# higher voltage for ac50



## Coulomb (Apr 22, 2009)

zafh15a said:


> can't seem to find anything about a controller for an ac motor other than the Curtis (max 130v 650a) I really would like to go at least 144v does anyone know of an alternative controller with regen. Or some other motor/ controller combo capable of similar performance to the original 4cyl ICE in a ford ranger?


Curtis themselves have a 144 V nominal AC controller in the works, though there is speculation as to whether it has been cancelled or not.

There are very few AC controllers that are designed for under 400 V DC bus. You might have to roll your own, e.g. the Tumanako project.


----------



## frodus (Apr 12, 2008)

The biggest problem will be finding a motor that works well with a 144V pack and 144V controller.

You'd likely have to get one custom from HPEVS.


----------



## Coulomb (Apr 22, 2009)

frodus said:


> The biggest problem will be finding a motor that works well with a 144V pack and 144V controller.


I think that the AC-50 has plenty of reserve power handling capacity. I'd say it would work fine on 144 V.

There are no brushes to arc over, and the windings will be good for at least 480 VAC, so that's not going to be an issue.


----------



## frodus (Apr 12, 2008)

"Works" and "works well" are two different things.

I know the AC50 frame has plenty of ability as a motor.... I'm not concerned about that. It's the windings and turns ratio. It's not wound to run optimally at 144V.

Why don't they run 277/480V motors at 120/208V on industrial equipment? They don't, they need to use the windings at the right voltages. Some motors have terminals that you can configure for one or the other, but not both.


----------



## steven4601 (Nov 11, 2010)

The limits to obey are insulation voltage limit, current limits, rpm limits.

Increasing the voltage of the traction battery to the inverter has no ill effectors for the motor as long the motor rpm, current, insulation voltage arent exceeded beyond manufacturers specifications.

What you get back from extra voltage is extend the torque- drop of rpm to a higher speed. If at 120V the constant torque starts collapasing/falling @ 3000 rpms, the going up to 240V the constant torque should go up in theory upto 6000rpms. Same torque, double the power! 

Only if the physical limits are respected.


----------



## Coulomb (Apr 22, 2009)

Coulomb said:


> Curtis themselves have a 144 V nominal AC controller in the works, though there is speculation as to whether it has been cancelled or not.


Well, this post seems to indicate that it's not cancelled, and is in fact being beta tested:

HPG AC30/31/50 owners thread

Edit: thanks for the info, Tom!


----------



## Tesseract (Sep 27, 2008)

steven4601 said:


> The limits to obey are insulation voltage limit, current limits, rpm limits.
> 
> Increasing the voltage of the traction battery to the inverter has no ill effectors for the motor as long the motor rpm, current, insulation voltage arent exceeded beyond manufacturers specifications.


Sorry, but no... as you increase the voltage to an AC motor you must also increase the stator frequency, and that causes the AC core losses to increase to the ~1.6 power, approximately.

You can use thinner laminations and/or different types of silicon steel to better tolerate a higher stator frequency, but this comes at the expense of a lower saturation limit at lower frequency (ie - less starting torque).

TANSTAAFL.


----------



## frodus (Apr 12, 2008)

steven4601 said:


> The limits to obey are insulation voltage limit, current limits, rpm limits.
> 
> Increasing the voltage of the traction battery to the inverter has no ill effectors for the motor as long the motor rpm, current, insulation voltage arent exceeded beyond manufacturers specifications.
> 
> ...


Can you take a minute to explain why don't they run Industrial three phase 120/208V motors at 277/480V? Why not just make them all 600V motors and run them at any 3-phase voltage?


----------



## steven4601 (Nov 11, 2010)

Two reasons.


