# New Build New Builder - Ninja 250 - Help!



## kek_63 (Apr 20, 2008)

Why don't you pop in at www.elmoto.net . It's an EV forum dedicated to motorcycles. There are a number of 250 Ninja conversions going on there. 

Keith


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## BradQuick (May 10, 2008)

I have a Ninja 250 that I've converted. Why settle for 30 mph, when you can fairly easily do 50 mph?

I'm using six B&B 35ah deep cycle AGM batteries, a Perm 132 motor and a Kelly 72v, 450 amp controller.

The bike is a little heavy, but it's a lot of fun. It will do 54 mph off the charger and 52 after 10 miles. Useful range is 15 miles when travelling around town at 40-50 mph.

This is a link to my build. I later switched to lead acid batteries and I ended up fixing the perm motor after they sent me a new rotor for nothing.

http://www.endless-sphere.com/forums/viewtopic.php?f=12&t=4546&p=67172#p67172


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## hppyfngy (Sep 25, 2009)

As I research it, I'm beginning to see the initial expenditures will be the largest, and I probably won't limit the build to a 30mph goal. 

But, I may have to add components as $$ permit. 

I have heard the heat may be an issue with this motor if I tried to run it at 72V. Also, the controller in this "kit" is 24-48 Volts/300 amp. Am I going to be really disappointed if I don't spend the $150 more for the 24-72 V/400 amp controller?

Also, I'm on the fence about batteries. Voltage and type. 

What's the best bang for the buck nowadays? Remember, this is a toy for me, not even a commuter. A grocery getter. I don't need great range or speed, although more is always better, no?

Thanks for the link...


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## Drew (Jul 26, 2009)

you might be interested in something like these

http://www.thunderstruck-ev.com/AC_drive_performance.htm

I don't know if anyone on here has used them but they're very cheap for AC and give you a much wider operating range which means better performance, AC is also typically a lot more efficient than DC


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## hppyfngy (Sep 25, 2009)

don't confuse me...


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## Qer (May 7, 2008)

hppyfngy said:


> don't confuse me...


You better not get confused since that's mainly bollocks anyway. It's true that AC *motors* are more efficient than DC but on the other hand DC *controllers* are more efficient than AC ditto so the difference won't be that big in the end, and with lead acid (which I presume you'll be using?) your main problem with efficiency will be the batteries anyway (because of peukert effect).

Also, for example a 20 kW AC motor and a 20 kW DC motor still gives 20 kW (duh), it's just that the AC motor will give more RPM where the DC motor will give more torque (since power = rpm * torque) and while the DC system will typically demand more current a AC system will demand more voltage (since power = voltage * current).

Get a motor that fits your frame, your wallet and that has a reasonable system voltage. AC or DC are just different technologies, it's simply not possible to claim that one technology is "best" or gives "better performance". It's like claiming that V-motors are always better than inline motors or that cake is better than pizza. Besides, I bet the pack will be the bottle neck anyway.

That said, those motors do look interesting. If they're better or worse than a DC system, well, that depends on WHICH DC system you compare with. Of course.


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## Drew (Jul 26, 2009)

Qer, I was under the impression that a matched set for an AC system was around the mid 90's region in terms of percentage efficency. Being that the Perm 132 motor has a peak rated efficiency of 86% at rated voltage and 88% at 72V that would mean that a DC controller would have to be about 110% efficient to match an AC system yes?

This isn't the main benefit I see to AC though, the main reason that AC interests me so much is because of the operating range, because an AC motor seems to reach peak power and then continue with overrun it means that you can gear the motor a lot lower than you would a DC motor with a single drive ratio and still get the same top speed. This would mean that you'd get better off the line performance and better responsiveness through the range.

This is just based on the information that you and a number of others gave me during the AC vs DC thread a while back, but I would assume that DC was presented in the best possible light considering that there are a large number of DC proponents on this site


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## Qer (May 7, 2008)

Drew said:


> Qer, I was under the impression that a matched set for an AC system was around the mid 90's region in terms of percentage efficency. Being that the Perm 132 motor has a peak rated efficiency of 86% at rated voltage and 88% at 72V that would mean that a DC controller would have to be about 110% efficient to match an AC system yes?


