# Planning NB Miata conversion



## JohannesVinke (Jan 24, 2009)

Hello everyone!

My dad and I are looking into converting a second gen Miata into an ev.
Specs would be 100km range and should have zippy acceleration (at least like original car, 0-100kmh in ~7 sec). We want to take away the picture people have about ev's being slow as much as possible.

Our motor will probably be Azure Dynamics AC55 with the standard DMOC445, in a direct drive setup. We are very interested in regenerative braking (adding 10% (?) to the range) and the higher efficiency to justify the costs.

I have been searching the web for Siemens AC motors like the 5135WS28, which I would prefer, but can’t find them anywhere, have they stopped production or something?

Ian Hooper told me that his Miata could do 120 km with his 20kWh pack and DC motor, so that looks like the size of pack we need.

We've been checking out the various options regarding battery options, and we're definitely going with LFP's.

The most obvious manufacturer would be Thunder Sky, but they have a rather slow maximum discharge rate (3C if I'm not mistaking), so later we found Headway, they can achieve much higher rates but aren’t as pricey as A123/LiFeBatt/K2.

The 38120L cell looks like the thing we need. This is the 1st ev conversion we’re doing and have limited knowledge in electrical systems, other than standard highschool formulas (very willing to learn a lot more though!) Would it be better for a first timer to look for a large pack so we don't have to make our own pack out of individual cells?

A lot of questions, I know, hope you have the time to answer some of them.

Thanks!

Johannes
(The Netherlands)


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## donmurray (Jan 21, 2009)

I question the cost benefit of building a regen system for a light passenger EV unless you spend time in stop-and-go traffic, or in hilly country. Regen systems seem to make more sense for heavy vehicles, and hilly country. Also, I understand you have to use an AC motor and controller which are more expensive. My reason for some doubt is that driving an EV will change driving habits where people will antipate stops more in advance so they can do more coasting and use the brakes less. Anticipating these stops will let EV drivers get off the throttle sooner, and this alone will save energy. Ideally it looks like you would go off throttle in time to almost coast to a stop. Traffic may not permit this ideal approach unless you don't mind a lot of middle finger salutes. Probably as a factor of age and rural living, I'm suprised at how little I used the brakes in my Ranger pickup with an ICE.


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## karlos (Jun 30, 2008)

Hi Johannes, have been thinking of a Miatta (MX5 in NZ) conversion myself and for the last few days have been driving past a good buy...
Also I was considering the AC55 Azure motor but would have preferred a Siemens motor and controller which had a built in DC DC converter as well. I understand Siemens is not selling motors or controllers for the home car builder anymore and Evisol in your part of the world is making something similar in the way of a controller to what Siemens used to make. I was also thinking of Thundersky batteries but am interested you might have found a good alternative. For and EV to work for me I would like a minimum 200km range so am looking at nearly twice the kWhrs you are thinking of but I have not as yet investigated if 40kWhrs would fit into a Miata and also would it make the car overweight?
I take donmurry's points but if range is critcal and if your driving conditions can make the most of regen then it seems you could save the not so insignificant price of extra batteries to compensate for the extra cost of an AC system like the Azure one. I believe an AC system is more efficient anyway so as well as regen savings you need a cheaper battery set or get better range. I'm looking at the headway batteries for my situation; have you looked into what/if you need a BMS for these batteries and if so, how would you set it up and what make would you use?
I look forward to hearing about where you are up to and wish you the best for your proposed project!


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## RKM (Jun 9, 2008)

Johannes and Karlos,

I'm just nicely started into my conversion of a gen I Miata. Dimitri has done a very nice gen II Miata conversion, sold it and has moved on to a Mazda 5 wagon. Notnull has a beautiful gen I conversion as well. There are quite a few out there.

I will be using a Warp9 DC and about 23KWh of LFP, likely TS. I expect to get 100-125 km range. I spent some time last evening figuring out where to place 44 or 45 160Ah cells. IMHO you will not get much more than 44 or 45 of these cells into a Miata. At least not if you're putting them in insulated boxes. I don't want to rain on your parade Karlos, but I can't see how you would be able to fit 40KWh of prismatic LFP into that car. LFP has comparable volume to Pb, though more usable Wh. Weight would also be excessive.

