# UK - Mazda RX-8 direct drive conversion



## Friday_EV (Dec 9, 2014)

Hello everybody!

I am new to the forum however I've been already reading quite few articles here to bring myself up to speed with the principles of electric car conversions. Thank you all for the vast amount of knowledge and practical tips. 

I am investigating now a conversion of Mazda RX-8 into electric in a direct drive system. The idea is to use the latest technology (wherever possible) to create an efficient vehicle with a range of at least 150 miles. The range will be increased in steps as the main focus in the first phase of the project will be the propulsion system.

I am planning on using 2 PM Axial Flux motors connected directly to the rear wheels. They will be controlled independently to allow for different speed of wheels at turns. The vehicle will employ regenerative braking as well.

The work is planned to start late Jan / early Feb 2015.

I am a newbie to a car conversion world, but with big motivation to learn this topic. If you've read this post and have any advice, contact for PM motor manufacturers (that sell to public), inverter solutions, information on prices, and anything else you consider helpful please share.

Please note my location is in the UK.


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## dougingraham (Jul 26, 2011)

The RX-8 is a beautiful car and is a good choice for a conversion. I have seen a couple of conversions done and there are several here on the forum.

150 miles is quite a lot of range. It will require a pack of around 50kwh for average driving conditions. This will be around 500kg of batteries using LiFe types. So your car is going to be somewhat overweight if you stuff that much battery in it. The more range you go for the more expensive your conversion. It would be prudent to keep careful track of just how much you drive now most days and then give yourself a 30% margin beyond that. Otherwise you are looking at approaching Tesla money for your conversion.

Best wishes!


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## Duncan (Dec 8, 2008)

Hi Friday

Your _ 2 PM Axial Flux motors connected directly to the rear wheels.
_Are a bit of a problem
Do you have such beasts?What are their specifications?
As a general rule PM motors are fragile - rarely used in cars
Torque is roughly proportional to motor weight - so almost all cars use gearing to get enough torque

Using a motor to drive each rear wheel will require TWO gearboxes!
Most of us just keep the diff and drive it


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## samwichse (Jan 28, 2012)

Duncan said:


> Hi Friday
> 
> Your _ 2 PM Axial Flux motors connected directly to the rear wheels.
> _Are a bit of a problem
> ...


My 2000 Insight is going on 15 years and 190k miles with a permanent magnet motor strapped directly to the side of a wobbly 3-banger with no balance shaft. Seems like they can be pretty tough to me...

Sam


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## major (Apr 4, 2008)

The PM motor in the Insight is hybrid duty and automotive quality built. Not all PM motors are junk. But most PM motors used by DIYers for EV car propulsion fail early on. And direct drive non geared  No chance of survival. Did you see Ripperton's Mira attempt? http://www.diyelectriccar.com/forums/showthread.php?t=82349&highlight=mira


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## samwichse (Jan 28, 2012)

major said:


> The PM motor in the Insight is hybrid duty and automotive quality built. Not all PM motors are junk. But most PM motors used by DIYers for EV car propulsion fail early on. And direct drive non geared  No chance of survival. Did you see Ripperton's Mira attempt? http://www.diyelectriccar.com/forums/showthread.php?t=82349&highlight=mira


I see it now 

What is the nature of the pm motor that makes it fail quickly... ie, what is beefier in an automotive quality unit?


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## major (Apr 4, 2008)

samwichse said:


> What is the nature of the pm motor that makes it fail quickly... ie, what is beefier in an automotive quality unit?


Honda, no doubt, did an excellent job on the Insight PM motor with application engineering and then product design and validation. None of which you regularly see with the DIY EV motors. In this case, it is kinda the opposite of what your question infers. The wound field motors typically used in the DIY EV are excessively robust and durable and often do very well. They are designed and constructed in such a way for their primary application (forklifts / industrial) that they tolerate overlaod and abuse. The PM motors seemingly come out of nowhere and are applied by marketing brochure or nameplate rating without regard for the actual duty cycle or environment of the EV.


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## dougingraham (Jul 26, 2011)

samwichse said:


> I see it now
> 
> What is the nature of the pm motor that makes it fail quickly... ie, what is beefier in an automotive quality unit?


Permanent magnets are sensitive to heat and powerful magnetic fields. Heat is the usual problem. Neodymium magnets are commonly used because they are reasonably inexpensive and quite powerful. However neo should be considered as a low temperature material. There are a couple of grades but the problem is that if the temperature reaches a critical point they demagnetize. They can tolerate temperatures up to between 310 and 400 degrees C (590-752 F) depending on the composition. Samarium Cobalt is good up to 800 degrees C (1472 F) but can not be magnetized to the same level as neo. Neo also must be protected from exposure to oxygen. Normally a coating of some kind is applied after production because they will rust away to nothing in very short order. Samarium Cobalt does not have this characteristic.

A PM magnet motor that utilizes neo magnets must be protected from debris scratching the protective coating on the magnets and must not be allowed to overheat. So an air cooled pm motor using neo is a poor idea.