Without going into boring math about power electronics (which is Tesseracts domain anyway) I'd say that it *might* be realistic to expect mid 90's efficiency for the AC-controller on a good day and under perfect conditions, but you'll probably see it drop lower than that when you start to push it (especially at low RPM's where everything dips fast towards 0% efficiency). So if you go find that 110% efficient AC motor I'll see if I can dig up a 110% efficient DC controller.

More seriously, you still can't compare *technologies*, you have to compare *systems*. If you say "THIS AC-system beats THIS DC-system" (for example, that AC system you pointed at looked pretty interesting), then I'm all game, but you can't claim that "Apples beat oranges" and hold that as an ultimate proof.



Drew said:


> This isn't the main benefit I see to AC though, the main reason that AC interests me so much is because of the operating range, because an AC motor seems to reach peak power and then continue with overrun[...]


¿Que?

All systems have peak power, after which the power will start to drop again. Nothing magical going on here.

- You cannae change the laws of physics, capt'n.

One of these days I think I'll have to put that in my sign.


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## Drew (Jul 26, 2009)

Sorry, I was thinking of permanent magnet AC systems rather than a squirrel cage setup, but the two systems I've found which I have found data for are the AC150 setup and the Azure Dynamics AC24 system and they are 91% and 87% peak system efficiency respectively. AFAIK that is electricity into controller vs mechanical output from the motor.

Either way, the point that I was getting at is that the AC24 for example reaches peak power at 4000RPM or so, but revs out to 12000RPM which means that you can gear the bike to generate something more like peak tractive effort for the tyres and still have enough overrun RPM to achieve a good top speed. From what was said about DC motors it is not possible to achieve such favourable gearing and still maintain a good level of overrun.


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## Qer (May 7, 2008)

Drew said:


> [...]but the two systems I've found which I have found data for are the AC150 setup and the Azure Dynamics AC24 system and they are 91% and 87% peak system efficiency respectively.


And if you can't cruise at the peak this will be good because of...



Drew said:


> From what was said about DC motors it is not possible to achieve such favourable gearing and still maintain a good level of overrun.


It isn't? Damn, I better tell Tesseract because that means our dyno isn't working!


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## Drew (Jul 26, 2009)

The constant power phase is the part that allows you to maintain a higher level of tractive effort throughout the range while only using a single gear. If you had a flat torque curve and a linearly increasing power then you end up needing a gearbox or getting poor performance.

Either way, I'm just explaining things the way I see them, which is that due to the constant power phase you can get better performance with one gear than you could with DC.

If I'm wrong then please explain where I've made a mistake in my logic.


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## major (Apr 4, 2008)

Drew said:


> Either way, I'm just explaining things the way I see them, which is that due to the constant power phase you can get better performance with one gear than you could with DC.
> 
> If I'm wrong then please explain where I've made a mistake in my logic.


"Constant power". How I hate those words 

Drew,

Take a look at my post http://www.diyelectriccar.com/forums/showpost.php?p=132057&postcount=156 and the entire thread. I think that has your explanation, somewhere. 

Regards,

major


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## Drew (Jul 26, 2009)

major said:


> "Constant power". How I hate those words
> 
> Drew,
> 
> ...


Major,

I understand that this region is not strictly constant power, but the rate of fall off of power for AC motors seems to be much less than that for DC motors, for example;

http://www.azuredynamics.com/products/force-drive/documents/AC24LS_DMOC445ProductSheet.pdf

This datasheet indicates as I stated above that the peak power is reached at about 1/3 of max revs, there is then a region that, whilst not constant power, certainly maintains an output at least reasonably close to the peak value for the motor, which enables use of gearing which is much higher than a DC motor would for direct drive. What I enterpret this to mean is that if I wanted a DC motor with similar off the line performance I'd have to have a gearbox and if I wanted a direct drive solution then I'd have to accept less performance for the same rated output... is this correct?


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## major (Apr 4, 2008)

Drew said:


> This datasheet indicates as I stated above that the peak power is reached at about 1/3 of max revs, there is then a region that, whilst not constant power, certainly maintains an output at least reasonably close to the peak value for the motor,


Hi Drew,

Reasonably close? Looks like power falls off down to 30 or 40% of peak. A similar thing happens with the DC motor. At speeds over that which peak power occurs, the power falls off. Perhaps a little different shaped curve.



