# HPEVS AC 75 vs AC 76



## DreamMachine (Sep 28, 2015)

So, while planning my build (and realising almost everything is based around the motor), so; 

My choices are:

Curtis 1238-7601 HPEVS AC-75 
or 
the Curtis 1239-8501 HPEVS AC-76

The AC-75 runs on 110 volts (and is "rated" at "78" HP continuous) , where the AC-76 running 170 volts (rated at "90" Hp continuous) . Now, if I can find a Smart car battery pack (6 tesla modules), I can connect them in 2S 3P, vs 3S 2P. Obviously, the 2S 3P setup would have a greater capacity (and therefor greater range). Not to mention, the AC-75 is approximately 1K cheaper $$$

BUT, the real question is: Is the AC-75 powerful enough for a 3200 pound vehicle? 

The Volvo V70 I'm looking at converting is not exactly light, so the trade off is really between acceleration and range as far as I'm aware. I'm not looking at tire-burning acceleration, but certainly not golf cart acceleration either. 

Does anyone have any experience with either motor, or what disadvantage there is with either motor?


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## onegreenev (May 18, 2012)

Im not absolutely sure about it but I believe HPEVS has discontinued the AC-75/76 series. Owing to the fact that the motors did not give any real benefit from the already power house of the AC-50 series motors. 

I'd contact them directly about what you plan on using and and what they might recommend. Have you gone directly to HPEVS to check their power graphs of the motors with the different voltages? It will give you a good eye opener as to what they can actually do for your needs. 

Checking on the site I see no more AC-75 or 76 motors or power graphs. Id nix your idea of the those motors unless you already have them. 

Pete


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## akseminole (Jan 5, 2014)

Evwest seems to still have both the AC-75 and AC-76 in stock (unless they have forgotten to take them down, which, seems unlikely).


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## Coulomb (Apr 22, 2009)

DreamMachine said:


> The AC-75 runs on 110 volts (and is "rated" at "78" HP continuous) , where the AC-76 running 170 volts (rated at "90" Hp continuous) .


I don't know these motors well, but surely these power figures (which are at the peak of the power curves) are the peak power, not continuous. The continuous power would depend on cooling as well as motor design (e.g. winding insulation rating). I think the continuous power rating would be much lower than the peak power.

Not that it matters that much at this part of the design perhaps.


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## dcb (Dec 5, 2009)

you can see some examples of ac-75 usage on evalbum
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=ac75 site:evalbum.com

i.e. a vw van pickup thingie that weighs 3800 lbs (kept the transmission).

I *think* the ac76 was designed for higher volts/less amps if you can find one. Also there may be oil cooled variants.


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## akseminole (Jan 5, 2014)

Those are in fact the peak ratings. Not the continuous ratings.

I think the continuous ratings were in the 10-20 hp range.

I was really hoping that HPEVS would make an oil cooled version, but, alas they discontinued the AC75/76.


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## dcb (Dec 5, 2009)

hpevs still has a few continuous graphs for the ac75

for the 144v500a controller
http://hpevs.com/Site/images/torque...c75-144v-500 amp imperial continuous TENF.pdf


for the 96v650a controller
http://hpevs.com/Site/power_graphs/...5-96volt-650 amp-imperial continuous-tenf.pdf

though I can't say I fully understand why the 96v version makes more hp continuous, they seem to have the current cranked up a bit more on the 144 graph (using a different v/hz setting), otherwise I would expect the 144 to make 50% more power at 50% more rpm for the same current, but 240 foot lbs off the line is nice too  

Why it makes more torque continuous is also a mystery, looks like there is a lot of room for tuning, or the graphs are wonky or it is a dynamic artifact on the peak graphs (i.e. add more load)


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## DreamMachine (Sep 28, 2015)

akseminole said:


> Evwest seems to still have both the AC-75 and AC-76 in stock (unless they have forgotten to take them down, which, seems unlikely).


Yeah, I was looking to order from them since they still have them in stock...



Coulomb said:


> I don't know these motors well, but surely these power figures (which are at the peak of the power curves) are the peak power, not continuous. The continuous power would depend on cooling as well as motor design (e.g. winding insulation rating). I think the continuous power rating would be much lower than the peak power.
> 
> Not that it matters that much at this part of the design perhaps.





akseminole said:


> Those are in fact the peak ratings. Not the continuous ratings.
> 
> I think the continuous ratings were in the 10-20 hp range.
> 
> I was really hoping that HPEVS would make an oil cooled version, but, alas they discontinued the AC75/76.


Hmm, well if that is the "maximum" (which seems pitiful compared to the 200 HP the car had stock (but maybe gasoline HP and Electric HP are rated differently?)



dcb said:


> hpevs still has a few continuous graphs for the ac75
> 
> for the 144v500a controller
> http://hpevs.com/Site/images/torque...c75-144v-500 amp imperial continuous TENF.pdf
> ...


Hm, odd. So the question still remains I guess; If I can find both motors, which do I order? They both seem to have their own downfalls...