The other problem is less common but could occur. And that would be demagnetization due to excessive magnetic flux in the electromagnets. These materials are magnetized by being placed in a powerful magnetic field and will be affected if the magnetic flux is too great. You could see this if you cranked up the currents to increase the torque a little too much. Again, SmCo has less problems with this but is quite a lot more expensive.


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## samwichse (Jan 28, 2012)

Hm, the insight/HCH motor must not be neodymium then... there's no direct cooling of the motor at all (even airflow). It's just in the enclosed space between the ICE and the tranny bell housing. Although I suppose the duty cycle helps quite a bit. And maybe through aluminum-aluminum contact with the engine block? 

Weird Honda was so obsessive about throwing sensors on everything, but there's no temperature sensor on the motor windings or something.

Thanks for the lesson , I'll stop stealing this thread now...

Sam


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## arklan (Dec 10, 2012)

i had 50 neo magnets for an axial flux alternator i made for a wind turbine
the magnets rusted within 6 months even with the nickel coating they had
edit to add they still stick to metal like shit to a blanket, 8 years on


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## skooler (Mar 26, 2011)

Hi Friday-EV,

Suggest you take a read of my build thread! 

If you are anywhere near to worcester feel free to pop in for a drive in my rx8 conversion.


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## Friday_EV (Dec 9, 2014)

Thank you skooler for the offer! I have read some posts from your conversion and seen the videos. I am greatly interested in examining your car. Will contact you in new year to arrange something then 

As for the PM motors, I've found two for now that I thought to be suitable for direct drive on a car like RX8. One of them is not available to the public (Yasa motors - company from Oxford, UK) and the other one I still don't know if can be purchased by individual and what's the price (Evo electric GKN AF-140). Will update you all though when I get that information.

They have been used in a Dryson racer (Yasa) that have beaten the world record for EV top speed.

Thank you all for taking interest in this thread.


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## Karter2 (Nov 17, 2011)

sorry , but you wont find any outlets for the EVO motors either.

They are OEM suppliers only and stopped selling even for research projects, last year.
Either way, both YASA or EVO would have cost you over 8k pounds for each motor, and a similar amount again for inverter to drive them.
.. not to mention the 700volt systems they use to produce that performance. !
some reading..
http://www.diyelectriccar.com/forum...ons-motor-most-power-weight-ratio-130370.html


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## major (Apr 4, 2008)

Friday_EV said:


> They have been used in a Dryson racer (Yasa) that have beaten the world record for EV top speed.


Excuse me  When did they exceed 307mph?


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## Friday_EV (Dec 9, 2014)

Agree major. Have checked and there are faster ev's. Drayson record is from 2013. 

Anyway, there is another company that produces PM motors for decent price but with much worse performance and efficiencies at direct drive speeds (around 1k rpm). At least for now. With 4 of those the car should achieve 60mph. It won't be a performance car and would drain more energy then on GKN or Yasa (poor efficiency) but will still offer less parts in the car (no gearbox and diff) and regen. They have some other motors in development (144v system) which may be better suited for ev. 
http://www.ashwoodselectricmotors.com/price/


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## skooler (Mar 26, 2011)

Let me know when suits you to have a look.

Why do you want to go direct drive over conventional gearbox.

I recently worked on a vehicle which had one motor on each rear wheel and it performed OK but would have been greatly improved by having another gear or two.

There are two big issues with this setup.


if you lose traction the motor can overspeed 
if you lose drive in one motor the car will pull strongly to one side.
 also, rx8 specific. You mention a large range - one of the best locations for batteries in the RX8 is under the boot floor. I suspect this is where you would want your motors so you would lose some battery space.

All the best,

Mike


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## Friday_EV (Dec 9, 2014)

Thank you Karter2, just read about those Emrax motors. They may be what I'm looking for.

Mike, the answer is because it seems pointless to keep a gearbox that is rarely used. It's pretty heavy part and it wears out. The direct drive with 2 or 4 independently controlled wheels can give several advantages in terms of maneuverability (eg when parking) and the mechanical system is far less complex. There's also less losses on gears and differential. 

I believe that with right motors the car can be pretty powerful and efficient in that configuration.

Lose of traction can be controlled by software that would cause motor controller to cut power to affected motor. As for losing drive in a motor I guess it's still better to drive slowly on one back home and repair it than stop in the middle of the road (conventional setup with one motor in drive system).

The ideal solution would be to mount the motor straight into the hub. It depends though on whether the available motor will fit in there. Otherwise as you say I will look into placing them under the boot floor. Those motors though are not very big so I suspect there will be still some room for batteries. Thanks for the tip though, will take into consideration when deciding on final configuration.


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## Duncan (Dec 8, 2008)

Hi Friday
The problem is - torque is (roughly) proportional to motor weight
So by going direct drive you need a motor that is about 8 times as heavy
(Tesla is about 8:1)
Using two motors means each motor is only four times as heavy

So replacing a diff/final drive that weighs -40Kg?? with an extra 300Kg of motors???
For what benefit???