1. Frequency
2. Power rating of the motor

Frequency:
In an EV, the AC motor is either driven in a bold Volt/Hz mode or a more elegant solution, FOC mode. In either control mode the speed of the motor depends largely on the frequency applied to it. Full torque / max of the motor depends on the requirement of a fully fluxed/magnetized rotor. This requirement can only be met if there's sufficient stator voltage to overcome the back EMF from the rotor. In many EV / traction / Industrial inverters the motor graphs start with a perfect flat torque band upto a certain motor speed. That moment the torque falls of is when there is not enough bus/battery voltage to flux the rotor for full torque and a reduction in rotor magnetizing current is made. Torque falls of. Sadly also power falls of with a lower rate. This rate it falls of depends on many things and cannot be explained briefly without causing misconceptions. 

Back on the question why more voltage helps, more available stator voltage (which is controlled by the motor controller) allows to stay in the flat torque region as the rotor at higher RPM's can still be magnetized to its maximum. Why does this work? Higher RPM's also require higher frequencies. This ratio is almost linear (copper & iron losses make it non-linear) If the motor speed is increased, so is the frequency and voltage in the same relative amounts. this keeps the rotor & stator flux the same! No saturation occurs. 



Power rating
Connecting an Induction motor of a lower voltage to a high voltage mains source causes many problems. But the speed of the (unloaded) motor will be the same (if the line frequency is identical). It is likely the stator saturates causing circuit breakers to pop instantly. 

Otherway around, connecting a higher voltage ac motor to a lower voltage mains causes a reduction in available torque. There's only half the allowed voltage applied, half the rotor flux. When loading the motor with the same breaking torque the speed will drop much lower.


----------



## steven4601 (Nov 11, 2010)

Tesseract said:


> Sorry, but no... as you increase the voltage to an AC motor you must also increase the stator frequency, and that causes the AC core losses to increase to the ~1.6 power, approximately.
> 
> You can use thinner laminations and/or different types of silicon steel to better tolerate a higher stator frequency, but this comes at the expense of a lower saturation limit at lower frequency (ie - less starting torque).
> 
> TANSTAAFL.


Hi,

Starting torque is irrelevant with AC motors once they are controlled through Field oriented control or V/Hz mode. 

Directly coupled mains AC motors do exhibit starting torque.
Starting torque comes from connecting them to the fixed mains frequency where a huge slip speed/frequency between the electrical field of the rotor and stator is made at start-up. (electrically 50Hz / 3000rpm mains) 0Hz / 0 rpms rotor rotor. The available start torque then is appalling as the rotor receives/produces very little current as its own inductance is far too high to produce current from the far too fast electrical field of 50Hz... Only once the rotor starts spinning, catching up with the electrical speed of 50Hz / 3000rpms the current in the rotor increases. The moment where the rotor current has become greatest is called the pull-out torque. Usually 4 to 8 times higher than the start torque. 

FOC and Volt/Hz mode inverters always try to (throttle input & available bus voltage requirement) operate in the pull-out torque region to maximise torque.


----------



## major (Apr 4, 2008)

steven4601 said:


> FOC and Volt/Hz mode inverters always try to (throttle input & available bus voltage requirement) operate in the pull-out torque region to maximise torque.










This is a typical torque-speed curve for a standard AC induction motor.

ref: http://ecmweb.com/mag/electric_understanding_induction_motor/ 

We usually call it breakdown torque (BDT)


----------



## frodus (Apr 12, 2008)

So what I'm seeing is....basically, yes, the AC50 as it is, will do the higher voltage, it doesn't care, but it won't work "AS WELL" as a motor wound for the higher voltage and lower current. As you increase the voltage, the current is lower for the same power. And in order to keep the torque the same on a 96V AC50 650A system, they would rewind the motor so it's got the same starting torque with a 144V 500A system (for instance).


----------



## bjfreeman (Dec 7, 2011)

so is the AC50 an induction motor?
could not find a spec on the # of poles


----------



## major (Apr 4, 2008)

bjfreeman said:


> so is the AC50 an induction motor?
> could not find a spec on the # of poles


Type in "AC50" to google. And it is 4 pole, IM.


----------



## bjfreeman (Dec 7, 2011)

major said:


> Type in "AC50" to google. And it is 4 pole, IM.


Actually I did and got a lot of links to people selling it in kits.
thanks for the info on the poles.


