, there must be a fuel tank... and that's a potential location for one or more battery modules, depending on volume, proportions, and module dimensions. Although front-engine vehicles essentially always have the fuel tank just ahead of the axle or behind it, mid-engine and rear-engine cars routinely have the tank in the front, just ahead of the cowl (base of the windshield). Since an EV conversion tends to increase vehicle mass, and the full fuel tank had significant mass anyway, it's probably a good idea to place some of the battery there. At the very least, a fuel tank location up front would be a good place for the charger.

Some mid-engine cars have a central fuel tank, in a tunnel between the seats (although that's unlikely in a kit). The Chevrolet Volt actually runs half of the battery in that location - the Volt modules are designed to fit in a tunnel like that, and might also be a good fit in the sills, if the sills are very large. The Volt's tunnel is long because it runs through both front and back seat areas; a two-seat mid-engine car wouldn't have this length of tunnel between the seats, but the "tunnel" row of modules could continue right up to between the front wheels (depending on vehicle structure and body design). Of course a car has either a large tunnel (and wide-spread seats) or large sills (and seats jammed against each other), not both.

I wouldn't want battery modules in sills unless they had very good enclosures and protective structure, because I wouldn't want a damaged (and therefore possibly flaming) module jammed into me in a severe collision.

The Tesla Model S/X modules are designed to lay flat under a floor, and so they work well for that. They can also stack in a large box-shaped area, such as a reasonably long or wide engine bay. They are a pain to fit in most other possible areas. I haven't heard of anyone using Tesla Model 3 modules yet; they are longer and narrower, so might be candidates for sill or tunnel locations. Most other modules are rectangular boxes which are closer to cubes, rather than very flat and wide.


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## sadcar (Mar 18, 2013)

i just completed the changeover of a mitsubishi express van, i used an older type of 24kw/144v dc motor (us$1200.-) and dc speed control (us$1400.-) attached to the existing clutch/gearbox, the delivery van (weight 2500lb) can go to 110km/h, send msg to [email protected] if you want to know more


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## gtwilliams (Apr 3, 2018)

Duncan said:


> 33,000 is nearly ten times what I spent! - for the whole car! suspension brakes, body, chassis, certification, the electric car bits - the lot
> 
> Getting space for the batteries is one of the most difficult things - I am using the "engine bay" for batteries - the gearbox location for the motor and everything else as per usual
> 
> ...


Hi Duncan, thank you for your reply. I did think the quote was a little hefty! 

I shall be going for a mid-engined layout. I've decided to can the idea of converting an existing chassis and instead plan to design a tubular chassis from scratch. Ambitious I know, but I'm going to try!

I like your plans for a Jaguar C-Type lookalike. Do you think you'll give it a shot?

I had considered putting battery modules in the sills, but my concern was fire safety regulations. Placing them directly behind the driver in a single block would make it far easier to firewall effectively. Also, I've feel safer with regards to side impact protection...

You've intrigued me with the Nissan Leaf battery modules. I hadn't come across these before, TBH. I've never seen inside a Leaf battery box! The modules are absolutely perfect for what I want to do. Absolutely perfect. The question is how many Leaf battery modules would I require to match 12 Tesla Model S battery modules and would a Leaf motor be able to provide similar performance?


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## gtwilliams (Apr 3, 2018)

*Re: Placing the battery modules*



brian_ said:


> If we knew the specific car design it would be easier to make helpful suggestions about configuration.
> 
> Regardless of the design, there must be a fuel tank... and that's a potential location for one or more battery modules, depending on volume, proportions, and module dimensions. Although front-engine vehicles essentially always have the fuel tank just ahead of the axle or behind it, mid-engine and rear-engine cars routinely have the tank in the front, just ahead of the cowl (base of the windshield). Since an EV conversion tends to increase vehicle mass, and the full fuel tank had significant mass anyway, it's probably a good idea to place some of the battery there. At the very least, a fuel tank location up front would be a good place for the charger.
> 
> ...


Hi Brain, thank you for your reply. I've decided to forgo the conversion and build a chassis from scratch. Ambitious, I know! However, this is a bespoke project and one I'm extremely focused on getting absolutely right.