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## Friday_EV (Dec 9, 2014)

Hi Duncan, where did you take that 300kg number from? I know I need around 250Nm torque at 1000rpm for my conversion. It looks like with two of those motors: http://www.enstroj.si/Electric-products/emrax-228-motorsgen.html it would be achievable. And the weight of two of those is circa 25kg.


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## samwichse (Jan 28, 2012)

And yet, look how much more power it puts out at 3-4k RPMs.


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## Friday_EV (Dec 9, 2014)

Hi samwichse. Thanks for the comment, you finally made me realise what did I miss. Indeed for a good trade-off between power and torque a reductor on each wheel would be a benefit to fully utilise potential of the motors. However I am not sure if I need all this power. Need to go through the calcs again. With reductor there's an issue of finding component with proper gear ratio (between 2:1 and 3:1) that is compact and light and fits the motor and wheel shaft.


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## Karter2 (Nov 17, 2011)

Now you are begin inning to see the issues around using in-wheel / hub motors and direct drive.
It's ideal in theory, but in practice, with available components, it is highly compromised.


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## Duncan (Dec 8, 2008)

Hi Friday

250Nm ....
The Mazda weighs 1400Kg
With tires that are 700mm diameter 250Nm will give (_357N-oops_) 714N forwards force
(I initially used the diameter instead of the radius)
That will give an acceleration of _(0.25m/sec2) - _*0.5m/sec2* 
Two of them will give 1m/sec2 ... - 25 seconds to 60mph ignoring all of the drag forces

To give a reasonable (not excessive) acceleration you need *1250Nm* of torque - and your 25Kg of motor goes to 125Kg

My car weighs 710Kg and I have a 102Kg motor and 4.1:1 reduction in the diff


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## skooler (Mar 26, 2011)

Quickly offering a bit of real world experience with hub motors and direct drive.

I have a 4KW chennic 'in wheel' motor in a large moped/scooter. The motor weighs 8KG and the whole bike around 150KG. It runs 72v 60AH (Sinopoly LiFePO4).

Its performance is OK but nothing spectacular. It easily gets up to 55mph and I've had it as fast as 70mph.

It would really benefit in having another 'gear' or two to give more low down torque and a higher top end.

The point I am trying to make is that the scooter is OK like this. Multiply the weight by 10 for a converted rx8 (mine is just under 1500KG ) and not increase the motor power and it will barely move.

I also recently worked on a small fibreglass car weighing around 400kg. It had two Curtis 1238 550a controllers running at 48v (26KW each) each controller connected to a single motor in turn connected to a single rear wheel using a 3.5:1 belt system. So 52KW (~70HP) available and a 400KG car. Should have gone like stink but in actual fact it only reached 35mph flat out. Again it needed gears.

By using a transmission you are effectively trading off some (relatively minor) efficiency losses for having the torque where you need it.

Hope this helps.


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## Friday_EV (Dec 9, 2014)

It helps, thank you. I will reconsider the configuration and do research on some reductors.


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## sexstrap (Feb 25, 2013)

Hi Friday_EV

I am also about to start my own RX8 conversion and I am also going direct drive but direct to the LSD (Limited Slip Differential) rather than direct to each wheel drive.
That way I can loose the gearbox but retain the single RWD LSD diff to simplify the coupling of a standard EV motor (Kostov 11 inch)
I (like you) will still have the extra complication of a set of contactors to enable reverse gear. (not to mention the power steering canbus fix that is required for RX8's) 
I hope that I can squeeze the motor in where the fuel tank used to go (or as close as possible, or I may put it where the gearbox was) and I plan on putting 25Kwh Traction Pack & Soliton 1 Controller under the bonnet.
My mechanic will start the build in Jan of 2015 I must have the car finished (legally drive-able) by September 2015.
Do you have a blog of your build progress? if not I suggest starting one and linking to it form here.
here is the link to my EV Blog, although it is mainly about my first EV conversion it will soon morph into the RX8 conversion proper.

http://electrobeatev.blogspot.co.uk/

Good Luck, cant wait to get a look at you blog/build as it progresses.

Graham Martin - AKA sexstrap, short for Sussex Bootstrap honest ;-)


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## Friday_EV (Dec 9, 2014)

Hi Graham,

I plan to start a blog but I thought to do it when I have concept ready. I wanted to explore feasibility of Direct Drive of the wheels but thanks to replies in this forum and further research and calcs I think I will keep the diff (not sure if stock one cause I need something around 4:1 ratio, need to ckeck what's in there now). The drawbacks of this solution are that max speed will be 125km/h (with the motor I'm looking into at the moment), but I should get it to accelerate from 0 to 100km/h in 7s (thx Duncan to make me look into this issue), and anyway you can't drive faster (legally). I am still looking though into motors so those calcs may change.

Cheers for the link, we will build it around the same time so we can exchange ideas  I'll post mine as soon as I get to it. I am planning to post my performance calcs spreadsheet for the referrence of others intending to build an EV. It will be done on the blog.

Where are you in the UK?