> which enables use of gearing which is much higher than a DC motor would for direct drive.


Sure, if you have a motor capable of 12 kRPM, you can double the ratio over that of a 6 kRPM motor. And that gives you double the wheel torque, right? But between an AC motor and DC motor of similar size, the DC motor can putout as much as 5, maybe ten times the torque of the AC depending on the current limit and battery capability. 



> What I enterpret this to mean is that if I wanted a DC motor with similar off the line performance I'd have to have a gearbox and if I wanted a direct drive solution then I'd have to accept less performance for the same rated output... is this correct?


I guess I don't follow you. You'll need a gear box (or some type of reduction) no matter what. I guess you mean a multiple ratio box, which I would call a transmission.

It all depends on your system design. People go both ways. The fast EV drag race guys go DC, direct drive (single ratio). The high end AC drives go direct (single ratio, likely 2 to 3 time that of the DC). It's up to you.

I personally like AC direct drives. I'd like an AC drive with a 2-speed transmission even better. If you have a big controller, DC direct. A wimpy controller and DC, better keep the tranny.

Get a medium AC system on a medium size EV, you probably want to keep the tranny. The same system on a bike will likely do with direct drive.

Looking back at your last sentence, you speak of ratings. Don't forget to compare peak torque of those similar hp rated AC and DC motors. That's where your launch is....wheel torque.

Regards,

major


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## Drew (Jul 26, 2009)

Actually thats one fairly serious misconception going around, when talking about motors of any kind torque is totally irrelevant except as a rating of power at speed.

A good example of this is that with a gearbox anything is possible, you can put 10's of kNm out from a whipper snipper motor. Torque is only relevant when you've got an associated RPM to determine power.

Added to that, torque is also meaningless, to determine actual vehicle acceleration you need a tractive effort, which is related to motor and wheel torque, but also involves tyre radius etc. It is most closely related to power and vehicle velocity.

From what you were saying in the AC vs DC motor thread if I run a motor at a reasonable voltage then I can expect to get a triangle type pattern, which is to say linearly increasing power and then a peak and then linearly decreasing power with no region which is even close to level, let alone able to maintain 40% of peak power at twice the speed. Again, this is what I gleaned from the conversation so feel free to correct me if I'm wrong. If the motor is run at higher voltages then from what I understand it is able to survive less and less overrun because of the risk of mechnical failure of the rotor.

What i was saying before is simply that a motor that can maintain something closer to a constant power over a region becomes useful as a single speed transmission solution because you can achieve a higher tractive effort at lower speed.


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## major (Apr 4, 2008)

Drew said:


> torque is also meaningless, to determine actual vehicle acceleration you need a tractive effort, which is related to motor and wheel torque, but also involves tyre radius etc.


Hi Drew,

Sir Newton disagrees with you. F = m * a. The force (F) is the torque divided by the wheel radius. Right? So he says that acceleration is proportional to the torque divided by the mass.

Isn't tractive effort the force? And isn't the force proportional to the torque? Sure, when you get going and have speed, then you can calculate power. But what about that first millisecond off the starting line? Speed is zero, right? So how do you use power to get initial acceleration? You need to use torque.

Regards,

major


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## Drew (Jul 26, 2009)

major said:


> Hi Drew,
> 
> Sir Newton disagrees with you. F = m * a. The force (F) is the torque divided by the wheel radius. Right? So he says that acceleration is proportional to the torque divided by the mass.
> 
> ...


Actually, the initial time period of takeoff is mostly governed by a sort of a squirm 

Here is how it is, if you want the best and easiest way to determine a good spread of gears for a vehicle then what you do is you determine two things, one is maximum tractive effort from drive wheels, the other is maximum speed attainable based on your engines power output. After you've done that you've bounded your spread of ratios... the next bit is pretty important though, because what you need to do is to select an appropriate first gear drive ratio and the easiest way to do that is to take your tractive effort, multiply it by your velocity and then you get a maximum power line, which governs the maximum power you can put to the ground for a given speed. Depending on your motor characteristics you then decide where you want the maximum power line to intersect your power curve for the motor.