I concur with your fears regarding sill-mounted modules. I will be going for a mid-engine layout, with a large battery box directly behind the drive and a motor behind that, ideally inline with the rear axles without too much rear overhang.

Do you think I could configure a modified Leaf powertrain to deliver the sort of performance I require?


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## Duncan (Dec 8, 2008)

*Re: Placing the battery modules*

Hi
One of my main aims was to keep all of the heavy bits as low as possible - batteries take up a lot of volume

If you have the "motor" and then a single height layer of batteries right across the car
With my car with limited range that would push the driver forwards by about 2 feet

I don't think that would be a good idea - too far forwards!

I started off by making a balsa wood chassis at about 12:1

Throw away the bodywork on my device - fit a Leaf power unit in the back
That would move the drivers seat forwards about 8 inches

You could then run a row of modules down the "transmission tunnel"

I have two rows of batteries in the front - engine bay - I could have made that part of the chassis a bit wider and put three rows in there 

That gets about twice my current range
The Volt modules are a bit larger than the Leaf ones - doing the same with Leaf modules could give more

I'm still struggling to get past 100 km 

That is why I would plan on using the sills!

get yourself some plastic cardboard and balsa and have a play!

As far as the Leaf power unit is concerned you should be able to get about 300 hp - which should be enough

BUT there should be more to come from a Tesla unit - it's just the cost and availability

I cheated when building a chassis from scratch - I used the Subaru front and rear subframes - made it easier but heavier


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## gtwilliams (Apr 3, 2018)

*Re: Placing the battery modules*



Duncan said:


> Hi
> One of my main aims was to keep all of the heavy bits as low as possible - batteries take up a lot of volume
> 
> If you have the "motor" and then a single height layer of batteries right across the car
> ...


So, you believe I could configure a Leaf powertrain to generate between 200-300bhp? How many of the individual Leaf battery modules would I require?

Perhaps I should post some images of the layout I currently have in mind?


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## Duncan (Dec 8, 2008)

*Re: Placing the battery modules*

You need the modules for range - not for power

I'm using 14 kWh of Volt cells but I draw 400 kW at peak that is about 30C - only for a second or so!

Full power run
Motor---------------------------------Battery
1200 amps - 10v -------------------340v - 35 amps
1200 amp - 34v --------------------340v - 120 amps
1200 amps - 68v----- --------------340v - 240 amps
1200 amps - 150v ------------------300v (sag) 600 amps
1200 amps - 300v-------------------300v - 1200 amps --------70 kph (ish)
900 amps - 300v -------------------300v - 900 amps
600 amps - 300v --------------------300v 600 amps -----------150 kph

Lot of estimating here my instruments throw a wobbly at full power and I am too busy to look down anyway

As you can see the batteries don't see 1200 amps for long - the current builds up to peak and then drops off again

You will get the same effect
But if you have 28 kWh and 300hp (225 kW) - you will only be loading your cells at 8C

Leaf cells are probably not as "robust" as Volt cells - 

This voltage/power/current effect is important

When I set up with only 130v the top current dropped off and my top speed was only 100 kph


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## gtwilliams (Apr 3, 2018)

*Re: Placing the battery modules*



Duncan said:


> You need the modules for range - not for power
> 
> I'm using 14 kWh of Volt cells but I draw 400 kW at peak that is about 30C - only for a second or so!
> 
> ...


Hi Duncan, I'm afraid most of that's gone over my head! Haha! I think I need to scrub up on my electronics as it's been a few years since I left school! So long as I could get track car performance for, let's say, 50 miles on full charge, I think the Leaf powertrain looks more viable than the Tesla option that I posted originally. Certainly in terms of mass. I'm not too bothered about a slight reduction in performance as they car would be incredibly light other than the batteries and motor. I think I'd have more than enough power with the Leaf option.


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## gtwilliams (Apr 3, 2018)

I am now extremely interested in the Nissan Leaf powertrain. I believe this option could be a far more accessible and affordable option that the Tesla option. From what I can see there are two versions of the Leaf motor - EM57 and EM61. Which is better in terms of customisation? I can see the newer version incorporates pretty much everything into a single unit and this simple needs to be hooked up to the batteries, whilst the older version sees various components bolted onto the motor and the charger at the rear of the vehicle.

