# HPEV motors



## onegreenev (May 18, 2012)

HPEVS does their own graphs and they are the ones that build the motors too. Curtis is used for the controllers but they have their own software for the controller. I'd trust HPEVS over anyone else. 

I guess it depends upon what voltage your going to use and what amperage. 

This is direct from HPEVS. Power Graph. 
AC-12 at 144 volts and 500 amps gives a pretty good 65 HP and 66 ft lb torque at just over 5000 rpm. Sounds pretty good to me for a decent little ride.


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## mrmeseeks (Jun 14, 2014)

I would be using the AC-12 at 72V not 144, and most likely with the 350 amp controller, 65 HP on an electric motor from the research I've done should be pretty ridiculous overkill for a motorcycle.

One of my main concerns with the graphs themselves though is they don't appear to be accurate to themselves even. At lower RPM I can calculate the HP by simply multiplying the voltage X current X efficiency and dividing by watts/HP but once I get into the higher RPM this no longer works. Either I am missing some source of loss that only applies at higher RPM and applies to the AC-12 more than the AC-9 or the graphs are wrong, I tend to assume that I have made the mistake and not the company who makes the motors but I can't think of what it is. This also only seems to apply to continuous power graphs by the way.


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## major (Apr 4, 2008)

mrmeseeks said:


> So given this, I would like to know if people have been using HPEV and whether they are reliable (specifically if anyone has actually tested their motors to confirm they get the values they are supposed to, or at least reasonably close to them). I would also like to know if anyone knows how long the motors are run to get the peak values, from what I have seen there isn't a set time for peak values for electric motors.


A few years ago I set up and ran two AC15 motors back to back as a motor to generator dyno. This way I was able to get some good accurate performance data. This was before they published all those graphs. But from what I recall, my data agreed with the published specifications fairly well.

Peak infers an instantaneous value. All that is really required is enough time to take the measurement. 

As far as the discrepancy you speak about, those graphs don't show efficiency. You cannot use a stated nominal or peak efficiency throughout the whole range of the graph. At higher power levels the efficiency typically drops. The hp curve is calculated from the RPM*Torque/5252.


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## mrmeseeks (Jun 14, 2014)

So peak is just an instantaneous peak eh? Interesting from what I was finding most places stated that the peak value was required to be able to run at that value for anywhere from 1 to 10 minutes.

The graphs actually do show efficiency values across the graph, here is the graph in question: http://hpevs.com/Site/power_graphs/...c12 72 volt imperial continuous graph FC.pdf as you can see the efficiency values are given for the entire range of testing and if you use the values on the graph for the higher RPM ranges they do not add up.


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## major (Apr 4, 2008)

mrmeseeks said:


> So peak is just an instantaneous peak eh? Interesting from what I was finding most places stated that the peak value was required to be able to run at that value for anywhere from 1 to 10 minutes.
> 
> The graphs actually do show efficiency values across the graph, here is the graph in question: http://hpevs.com/Site/power_graphs/...c12 72 volt imperial continuous graph FC.pdf as you can see the efficiency values are given for the entire range of testing and if you use the values on the graph for the higher RPM ranges they do not add up.


Yes, peak is universally used for an instantaneous value. Certain manufacturers may choose to further quantify it with a duration. If you see it used without a time duration, it is instantaneous. With a duration, use that time.

Yes, that graph has a problem with the efficiency curve. I took the 6000 RPM point. I get 6808 W out & 11,500 W in, so 59%. The graph shows 90%. It isn't the first error on a manufacturers' motor performance characteristic graph we've seen. At lease these guys publish the stuff. A lot of times there is nothing available. Brian or one of the guys from there frequent this forum. Maybe he will chime in. Or send him a pm. Try member HPEVS.


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## frodus (Apr 12, 2008)

That graph doesn't show battery voltage. The pack, no matter how stiff, will sag a little under load. So while you know the DC current, you do not know the DC voltage.... so maybe that is it. Using 72V as a constant voltage may not be correct.


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## major (Apr 4, 2008)

frodus said:


> That graph doesn't show battery voltage. The pack, no matter how stiff, will sag a little under load. So while you know the DC current, you do not know the DC voltage.... so maybe that is it. Using 72V as a constant voltage may not be correct.


Yep, that might be the problem. However since this was a "lab" test, they could have used a constant voltage for the test. And since it was not specified otherwise, the observer is justified to assume it was 72 Volts constant.


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## frodus (Apr 12, 2008)

Yeah, but even with the voltage sagging to lets say, 65V, the numbers are still a bit off. The efficiency seems a bit high IMHO, esp since its controller + motor eff.

I will say this: The HPEVS packages are good motor/controller setups. I've sold dozens of them and I've had no issues with any of them.


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## HPEVS (Jun 6, 2012)

I'm going to go talk to Sean about the efficiency numbers and see what's up. We run the dyno on batteries, so there will be some sag, I will look and see if we have the battery voltage data. On an AC12, system efficiency is around 82%. Now, the other thing to consider is this graph is showing the power the motor can deliver continuously, it is not however the peak efficiency, this may be at a different motor load, RPM and other factors.


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## mrmeseeks (Jun 14, 2014)

I got a response from HPEVs technical support, they say the loss is due to the controller going into field weakening and its efficiency declining. Perhaps the stated efficiency is only the motor and not the motor/controller combo (although that would then put off the early numbers) or maybe they only monitored the motors efficiency and multiplied it with a constant value for the controllers efficiency.

I'm not entirely sure what field weakening refers to with the controller (if it was field weakening in the motor I would assume hysteresis or eddy current losses, whichever one it was that was caused by rapid changing of the field [I believe it was hysteresis]), I will try and look it up.


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## major (Apr 4, 2008)

mrmeseeks said:


> I'm not entirely sure what field weakening refers to with the controller ....