Good luck for your project!
Kris


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> Hi Graham,
> 
> I plan to start a blog but I thought to do it when I have concept ready. I wanted to explore feasibility of Direct Drive of the wheels but thanks to replies in this forum and further research and calcs I think I will keep the diff (not sure if stock one cause I need something around 4:1 ratio, need to ckeck what's in there now). The drawbacks of this solution are that max speed will be 125km/h (with the motor I'm looking into at the moment), but I should get it to accelerate from 0 to 100km/h in 7s (thx Duncan to make me look into this issue), and anyway you can't drive faster (legally). I am still looking though into motors so those calcs may change.
> 
> ...


Hi Kris

I am near Newhaven in East Sussex, where are you?

I guess you are still figuring it all out (parts wise) I have managed to source 350 x EIG C020 20AH LIPO cells for this conversion which should work out at around 25KWH total (more than double my first EV) I will be using Soliton 1 and a Kostov 11 inch.

I also was not sure about the Diff as 4th is a 1:1 and 5th would have been the overdrive if I kept the gearbox, As I want to loose it I am not 100% sure about the top speed but I am hoping that as the original wankel engine was a high revving engine there should be no problem sustaining a high RPM (well as high as the Kostov can take anyway)

Are you going DC or AC Motor? what batteries are you looking to fit?

Good luck and look forward to your blog, I use e-blogger but tumbler is also a good one.

Graham


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## Friday_EV (Dec 9, 2014)

Hi Graham,

I am in Derby, East Midlands. I've been recently in East Sussex though, beautiful place with those White Cliffs! 

Indeed I am still figuring everything out. Lately I am focused on the motor and drive system. As for battery I will look into around 30kWh, but exact config of it will depend on the voltage I need for motor.

Out of curiosity, what is the range you've got from you first EV and what was the config of battery? and vehicle weight?

Skooler, can you please offer also same answer for your RX-8? And additionally I am interested as well in acceleration with K11 alpha that you've achieved ( your conversion kept the gearbox, so when starting from e.g 2nd gear your torque is multiplied by a factor of 2.269*4.444=10.08, giving around 1900Nm peak torque). That should give acceleration of around 7.5 seconds from 0 to 100km/h (probably change of gear/gears is required during that run).

Unfortunately Graham, there's no good news for you as without gearbox the available torque at wheels after multiplication of 4.444 (diff) of the motor output will give you around 18 seconds acceleration from 0 to 100km/h. I am assuming 190Nm peak torque of Kostov K11 motor available through the duration of this acceleration which may be shorter in reality.

As for the top speed you should achieve >150km/h with K11 (higher max rpm than motor I'm looking at now) but it won't be fast to get there. With K11 motor I think you will be better off with gearbox to be sincere.

I am currently looking into EMRAX motors, in particular EMRAX 268 (http://www.enstroj.si/Electric-products/emrax-268.html). It's an AC PM Axial Flux motor with peak torque of 500Nm and continuous torque of 250Nm. It also gives continuous power between 50 and 100kW (with combined cooling). Unfortunately the rpm is limited to 4000rpm on this motor, therefore with diff only, the RX-8 top speed is limited to 112km/h (stock diff) and 125km/h (4:1 ratio diff that would be more suitable).

Thanks for the tips on the blog field!

Kris


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## skooler (Mar 26, 2011)

Range can be 60 miles if driven carefully. Agressively more like 30.

74x sinopoly 100ah cells. (24kwh)

1/4 mile time of 16.7seconds crossing the line at about 90mph.

Usually start in second which is good for 40mph.

1st for hill starts. Good for 15mph.
3rd 50mph
4th 85mph
5th i've had 105mph

Thats with the k11alpha


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> Hi Graham,
> 
> I am in Derby, East Midlands. I've been recently in East Sussex though, beautiful place with those White Cliffs!
> 
> ...


Hi Kris

My first EV is a Honda Beat curb weight is 760Kg (as listed on wikipedia, I have never weighed it) It has a Kostov K9 with Soliton Jr and 108 Turnigy 5Ah 5S1P LIPO cells (540 1Ah cells total) they are configured as 60S9P I get a range of around 40Miles I do a 20 mile round trip every day in it and recharge every night, have been driving it for approx 1 year so far and despite the (major) teething troubles (on blog) I love it, EV's are very definitely the future.

Thanks for the info on the motor configuration I may well have to keep the gearbox then (Again!, Bummer!) or can you suggest a different diff that might fit and give me a simple way to loose the weight added by the gearbox and get a reasonable gearing ratio?

I was planning on a 70S5P config on the new cells but it has already been suggested I push that to nearer 80S so I may purchase a few extra cells to achieve this.

Also My existing Honda EV is off the road currently as I have blown something in the gearbox (grinding teeth noise in all gears!), I guess due to the massive torque the K9 puts through the mini Beat gearbox, It has just had new brushes and a new bearing in the K9 after just 1 year! So I am assuming that some damage has also been inflicted on the gearbox as well as the motor, and before you ask yes I do drive like an adolescent ;-) I am currently looking at alternative gearboxes that might take straight cut gears and or a dog box to take all that extra torque, although this would be damn noisy for a road car.