Does anyone know where I can find dimensions for each unit or each individual component? The fully incorporated unit looks rather tall...


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## gtwilliams (Apr 3, 2018)

If Nissan Leaf battery modules are the following dimensions:

L: 30.3cm
W: 22.3cm
H: 3.5cm

Then I believe I can fit at least 64 battery modules into the space I've made available for batteries. Am I correct with those dimensions?

The battery box would have to wrap around the following dimensions:

L: ~60.6cm
W: ~56cm
H ~44.6cm

I'm not sure how much extra the battery box itself would add or whether 64 battery modules can be packed quite so tightly... I'm guessing not.

Is there any way of calculating how much range I'd get from 64 battery modules for a given speed? How can I calculate the performance I'd get from this setup? How many battery modules does a standard Gen I Nissan Leaf feature? Is it 48?


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## brian_ (Feb 7, 2017)

*custom layout*



gtwilliams said:


> I shall be going for a mid-engined layout. I've decided to can the idea of converting an existing chassis and instead plan to design a tubular chassis from scratch. Ambitious I know, but I'm going to try!





gtwilliams said:


> However, this is a bespoke project and one I'm extremely focused on getting absolutely right.


It is certainly ambitious, and most people who intend to build this sort of vehicle (with an engine, or an EV) never start, and most who start never finish.

On the other hand, it is the most effective way to get a vehicle that works with the components, and it has been done many thousands of times by dedicated hobbyists. Duncan is one of them.



gtwilliams said:


> I will be going for a mid-engine layout, with a large battery box directly behind the drive and a motor behind that, ideally inline with the rear axles without too much rear overhang.


This classic racing and sports car layout is a rational choice for a custom performance-oriented EV build for multiple reasons:

it inherently suits rear wheel drive, which is what you want for a two wheel drive performance car,
it suits a rear-heavy weight bias, which is good for drive traction and to maximize the amount of braking which can be done by regeneration (rather than conventional friction braking, which is all you have at the front), and may even enable unassisted steering and braking (avoiding cost and complication with those systems), and
it provides a large chunk of conveniently-shaped space for a battery pack in the middle.
If you were to keep all the battery in one easy block between the seats and the rear axle, you are essentially duplicating the layout of the original Tesla Roadster. They used a stretched Lotus Elise chassis... it's not actually necessary to custom-build if you start from a transverse mid-engine design.



Duncan said:


> If you have the "motor" and then a single height layer of batteries right across the car
> With my car with limited range that would push the driver forwards by about 2 feet
> 
> I don't think that would be a good idea - too far forwards!
> ...


I agree. If the modules used are small enough, some can run down the tunnel. Many rear-engine and mid-engine vehicles have the fuel tank in the front - that's a good place for a portion of the battery, both because the space is available and to avoid an excessively rearward weight bias. Don't put any modules ahead of the front axle or behind the rear axle, though, since mass out at the ends of the car is bad for handling response.

Modeling the layout, either in CAD (preferably 3D) or a simple physical model, seems like a very good idea to me. Building and re-building because something didn't fit as expected is a huge waste of effort and expense.



gtwilliams said:


> Perhaps I should post some images of the layout I currently have in mind?


Yes, that would be good, but I think we're imagining the same things.


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## brian_ (Feb 7, 2017)

*suspension*



Duncan said:


> I cheated when building a chassis from scratch - I used the Subaru front and rear subframes - made it easier but heavier


While the stock subframes from just about any car will not be ideal for a custom design, this is an effective approach. Using the complete suspension but not the subframe - just copying the component positions used with the stock subframe - allows a more optimal design. In Duncan's Device, the Subaru final drive unit (differential) is used at the rear, so the stock rear subframe is perfectly suitable.