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## Yabert (Feb 7, 2010)

DreamMachine said:


> Hmm, well if that is the "maximum" (which seems pitiful compared to the 200 HP the car had stock (but maybe gasoline HP and Electric HP are rated differently?)


No... and yes! Hp = Hp but gas engine are rated at peak and electric continuous. Instant torque from electric motor give the impression of high power.
With an ICE, you need to heavily press your foot down the throttle and wait few seconds to the motor reach insane RPM to feel the ''rated HP''.


> Hm, odd. So the question still remains I guess; If I can find both motors, which do I order? They both seem to have their own downfalls..


Look further than the motor.
Between 144v and 96v, you will need to consider the design, availability and price of battery configuration, charger, DC-DC, etc...


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## akseminole (Jan 5, 2014)

The major difference between an electric motor and an ICE is that the electric motor develops peak torque from 0 rpm and has a more or less flat torque curve out to where the torque starts to drop off. I would suppose that the continuous torque curve is also more or less flat, until it reaches its respective drop off point also.

The Internal Combustion Engine starts at 0 rpm with 0 torque and spools up towards peak torque as the rpm goes up. Eventually you reach peak torque right next to the redline and this is why people rev up their engines and dump clutches.

Usually with an ICE powered vehicle, you spend much of your time at lower RPM levels which corresponds to lower than peak torque. I have no idea what that would be, but let's say that hypothetically you drive around in the 1,500 - 2,500 rpm range for the most part and your 200 hp car engine has peak torque at 5,000 rpm. This would mean that you are driving around on a fraction of your cars peak hp. 

I've read (but have no actual experience to know if this is true) that given a specific peak torque from an electric motor, a car will behave at starting off the line the same as an ICE vehicle with double that torque.

If this is true, then, as an example; a car with a motor which outputs 180 ft lbs of torque from 0 rpm May have similar acceleration as a car whose ICE has a peak output of 360 ft lbs. 

I assume that this involves a bunch of caveats. Also, once you reach the ICE cars peak torque, that car would continue to accelerate while the 180 lb ft motor would only be putting out half the torque (less actually, because at the peak hp of the electric motor, the torque peak is usually starting to come down).

Essentially this means that the 75 or 90 hp peak motor performs off the line, similar to a higher hp rated car engine. It is at higher speeds that the higher hp car engine outperforms the electric motor. 

I'm not here to go fast, so I have only limited knowledge of the specifics. Since my project is still incomplete, I have only forum learning to back my words rather than any real world experience.


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## dcb (Dec 5, 2009)

DreamMachine said:


> Hm, odd. So the question still remains I guess; If I can find both motors, which do I order? They both seem to have their own downfalls...


Note, I was looking at the same motor with two different controllers (both the ac75), the ac76 is designed to go with the 144v 500a controller AFAIK. The AC75 is for a 96 or 108v controller. The only difference between them is the ac76 has more turns of wire and less cross sectional area, so that it makes the basically the same power as the ac 75 at the same rpm at a higher voltage and a lower current. Typically higher voltage is better these days and there is a lot of 144v equipment out there so I would probably go with the AC76 if I needed the extra torque but the ac51 @ 144v makes the same power for less weight (and is not discontinued) so if you have control of the gearing ratio then you can go that route.

peak ac75 @108v 160a is similiar to peak ac76 @ 144v (108v*650a=70200watts, 144v*500a=72000watts)
http://hpevs.com/Site/power_graphs/imperial/peak/pdf/ac-75/ac-75 108 volt 650 amp imperial peak.pdf

http://hpevs.com/Site/images/torque-curves/ac-76/imperial/ac76 imperial peak 144 volt 500 amp.pdf

Since you are probably gonna have to keep the transmission, the ac51 @144v might be your best bet.
http://hpevs.com/Site/images/torque...51 144 volts 500 amps imperial peak graph.pdf
there are a lot of ac50 projects out there, it has the same relationship to the ac51 that the ac75 does to the ac76 (same motor, different windings to trade volts for amps). plus they have other motor models too  (and picking the *best* one is rather involved, but the ac35 @144v should be considered as well)

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=ac50+site:evalbum.com


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## DreamMachine (Sep 28, 2015)

akseminole said:


> The major difference between an electric motor and an ICE is that the electric motor develops peak torque from 0 rpm and has a more or less flat torque curve out to where the torque starts to drop off. I would suppose that the continuous torque curve is also more or less flat, until it reaches its respective drop off point also.
> 
> The Internal Combustion Engine starts at 0 rpm with 0 torque and spools up towards peak torque as the rpm goes up. Eventually you reach peak torque right next to the redline and this is why people rev up their engines and dump clutches.
> 
> ...


Ah! That makes a lot more sense! Thank you for explaining all that. Just somewhat hard to get over the immediate idea of "hey, my current motor is "200HP" so there's no WAY this "80 HP" electric motor can do the same!"


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## akseminole (Jan 5, 2014)

If it helps: horsepower is RPM x lb ft of torque/5252.


