# Got a free AC 15hp, it is strong enough for EV car conversion?



## BigChief (Mar 20, 2011)

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## DawidvC (Feb 14, 2010)

Have a look at the AEVA forums, they have a lot of information on using ac motors. That motor might be do-able, but you will need to have it rewired to make it really useful. I would suggest keeping the donor gearbox, as you may not have a lot of torque available.

That motor should be able to supply 17.25hp continuous as is. Wiring for 230V and having a 630V pack for 460V nominal, should give nearly 30hp continuous. That bumps up your base speed from 1745 to 3490, which will also be more useful.

Remember that these motors can deliver about 3.6x their continuous torque rating.
Continuous torque at the rated current should be (5252x15)/1745 = 45lbft. Assuming an overloading to get 3.6x, that would be 45*3.6 = 162ftlb. If this is sufficient for your intended vehicle, the motor will work. If it is much lower that the torque of the ICE, you will get much lower speed and acceleration out of it. 

BTW, how is that motor cooled - it looks to be internally cooled, but it is not quite clear from the photo.

Regards
Dawid


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## nimblemotors (Oct 1, 2010)

Unfortunately, the motor is one of the least expensive items in a EV,
next to maybe the donor car itself, so scoring a free motor doesn't really help much, particularly an AC motor. There are not good controllers for this motor suitable for a car. AC motors are great for constant speed.

My opinion however, is that it would be great to make use of these very inexpensive motors by using an automatic transmission and retain the torque converter. This avoid their biggest flaw of lack of starting torque, since you can keep them spinning. But unless you want to be a pioneer/researcher and give away all your hard-earned lessons to the freeloaders around here, it isn't a good option to pursue.
I'd just sell it and take the $100 profit and look for a DC forklift motor.



BigChief said:


> Hey guys, I was asking about this in EndlessSphere and they told me I should ask here. I've successfully done an electric bike conversion and have been researching for months about stepping up to a car conversion, but I'm still fuzzy on some concepts. Now I found a 15hp 3-Phase AC motor in the basement at work and my boss let me have it free! It shows little wear and spins smooth as silk by hand, even though Googling the serial number reveals it was discontinued in 1989.
> 
> I would like to know if this is viable for a Bug/Metro size conversion, and if it can hit highway speeds. I don't have a lot of money but I have access to:
> 
> ...


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## Coulomb (Apr 22, 2009)

BigChief said:


> I would like to know if this is viable for a Bug/Metro size conversion, and if it can hit highway speeds.


That should be possible, but it will be no drag racer.



> The main thing I was wondering about was Variable Frequency Drives. I get that they can change the 60hz into 120hz to double the RPM on the motor, but how do they accomplish this?


They rectify the AC (not needed with a battery pack), and use 6 IGBTs to chop the DC to generate 3 phase output.



> Do they need double the volts/amps, or do they halve the torque?


You need double the volts to maintain the V/Hz to the motor. The current remains the same (at nominal power). So that would double the continuous power to around 30 HP. The peak power will be around three times that, or about 90 HP (67 kW). 

Note that you will want a controller that can peak at about that power, say around 75 HP (if it peaks at about 90 HP). With a 15 HP controller, your peak power would be perhaps 19 HP for one minute. So getting an appropriate controller will be the critical factor. You likely won't get a 75 HP controller from Ebay, at least not for $1000.

It's good that the motor can be configured for 230 V. Do lots of reading.


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## BigChief (Mar 20, 2011)

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## DawidvC (Feb 14, 2010)

BigChief said:


> OK, I've been doing lots of reading. Spent the last two days doing nothing but reading - doesn't mean I'm smart enough to comprehend everything though, don't be afraid to use layman's terms
> 
> First off to Dawid, the motor is fan cooled. I think I have some ideas here, if anyone could hint to whether they are feasible it'd be appreciated.
> !


Sorry, my fault. I actually wanted to know if the fan blows into the motor or just outside ie internally cooled. The internally cooled motors can handle a bit more overload from my experience.

Answer to 1: The AC-50 has double the poles of your motor. It would be possible with rewiring your motor to equal the power of the AC-50, but you lose out on torque. This is on of the reasons to look at the torque the e-motor produce, rather than the kw. ICE kw are peak output, and e-motors are continous output at rated voltage and current - big difference.

Answer to 2: If your potential 162ftlb is enough to run without gearbox and the acceleration is fine with you, you can do it. Better try and source a 2-speed tranny, it will work better with a low-powered motor.