Johannes... My understanding is that TS cells have a max discharge of about 3C with momentary burst (10 seconds) of up to 10C. Not too bad.

I love the Miata for a conversion vehicle, but it is certainly not the most practical or cost efficient. Having said this... convert a car that you will want to drive (word of wisdom from this forum).

Good luck and welcome. 

Rob


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## karlos (Jun 30, 2008)

Hi Rob, thanks lots for your reply and it's great to hear from someone with your experience. Yes, I thought I might be really pushing it to get much more then 120kms, I need 200kms to get between to cities relative to me so will have to consider a more suitable donor car, any suggestions welcome! I have a 97 Toyota Celica already which I bought for a conversion but have gone away from the idea of a front wheel drive despite the practicalities and yes Rob, a car that you really enjoy driving should sway the decision big time as in my case I intend to have the car a long time. I might once again look at the idea of a home built roadster.... any suggestions welcome


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## tj4fa (May 25, 2008)

Since seeing the Mazda Miata's people have done here, I have fallen in Love with the car.  

I think it will be a great car to convert and probably a lot of fun to drive.


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## DIYguy (Sep 18, 2008)

tj4fa said:


> I'm thinking a 12V magnetic AC clutch coupled to a small alternator/PM motor coupled to the drive motor's tailshaft ought to do it as long as the alternator/PM motor sends more than battery pack voltage back to the batteries.
> 
> By mounting the regen setup on the drive motor's tailshaft should also provide some drag when energized to actually assist with braking. When not energized will have minimal loss as the clutch/regen motor will only be free-wheeling on its internal bearings.


Hey TJ,

I'm planning to do a similar thing with regen on my Mazda truck. If you mount the electric clutch on the drive motor instead of the regen alternator, you won't have to spin anything while driving... alternator is motionless. Enabling regen engages clutch on motor tailshaft and then spins alt. . . at least this is my plan. A few folks have done this.

One fellow mounted a small pushbutton switch on the side of his shifter knob to energize the regen. I kind of like this idea after thinking of it for a while since, you certainly don't want to be braking when you want regen (well not until the late stages of the stopping process anyways). I know you could set up the pedal switch to work early in the pedal stroke....but I would worry that I had some brake drag while initiating regen. 
Something to consider.

Cheers.

Gary


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## tj4fa (May 25, 2008)

DIYguy said:


> Hey TJ,
> 
> I'm planning to do a similar thing with regen on my Mazda truck. If you mount the electric clutch on the drive motor instead of the regen alternator, you won't have to spin anything while driving... alternator is motionless. Enabling regen engages clutch on motor tailshaft and then spins alt. . . at least this is my plan. A few folks have done this.
> 
> ...


Thanks Gary. Maybe the Original Poster can benefit from your recommendation.


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## dimitri (May 16, 2008)

> Our motor will probably be Azure Dynamics AC55 with the standard DMOC445, in a direct drive setup.


Have you seen the size and weight of AC55? Its a monster, way too much for a Miata. You will not have space left for batteries.

Seems that range is more important to you, so you should really try and go for max battery capacity and smaller motor. And think real hard about AC and regen, do your math and consider your terrain. Regen is not that great on flat roads, but it complicates the project big time.

Also, look at some typical LiFePo4 cells and think of their total weight and volume at your target energy level. Sure, they are better than Lead, but they take same volume and still weigh enough to require suspension upgrades.


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## DIYguy (Sep 18, 2008)

tj4fa said:


> Yes Gary, this is how I would probably need to do it as well. My front battery box would get in the way if I have too much stuff in front of the tailshaft.
> 
> From looking at the Miata someone else did, I would think there is room to do it on the drive motor tailshaft like you mentioned if it is considered up-front in the conversion like the Original Poster is doing.
> 
> Worse case (or maybe another option for him/us) is to mount it connected to the driveshaft at the rear end flange.


Off topic...last post here on this...but I have a link to a real nice job on one of these on home PC. Could send it if you like.

