# HPEVS AC-51 vs AC-76



## Caps18 (Jun 8, 2008)

What will the difference in these two motors be in the real world? Is the one that can get to power with fewer RPMs going to be faster or more powerful? I don't like how one has a 144V pack and the other has a 156V pack, but it looks like the amount of energy they need to get the same horsepower is similar. One generates a lot more torque though. And it operates at a lower rpm, is that a good thing?

Is the top one worth the 10% increase in price?


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## onegreenev (May 18, 2012)

Go with the HPEVS AC-75 with 144 volts instead. Much better overall power and excellent torque to 4000 rpm.


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## Caps18 (Jun 8, 2008)

What is better about that motor compared to the AC-76? It looks like the AC-75 needs higher rpms and has lower torque... What does it mean that torque starts rolling off at 3000 rpms with the AC-76? Does it mean that you have to shift more often? Will there be top speed implications?

Those two are the same price, so money isn't a factor.


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## onegreenev (May 18, 2012)

You will have good power out to 4000. When in 5th I would only be doing 2600 so I'd have excellent passing power to 4000. Still good power even past 4000. The AC 76 has Hobbs of torque only to 3000 rpm and then drops fast. You will have speed limits with lower voltages. Still like in a bug an AC 50 would do great even at 96 volts.


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## onegreenev (May 18, 2012)

What are you planning on putting the motor into? I am going to be doing the AC 75 144 volt in my Porsche 914.

Did you watch this video yet? He is using the AC 75 with the 108 volt setup with 180ah cells. He said it would do 70 no problem. Its only a 4 speed and heavy. Watch his follow up about the distance checking. Quite impressive for this motor and in a huge heavy vehicle like this.


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## Caps18 (Jun 8, 2008)

I am putting it into a Chevy S-10. I have removed all the ICE stuff and am just finishing up the last of the cosmetic stuff.

Thanks for the video. That is exactly what I wanted to see. The 108V, 650A controller was able to power that heavy vehicle very well. The acceleration was impressive too. I am trying to make my S-10 somewhat lightweight, and with 144V, it should have no problems with acceleration or speed. I don't have the money to buy the 180Ah cells like were in that conversion, but I hope that by reducing weight and perfect driving, I will be able to go 50 miles. Not often, but maybe 6 times a year.

I think I remember now reading that the AC-76 is designed for cars that have automatic transmissions...


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## dougingraham (Jul 26, 2011)

Caps18 said:


> What will the difference in these two motors be in the real world? Is the one that can get to power with fewer RPMs going to be faster or more powerful? I don't like how one has a 144V pack and the other has a 156V pack, but it looks like the amount of energy they need to get the same horsepower is similar. One generates a lot more torque though. And it operates at a lower rpm, is that a good thing?
> 
> Is the top one worth the 10% increase in price?


The motors can be thought of as converters of electricity to mechanical motion. The only real difference is apparent gearing. Note the horse power peak is 89 hp. It just occurs at different RPMs. This limt is imposed by the curtis controllers and not the motor. From a practical standpoint the AC3X, AC5X and AC7X lines all put out exactly the same power because none of them are the limiting factor. The 1238 can do 650 amps at a max of about 75kw watts (36 cells * 650 amps * 3.2 volts) which is 100 hp into the motor. The 1239 can do 500 amps at a max of about 74kw (46 cells * 500 amps * 3.2 volts) which is 99 hp into the motor. The HP out of the motor as shown in that graph is the iron and copper losses which is about 10%. The smaller frames have slightly higher losses but weigh less. The larger motors can sustain the full power level for longer if that is necessary. The choice really depends on how the torque curve matches your transmission gear ratios. Given a choice of an inverter that could do higher voltages and currents there would be more variation. If your goal is to eliminate the transmission and go with a single stage reduction you might want to pick the motor that hits its peak right at the 8k rpm limit and gear for top speed. Otherwise matching the motor to the transmission and final drive ratios could be an interesting exercise.