----------



## major (Apr 4, 2008)

bjfreeman said:


> Actually I did and got a lot of links to people selling it in kits.
> thanks for the info on the poles.


http://hpevs.com/drive-systems/ac-50


----------



## tomofreno (Mar 3, 2009)

frodus said:


> So what I'm seeing is....basically, yes, the AC50 as it is, will do the higher voltage, it doesn't care, but it won't work "AS WELL" as a motor wound for the higher voltage and lower current. As you increase the voltage, the current is lower for the same power. And in order to keep the torque the same on a 96V AC50 650A system, they would rewind the motor so it's got the same starting torque with a 144V 500A system (for instance).


 I think you give up some low end torque but gain higher base speed. HPEVS said the difference in the AC50 and AC31 is that they "traded off low end torque for more running torque". By that I think they meant lower rotor flux and less back emf at higher rpm so you have more torque at normal running rpm range (higher base speed), but you give up torque at the low end (peak torque AC50: 92 ft-lb, AC31: 117 ft-lb). Their new water cooled motor has higher peak torque, 150 ft-lb, but lower base speed (compensated for somewhat with the higher voltage). With the 500A/144V controller the AC50 will have only about 80 ft-lb peak torque, but I think it should have that out to about 5000 rpm with a 49 cell pack (max V is supposed to be about 170V). Would have been much nicer had Curtis made it 650A/144V. I don't think there is any "perfect" one motor design for a given current and voltage. Depends on what you want.


----------



## bjfreeman (Dec 7, 2011)

tomofreno said:


> I think you give up some low end torque but gain higher base speed.


that is a function of the number of poles. Increase poles increase Torgue, AND decrease RPM for a given frequency.


> but I think it should have that out to about 5000 rpm with a 49 cell pack (max V is supposed to be about 170V).


Voltage Gives you Power and lower Current for the same Power.
RPM is controlled by Frequency and poles.


----------



## Coulomb (Apr 22, 2009)

bjfreeman said:


> that is a function of the number of poles.


While that's true, the efficiency (in terms of power for a given frame size) of an induction motor seems to decrease dramatically past two pole pairs (4 poles). There are certainly 6, 8, and higher pole industrial motors, but these are for unusual applications where they can put up with the lower efficiency to gain the benefit of not having to install a gearbox.

So most EV AC motors are 4 pole, and occasionally 2 pole. We're going two pole in our MX-5/Miata because with modest over-voltaging (equivalently over-speeding), the resultant RPMs are a better match for our gearbox (the ICE had around a 6500 RPM redline, as is fairly typical).


----------



## Coulomb (Apr 22, 2009)

Tesseract said:


> Sorry, but no... as you increase the voltage to an AC motor you must also increase the stator frequency, and that causes the AC core losses to increase to the ~1.6 power, approximately.


Tesseract, is that something that only applies when running DOL (Direct On Line) ?

I imagine that if you took a motor designed for 60 Hz, and connected it unmodified to the same voltage but at 400 Hz, DOL (so giving it a frequency 6.67x higher than it is designed to run at), then it might have appalling iron losses, about 6.67 ^ 1.6 = 21x worse.

But a 1500 RPM industrial motor running at 6000 RPM (4x, say ~ 240 Hz vs 60 Hz electrical) would surely not see a 4 ^ 1.6 = 9.2x increase in iron losses, with the inverter able to allocate the proportion of field current and stator current as needed? Obviously, with DOL, you connect the motor (perhaps via a starter), and the power factor you get is what you get; you can't change it, so at higher frequencies, a DOL motor will be starved of field excitation due to the higher inductive reactance, so the torque will be low.

A properly driven inverter can allocate close to the optimal amount of field current for any particular speed and load, once it's "learned" the basic motor characteristics. Having said that, the way that the silicon steel reacts to changing frequencies isn't typically something I'd expect a typical inverter to "learn".