Anyway that's enough hijacking of your thread!

Keep posting, Graham


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## Friday_EV (Dec 9, 2014)

sexstrap said:


> Thanks for the info on the motor configuration I may well have to keep the gearbox then (Again!, Bummer!) or can you suggest a different diff that might fit and give me a simple way to loose the weight added by the gearbox and get a reasonable gearing ratio?


Hi Graham,

I am sorry but there is no magic diff solution, unless you want a ridiculous top speed of 70km/h (see skooler post and top speed at 2nd gear), then you could try and find a diff of around 10:1 ratio (they may not exist however for a car under 3.5t, cause it seems pointless for typical car, all have gearboxes to get to that ratio). I guess you could maybe try and find a different gearbox with less gears (3 should be enough), maybe something like, 2nd (2.269:1), between 3rd & 4th ((1.645 - 1.187)/2 = 1.416) and 5th (1:1) ratio of stock RX-8 gearbox. Obviously this will complicate the conversion, and again such gearbox may not exist.

I understand the will of loosing the gearbox but looks like with Kostov motors it's not the optimal solution. More powerful motors are required if only diff ratio is to be used.

Sorry to hear about your ill EV and best of luck repairing it.

Thx for battery and range info to both yourself and skooler.

Cheers,
Kris


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> Hi Graham,
> 
> I am sorry but there is no magic diff solution, unless you want a ridiculous top speed of 70km/h (see skooler post and top speed at 2nd gear), then you could try and find a diff of around 10:1 ratio (they may not exist however for a car under 3.5t, cause it seems pointless for typical car, all have gearboxes to get to that ratio). I guess you could maybe try and find a different gearbox with less gears (3 should be enough), maybe something like, 2nd (2.269:1), between 3rd & 4th ((1.645 - 1.187)/2 = 1.416) and 5th (1:1) ratio of stock RX-8 gearbox. Obviously this will complicate the conversion, and again such gearbox may not exist.
> 
> ...


Hi Kris

I will probably go direct to diff anyhow I like the top speed and I realize that it will take a while to get there but I am planning on loosing as much weight as possible by going CF wherever possible, you can get complete doors front and rear in CF for the RX8 as well as the boot and bonnet, you can even get lexan window kits for the RX8's. I hope to get the weight down from 1400Kg to nearer 1000kg by loosing the engine/gearbox and changing the boot/bonnet and doors front and rear for CF.

The 0-60MPH will be a little slow but seeing as my current EV has the exact opposite problem (too much power for the OEM transmission) at least I wont be blowing it up any time soon (I am sure I will find a way to blow it up somehow, I usually do.)


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## Friday_EV (Dec 9, 2014)

I guess it's fair approach if you're not worried about acceleration. At least you won't bother with shifting gears and no more worn gearbox. Worth to speak with skooler on how the car behaves at hills on 5th gear. That would give you a feel of what are you likely to achieve with your conversion.

Losing weight will cetrainly help, but I am not sure if you can strip it to 1k kg. Do you know maybe already how much those CF parts cost? 

The issue is that batteries weight, so any weight you lose will go probably into batteries. From my initial calcs it looks like around 300kg of batteries are required for 25kW.

Skooler's Mazda weights around 1500kg, removing the gearbox (~40kg?) and going into CF (~100kg?) will basicly allow the car to return to stock weight (~1350kg).


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> I guess it's fair approach if you're not worried about acceleration. At least you won't bother with shifting gears and no more worn gearbox. Worth to speak with skooler on how the car behaves at hills on 5th gear. That would give you a feel of what are you likely to achieve with your conversion.
> 
> Losing weight will certainly help, but I am not sure if you can strip it to 1k kg. Do you know maybe already how much those CF parts cost?
> 
> ...


Hi Kris

I am using advanced NMC LIPO's so the weight is approx 150KG (428G each cell), This comes from the lack of the iron component (LIPO as opposed to LIFEPO) and the EIG's are 170wh/kg so very energy dense (however this is all without the additional Traction Pack construction battery boxes etc, hence the "Approx" 150KG, maybe nearer 170Kg), The Turnigy LIPO's I used in my previous conversion were 135wh/kg so not quite so dense. (this may go up slightly if I add another 50 cells)

I am aiming for 1000KG but as you say this will be difficult to achieve retaining the interior (which I am) but I will give it my best shot, CF is expensive but then so are coupling plates for the motor to a gearbox, my Honda's was £500 for just the plate and low inertial spline'd collar. (that's 1 CF door right there!)

To be honest I am learning fast from my mistakes on my previous build (The Honda Beat) I kept the Gearbox on that one as I was advised that it would be simpler and therefore cheaper to keep the Gearbox rather than source a different Diff/axels and rear wheel bases that could take the extra torque.

In hindsight this was a mistake as it appears that I may have now blown the gearbox after just 1 years (heavy) use, We will see (booked for January mechanics appointment) 

So I am interested to see just how it performs without a gearbox as my main requirement for this car is "4 seated" comfort rather than acceleration, the motor & controller came out of a Mazda MX5 conversion with a Turnigy (heavier) LIPO pack of around the same 25KWH size and that flew of the line, I know the MX5 is considerably lighter though at around 1050Kg, hence me wanting to achieve close to that weight if possible.

