# Miata AC55 build MX-AC55



## etischer (Jun 16, 2008)

Without running the numbers, a 9 second 0-60 direct drive seems a bit optimistic to me. The ratio you want to use would be like starting the car in 4th gear, I don't think it will work well. It is possible to go direct drive, but not with the 4.3:1

I've always been curious to see some of these AC55's in use, there aren't many small cars on evalbum that use them.


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## evlowrider (Jul 23, 2009)

I'll be following your build thread. I don't have any experience with AC-55 so I don't have anything to say on that front. I'm converting an MX5 aswell, however its DC with a Warp9 motor. 

Good luck on your build.

Pete.


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## Stunt Driver (May 14, 2009)

Definitely post build news here, and add to garage as well. 
Community is growing!
Where are you geographically?
What is your budget?


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## RKM (Jun 9, 2008)

Jim,

My Miata conversion is all but complete, at the paint shop now (Warp 9, Belktronix stuff, 800A controller, 144V TS 180Ah, clutchless). I need to take a post conversion weight, but am estimating a gain of 350 pounds. 

It's been a long time since I've looked at the specs for the AC55. As I recall, its large and heavy. The Warp 9 is tight in the Miata, moreso for diameter than length. You've checked that you have space to the AC55? Oops, forgot, you plan to direct drive. That changes everything. You'll likely be able to move the motor into the tunnel a bit.

I suspect etischer is right about the acceleration. You would need huge torque (massive amps) to accelerate briskly with that ratio. I know you're using high voltage but I suspect the bottom end acceleration will feel a bit soft. I may be wrong, frequently am.

Getting to be lots of Miata conversions out there. Good luck, have fun.

Rob


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## CroDriver (Jan 8, 2009)

I wouldn't recommend direct drive with a AC55 since the power output decreases rapidly with rising RPM... 










You need 4X more power to double your speed. If the power is decreasing while speed is rising you won't go very fast...


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## dimitri (May 16, 2008)

Why is there such obsession with direct drive? What do you gain vs. what you loose? You eliminate 40-50 lb transmission, but you picked a motor that weighs 100 lb more than comparable DC Warp. You eliminate few percentage of mechanical losses, but you waste tons of precious amps during acceleration, while killing your battery in the process. People assume that electric motors have tons of torque and that is a ticket to direct drive, but all that torque comes at the price of huge amps, heat losses, battery losses, etc. 

Sorry, but I just don't get it......

SolarJ, this was not against you personally, it just seems to be a common theme lately.

I converted Miata and let me tell you, if I was to lock it in 3rd gear, it would suck big time, it would be an embarassment to drive. I'm sure some will come here and argue that they drive in one gear, but they don't go 80 mph and 0-60 in 9 sec all in one gear, and if they say they do, then they are big fat liars . Oh, and they don't get 60 miles range in one gear, not with 16kWh usable pack energy.

Please calculate all details before you jump into direct drive, or wait for Brian to finish his Kia with same exact motor and direct drive and see how it turns out. Some posts in Brian's thread talk about compromises of direct drive, such as picking either acceleration or top speed, but not both.

Hope this helps.


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## EV-propulsion.com (Jun 1, 2009)

I agree that the gear ratio isn't low enough (higher numerically). It will be tough to get that acelleration and top speed of 80 you desire. If I remember right, the max rpm of that motor is 5000 to 5500 which is limiting how much you can gear down and still have a high top speed. Why not at least gear it down for acelleration, and make the top speed 55-60. I personally would use the transmission.
I also agree that if you do use the transmission there may be a clearance problem with the crossmember. For proper driveline angularity (with trans), a 9" motor is very close to the frame, that large diameter ac55 probably wouldn't fit without possibly removing some of the cooling fins? or more?
If you use the gas tank area for batteries, there is approximately 9.5 inches between the doghouse (the gas tank area behind the seats) and the rear axle supporting structure so be sure to check your battery dimensions (unless you will be raising the doghouse)
For some pictures of this gas tank area on our site see
http://www.ev-propulsion.com/projects.html
And yes its starting to look like the miata is the #1 conversion car....
Mike
www.EV-propulsion.com


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## etischer (Jun 16, 2008)

400A @ 312VDC is 125kw, but the graph shows a peak of only 60kw. 