----------



## Tesseract (Sep 27, 2008)

Coulomb said:


> Tesseract, is that something that only applies when running DOL (Direct On Line) ?
> 
> I imagine that if you took a motor designed for 60 Hz, and connected it unmodified to the same voltage but at 400 Hz, DOL (so giving it a frequency 6.67x higher than it is designed to run at), then it might have appalling iron losses, about 1.6 ^ 6.67 = 23x worse.


The iron losses in a transformer (after all, an induction motor is essentially a 3ph. transformer with a shorted 1 turn secondary) go up with frequency to approximately the 1.6 power, not 1.6 with the multiple as the exponent, and this also assumes that the voltage is scaled with frequency (ie - not in the field-weakened part of the curve where torque decreases as RPM increases).

For example, - if you run a 240V/60Hz motor at 480V/120Hz - doubling the RPM while keeping the max torque the same - then the iron losses will triple (because 2^1.6 = 3).

This applies no matter how the motor was started or whether it is supplied by a VFD or the line; if you double the voltage and frequency to an induction motor you treble the iron losses.

You can use thinner laminations and/or of a different grade of silicon steel to reduce the losses at the higher frequency, but this always comes at the expense of saturation flux density, which directly affects the amount of breakdown, or maximum torque available from the motor, and this also applies whether the motor is started DOL or with an inverter. 

Note that I was responding to Steven's inaccurate comment that the induction motor will experience no ill-effects from increasing the voltage and frequency driving it. If you simply increase the frequency but keep voltage constant - once again, in the field-weakened region of the speed/torque curve - then losses increase only slightly as flux is declining in proportion to frequency.


----------



## Coulomb (Apr 22, 2009)

Tesseract said:


> ... go up with frequency to approximately the 1.6 power, not 1.6 with the multiple as the exponent, ...


Arrgh! 

I had the feeling when I started that post that I was "removing all doubt"! 

Such a silly mistake. I'll blame it on my slight headache today, yes, that's it, not senility at all! 

I think that this may have been discussed in the looong discussions over at AEVA on overvoltaging, and from feeble memory, the iron losses are moderate to start with, so increasing them by a good chunk (tripling certainly qualifies) is not too bad, especially since you are getting a lot more power out of the motor at the same time. Obviously, with the exponent over unity, you will be losing more than you gain (in the sense that the losses will climb faster than the shaft power, so the losses as a proportion will still increase, so the efficiency must fall).

I guess that's another advantage of keeping the gearbox; you can keep the speed lower at crusing, to keep the frequency lower, to keep the iron losses lower and efficiency higher. Though as Otmar has posted recently, there are other reasons to keep the speed higher and torque lower.

Now that I think about it, our relatively modest overvoltage factor of some 2.3:1 (525 V / 230 V, but likely less than 2:1 with battery sag) was partly to do with keeping the iron losses sane. (Others have been suggesting 3:1 overvoltaging, and even more). It all seems such a long time ago.

Oh, wait!  It actually was a long time ago


----------



## Tesseract (Sep 27, 2008)

Coulomb said:


> Arrgh!
> 
> I had the feeling when I started that post that I was "removing all doubt"!


S'alright... I'll probably get roasted by major for oversimplifying things here too much myself... 



Coulomb said:


> I think that this may have been discussed in the looong discussions over at AEVA on overvoltaging, and from feeble memory, the iron losses are moderate to start with, so increasing them by a good chunk (tripling certainly qualifies) is not too bad, especially since you are getting a lot more power out of the motor at the same time....


Sure - iron losses (and copper losses, too) are typically quite low when the motor is run at the recommended voltage/current/frequency combination to deliver its continuous power rating. That, after all, is a necessary prerequisite for achieving high efficiency, an attribute often used as evidence of the superiority of the AC motor, though I must note that the efficiency of the typical ACIM is no higher than an equivalent size DC motor (around 85%) if it is not otherwise claimed to be a "high efficiency" type. 

At any rate, any efficiency advantage is soon lost when the motor is "overvolted" because of the aforementioned rapidly increasing iron losses. Thus, efficiency drops in the AC motor when it is overloaded in much the same fashion as when a DC motor overloaded... 