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## rwaudio (May 22, 2008)

dougingraham said:


> The motors can be thought of as converters of electricity to mechanical motion. The only real difference is apparent gearing. Note the horse power peak is 89 hp. It just occurs at different RPMs. This limt is imposed by the curtis controllers and not the motor. From a practical standpoint the AC3X, AC5X and AC7X lines all put out exactly the same power because none of them are the limiting factor. The 1238 can do 650 amps at a max of about 75kw watts (36 cells * 650 amps * 3.2 volts) which is 100 hp into the motor. The 1239 can do 500 amps at a max of about 74kw (46 cells * 500 amps * 3.2 volts) which is 99 hp into the motor. The HP out of the motor as shown in that graph is the iron and copper losses which is about 10%. The smaller frames have slightly higher losses but weigh less. The larger motors can sustain the full power level for longer if that is necessary. The choice really depends on how the torque curve matches your transmission gear ratios. Given a choice of an inverter that could do higher voltages and currents there would be more variation. If your goal is to eliminate the transmission and go with a single stage reduction you might want to pick the motor that hits its peak right at the 8k rpm limit and gear for top speed. Otherwise matching the motor to the transmission and final drive ratios could be an interesting exercise.


It's too bad there aren't better calculators for this.
In my initial configuration Warp11HV/Soliton1/300v pack, the ideal gear ratio would have been 5.5 or 6:1 (3000lb car) I had ratio's higher and lower than this in my transmission, but round 5.5:1 is what I would feel as ideal. 

I'm changing to a Siemens/DMOC combo and on paper it looks like 8 or 9:1 would be ideal (again not included in my box) however the 11.x:1 1st gear should provide amazing acceleration up to about 75km/h if I can keep the tires from breaking loose, then 2nd gear 6.969:1 will give me plenty of top end for normal driving, I may use 3rd gear for cruising at 110km/h but 4th/5th are likely useless.

I will likely drive in 2nd gear 90% of the time but it all depends on how it "feels". Depending on the results I may try to build myself a single speed gearbox with what I determine to be the ideal ratio for my car, out of a spare transmission and strip out the unused ratio's.

You can get an idea of the useful ratio's by multiplying the motor torque by gear ratio then tire diameter (if your tires are in the ballpark of 24" diameter you don't have to compensate because it's already in ft-lbs because of the 12" radius)
So for my 11HV setup with ~290ft-lbs x 11.81:1 ratio and 24.5" tires = roughly 3424.9ft-lbs. With 1700lbs on the rear wheels that's basically twice the torque as weight so without fancy suspension and amazing tires, traction is a major issue. So for me 1st gear is useless.
2nd gear gets better 290ft-lbs x 6.949 = 2015ft-lbs, this is just over the weight on the rear tires, and with some weight transfer during acceleration (rwd car) on a perfect surface I didn't have traction problems, on most roads I had to be a bit careful not to break the tires loose.
3rd gear 290 x 4.725 = 1370 which is significantly less than the weight on the rear tires and I almost never had traction problems, however acceleration was quite a bit slower than 2nd gear.

The Siemens motor has a higher RPM range, there is some power out to about 7500rpm before it really starts to fall off, so that's my red line. The motor doesn't make as much torque though.
1st gear means 220ft-lbs x 11.81 = 2600, which is beyond normal traction, but with careful driving could provide very good acceleration to 75km/h.
2nd would likely be the gear I use, 220 x 6.949 = 1528 which should be fine at full throttle on most dry surfaces with no problems but won't equal the same kind of acceleration the 290ft-lbs from the 11HV provided. 2nd gear will also take me up to about 127km/h at 7500rpm so depending on the noise/vibration I may never need to shift.
I think the ideal solution would be a single ratio box that allowed me to use the full 10,000rpm from the motor, with a limited top speed (150km/h or something) and a higher ratio somewhere around 8 or 9:1 to give better acceleration and a real world top speed. Who actually needs 250-300km/h in a street car.


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