[PStechPaul]

There's another thread which says that a 10HP motor may work, but you will be limited in acceleration, hill climbing, and top speed. However, you can figure out what to expect by using some basic formulas and information on the vehicle weight and drive train ratios.

The motor torque in lb-ft is simply HP*5252/RPM, so your motor will supply about 22 lb-ft continuously and a maximum of 2-3 times that, or about 50 lb-ft. Now you need to figure the drive train ratio. You can do this by reading the tachometer and speedometer in each gear, and you might as well use 3600 RPM because that's your motor spec. So, I think my car will probably go 20 MPH at 3600 RPM in first gear. You have to measure the tire diameter to determine the axle RPM, so I'll guess at 2ft diameter which is about 6ft circumference. So every rotation will go 6ft, and a mile is 5280ft, so it will spin 20*5280/6 Rev/hr or about 290 RPM. So the drive train ratio is 3600/290 or 12.3/1.

Now the torque you need to climb a hill is related to the vehicle weight and the incline of slope. For a 20% grade, and a 3000 lb vehicle, you need a force of 3000*0.2 or 600 pounds. Since the tire has a radius of 1 foot, that is also 600 lb-ft of torque. The motor needs 600/12 or 50 lb-ft of torque. So, your 15HP motor will just barely meet that, and it will be overloaded so it will probably only be able to climb that hill for no longer than about 5 minutes (at 20 MPH max). Since you want some extra torque so you can accelerate, the vehicle will be severely limited. It may be OK in KS or FL, but not in WV.

And if your 3000 lb does not include batteries, you must add that weight as well. And my top-of-the-head calculations do not factor efficiencies and wind resistance.

 

[PStechPaul]

Using two 15HP motors should give you enough power, but there is the issue of synchronizing their speed and torque, as well as the mechanical problems of connecting the motors to the axles rather than using the existing drive train. If you go that route, it may be better to use a 4WD and use one for the front and one for the rear, but you still have only the single transmission. If the differentials are a high enough ratio it might work, but I think you will need the low gear for the hills. It may be possible to couple the motors together, especially if they are dual shaft. Or you might be able to use pulleys or chains and sprockets. But that will add cost and complexity and other problems.

If your motors were 4 pole or 6 pole, they would have more torque at a lower RPM so they would be better suited. It should be possible to get them rewound, but probably cheaper and easier to just buy the motor you really need. You can't go too far wrong to use a bigger motor than you think you need, as long as it fits. A 40 HP motor putting out 10 HP will not draw much more than a 10 HP motor, and maybe even less.

I had considered rewinding and overclocking about 8 years ago, and I rewound a 1/2 HP single phase 120V motor to three phase, 12 pole, 8 VAC. I overclocked it to about 3x or 4x and got 1800 or 2400 RPM. But I did not perform a dynamometer test so I don't know if it really had that much more power. My idea was to be able to run it directly on a 12 volt battery, and I made a three phase controller using a PIC18F2331 with a trapezoidal drive and it worked, but the MOSFETs eventually blew after a few runs. It actually happened as I was demonstrating it to some technicians and engineers at a nearby motor rewind shop. But I did not have snubbers or other protection and I was using 30V MOSFETs. Although it "worked", I could see that it was impractical to run a motor any larger than 1 HP or so on just 12V or even 24V, because of the size of the wire.

So winding it for about 100V and boosting voltage to 500V or so is the way to go. And I think the highest overclocking for a motor with standard 50-60 Hz laminations is about 3-4x. 400Hz will probably require thinner laminations of higher grade steel. Unless size and weight are truly critical, as in aircraft or bicycles, using standard motors may be "best" when all factors are considered.

 

[PStechPaul]

I am still concerned that a 15 HP standard motor will be insufficient for hilly terrain and safe road speeds and acceleration. Most people say that 40 HP is about right for a small EV. If you don't use the power, a larger motor won't cut your efficiency and it might even be better. It's a lot of work to adapt and install a motor and get all the controls working properly, and the cost of labor is about the same for any motor. But if you have to do it over, you lose the original cost of the smaller motor plus another round of R&R and fitting and wiring.