G


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## JohannesVinke (Jan 24, 2009)

Wow, great to get such a lot of reactions, thanks a lot!



karlos said:


> I understand Siemens is not selling motors or controllers for the home car builder anymore and Evisol in your part of the world is making something similar in the way of a controller to what Siemens used to make.



I contacted Evisol a couple of days ago, they said they're not selling to consumers and small businesses anymore due to capacity shortages.

They are setting up a company to cater for consumers and hope to have it up and running by the end of this year.


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## JohannesVinke (Jan 24, 2009)

Hi Rob!



RKM said:


> Johannes and Karlos,
> I'm just nicely started into my conversion of a gen I Miata. Dimitri has done a very nice gen II Miata conversion, sold it and has moved on to a Mazda 5 wagon. Notnull has a beautiful gen I conversion as well. There are quite a few out there.


Yeah, I saw them, they look really good!



RKM said:


> Johannes... My understanding is that TS cells have a max discharge of about 3C with momentary burst (10 seconds) of up to 10C. Not too bad.


Can I find this anywhere, because I never saw a 10C number stated anywhere with TS batteries. Can anyone else confirm 10C discharge?

We chose for the Miata because we would like to have a (reasonably) modern convertible, so we don't have to worry about rust etc, which will probably occur way before we have to change batteries or drive system.

Looking at a DC setup, what kind of acceleration could we expect with a 20kWh pack and a Warp 9 or 11 with 1000A Logisystems (the biggest (???) available DC-DC converter since Cafe Electric stopped production)?


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## RKM (Jun 9, 2008)

http://www.thunder-sky.com/pdf/200871782241.pdf

This spec sheet from TS shows a max burst current of 10CA. A vendor confirmed for me that a 10 second burst up to 10CA is acceptable.

With respect to acceleration.... I've never driven an EV so don't have first hand experience but... with a controller capable of feeding 1000 A for a couple of seconds and then gradually reducing the output, should be capable of launching a light car very very quickly. Perhaps 0-96 kmh in 6-8 seconds. The motor size and pack weight will also be a factors. I would also expect that the strongest acceleration will be in the 0-50 kph range. This is where the torque characteristics of electric motors really shine. Others will chime in to correct me on all of this!

A large pack size, as measured in KWh, will of course hurt acceleration as the larger the pack the more weight. You would need to be sure that your pack is capable of feeding the current to the controller. Theoretically, 160Ah cells with a burst of 10C should be more than up to the task.

Note: The DC-DC converter supplies 12V power to the 12V system of the car from the traction pack. The controller powers the traction motor (I know you already knew that). 

Rob


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## JohannesVinke (Jan 24, 2009)

Well, we made a decision about our budget, and at current exchange rate it's about 15-16K usd for the conversion.

RKM: Thanks I didn’t see that before I guess TS is the best option currently available then! What BMS and charger would you all recommend?

Rob: Haha, yeah I meant power inverter lol



dimitri said:


> Seems that range is more important to you, so you should really try and go for max battery capacity and smaller motor. And think real hard about AC and regen, do your math and consider your terrain. Regen is not that great on flat roads, but it complicates the project big time.


Yeah, we're ditching AC, The Netherlands is about as flat as you're gonna get, so added value of regen braking doesn't outweigh the extra costs.

Range is not carved in stone, just looking to make an electric car and if it would go 100kms it would be nice, but a little bit of zippyness is more important.

What kind of acceleration were you getting with your car? Top speed not really important, 60-65mph would be more than enough.

Would the NA or NB model more suited? We didn't buy any car yet so either one is possible. I think the NA is a bit ligher, but I don't know how they compare to the amount of room for batteries. Or would we get the best results with a VW beetle convertible, just thinking out loud, don't know how they all compare w.r.t. room for batteries, the beetle is the lightest one of all with the original ICE.


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## tj4fa (May 25, 2008)

JohannesVinke said:


> ...We are very interested in regenerative braking (adding 10% (?) to the range) and the higher efficiency to justify the costs.
> 
> Johannes
> (The Netherlands)


There's a breakeven point somewhere and if it seems worthwhile to you, don't let anyone talk you out of it especially if you do a lot of stop and go in your location.