Their data sheet states max current is 250A @ 312v, I think this is the correct number to acheive 60kw. 






CroDriver said:


> You need 4X more power to double your speed. If the power is decreasing while speed is rising you won't go very fast...


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## SolarJ (Sep 12, 2009)

Wow where do I start. I am in the Seattle area. My budget for the project is 17K and I am off to a great start on the budget since I planned for orig car cost of $3000. I picked up a 90 Miata with a bad engine for $900.

If the car needs a tranny after I try out the direct drive, Then I will figure out a way to get it in there or go with a Warp 9 and use this AC-55 for a different project.

This motor is huge and should not have any problems driving this little car.

Also it looks like at least half of it will be able to fit into the tunnel. Good News 

Thanks, Jim


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## Sutitan (Feb 23, 2009)

Im still puzzled as to why more people arent trying out powerglides in ev (actually, I might know. the pain of adapting the PG to the rest of the driveterrain). there have been tons of threads talking about powerglides, and it all seems pretty positive. you have a 2 speed transmission, tq converterless manually shifted auto tranny, which can handle more then enough of the torque that is thrown its way (from a typical conversion). it has a low 1st gear, which would be good to around 50-60mph (depends on diff ratio, tire size and motor rpms, but thats what my calcs worked out to when i checked it out), and a direct drive " 2nd gear", which can provide your 80mph. they are light, cheap, tough, and plentyful. I might have missed the negatives, and I bet your there are a few, but I think powerglides definatly have a place in EV's. the only application I can think of is of "poormansev". Anyways, ill let everyone else chime in on my opinion, but I definatly think you should consider a powerglide.


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## etischer (Jun 16, 2008)

dimitri said:


> I'm sure some will come here and argue that they drive in one gear, but they don't go 80 mph and 0-60 in 9 sec all in one gear, and if they say they do, then they are big fat liars . Oh, and they don't get 60 miles range in one gear, not with 16kWh usable pack energy.


Unless they drive a Tesla...


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## Propellator (Oct 13, 2009)

a quick check shows that
at 2400lb and a cd of 0.34 (which is purely estimated)
you'll approximately make 60mph on a 10% incline and 90mph driving level with nominal motor specs.
Using motor peak specs you'll make 55mph on a 30% incline 75mph on a 10% incline and sadly no more top speed.

I could of course be completely wrong. 
Motor specs are from Azure Dynamics pamphlet. 
In my calculation I use the rolling friction (not the drag neither the weight) of a 4000lb car, so above values may be on the lower side.

Oh, and I hope I will not completely embarrass myself with my first posting here.

torque in Nm, speed in mph


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## SolarJ (Sep 12, 2009)

What are the two blue lines one is dashed? Cool chart BTW


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## 280z1975 (Oct 2, 2008)

Sutitan said:


> Im still puzzled as to why more people arent trying out powerglides in ev (actually, I might know. the pain of adapting the PG to the rest of the driveterrain). there have been tons of threads talking about powerglides, and it all seems pretty positive. you have a 2 speed transmission, tq converterless manually shifted auto tranny, which can handle more then enough of the torque that is thrown its way (from a typical conversion). it has a low 1st gear, which would be good to around 50-60mph (depends on diff ratio, tire size and motor rpms, but thats what my calcs worked out to when i checked it out), and a direct drive " 2nd gear", which can provide your 80mph. they are light, cheap, tough, and plentyful. I might have missed the negatives, and I bet your there are a few, but I think powerglides definatly have a place in EV's. the only application I can think of is of "poormansev". Anyways, ill let everyone else chime in on my opinion, but I definatly think you should consider a powerglide.


