# AC51 motor



## Richard Wood (Jun 27, 2008)

Has been some time since I looked at my BMW 318ti conversion project. Since then HPEVS have added new AC motors on their site and availability of other motors in my part of the world appears to remain patchy.
I had considered the AC50 but concluded I'd need to keep the transmission.
Now I'm looking at the AC51 and it seems that for the same 108V/650A I can get 20% higher torque at the low end and have peak power back to 3000rpm. I'm wondering if that re-opens the possibility for me of going direct drive. At 3000rpm I'll be going 80kph and I need to do this up a hill, I'll only be going above that on the flat. 
That leaves the question of whether the extra 20% torque at the low end will get me off the kerb nicely.
Any thoughts? This is a compact car that weighs 1260kg in ICE configuration.
I could go AC7X series and get higher torque again but not keen on the extra size and weight of the motor.
Or could consider the AC51 at 144V but would need to find a higher ratio diff and my car already has the highest (4.44 ratio) usually seen on this type of car - any thoughts on this as well?
Cheers
Richard


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## onegreenev (May 18, 2012)

For the size of the car and the size and power of the AC-50 or 51 I'd keep the transmission. No matter what in a low voltage system you should take advantage of the transmission. I think the AC-50/51 is too small for your vehicle. I am working on a Porsche 914 and I am putting in an AC-75. For your vehicle either an AC-75/76 or a Siemens/DMOC controller with high voltage and lower amps if you intend to go direct drive. Even so. I think since you have a transmission you should build around that and take full advantage of the transmission. An AC-75 with the 120 volt and 650 amp controller might do just fine. I am still struggling which to go with. 120 volt 650 amp or 144 volt and 500 amps. The second choice will allow me to rev up to 5000 rpm in each gear with loads of power. Still not quite sure.


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## drgrieve (Apr 14, 2011)

Knowing the hills in Wellington I'd keep the transmission.

Instead of the highest diff, do the reverse and get the closer to the lowest you can find this way the transmission becomes more useful. You want to be able to have some torque in reserve at 110 kph in case of a need to do high speed overtaking (For the US folks NZ highways are mostly single lane). RPM maths will tell you the right answer.

Since all the HPEVS motors & controllers produce the around the same power, just different torque curves, by keeping the transmission you can just simply buy the cheapest one. The AC50. BTW you can run this with 36 cells to bump up the voltage a tad.


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## Siwastaja (Aug 1, 2012)

"Direct drive"* works best if these two conditions are met:

*) meaning direct to the rear differential, which will have reduction gear.

(1) The reduction gearing is just right for the motor and top speed. Usually this means at least 1:5 for an AC induction motor. OEMs go as high as 1:10. Typical rear diff is less than 1:5 and, hence, usually less than optimum.

(2) The motor is large enough, i.e., has enough power for a good top speed. If it has enough torque to overcome the high drag at high speeds, it surely has enough torque for good acceleration at lower speeds, too.


OEMs can easily design the system to satisfy these conditions, in which case the transmission can be eliminated as it only causes additional losses, complexity and weight.


The original transmission:

(1) Allows choosing an optimum gear, even if you just locked it there. (So you don't need to order a special rear diff or compromise the optimum gear ratio.)

(2) Can give better acceleration at low speeds or uphills by shifting gears, in case the motor is "undersized".

Note that these are two separate points and they apply to any type of motor.


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## crackerjackz (Jun 26, 2009)

Has anyone actually tride yet with a ac75 or 76 to do a direct drive system ? Would it be enough power say for a 1300 kg car ? 
Im asking because the automatic transmsiion in my car a bmw 320 i know is gonna be a major pain in the ass and this might be a good backup  ...


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## crackerjackz (Jun 26, 2009)

? No one has herd of a hpev system used as direct drive on a car ? :s


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## onegreenev (May 18, 2012)

Not likely you will either. There too low voltage and amperage so not likely. Best to take full advantage of the transmission. It's already there, why not!


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## crackerjackz (Jun 26, 2009)

I plan on using it ... But its an automatic with shiftronic so im anticipating some control issues ... Hopefully i can sort it all out but if i cant i liked the idea of a backup direct drive system ...


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## onegreenev (May 18, 2012)

The controllers now have idle function. Contact HPEVS and ask them. They are real good at helping.


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## crackerjackz (Jun 26, 2009)

Yes im aware of this feature as it will be useful to me considering i want to use the motor to drive my ac and power steering  ... My issue will be for controlling the shifts of the transmission one the computer doesnt get any more inputs from the ice dinosaur


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## onegreenev (May 18, 2012)

Are you sure your main computer does the transmission inputs? Could be an aux computer box. If so what does the transmission require for proper shifting. Might be an easy thing. When your done you will know more about your transmission than you ever wanted. 

Some transmissions shift on vacuum and rpm. 

Pete


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## Richard Wood (Jun 27, 2008)

onegreenev said:


> Not likely you will either. There too low voltage and amperage so not likely. Best to take full advantage of the transmission. It's already there, why not!


With the 108v and 650Amps the AC51 doesn't seem that low compared to typical DC systems, although I know there are other factors and had discounted the AC50 originally. The point here was the AC51 has improved torque at low end and better fits with my target power peak at a particular speed need.
You ask why not take advantage of the transmission - in my case it's just taking up space in the tunnel where the motor could go, which would in turn probably enable all the batteries to be where the motor was, saving a lot of hassle. It's also extra weight and undoubtably introduces losses. 
If I can get the car moving reasonably off the kerb and enough power at 70-80kmh then direct drive looks good. It's the first of those issues I can't seem to get a fix on. It may have to be trial and error. 
I have no need in commuting to go over 100kmh and anything above 80 would be on the flat.
What would be good would be if I there was a lighter weight two speed gearbox generally available as a back up option but suppliers I have emailed about that have not responded.
Another question I'm not sure of is whether there would be any improvement at the low end for example if I used the other combination of voltage and amps - 144 and 500 - with a custom diff to get a higher speed RPM. Anyone know whether that would make any difference or is it just the same as it's similiar power at a given final speed?


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## onegreenev (May 18, 2012)

You know, going transmission less might just work but it seems so much easier to just use the existing transmission an leverage the gears to get you moving with much less effort.

I also understand that folks want to ditch the weight of the transmission but in the end would it really be a savings? I say it because with the gearing you can go through the gears as you gain speed but with direct you must muscle through the low end to get to a nice top end. Kinda like riding a single speed bicycle geared for speed. That low end start is a bear. You gotta huff and puff until you get to your optimal speed. With a 10 speed you breeze through the gears from start to finish with hardly breaking a sweat. 

It would be that way for your motor too. 

Use the transmission. If need be swap in a manual transmission. I'd just stick with the automatic transmission.


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