It certainly makes sense to use a production suspension design. Most builders don't even understand what they would need to consider in the design of their own suspension, and building components such as hub carriers is just a pointless black hole to consume time and money for anyone other than a very serious race team. I think it makes sense to pick suitable suspensions which will fit with the drive unit and driving characteristics, and design around them. Preferably these would be a complete front and rear set from the same car for compatibility. Of course the original should be a rear-wheel-drive car, but it doesn't need to be mid-engined, especially if you are not using the stock rear subframe.


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## brian_ (Feb 7, 2017)

*Leaf module configuration*



gtwilliams said:


> If Nissan Leaf battery modules are the following dimensions:
> 
> L: 30.3cm
> W: 22.3cm
> ...


Those look like the dimensions of the early Leaf modules. Later modules (still in the first generation, so pre-2018) were glued together in pairs (still separate electrical connections), somewhat limiting how you can rearrange them.



gtwilliams said:


> The battery box would have to wrap around the following dimensions:
> 
> L: ~60.6cm
> W: ~56cm
> ...


The modules are intended to be stacked with their flat sides together, then clamped that way by bolts - that's true of almost any modules made up of pouch cells, as these are.

In the Leaf, the module arrangement is determined by available space under the floor. Under the front seat, they're horizontal and stacked four modules high. Under the rear footwell, they're horizontal again and only two modules high. Under the rear seat there's more height, so 24 are arranged in one long stack so the height is the 22 cm "width", the front-to-back dimension is the 30 cm "length", and the stack is 24 times the 3.5 cm "height".

In any reconfiguration of the Leaf modules, I would want to use long stacks like that rear (under the rear seat) stack in the original Leaf, even if it was less (or more) than 24 modules. This makes wiring and clamping them together easier.

It looks like you would be assembling four stacks, each of 16 modules, then laying two layers of those stacks across the car. That sounds reasonable to me, for a physical arrangement. It is tall compared to most production EV configurations (which put the modules under the floor), but if you want low seats and want to group the modules together in the middle of the car, that's going to happen.

You also need to consider the electrical arrangement. If you put 64 Leaf modules in series (instead of the stock 48), you'll have a nominal pack voltage of 480 volts, which is probably too much for the Leaf controller/inverter. If you arrange them with pairs of modules in parallel and the pairs in series, you'll have a nominal pack voltage of only 240 volts, which is much lower than the stock 360 volts and will severely limit performance at high motor speed.



gtwilliams said:


> How many battery modules does a standard Gen I Nissan Leaf feature? Is it 48?


Yes, the pre-2018 Leaf packs have 48 identical modules.



gtwilliams said:


> Is there any way of calculating how much range I'd get from 64 battery modules for a given speed? How can I calculate the performance I'd get from this setup?


The rational way to do this is by considering the energy (for range) and power (for performance) basis. If you change the number of modules you change the energy stored and power available, in proportion to the number of modules.

Leaf packs (in the first generation, pre-2018) are either 24 kWh or 30 kWh (with the 30 kWh apparently only in some 2016 variants). If you can predict how much energy your car will use per distance driven (kilometre or mile), and divide the available energy from the pack by that, you have the range. It's really that simple... although energy used per distance is affected by many factors.

The entire early Leaf pack is only used in the Leaf to deliver up to 80 kW of power. The motor's controller is programmed to avoid ever using more than this, to protect the battery. I think it's generally understood that the Leaf pack is limited to only 80 kW because it does not have active cooling - sustained operation at higher power would cause overheating problems.


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## brian_ (Feb 7, 2017)

*Tesla versus Leaf modules*



gtwilliams said:


> The question is how many Leaf battery modules would I require to match 12 Tesla Model S battery modules and would a Leaf motor be able to provide similar performance?


12 Tesla modules is not a full set for any Tesla model, and would have a nominal pack voltage (assumed they are all connected in series as they are in a Tesla) of only 270 volts. That might be enough, and is the plan for some other projects, but would limit performance at high motor speed.

Tesla Model S/X modules have come in two different capacities, due to a different number of cells. The ones with 74 cells per group (from the 85 kWh packs) have a capacity of 5.4 kWh each, so a dozen of them have a capacity of 64 kWh, equivalent in energy capacity to 128 early Leaf modules (at 0.5 kWh each).

