# Mazda RX7 FC electric conversion build



## JetPack (Oct 1, 2012)

Hi guys! I have been planning this for sometime and Im about ready to start.

Im doing two motor rwd.. cutting out the inside of the rear of the car and will build a subframe to mount two motors and then the simple two axles direct to the motors. Should be pretty easy. 

I wanted to start this here as it will gain interest and you can help me some with the simple questions. 

Was thinking of the A123 pouch cells.. so that should work unless there are better units. The kokam looked good but hard to find and price is too high. 

I was looking at KHB14301 Kelly Controller but others are welcome. I imagine some of you are more in the loop then I have been so Im happy to hear any advice!

Thanks


----------



## Yabert (Feb 7, 2010)

JetPack said:


> Im doing two motor rwd.. cutting out the inside of the rear of the car and will build a subframe to mount two motors and then the simple two axles direct to the motors. Should be pretty easy.


Many of us would like to do this, but there are always the same problems in direct drive application (without ratio): 
-Low torque at wheels (unacceptable performance)
-Low motor rpm (overload, overheat).


----------



## JetPack (Oct 1, 2012)

Its getting done so guess we will find out. I custom built these two motors. 3phase 48 pole perm mag motors and in cnc aluminum housings with -10an fittings that run fluid over the motor. Cooling will not be a issue. They are pretty high tq and peak at about 80hp each. The rpm of the motor and car is good too. I estimated about 130mph.


----------



## Yabert (Feb 7, 2010)

80 Hp is useless if you can't reach it (at proper rpm).

If you can build custom motor able to output 500-800 lbs-ft of torque each, that will be awesome.
Good luck.


----------



## JetPack (Oct 1, 2012)

Yes each motor will supply 200 lb-ft and spin to 6000rpm safely.

Im looking for a great controller if you have any recommendations for 3 phase motors.. that Kelly controller looked good. Iv contacted other companies such as Zilla but they didnt get back with me.


----------



## JetPack (Oct 1, 2012)

Have a dyno here Ill post the dyno sheet when its running. I ran a tiny perm132 on a 91 honda crx. altrax golfcart controller, 4 pc680 batteries so 48v and direct to the transmission and left it in 5th gear all the time. Went 30mph.. I just build stuff, no fun sitting around with pen and paper. It accelerated pretty well for a motor that is said to have 6-15hp and 133 lb-ft so.... This will work haha If not you gents warned me and Ill mod something. My motor design is stackable just like a 13b motor.. so i can line 2-3 of these up and connect to the trans if you really wanted me to. Im more worried about a good controller... Im going to need two.


----------



## matthieu149 (May 9, 2011)

Maybe you could show us some picture of your custom built motor you are talking about.

Sound very interesting project!!

As Yabert stated in-wheel or direct-axle motor are very difficult to achieve.
A 215/40/17 wheel will turn only at about 852RPM while driving at 60mph.
That give you a 0-850RPM power range... with a motor that can rev up to 6000RPM.

With the same wheel, 6000RPM give you 424mph.

A gearbox on each motor, with a ratio between 1:4 and 1:6 should give best results!

For the controller, I do not know much about the AC ones but i do know a few exists!
http://www.metricmind.com/category/ev-ac-drive-systems/ev-ac-power-inverters/
http://curtisinstruments.com/index.cfm?fuseaction=cProducts.dspProductCategory&catID=8

Hope it help!


----------



## JetPack (Oct 1, 2012)

I was planning on running the motor on dc, thats why i was looking at that specific controller. 3 phase dc

Ya i had that wrote down.. think my work was right.. 30mph=453rpm
70 miles per hour = 1hour 63420 rev per hour = 1057rpm
120mph= 1812rpm 

I didnt plan on going to 6000rpm but its there... the controllers sensing that high of a rpm actually have issues.. most controllers only go to like 40,000 erpm So 6000*48/2=144,000rpm haha its too high for this kelly controller I was looking at.


----------



## Coulomb (Apr 22, 2009)

JetPack said:


> Yes each motor will supply 200 lb-ft and spin to 6000rpm safely.


As Yabert has stated, you will need a minimum of 1000 lb-ft torque (for decent performance), so 2 x 200 lb-ft won't cut it.

With 48 poles (!), I would expect more torque and less speed than these figures. A 4-pole motor typically has a base speed around 30 Hz (1800 RPM), so a 48-pole would have a base speed around 150 RPM. An 80 HP motor 4-pole motor might have a peak torque around 235 lb-ft (I hope I got that right; I'm not familiar with American units). With 48 poles, you would expect around 10x as much torque.

Those numbers sound about right for a 4-pole motor. Are you sure about these numbers?