Nice talking to you

Graham.

PS. If you end up building your own charger make sure it is PFC it may be a little more expensive and larger but will allow much better charging on the go from EVSE.

Skooler, Did you ever finish your EMW charger (yours was PFC was it not) and what charger do you use for your RX8 now (is it on-board)? Sorry Kris Hijacking again ;-)


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## skooler (Mar 26, 2011)

Never finished the emw charger. Too many parts missing and quality is just not there. I wanted to know that my car was fully charged every morning. Mine was pfc which I believe is now a ce requirement, as is isolation.

I now run a single brusa nlg513 which is perfect for my needs. I did have two in there at one stage but needed it for a testbench. I plugin when I get home at night and I have a 100% charge by the time I leave in the morning.


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## Friday_EV (Dec 9, 2014)

Graham, 

May I ask where did you source those batteries from and what is their price? Their characteristics seem better then LiFePo I was looking into (higher cell voltage and lighter cell). I must say I don't know much about this technology yet but as you were using it for 12 months and you're still alive I guess they are safe to use  need to look more into those batteries.

Thanks,
Kris


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> Graham,
> 
> May I ask where did you source those batteries from and what is their price? Their characteristics seem better then LiFePo I was looking into (higher cell voltage and lighter cell). I must say I don't know much about this technology yet but as you were using it for 12 months and you're still alive I guess they are safe to use  need to look more into those batteries.
> 
> ...


Hi Kris

Unfortunately I can t give you details on where they came from as part of the reason for me getting them so cheaply and in such quantities was a non disclosure agreement.

However I do have a contact who can supply in bulk (hundreds) they are £20.00 per cell which is <1/3 of their OEM price. (Normally around £65.00 per cell new) I can only get them in batches and fairly infrequently (every few months) but as the average EV build takes a year anyhow this is not really a problem.

Bear in mind that they are not brand new but I have been assured that they have had very little full cycles on them, obviously as with almost all DIY EV kit they have no warranty to speak of other than a gentlemen's agreement to replace and completely dead cells after testing them. (the same would be true of any new cells to be honest)

I have had to test every single cell (as you would need to) using a discharge and graph test via Powerlab 8 from revolectrix to get an indicator as to the health of the cells, so far I have found 1 single bad cell in 250. And as yet they are untested under very high Amp loads, My best test is a 40A load, light for EV use, However they are specifically designed for EV use hence the 20AH per cell capacity so I am optimistic. Oh and I have had to copmpletely rework the way in which they were originally mounted/packed as it was crazy for EV use (aluminium separators for example, I have bought £300 worth of silicone as separators instead). Traction pack construction is never cheap and when you are investing this much cash in a battery you want it wrapped up nicely firmly packed and properly secured 

This testing scheme is recommended (essential IMHO) for all Traction Pack constructions I had the same done to the previous TP in the Honda but I bought them pre-tested by an EV expert colleague. Paying well over the retail for the privilege but when you consider the time they take to test it was money well spent at the time, I have since invested in my own testing equipment.

The EIG C020 170wh/kg NMC cells are by far the best that you can get anywhere on this side of the globe and to be honest I was amazed to find a source in the UK hence me jumping on it and buying the first batch more or less outright.

Oh and the projected number of total cycles on these cells could number 5-6000 cycles, that is 10 -12 years normal daily EV use!

However be warned LIPOS are by far the most dangerous batteries you can get and if you miss treat them they will burn you or your house down, these cells must be constructed in a Traction Pack using LVC/HVC electronic circuits to cut off the charge in the event of overcharging and even more importantly to cut the throttle in the event of discharging below their 3.0v bottom limit.

I have learned this the hard way in my Honda (see blog) I do not intend to make the same mistakes again. 

http://electrobeatev.blogspot.co.uk/2014/10/testing-eig-cells.html

All that said they are by far the dogs nuts of batteries you wont find better anywhere AFAIK


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## Friday_EV (Dec 9, 2014)

Thank you Graham. The 'offer' is indeed very interesting and I would appreciate a poke when some of those cells are available for sale. It equates to the same price as the LiFePo batteries I wanted to use but are half the weight!

I need to learn though how to secure them properly in Traction Pack. Do you know of some good guide on how to build and wire the traction packs? I can see some info on your blog but as it was made by someone else there are not enough details to understand how it's been done.


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## sexstrap (Feb 25, 2013)

Friday_EV said:


> Thank you Graham. The 'offer' is indeed very interesting and I would appreciate a poke when some of those cells are available for sale. It equates to the same price as the LiFePo batteries I wanted to use but are half the weight!
> 
> I need to learn though how to secure them properly in Traction Pack. Do you know of some good guide on how to build and wire the traction packs? I can see some info on your blog but as it was made by someone else there are not enough details to understand how it's been done.