Answer to 3: If you rewire, remember that everytime you halve the voltage, you double the current. At 230V your full-load current is 36A IIRC, so at 115V you would need 72A, and at 62V 144A. This is not the maximum Current, so you still need to multiply it by at least 3 to size a drive. Power = Volts x Current. For the drive you are interested in, leave the wiring at 230V, and build as high a pack voltage as the drives DC bus will allow you.

Answer to 4: Yes, but it is a bit wimpy. Maximum current <100Amps, it will not allow more than 3x overcurrent on the motor. Check the drive manual on the maximum bus voltage allowable before even thinking of batteries. This drive will be happy with batteries specced as low as 36ah. You can of course look into hacking the drive to allow more current - it has been done on this forum and aeva. Search around if you feel it is worthwhile.

I couldn't find a decent online manual on the drive, but there is one point to consider - if the drive does not offer vector drive in some form, you will be disappointed by the performance of that motor - normal VFD make very disappointing ev-drives.

Good luck with your build. I hope that answers some of your questions.
Dawid


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## Coulomb (Apr 22, 2009)

BigChief said:


> 1) The first and most interesting thing I've seen is that the AC-50 kit, which is considered a powerful medium-size car EV motor, is actually rated for 15hp continuous like my motor. Am I misunderstanding, or could my motor have the potential of an AC-50 with the right wiring/winding?


Yes, the AC50 motor is rumoured to be a standard Remy motor wound for lower voltage. So your motor could behave similarly.



> 2) The RPM of my motor is currently 1745 at 60hz - slow for transmission, but isn't that more of an optimal RPM for skipping the tranny and hooking straight to a truck's drive shaft?


Err, no. 1800 RPM would be good for direct to wheels (i.e. no final drive / differential), but it needs to be a torque demon for that. Think 24 pole or so. Yours is a 4-pole motor.

Think about a typical ICE vehicle in top (say 4th) gear. The transmission ratio for "top" gear is usually 1.00:1 or close to it. 60 MPH in top gear is often about 3000 RPM; 1800 RPM would only be about 36 MPH. So having torque drop off at 1800 MPH in a direct drive situation would probably be bad.

But a 4-pole motor is good, if you can give it more frequency (easy) and more voltage (harder - you need a higher voltage pack or a powerful DC-DC converter). So you would want to drive your 230 V ~1800 RPM 15 HP motor at more like 400 VAC and ~ 3000 RPM for around 25 HP continuous (and some 75 HP peak). 400 VAC requires about a 570 VDC pack. Even higher pack voltages, to around 700 VDC, would give you more power and speed. Much above 700 VDC and you would be pushing the limits of a typical 460 VAC max controller, and the insulation of the motor. With around 650 VDC, you would be running out of voltage (entering the "constant power" zone) at about 4000 RPM, which is about right for a typical conversion's drivetrain.

That's why conversions using industrial motors usually use a high voltage (400+ V) pack, unless the motor is rewound or rewired.



> I understand the acceleration wouldn't be stellar with AC,


There is no reason that an AC conversion can't have stellar performance. Machines like the Tesla Roadster and I think the T-zero have been induction motor AC. This business of DC motors having maximum torque at zero RPM is a bit of a misunderstanding. At very high currents, the series DC motor will saturate its field, lose some inductance, and possibly not get as much field as at more sane currents. Also, AC motors can overvoltage to get more field and torque.



> but it'd be good to know if this can work since it seems like a simpler/cheaper conversion than transmission coupling.


For direct drive, you need a motor with a wide RPM range, preferably with a wide "constant power" band. AC motors (but usually not industrial motors, which usually top out at around 4500 - 6000 RPM) have this characteristic. For series DC motors, there seems to be little alternative to oversizing the motor for direct drive.



> 3) The guy in this link "rewires" an AC motor to operate on 1/4 the voltage without rewinding the thing: http://www.aeva.asn.au/forums/forum_posts.asp?TID=1237&PN=1
> Frankly, it's making me wish I didn't skip college. Would his method theoretically reduce my 240v motor down to 120v, or possibly even 60v?


Yes, it will. You lose little to no torque as a result. The catch is that in my limited observation, only the tiny motors seem to be wound in such a way that a "rewire" is possible. Larger motors tend to need a "rewind", which means burning out the old wiring and starting again. This rewinding can cost about the same as a new motor.



> It sounds like the repercussions involve more energy lost as heat.


Well, yes, but only because you are now putting more power through the motor. So absolute losses increase, but losses remain about the same proportion of motor power.


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