I've been thinking of a Powerglide transmission in my conversion (being done next year, summer time) but I haven't found any that not in the 1,000+USD range ... I think a good DC motor + PG transmission (lightweight racing one, three speeds, electronicly programmable) + a HV controller would make a killer combo. You could even program the transmission for "city" driving, "highway" mode and then "Light up the tires mode" ... that would be perfect.

If anyone has bookmarked a PG that would fit the 3 (or possibly 3) speed, electronically programmable, please post a link to it. Thanks.


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## Propellator (Oct 13, 2009)

The blue lines are the wheel torque available at a certain speed considering the gear ratio.
The dashed one for the peak and the continuous for the nominal motor specs.

The other lines show the wheel torque needed to negotiate the incline in percent over the speed achieveable.


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## SolarJ (Sep 12, 2009)

So my starting weight was 2300 lbs. - the ICE components and tranny removed and I am down to 1550 lbs. It sure is nice to be next to a truck scale. Thats a loss of 750 lbs and I calculate that I will add about 850-900 lbs, thats pretty close. BTW I am pretty sure that tranny and clutch weigh more than 50 lbs. I put it closer to 100.


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## dimitri (May 16, 2008)

So this motor has 250Amp max current, is that continuous or peak? With 60AH cells this is over 4C discharge, which with direct drive you will be doing very frequently. Have you considered impact on LFP cells lifecycle?

Also, with 60 kW power and not so impressive max RPM for AC motor, how does this motor power compare with Warp9, which weighs in 100 lb less?

I push 64kW thru Warp9 at hard accelerations, but I am using all gears so 64kW only gets applied for few seconds and then falls off as RPMs rise. I can't imagine doing it in 3rd gear, it would be murder of batteries and the motor.

Please don't let me discourage you from trying, I am just thinking outloud here  it would be nice to see real results from direct drive conversion for once. Like you said, you can always put the tranny back in if need be...
although fitting the monster motor with the tranny maybe tough in Miata.


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## SolarJ (Sep 12, 2009)

Did some test fitting today. That motor fits like a glove about half way down the tunnel. 2 in at the top should give me enough room for some small motor mounts. Some adjustments will need to happen where the power cords come out but thats not bad.


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## Sutitan (Feb 23, 2009)

280z1975 said:


> I've been thinking of a Powerglide transmission in my conversion but I haven't found any that not in the 1,000+USD range


check craigslist, ive seen pgs go for 100$ or so.


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## electromet (Oct 20, 2009)

Sutitan said:


> check craigslist, ive seen pgs go for 100$ or so.


 
However, the trick is to find one that's been modified for manual use for a reasonable price. If you use a stock powerglide and shift it manually, you'll burn up the pump.

Mike


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## EV-propulsion.com (Jun 1, 2009)

If you use a powerglide, why shift it manually? Just let it shift.....I just let the transmissions shift automatically in our miata conversions (after adjusting the shift points for the most electrically economical speed)
BTW, I have never heard of the pump burning up from manual shifting- care to expand on that?
Also, btw, the miata automatic transmission, with torque converter weighs 255 lbs.
Mike
www.EV-propulsion.com


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## electromet (Oct 20, 2009)

Mike, from my understanding, and I'm not a transmission tech, if you let a PG run happily all day long shifting by itself, there is no problem. However, with some of the earlier transmissions (the PG was built from about 1955-1968) there is a seperate front pump in the transmission. By driving one of these older transmissions in town and manually holding it down in low range, the front pumps would burn out. This same front pump also gave these older transmissions the ability to to pump up enough fluid pressure while being towed or pushed to actually spin the crank on the ICE and start the engine. Ford, GM and Chrysler all used this design in the 50's.

As far as manual vs auto shifting the PG, my thought was that it would be much less drain on the battery pack if a clutch-coupled PG was used instead of a torque converter-coupled transmission. The racing PG's use a clutch for launch, then no clutch for upshift. If you ran no current at idle, you wouldn't need the manual clutch or torque converter.

Mike


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