Hi Kris

Hope you had a good xmas and new year, Although the Honda Traction Pack was put together by my mechanic it is fairly straight forward.

The basics are to get the Ali battery boxes made to a strict tolerance so they are mm perfect fit for the cells you intend to pack in them (plus the packing material, I used 3mm rigid packing material which I obtained free of charge from a local industrial estate, it was the lining of large deliveries of flat packed material).

You might also want to consider breaking your total traction pack into several "lift-able" chunks and getting several separate boxes made to pack them in.

It is a good idea to make the boxes removable if you need to service them, if you make them human lift-able then you can lift each separate box out without the need for lifting equipment, This does complicate the wiring slightly but it is worth the extra complication to allow you to service the batteries yourself, Also if (god forbid) you have a fire in the battery compartment it might well be confined to a portion of the total battery pack rather than the whole lot.

But firstly you would need to work out the layout of your batteries and how you are intending to wire them, For example with these newer EIG LIPO's I have decided to dump the aluminium separators and replace with 1.5mm silicone pads (bought separately)

I am also going for a 5P (five in parallel) probably 70 or 80S (serial) and to simplify the manufacture of the buss bars I am going to arrange the batteries in blocks of 5 (5P) and then place them in a line (a row) of 5 in serial so that I can simply place flat copper plate (3mm) buss bars drilled correctly to allow the screws to connect all the batteries in a row of 5P 5S this fits conveniently under the bonnet of the RX8 in the space available (the 5S is simply 1 row that happens to fit the width of the bonnet space available) I will need 14-16 of these rows of 5P 5S to fit the whole 350-400 cells in the space under the bonnet I (think I) will be making 3 separate battery boxes (maybe more if they are to heavy to lift out on my own) or I may just rely on a chain lift for this one.

I have had to modify the cassettes that the EIG cells came with as they has a couple of "issues" as far as I am concerned.

1) They had Ali separators (bad idea)

2) They were vertically arranged meaning that if I remove the cassette housing and don't change the orientation the cells could be potentially hanging on their electrical connection tabs (not a good idea) so I have opted to lay them flat in piles and wire the 3 (or more) boxes in series.

So actually the traction pack layout is what you need to get straight and this will depend on the cell choice, Space available and how you intend to wire them all up, LIFEPO cell blocks are a lot simpler to wire up as the connections are all fairly standard and you simply have to load them in an Ali box and connect them all up in your chosen arrangement (with or without BMS) but then LIFEPO at best give around 3C (charge discharge rate) the Turnigy's have over 20C and the EIG's 10C burst 5C nominal, and as you already discovered they are a lot heavier (with the iron chemistry)

The other issue with custom traction packs (rather than off the shelf sealed LIFEPO blocks) is you need to have the buss bars manufactured, Buss bars are best made from copper bar or plate (I am using plate for the EIG's, the Turnigy's needed bars due to the bullet connectors on those type of cellpacks) the EIG's can use simple copper plate however I can assure you that copper plate or bar is "Impossible" to drill with a standard drill press due to its malleability it has to be drilled on a milling machine, For the Turnigy's I had the buss bars professionally drilled and soldered as they needed bullet plugs and sockets, luckily for me since then I have invested in a small CAD CAM milling machine so I will be drilling the copper plates for the EIG's myself, You could get this done quite cheaply in your local industrial estate, I tend to commission the stuff I cant handle and do the rest myself.

As for actually securing them they should be packed tightly in the Ali boxes and so should not have any room to move at all, The EIG's have bolt holes in the top of the cassettes to allow the "blocking" of cells (physically bolting them in blocks) I will also be "clamping" (snugly not tightly) them in blocks to stop any potential for cell swelling when in use.

I am of course assuming that you already know that to work out what battery arrangement you will need. You will need to arrange any cells you are going to use in series and add up their max voltages to get to your burst (max) voltage on your motor. Once you have your series count of cells you then put the rest in parallel with those series cells to achieve the range you want, I would think you will need around 20-25Kw pack to get 50-60 mile range out of an RX8. 

Any news on your blog yet?

Graham

P.S. I do not profess to being an EV expert at all, I am merely relaying what I have learned since I first started on the EV road in Dec 2012.

Good Luck


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## Friday_EV (Dec 9, 2014)

Hi Graham. 

Yes, that was good time and between meetings with family and friends I've managed to pinpoint the final concept for my ERX-8. Hope you had good holiday as well. 

I am now continuing to search for charging and BMS solutions which will help determine as well how to divide the traction packs. I have bought albo 'Build your own electric vehicle' book so will spend some time on that before I move any forward, to make sure I'm not missing something important.

The blog is now on top of my list but January seems to be pretty busy so I expect to have it online not earlier then end of the month. 

Your experience is definitely larger than mine as I did 0 EVs by now and did not really handle this kind of battery yet. And as much as I understand most of the math and physics behind the EV this is far from having a proper know-how and practical experience. Thanks for the tips, that gives me some idea of what is required to make the TP. 

With your new conversion, did you think about cooling of TP?