It is the motor controller combination.  It refers to the region above base speed, which is recognizable on the performance graphs as speeds above peak power.


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## Ivansgarage (Sep 3, 2011)

Field Weakening

As the frequency supplied to an AC induction motor is increased (with voltage held constant), the "field weakening" causes a reduction in the motor peak torque capability. The fact that the peak power (torque ) decreases as speed is increased by field weakening is the most "inherent" limitation to the "constant power speed range" of an AC drive system..

So in a nut-shell as you loose power (torque) you want to give it more gas raising the current....

Here is a small excerpt from the Curtis manual.


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## mrmeseeks (Jun 14, 2014)

In relation to field weakening, I understand that it is a factor involved in lowered efficiency, that was kind of implied when it was given as the cause of the lowered efficiency, what my question was is what it actually is.

I am an electrical engineering student and I like to understand the actual causes of these kind of things. I guess my question is what field is actually being weakened and what is causing the weakening? My current thought as I stated before is that it is most likely hysteresis in the coils of the motor but the answer I got stated that the field weakening is in the controller, and curtis apparently defines it as a factor involved in the controller. I don't know much about how these kind of motor controllers work (I have built an ac motor/controller before for class but the controller I made was simply an arduino and cmos transistor combination, there isn't really a field to be weakening in the controller as far as I am aware). I am now starting to think that the controller may just be lowering the current once it gets into high enough frequencies that hysteresis starts to become a noticeable factor to reduce the loss from it but that should lower the current draw and I'm not seeing that in the graphs.


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## Tesseract (Sep 27, 2008)

mrmeseeks said:


> ....I am an electrical engineering student and I like to understand the actual causes of these kind of things. I guess my question is what field is actually being weakened and what is causing the weakening?


This will get covered in "electrical machines" or a similarly named course. It was a 4000 level course at GaTech and one of the more difficult ones at that. Good luck...  

The field being referred to in "field-weakening" is the static magnetic field that the rotating magnetic field interacts with to produce useful work. Historically, the static magnetic field is called the "field" while the rotating magnetic field is called the "armature", but be warned that these terms are not necessarily the equivalent of the modern terms "stator" and "rotor"; the former refers to the stationary part of the motor itself while the latter refers to the part of the motor that spins. In both the AC Induction Motor (ACIM) and the most common form of the Permanent Magnet Synchronous Motor (PMSM), the field is the rotor and the armature is the stator; this relationship is totally inverted in most DC motors.

Without launching into a detailed explanation of how AC induction motors work, suffice it to say that the speed of a motor is proportional to applied voltage (and armature frequency) while the maximum torque from a motor is proportional to field strength (which, if I may be permitted to [over]simplify, means it is proportional to current). 

In other words, you can get full torque from a given motor up to a certain supply voltage/RPM, but beyond that point the torque must fall (this point is called "base speed", btw).

How this is accomplished in the ACIM is by altering the timing of the switches in the inverter so that less current is induced into the field (which is the rotor, remember). This results in a higher RPM (as long as armature frequency is increased) for a given supply voltage at the expense of torque.

In a nutshell, then, field-weakening equals less torque and more RPM. Why efficiency is lower in the field-weakened region is mostly because of iron losses (hysteresis and eddy), but also because the power factor of the motor decreases both above and below base speed/full torque.


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## mrmeseeks (Jun 14, 2014)

Thanks Tesseract, if I understand you correctly it seems like my second hypothesis was closer to being correct. However I have just looked back at the graphs and the efficiency for the AC-12 actually goes up as the RPM goes up, clearly that shouldn't be. If the representative from HPEV is still reading this I would be very appreciative if you could explain what is happening with that.


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## major (Apr 4, 2008)

Tesseract said:


> Why efficiency is lower in the field-weakened region is mostly because of iron losses (hysteresis and eddy), but also because the power factor of the motor decreases both above and below base speed/full torque.


It is not universally true that motors operate at lower efficiency in the weakened field mode. Take the AC12 for example. Use this graph: http://hpevs.com/Site/power_graphs/.../ac12 72 volt 550 amp imperial peak graph.pdf Calculate the efficiency at equal power outputs in the full field region and compare to the weakened field point. For instance at about 21-22hp 1400 RPM vs 5000 RPM. The high speed (weak field) point is about 25 points higher efficiency.

That graph also demonstrates the peak power point defining base speed at about 2400 RPM or 80Hz. At frequencies higher than that, there is insufficient voltage to fully magnetize the motor and therefore is called field weakened.


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## Tesseract (Sep 27, 2008)

major said:


> It is not universally true that motors operate at lower efficiency in the weakened field mode. Take the AC12 for example.....


That graph shows power declining above base speed, whereas true field-weakened operation should show power remaining constant as torque declines (at least out to some percentage past base speed). For example, see the graph on this Reliance Electric page.


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## major (Apr 4, 2008)

Tesseract said:


> That graph shows power declining above base speed, whereas true field-weakened operation should show power remaining constant as torque declines (at least out to some percentage past base speed). For example, see the graph on this Reliance Electric page.


The constant power region is a relic of rating specifications for continuous operation. When dealing with peak output, it becomes a singularity (peak point) as shown on the curve I referenced. Below the graph you reference, notice this comment: 



> The fact that the peak power decreases as speed is increased by field weakening is the most "inherent" limitation to the "constant power speed range" of an AC drive.


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## Tesseract (Sep 27, 2008)

major said:


> The constant power region is a relic of rating specifications for continuous operation. When dealing with peak output, it becomes a singularity (peak point) as shown on the curve I referenced. ...


Right... the graph is for *550A*. I really shouldn't have overlooked that. 

I'll leave my posts as-is for posterity and to serve as a stark reminder to not argue with ol' maj.


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