You can do the same thing with power output. It's not clear what the power limit of the Leaf modules is, but you could assume 80 kW for 48 modules, or 1.7 kW each; of course some people presumably run them much harder than that. You can estimate the power output capability of the Tesla modules by dividing the claimed total power of a given Tesla model and dividing by the number of modules (Wikipedia's Model S article has a nice table of the variants of the Model S), and multiply by the number of modules you are using. It's basically a matter of multiplying the power per module by the number of modules in each case.

The Leaf motor performance seems to have been limited by the controller in the stock Leaf to protect the battery. That was 80 kW in the first generation, 110 kW in the second generation with the base 40 kWh battery, and apparently higher in the big-battery version that has just come out. I don't know that this motor might be capable of with different controller programming and sufficient battery.


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## brian_ (Feb 7, 2017)

gtwilliams said:


> I am now extremely interested in the Nissan Leaf powertrain. I believe this option could be a far more accessible and affordable option that the Tesla option. From what I can see there are two versions of the Leaf motor - EM57 and EM61. Which is better in terms of customisation? I can see the newer version incorporates pretty much everything into a single unit and this simple needs to be hooked up to the batteries, whilst the older version sees various components bolted onto the motor and the charger at the rear of the vehicle.
> 
> Does anyone know where I can find dimensions for each unit or each individual component? The fully incorporated unit looks rather tall...


All versions of the Leaf have the controller/inverter stacked on top of the motor. The difference is that the later version is more tightly integrated, with the high voltage connections made internally by pins the stick up from the motor into the inverter (and from the inverter into the charger on top of that), avoiding external cables. There should be enough height for all of this in the back of a mid-engine car, but if separating the components then the earliest version would be easier.

Dimensions have been posted in some discussions here, but I don't have a link handy. It will take some searching, unless someone doing one of those projects responds in this thread.

Most drive units (motor with transaxle and inverter) from production EVs with the motor in front (replacing the engine and transaxle of the model from which the EV was derived) are arranged this way, because that's the space which is available. The Tesla inverter is beside the motor, on the opposite side of the transaxle, because the Tesla unit was designed to fit under the trunk floor and the car was wide so it fit there.


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## JasonA (Aug 8, 2013)

Not to get too technical but the Tesla S 70/D70 is only a 350v nominal setup but goes down to like 240v or something when its super low.


Might be worth looking into a wrecked one of those if you need a lower voltage pack/setup.


Just food for thought.


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## brian_ (Feb 7, 2017)

brian_ said:


> 12 Tesla modules is not a full set for any Tesla model, and would have a nominal pack voltage (assumed they are all connected in series as they are in a Tesla) of only 270 volts. That might be enough, and is the plan for some other projects, but would limit performance at high motor speed.
> 
> Tesla Model S/X modules have come in two different capacities, due to a different number of cells. The ones with 74 cells per group (from the 85 kWh packs) have a capacity of 5.4 kWh each, so a dozen of them have a capacity of 64 kWh, equivalent in energy capacity to 128 early Leaf modules (at 0.5 kWh each)...





JasonA said:


> Not to get too technical but the Tesla S 70/D70 is only a 350v nominal setup but goes down to like 240v or something when its super low.
> 
> 
> Might be worth looking into a wrecked one of those if you need a lower voltage pack/setup.


Smaller/earlier Tesla Model S variants had 14 modules, and larger/later variants have 16 modules... that's why 12 isn't a full set for any model, and will limit the performance of any Tesla motor.

Within variants having the same number of modules, the difference in capacity comes from a different number of cells in parallel, and changes in the cells; that doesn't change the voltage, since (as far as I know) they're still arranged as 6-in-series per module. That's (assuming 3.75 V nominal per cell)

12 x 6s = 72s or 270 V for a 12-module set (not used by Tesla)
14 x 6s = 84s or 315 V for a 14-module set such as in Model S "60" variant
16 x 6s = 96s or 360 V for a 16-module set such as in Model S "85" and "100" variants
Of course that's the nominal voltage. Actual voltage (per cell or for the pack) varies depending on the state of charge, so a nearly discharged 96s battery could be down under 300 volts.


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