Cheers,
Kris


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## sexstrap (Feb 25, 2013)

Hi Kris
I went for the EMW open source 12kw charger in kit form, Be warned this kit is not for the faint of heart it took me 3 months to build it and get it working, And it is still not 100% (it does not switch itself off for example however it does reduce the duty cycle as it nears 100% SOC to give the slower charging cells a chance to catch up, so it wont overcharge the cells) Don’t get me wrong it is a great intelligent charger and probably the best you can get at this price, If I were to get another (and I may get a PFC version soon) I would make sure it was the PFC version and just buy the PCB's and source all the components locally as after the considerable duties shipping and taxes of importing into the UK from the US it does not make much of a difference.
I opted to skip the BMS and just manually mange the SOC with a simple battery monitor, and although I would love a BMS my financial consultant (the missus) would not allow the additional expense at the time of the build. However I am looking at building a BMS with the help of a guy called Simon Rafferty (the original designer of the precursor to the EMW intelligent charger). Who also happens to live fairly locally.
The only book I used was the web and particularly this forum, Although I would say it is critical for you to find someone local to yourself who has already built an EV, I can honestly say that without Steves (Jozzer from Jozztek.co.uk) help (my local EV expert) there is no way that I would have gotten the build done in the year IMO this is essential, You could just rely on the forums but you might well get confused with the constant conflicting differences of opinion that you will find on the EV forums.
I have done literally nothing about cooling of the Traction Pack, in normal use in the UK cooling should not be necessary, If the batteries reach dangerous temperatures than something is seriously wrong with the charger, The LIPO batteries I used have a very high C rating which means they are designed to discharge (and charge) very quickly without going critical.
Good luck and I look forward to reading your blog.


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## tylerwatts (Feb 9, 2012)

Hey Friday_EV
Regarding the motor you mentioned in Berlinger's Latvian rx8 thread, that seemed incredibly expensive for what it was. Have a look for Scott drive on the forum. Also, I noticed between the 25 and 35 models that the smaller motor may make less torque but has higher rpm so when you gear for the same speed the smaller motor actually has higher output due to the gearing. And it weighs less so can accelerate faster also and take up less space. Worth noting. 
Regards 
Tyler


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## Friday_EV (Dec 9, 2014)

Hi Tyler, I did asess that option as well. The thing is that gearbox has some weight as well and is difficult to find one with suitable ratio and in sensible price. Hence I thought it's less hassle to just have the more powerful motor and no gearbox. The output is similar enough not to go into looking for gearbox (which adds to the cost also).

I'll look into Scott drive.

By now the best motor I've found in terms of power, rpm and weight is Siemens 1PV5138-4WS20, bit is difficult to source and also expensive. It would allow though with a 1-speed gearbox (1:96 ratio) to achieve increadible acceleration.


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## tylerwatts (Feb 9, 2012)

What ratio is that? Are you not linking straight to the diff? Then you should use the diff ratio. And on that note I was expecting you can use an aftermarket diff gear set for higher ratio for the faster motor and save more weight. Never considered the gearbox as I thought you intend to not use one. 

The Siemens motor is very expensive. Metricmind sells them, and EVTV might have some also, their stock seems to fluctuate.


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## Friday_EV (Dec 9, 2014)

Yes, the intent is straight to diff. But I did not come across an aftermarket RX8 differential with higher ratio than standard 4:444:1 and can't imagine someone manufacturing something above 5 for this car. Trying to match one from any other car seems to be very complicated based on metricmind experience (his Audi project). 

Therefore I was thinking that if rpm of the motor is high I could add a 'small' 1 speed reductor between motor and diff. For Siemens the final ratio would be around 8.7:1 to achieve top speed of 140km/h and acceleration of below 5s to 100km/h.

Obviously best would be to avoid this and get strong enough motor to link direct to diff. Apparently GLELEC can customise their motors, therefore I'll try this route as well.

To clear things. My main goal is not top speed but rather acceleration. RX8 is a sports car and I'd like to keep it that way in electric version. Although most of the time I'll drive economically to save range I'd like to be able to drive more sporty from time to time, especially since the whole project is a major investment.


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## mira9_cz (Feb 27, 2013)

Hi Friday EV. I wish you good luck with your project!

I also had thought a lot about using 1 speed reductor, but I had no luck finding anything suitable and reasonably priced. Eventually I found out that offroad 4x4 cars usually have 2 speed reduction gearbox with 1:1 and 1:2 ratio. They are widely available and cheap as second-hand spare part, in different shapes, manually or servo-shifted, so this might be the way to consider. Sometimes the reduction gearbox is even synchronized, therefore you can shift it while driving. Also they offer output for FWD, which might be usable for some additional recuperation for example. But removing the front driveshaft carrier is probably more reasonable. Also the gearbox which shifts between 4x4, 4x2 and 4x4L is needed. The secondary gearbox from permanent 4x4's have integrated differential which makes it not suitable.
Recently I had purchased nice Suzuki X-90 which really asks for conversion  I was thinking removing manual gearbox and keeping only two speed reduction gearbox, this is quite the same thing.


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