The problem with direct-to-the-wheels drive is that motor size is roughly proportional to maximum torque. Without a single ratio reduction (as you get with direct-to-the-diff), the motors become very large. However, that rule doesn't take into account pole count. Leakage flux seems to reduce the efficiency of motors with 6 and more poles. 24 and 48 poles are usually only seen in axial flux motors. Are yours axial flux? This may overcome the flux leakage problem.


----------



## Coulomb (Apr 22, 2009)

JetPack said:


> 3 phase dc


Huh? That makes no sense.


----------



## JetPack (Oct 1, 2012)

Brushless 3phase DC motors are very normal.

But yes 3 phase so 3 poles 16 each so 48.. its brushless and I was planning on DC so any great controllers is what Im looking for here. 

Im not familiar with the term axial flux I dont think it is.. thats when the say winding plate turns on top of a magnet plate... I have a center that has perm magnets and it spins inside a winding that doesnt move. 

Like I said I was looking into the KHB14301 If Kelly seem so be ok around here I guess Ill just go with testing that unit out.


----------



## Coulomb (Apr 22, 2009)

JetPack said:


> Brushless 3phase DC motors are very normal.


Oh, right, "brushless DC". That's such a misnomer, especially for EV-sized motors. It makes a little sense when the motor is so small that the controller is built into it, so you only see the two DC terminals.

For EV-sized motors, the controller is external, and the only thing that is DC is the input to the controller. But the input to all EV controllers is DC, since batteries are DC.

Just making sure you're not actually putting DC into the brushless motor.


----------



## Coulomb (Apr 22, 2009)

JetPack said:


> Im not familiar with the term axial flux


It's where the magnetic flux is parallel to the axis of the motor, rather than radial. Generally, axial flux motors have a larger diameter but are much shorter, sometimes called "pancake" motors. Sometimes these are also ironless.


----------



## JetPack (Oct 1, 2012)

I know about dc brushless motors, dont know why your telling me about them and their controllers. I knew what the axial flux was just didnt know thats what it is called. I dont think iv ever seen a powerful motor in that configuration. They are only used in home made wind generators and small fans it seems from my few years of messing around. 

If you seen my first post I showed you the controller I was looking at and everything might have made sense to you. Ill post it again.. KHB14301 kelly controller. Looking for good units like this type or anyone who has used Kelly with horror stories  Iv heard a few good and bad things so just wondering if anyone has better suggestions.


----------



## tylerwatts (Feb 9, 2012)

Jetpack, FYI
The way you are wording your posts leads us to belieave you're asking questions because you don't understand these motors, and your terms were a bit misleading. Coulomb was only trying to assist. I understand you are also not meaning to be offensive or rude, just the way your wording comes accross. 

It seems we have as mall language hurdle to overcome, and since I know everyone is keen to find out about your motors that might be capable of direct drive, please help us understand you and help you understand us. We look forward to hearing about your motors and helping each other out.

Re controllers, sounds like your motors would run with any versatile AC controller, what are the specs of the motors? Voltage, current, configuration etc. some controllers are better than others for certain applications.

PS Coulomb has built his own AC controllers and is a VERY knowledgeable chap, if we get some clear specs listed I'm sure he'll have loads to share, as will may others!

Regards


----------



## JetPack (Oct 1, 2012)

Yes the motors could run AC but then you need a ac to dc converter dont you?

I thought it would be less costly and less hardware to go bad just using the BLDC controller.

Iv been on here since 2008 I just couldnt get my old account password as the email is not used haha 

The motors will handle quite a bit, im not sure since they are just custom. I like to break things and actually test parts and situations out. The motor I looked to when putting mine together were 650v ac max. But Im just planning on building a pack and using the DCBL controller at say 144v 

I was using a perm132 to drive a honda crx... the 5th gear is 0.771 and 4.2 final drive. 3.2:1 right. So if that little motor had about 30 Nm = 22.13 ft lbs you can multiply that by 3.2 and thats how much work it did? So we could say with only 100 lb-ft I could direct drive? You guys can do the math but If that little motor can move the crx with ease then these large motors will move the mazda.


----------



## Yabert (Feb 7, 2010)

JetPack said:


> You guys can do the math but If that little motor can move the crx with ease then these large motors will move the mazda.


Isn't just about math, it's about fact!

First, my little car (1900 lbs) has a poor acceleration in 5e gear with roughly 500 lbs-ft at wheels (172 lbs-ft x 2.93 ratio).
Now, if you add weight (lets say 2400 lbs??), reduce the torque (400 lbs-ft at wheels) and increase the wheel radius (bigger tires), the acceleration will be something dangerous on normal road and starting from stop on a slope will be impossible.