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## piotrsko (Dec 9, 2007)

If it helps also: the mighty 426 only makes about 10 hp at idle , 25 hp at 1000 rpm and it is a straight line to max. In this case the ramp is pretty steep.


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## WolfTronix (Feb 8, 2016)

To give you an idea of what to expect, my truck uses about 200A at 144V to maintain highway speed (70MPH), so:

144V * 200A = 28.8KW
28.8KW / 746 = 38.6HP


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## tomofreno (Mar 3, 2009)

Yabert said:


> ...Instant torque from electric motor give the impression of high power.


This could lead one to believe that fast acceleration is the result of high power. That is only correct at higher motor rpm. Vehicle acceleration is the result of wheel torque. Period. Wheel torque divided by tire dynamic radius gives the tractive effort - the force the tires apply to the road to move the vehicle.

Power is the product of torque and angular velocity of the motor. At lower rpm an electric motor has high torque and there is little power output. It is only at higher motor rpm that high power is required to maintain high torque.

The typical torque vs rpm curve for an electric motor is approximately flat out to the rpm where back emf of the motor is large enough to start reducing current through the motor, the "base speed". At higher rpm than this current and torque start decreasing, and so does acceleration. Motor power output may remain approximately constant for a bit above this point, but the vehicle is going faster so more power is required to continue accelerating at the same rate. This can be increased to higher rpm by increasing voltage to the motor. The lower peak power of the HPEVS motors (actually due to Curtis controller power limitation, not the motors) limits the motor torque at higher motor rpm, so acceleration will decrease there. Depending on vehicle mass, it may be quick off the line, but fad at higher vehicle speeds because it can't maintain high torque to higher motor rpm. 



akseminole said:


> The major difference between an electric motor and an ICE is that the electric motor develops peak torque from 0 rpm and has a more or less flat torque curve out to where the torque starts to drop off. I would suppose that the continuous torque curve is also more or less flat, until it reaches its respective drop off point also...


If you "floor it" an electric motor will output peak torque up to its base speed rpm. Motors operated under continuous load for long times have a limit on how much power they can supply due to overheating from the small portion of energy they dissipate as heat. Most motors for such applications have cooling fans to increase heat removal and thus increase the continuous power rating. There is no "continuous torque" rating, only continuous power. The amount of torque this corresponds to will depend on motor rpm.

There is some wheel torque required to maintain a given vehicle speed. Any wheel torque the motor can output above that value can be used to accelerate the vehicle. Vehicle speed after accelerating over some time period will be proportional to the integral of this "extra" tractive effort or wheel torque over that time period. This varies over time since the
vehicle speed is increasing. One way to estimate vehicle acceleration is to use a piecewise continuous curve to approximate this "extra" wheel torque, i.e. assuming this "extra" wheel torque is constant over small time intervals, say a few seconds. I think there are some spreadsheets posted here that will do such a calculation which you might find if you do a search, but they must have the torque-speed curve for the motor you plan to use.

Looking at the torque-speed curves at EVWest for the AC76 and AC75 you can see that the former has about 155 ft-lb torque up to about 3000 rpm and the AC75 has about 165 ft-lb torque up to about 2500 rpm, so the AC75 has about 6.5% greater torque up to about 2500 rpm, which will result in about 6.5% greater acceleration over this range of motor rpm compared to the AC76. But it has a bit less torque than the AC76 above that rpm, which will result in less acceleration over that range. As a result, I would expect a little faster 0 to 60 mph time from the AC75, but faster 0 - 30 mph time with the AC76. These can both be operated at higher voltage since the Curtis 1239-8501 has max input voltage of 170V, and the 1239-7601 has max of 130V. This will result in higher peak power than shown in the curves - approximately increased by the voltage difference.
Neither one will likely give you 0 - 60 mph time as fast as you would get with a 200 HP gas engine. Both will likely give faster 0 to 30 mph time.

Agree with dcb's comments on the HPEVS motors. The main difference in the AC50/AC51 and AC75/AC76 is bottom end torque, which is substantially higher for the AC75/AC76, but they are all limited in peak power by the Curtis controllers.


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## Caps18 (Jun 8, 2008)

I'm kind of surprised that HPEVS or any of the distributors haven't done some track testing to prove what differences the motors have if put in different types of vehicles. I have the AC-75 and will run it at 115V, but I don't know if it would be any better than the AC-50 or AC-30 in terms of acceleration or range.

I do know that the AC-75 is very heavy. Way heavier than I expected. I don't know about the other motors, and if one person could pick them up. I don't know if there are any benefits to efficiency in a bigger motor, or if a lighter weight smaller motor would be better for range.


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## Frank (Dec 6, 2008)

The other factor that never gets mentioned is that ICE's use transmissions, and a lower torque output can get multiplied so torque at the rear wheels is just as high, or higher, than an EV. That electric motors can provide adequate torque without a transmission is one reason they are great for everyday vehicles. Racing can be different!


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