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## tj4fa (May 25, 2008)

DIYguy said:


> Off topic...last post here on this...but I have a link to a real nice job on one of these on home PC. Could send it if you like.
> 
> G


The OP might want to take you up on that offer so he can consider it in his conversion.


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## JohannesVinke (Jan 24, 2009)

tj4fa said:


> There's a breakeven point somewhere and if it seems worthwhile to you, don't let anyone talk you out of it especially if you do a lot of stop and go in your location.


Yes, there is a breakeven point, and you're using less energy than with dc, which is all what ev's are about.

Looking at the costs for a 20kWh system:

Azure Dynamics AC55 with the DMOC445 is 5300 usd
Batterypack needs to be around 300v, so with TS that would be 104x 60Ah 3,2v cells (=14440 dollar from Everspring, including volume discount) and 104x BMS (28 usd from BEV).

Total price: 5300+14440+104*28= 22652 usd
Total weight motor, controller and batteries: 106+15+260= 381 kg


Warp 11 with Logisystems 1000A controller is 3025+1825
Batterypack can be 39x 160Ah (=10982 dollar from Everspring, including discount) and 39x bms

Total price: 3025+1825+10982+39*28=16924
Total weight motor, controller and batteries: 101+4+218= 323 kg

I didn't include the charger in the equation, but I assume a charger for 120v is cheaper than for 300v+

When comparing a 20kWh system, DC is 5700 dollar cheaper, and 58kg lighter.

How do the 2 compare performancewise?


What kind of range gain can I expect when choosing for ac?

If I can get away with 10-15% less batteries this means less cells, less BMS systems and less weight, then the difference is smaller.


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## TheSGC (Nov 15, 2007)

Your price difference is due to the battery choices: 

Your AC setup has 102 x160 cells, or 3.2v*104*160 = 53.248 KWh of juice! Your talking 150+ miles of range with that!


Now your DC setup has 3.2*39*160 = 19.968 KWh, which is probably 50-60 miles of range with the lithium.


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## DIYguy (Sep 18, 2008)

tj4fa said:


> The OP might want to take you up on that offer so he can consider it in his conversion.


Check out this link and go to the Regen section. I love almost everything this guy did! Right from the motor blower to the regen switch and alternator. Very nice. I will copy much of this. 

http://www.northrim.net/wyanders/ev/


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## karlos (Jun 30, 2008)

DIYguy said:


> Check out this link and go to the Regen section. I love almost everything this guy did! Right from the motor blower to the regen switch and alternator. Very nice. I will copy much of this.
> 
> http://www.northrim.net/wyanders/ev/


I see what you mean, the guy really knows how to cut some corners! His solution for changing the voltage output of his regen alternator is very clever but the grinding noise sounds like he might get a bit of heat output as well...


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## DC Braveheart (Oct 12, 2008)

TheSGC said:


> Your AC setup has 102 x160 cells, or 3.2v*104*160 = 53.248 KWh of juice! Your talking 150+ miles of range with that!


Actually he was talking about the 60Ah cells with the AC setup so total capacity is about the same as his DC equivalent ... though I suspect he'd b hard pressed to find space to fit that number of cells in a Miata even though the 60Ah cells are quite a but smaller than the 160s.


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## JohannesVinke (Jan 24, 2009)

TheSGC said:


> Your price difference is due to the battery choices:
> 
> Your AC setup has 102 x160 cells, or 3.2v*104*160 = 53.248 KWh of juice! Your talking 150+ miles of range with that!


No, my post says ac setup 102x 60Ah cells, so the total would be 3.2v*104*60= 19.968kWh



TheSGC said:


> Now your DC setup has 3.2*39*160 = 19.968 KWh, which is probably 50-60 miles of range with the lithium.


Indeed, Ian Hooper told me that his 20kWh pack and Warp 11 would go about 120km (about 75 miles)


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## JohannesVinke (Jan 24, 2009)

Ah, you saw it before me, thanks DC Braveheart


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## JohannesVinke (Jan 24, 2009)

Braveheart,

I don't really need a lot of bootspace, as this is just for giving ev's a try and see how converting it will go. I do want it to work of course!