Hence why I put "TANSTAAFL" in my initial response to steven4601.


----------



## bjfreeman (Dec 7, 2011)

Here is a white paper on Optimum Pole Configuration of A-C Induction Motors Use On Adjustable Frequency Power Supplies
http://www.reliance.com/pdf/motors/whitepapers/B7100.pdf
and
High Efficiency Squirrel Cage Induction Machines
http://www.icrepq.com/ICREPQ'09/308-tudorache.pdf


----------



## bjfreeman (Dec 7, 2011)

Coulomb said:


> While that's true, the efficiency (in terms of power for a given frame size) of an induction motor seems to decrease dramatically past two pole pairs (4 poles).


from charts I looked at seems like there is about a 10% drop in efficiency per pole set. Yes 4 pole does give a 4 fold range of Torque compared to more or less 


> There are certainly 6, 8, and higher pole industrial motors, but these are for unusual applications where they can put up with the lower efficiency to gain the benefit of not having to install a gearbox.


max loss is 25% is that considered a lot for the ability to not use a gear box? However it is less with 4 pole and you can get 10,000 ftlbs max. which seems to me more than enough for most passenger EV's.


> So most EV AC motors are 4 pole, and occasionally 2 pole. We're going two pole in our MX-5/Miata because with modest over-voltaging (equivalently over-speeding), the resultant RPMs are a better match for our gearbox (the ICE had around a 6500 RPM redline, as is fairly typical).


----------



## Chad (Aug 1, 2008)

This may be of some help, but maybe not. In the R/C industry you can purchase a single "brushless" (AC motor) in several different windings. Every motor will have the same power output, IE 1500 watts, yet will be designed for different battery voltages.

The rating we use is Kv (not KV) it stands for RPM / VOLT

for boats, desired motor RPM is 30,000 so

1400 Kv @ 21 volts = about 30,000 rpm but needs 71 amps for max power (1500 watts)
1800 Kv @ 16 volts = about 30,000 rpm but needs 93 amps for max power (1500 watts)
2200 Kv @ 13 volts = about 30,000 rpm but needs 115 amps for max power (1500 watts)

see here http://www.offshoreelectrics.com/proddetail.php?prod=leo-4074&cat=148

I do not know if these are induction motors or not though


----------



## steven4601 (Nov 11, 2010)

From their site*:

Comes with high quality bearings and **neodymium** magnets for high power.

*That would imply these are Unilateral phase detractors and lunar flange retro-encabulators

For more info on that can be found here: http://www.youtube.com/watch?v=TuhYd9L_d7w


----------



## Coulomb (Apr 22, 2009)

Chad said:


> In the R/C industry you can purchase a single "brushless" (AC motor) in several different windings. ... Every motor will have the same power output, IE 1500 watts, yet will be designed for different battery voltages.
> 
> The rating we use is Kv (not KV) it stands for RPM / VOLT


Right. K for constant, subscript "v" meaning "the voltage constant". Basically, they vary the number of turns, so that you get higher or lower back EMF, so you end up with a higher or lower voltage motor. They probably make the higher number of turns motors with thinner copper, so they can fit it into the same frame.



> I do not know if these are induction motors or not though


No. As far as I know, these are all "brushless DC" motors, with permanent magnets. Induction motors, while they have no brushes, aren't called brushless, and have no permanent magnets. These motors with PMs are synchronous (so for 30,000 RPM mechanical, you give them 15,000 RPM electrical (assuming 4 pole); an induction motor has slip, so for 30,000 RPM you drive them at say 15,200 RPM electrical (again, assuming 2 pole pairs, i.e. 4 pole).


----------



## Chad (Aug 1, 2008)

steven4601 said:


> From their site*:
> 
> Comes with high quality bearings and **neodymium** magnets for high power.
> 
> ...


That was awesome! So forget my post, these motors are all together different.


----------



## Jaesin (Mar 6, 2011)

etischer here might be able to get you set up with a controller. He built his own by modifying an industrial variable frequency drive. It runs at 300 volts.


----------