Second, a PMG 132 can supply 22 lbs-ft of torque with as little than 160A. How much Amps do you supply during your acceleration? At 300A or 400A it's a different story!


----------



## JetPack (Oct 1, 2012)

My controller was 300amp max.. I had it set to do 200amp but the pc680 batteries at 48v were kinda low performance and abused so it couldnt have been dishing out peak. 

Please answer my questions if you know them on that last post. Thanks


----------



## tylerwatts (Feb 9, 2012)

JetPack

Re AC controllers, a BLDC motor is very similar to an AC motor, except the magnetic forces in the rotor are not induced by those in the stator, they are already there from the magnets, so AC controller should work. For ref, all controllers input DC from the batteries! Your BLDC motor controllers 'chop' this DC up to produce the AC needed, it will just be a slightly different 'pattern' for a BLDC to that of an AC motor. THis is why we need to know specs of the motors.

Then we can better look at the questions in your long post. In theory your motors could have the potential for direct drive, but they need to have been built specifically for this type of application. SO, how are they designed?


----------



## JetPack (Oct 1, 2012)

tylerwatts said:


> JetPack
> 
> For ref, all controllers input DC from the batteries! Your BLDC motor controllers 'chop' this DC up to produce the AC needed,


The BLDC (brush less Direct current) controller takes DC from batteries and feeds it into the motor as DC.. not ac like you are saying. 

There are motor controllers that take AC and put it into a perm magnet motor as AC so its not always DC input. 

I did not know that AC motor controllers had a inverter built into them? So you can do DC in on the AC motor controller and get the 3 phase AC out? Ill have to look into that then. I didnt think it was that easy.


----------



## tylerwatts (Feb 9, 2012)

Yes, These are EV controllers so they are designed to input DC and convert it to the required AC signal.

Can you clarify how your motors work please? You say they are brushless but unless brushes are used the controller is essentially an AC controller. That is to say it would be a pulsed DC controller that switches between the 3 groups of poles (forgive my poor terminology) hence alternating where it pulses the DC, similar to the operation of an AC motor.

Forgive my misunderstanding please, I'm keen to learn about your motors, but am struggling to understand what sort of controller you require. If you say it simply needs DC, there are loads of options, EVNetics, Netgain, Kelly, to name a few.


----------



## JetPack (Oct 1, 2012)

I know about Kelly... EVNetics and Netgain dont make a 3 phase controller from the looks of it.. Do you have a link?

I can run AC that is not a problem. I wanted to run DC for the conversion reasons but looks thats not a issue, so either will work. Is there a benefit to running one or the other? Such as maybe a loss when you go from DC to AC through the controller? So DC to DC doesnt result in a loss? Kelly makes the DC to AC 3 phase controllers but with a lower max voltage then the controller I was already looking at that is KHB14301 BLDC 144v (max 180v)


----------



## tylerwatts (Feb 9, 2012)

That KHB controller is a Kelly. The 3 phase DC and AC controllers will have similar losses. You say you can use AC, is that with your BLDC motors? At what Voltage and current?

Given your application I'd assume the Curtis AC controllers are ideal due to their lower voltage and higher current capabilities and they can be paired as you wanted, but then we still don't have any info on the design of your motors. Please do share this info.

Thanks


----------



## dladd (Jun 1, 2011)

JetPack said:


> I was using a perm132 to drive a honda crx... the 5th gear is 0.771 and 4.2 final drive. 3.2:1 right. So if that little motor had about 30 Nm = 22.13 ft lbs you can multiply that by 3.2 and thats how much work it did? So we could say with only 100 lb-ft I could direct drive? You guys can do the math but If that little motor can move the crx with ease then these large motors will move the mazda.


I'm not familiar with the perm132, but I did a quick experiment today.  With my Saturn in 5th gear (.73 x 4.06 final drive) and on flat land, I floored it from a stop. Motor current went right up to 500a (the limit I have set in my controller) in my Warp9, which I believe is right around 100 ft-lb. Movement was painfully slow... I gave up at around 20mph and dropped down to 3rd gear. Any incline at all, and I would not have moved.

Not saying you are lying here, but something is fishy. I don't buy the above story you tell about driving your crx in 5th gear with 'ease'.


----------



## JetPack (Oct 1, 2012)

A crx is alot smaller/lighter then a saturn. It worked though didnt it  Did you do 48volts or 72? I even went up a pretty step hill. (oh you used a diff motor nm) But I seen a chart that side your motor at 360amps was doing about 50 lb-ft of torque @ 72v

Anyways... Back on the subject.. still looking for some controller options here.. there dont seem to be many good units out there yet.


----------



## tylerwatts (Feb 9, 2012)

Jetpack, please tell us a little more detail about your motors! It'd help us to help you!


----------