If I take some bootspace, will that be sufficient to house the number of batteries?


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## DC Braveheart (Oct 12, 2008)

JohannesVinke said:


> Braveheart,
> 
> I don't really need a lot of bootspace, as this is just for giving ev's a try and see how converting it will go. I do want it to work of course!
> 
> If I take some bootspace, will that be sufficient to house the number of batteries?


Note I was wrong about the space you have anyway. With a bit of surgery in the rear you can fit c. 70 of 104 60Ah cells in the space this conversion (http://home.comcast.net/~aschwarz7/) used to fit 11 US Battery 8V PbA batteries according to the spreadsheet I just put together! Granted he did some MAJOR surgery, but with cells in front and in the trunk cavity I'm sure you'd be able to get all 104 in the Miata.


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## weber (Apr 22, 2009)

JohannesVinke said:


> My dad and I are looking into converting a second gen Miata into an ev.
> Specs would be 100km range and should have zippy acceleration (at least like original car, 0-100kmh in ~7 sec). We want to take away the picture people have about ev's being slow as much as possible.


Hi Johannes,

My friend and I are converting an NA 1.6 Miata (called an MX-5 in Australia) using AC. We set ourselves the task of giving equal or better performance than the original so we are going for the magic figure of 100 kW peak (maybe for 15 seconds). But we are going somewhat over the budget you mentioned.

We have figured out, in theory, how to fit 208 x 40 Ah Thunder Sky or Sky Energy cells without taking up the already small boot (trunk). It sure wasn't easy, but using smaller cells means we can fit them in more places. We expect this to give us a range of about 160 km at city speeds and 100 km at highway speeds. We are using an industrial 415 volt induction motor and controller, so it's a nominally 624 volt battery (all 208 cells in series). 

I believe that 10C from Thunder Skys for 8 seconds is possible, when new, but the cells would have to be at 25°C or more and the voltage per cell will pull down to about 2.0 V for the duration. And we don't know how much capacity you lose every time you do this. We are only going for 6C from them, or from Sky Energy SE cells which are supposedly a little better.

We don't think we can get the performance without keeping the transmission, and if you keep the transmission, and mount the motor inline with it, you can't fit a motor whose shaft height is greater than about 132 mm unless you can do some very fancy engineer-approved cutting-away-and-reinforcing-elsewhere of the front subframe. The AC55 has a 160 mm shaft height. We are using a 132-frame motor from ABB and a variable frequency drive from Control Techniques.

You can read more about our progress so far, here:
http://www.aeva.asn.au/forums/forum_posts.asp?TID=980


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## kittydog42 (Sep 18, 2007)

I just finished converting a 2000 Miata using 13 Valence UCharge XP group 27 batteries. They are 42 pounds each. I put six in the front, with 2 upright on either side of the motor, and two on their side above the motor. I put two on their side in the space formerly occupied by the fuel tank, and one in the space beside the differential and driveshaft. Those three are accessed from below and from the access cover provided for fuel tank maintenance located under where the top folds down. Mounting the fuel tank batteries required lowering the differential about 1.5" by loosening the bolts. That was for clearance. The remaining four batteries are in the spare tire well, which was cut out and a box dropped in. I cut out much, much less than what was cut out on that Miata with the 8V golf cart batteries. I still have a lot of room under the hood and in the trunk if I wanted to place any more batteries, as the trunk was left with enough free space to be usable.

I haven't posted pictures yet but I will post a link to some in the near future.


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## karlos (Jun 30, 2008)

Hi Weber, sounds like you have been doing some great research for your MX5 project and you have found a source of controller and motor I did not know about. Thanks for letting us know about ABB motors and Control Techniques. Can you please specify the model numbers of the units you are using and how cost effective are they relative to the AC55 motor and controller from the same company? Is there any drawbacks using the motor and controller, is regen possible?
Thanks for any help you can be, I have been close to getting started on a similar project myself.