Usually when I'm doing this I use a Mu of 1.1-1.3 depending on application and then target peak power, which usually gives you a bit of excess power during the buildup... then you work out the speed that your vehicle is travelling, the motor RPM and at the end of that you end up with a total system ratio, which takes into account tyre diameter (which converts torque to tractive effort) and system ratios. Then you select an appropriate tyre based on how much money you want to spend and what your goals are, then you select a final drive ratio out of the available ratios to you, then you put together a gearbox which has ratios basically evenly spread between the first gear ratio you determined and the top gear ratio you determined...

You might notice that I didn't actually mention torque in there at all, this is because torque is absolutely meaningless. To prove this further I'll give you another example, which do you think is quicker? A vehicle powered by a 280kW CAT diesel tractor motor which puts out up to 2200Nm of torque or a GM gen 3 V8 which puts out something less than 500Nm of torque and the same power? Assuming all other things are equal of course.

If you're interested, here is a graph I did a while ago based on the AC24LS and an earlier rough calculation set I did for a motorbike weighing 150kg with me on it and a road oriented tyre.










Its a pretty rough calc set, without losses etc taken into account but all that were used in this calc set were speed in m/sec and tractive effort in Newtons which gives power in Watts. Torques would be important once I'd decided on a tyre size and worked out the drive ratios, but of course torques in that sense are only important to work out belt tensions and hertzian stresses. Again, torques are meaningless unless you're doing up non-critical bolts.

EDIT: in case you're interested I determined that the AC24LS would give me a 4.5 second 0-100 and a top speed of approximately 145-150km/h, but i'd decided that the 15kW continuous wouldn't give me good gradeability at 110km/h and I worked out I'd want something more like 30kW continuous minimum to give me good hill climbing etc.


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## major (Apr 4, 2008)

Drew said:


> one is maximum tractive effort from drive wheels,


Drew, 

Here is the definition of:



> tractive effort
> 
> _–noun _the force exerted by a locomotive or other powered vehicle on its driving wheels.


How is that not torque on the drive wheel?

Here's another:



> *Tractive Effort*The tractive effort is obtained by multiplying the torque by the total ratio of power train and dividing this sum by the rolling radius of the driving tyres.
> 
> 
> 
> ...


Regards,

major


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## hppyfngy (Sep 25, 2009)

Geez, you guys get a room will ya?


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## Drew (Jul 26, 2009)

Thats right, tractive effort is a force, not a torque, the force at the wheel for a given speed is related to tyre diameter, differential ratio, gearbox ratio as well as any transfer cases involved.

Take the previous example, if you use a CAT diesel engine with 280kW and approx 1500Nm at 1800RPM vs a small helicopter turbine with 280kW and approx 52Nm of torque at 52000RPM. Assuming that both of these engines are geared to produce maximum power at 50km/h then what would the tractive effort be in each case? Simple answer, the same.

More complex version is that if you assume that you're talking about a medium to large truck with a 295/80R22.5 and a rolling diameter of approximately 1.050m and rolling circumference of 3.3m making for a wheel RPM of 252.5RPM, so your total system ratio for the CAT diesel will be around 7.14:1 and the turbine will have a total system ratio of 206:1 but the wheel torque is the same for both, the torque might diverge at the differentials based on different ratios, or there might be portal hubs, or they might even be using the same driveline, but the turbine has a planetary reduction gearbox of 28.8:1 before it goes into the transmission... the point is that torque is totally irrelivant unless you're designing components in a driveline, but its certainly not relevant when talking about engine power outputs or vehicle performance.

EDIT: Sorry for the thread derailment Hppyfngy


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## major (Apr 4, 2008)

hppyfngy said:


> Geez, you guys get a room will ya?


Hey hppy,

Sorry about consuming your space. I started a new thread: http://www.diyelectriccar.com/forums/showthread.php?t=36904 

So if Drew would like to continue the discussion, we can meet up there. Seeing as how we are half a world apart, geographically speaking, your room idea is a bit costly. 

Regards,

major


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