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## weber (Apr 22, 2009)

Hi Karlos, the ABB motor is 3GAA 131 008-HSE (22 kW 2 pole 132-frame)
http://www.abb.com/product/seitp322/6d46d8c65eb9d173c125744f003f527f.aspx
around AU$3000.
The Emerson/Control Techniques drive is the Unidrive SP5402 (75/90 kW 400 V)
http://www.controltechniques.co.in/unidrive.htm
around AU$13000 including software development system.

 The drive is capable of 112 kW peak, and so is the motor when we overvoltage and overspeed it by using its 230 V winding at 415 V, and run it to 80% of breakdown torque. They, and the battery (208 x SE40), should maintain that power level for long enough to get arrested for speeding (15 seconds). 

That's slightly less than twice the power of the AC55 and DMOC445 for slightly less than twice the price. But there are some AC55's and UMOC445 controllers going for about half the price again of the AC55 and DMOC from EVComponents at the moment. But can't fit an AC55 in an MX-5 due to diameter (shaft height).

Control techniques have a less expensive version of that drive, the Commander SK5402. This doesn't have the same level of programmability, e.g we are planning to use the VF drive as charger as well. All VF drives give you regen braking for free.


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## karlos (Jun 30, 2008)

Many thanks Weber for all the most helpful info.
I guess you are after high torque options to the wheels so are you planning to leave the gearbox in or are you going for a direct drive of the prop shaft? By supplying the higher voltage to the 240V motor, what revs will you then get from the motor? I have been quite keen to go for the direct drive option. 
How likely is it that your will get the Unidrive SP5402 to be a battery charger as well? That would be ideal.
If you get any discount for any orders of more than one, i could be quite interested in purchasing components with you.
Did you get a price for the Commander SK5402 Controller?
Cheers!


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## weber (Apr 22, 2009)

karlos said:


> Many thanks Weber for all the most helpful info.
> I guess you are after high torque options to the wheels so are you planning to leave the gearbox in or are you going for a direct drive of the prop shaft?


We oscillated back and forth a few times about that. But have settled on keeping the gearbox and clutch. Part of the fun of driving an MX-5 is changing gears. Direct drive can certainly be done, but although the ratio between max and min rpm at constant torque is way larger for an induction motor and VFD than it is for an infernal combustion engine (ICE), it seems that you still really want 2 gears.



> By supplying the higher voltage to the 240V motor, what revs will you then get from the motor? I have been quite keen to go for the direct drive option.


You are probably aware that the revs are independent of the volts for an AC motor, however to maintain constant torque the two must go up in proportion. When you run out of volts the torque starts to drop off.

Since it is nominally a 240 V 2-pole 50 Hz (3000 rpm) motor, when you overvoltage it by sqrt(3) it becomes effectively a 415 V 2-pole 87 Hz motor (5200 rpm). The manufacturer only guarantees it to 4500 rpm but we will get it balanced to 6000 rpm and take the risk for short periods. At some point the rotor explodes due to centrifugal force. 

We will replace the existing 4.3 ratio diff with a 3.636 ratio diff to compensate for the fact that the original ICE hit peak power at 6500 rpm.



> How likely is it that your will get the Unidrive SP5402 to be a battery charger as well? That would be ideal.


I can only give it 50/50 at present.



> If you get any discount for any orders of more than one, i could be quite interested in purchasing components with you.


That's a thought. Unfortunately we just bought the drive and wouldn't the fact that I'm in Australia be a problem? However, if this works out, we do plan to do more MX-5s.



> Did you get a price for the Commander SK5402 Controller?
> Cheers!


Yes we did. It was around AU$9000.

In case you are looking for our MX-5 thread on the AEVA forum, I'm sorry to tell you that the AEVA server has been down for some days.


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## ehustinx (Dec 23, 2009)

JohannesVinke said:


> Hello everyone!
> 
> My dad and I are looking into converting a second gen Miata into an ev.
> Specs would be 100km range and should have zippy acceleration (at least like original car, 0-100kmh in ~7 sec). We want to take away the picture people have about ev's being slow as much as possible.
> ...


 

Hello Johannes,

The Siemens AC motors of the 1PV5.. series can be obtained through HEC (located in The Netherlands). www.hec-drives.com

Best regards,

Eddy Hustinx 
HEC


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