Here is a 50 HP motor for $450 with free shipping:
http://www.ebay.com/itm/General-Ele...116?pt=LH_DefaultDomain_0&hash=item3a74d2fb4c

A 30 HP premium efficient 3600 RPM motor for $500:
http://www.ebay.com/itm/BALDOR-RELI...105?pt=LH_DefaultDomain_0&hash=item2ebe0e8499

An older 50HP 1500 RPM motor for $325:
http://www.ebay.com/itm/U-S-ELECTRI...471?pt=LH_DefaultDomain_0&hash=item2c64df95af

If you get a 4 pole motor (1700-1800 RPM), you might be able to connect it for 240 and overclock it to 120 Hz and 480V and get twice the HP. You really can't do that with a two pole motor.

Of course if you rewind it you can change things, but it's expensive and risky if you don't know what you're doing.

Good luck!

 

[PStechPaul]

I found another one that might be even better, an almost new Baldor Super-E 25 HP 1770 RPM, for $675. It is 93.6% efficient, which is excellent, and since it can be connected for 240V and is 4 pole, you should be able to overclock it to 120 Hz at 480V and get 3540 RPM, which is a reasonable match for an ICE. You can probably push it to 180 Hz to get 5310 RPM which is a reasoble "redline".

These motors will be heavy, and the higher the efficiency the heavier they will be. But you want them to run cool and have minimal losses, especially if you want to push more HP out of them.

The only problem I see with this motor (and some of the others), is that it is horizontal flange mounted and it might be easier to adapt with a C-face, which mounts on a flat surface with four bolts around the shaft. But you are going to have to make an adapter anyway, so maybe some of the experienced EV experts here can give you some ideas.

Here is what a C-face motor looks like. This is a 60 HP motor which is also on eBay. There are 34 pages of motors 10 HP and larger:

I suggest you look at all of them and choose a few that are near you so you might be able to do a local pickup. I would suggest a 4 pole motor (1700-1800 RPM), at least 20 HP, or possibly a 6 pole (1100-1200 RPM) which has more torque but is slower. If you overclock it you can get at least 2400 RPM if not 3600, and that is fast enough to do 60-80 MPH.

The frequency is not critical, and should be 50/60 Hz. There may be special motors with oddball frequencies, but they are rare. If you have a donor car, take out all the ICE stuff you won't need, and determine what size motor will fit. Then make sure whatever motor you get will fit and be safely supported by the existing motor mounts, or you will have to make your own. Motors come in standard frame sizes, so there may be standard adapters and compatibility charts.

Sound like you're going to have a lot of fun with this. I can help on the theoretical technical aspects of this, but you really need the guidance of actual EV folk who have done conversions, and specifically AC induction motors. The motor is less than 1/3 the package. You also have the controller and the batteries. Good luck, and keep us posted!

 

[PStechPaul]

In this usage, motor HZ is less important than controller HZ. It tells the motor what to run at.

BTW: do not go to http://forums.aeva.asn.au/forum_topics.asp?FID=41&title=electric-motors-and-controllers

As those zany Aussies do a lot of stuff AC. And might pollute your mind.

Miz

Oops! I just went there (my mind is already polluted ), and I found a thread about DC-DC converters such as the one I am designing, but they are still discussing inductive boost converters rather than what I consider more obvious and practical, driving a center tapped transformer with a square wave in push-pull. I expect to be able to do a DIY build, for well under $200, of a 3.5 kW (5 HP) booster using 48 VDC to 650 VDC to run a 480V 3 phase motor in my larger tractor. The same principles could be extended to more power, but even a 5 HP DC-DC would be enough to power a 20-40 HP controller and motor just to move the vehicle around on a flat surface, to test the system before making a major investment.

If you haven't seen it yet, I have built a DC-DC converter and I'm using it to power a little lawn tractor on one or two small 12V batteries. I have found that it only takes about 300-400 watts to carry me and the tractor (about 350 lb total) over uneven terrain and even up a small hill, although in low gear and only a maybe 2 MPH. This is my latest (mis)adventure:

http://www.youtube.com/watch?v=j5TyhdY-cHQ

 

[PStechPaul]

I assume this is a DC motor. But can somebody explain if this would be a good motor for my first run? 24 V but it says 578 hp! Is this accurate?

24V 2000rpm 26amp 578 hp

No, that can't be. 24*26=624W. I think it is actually 5/8 HP, which is 469W, with an efficiency of 75%. This motor might work on a small tractor, or as an experimental load for a controller, or as a learning tool if you take it apart and see how it is constructed. But it would not be any better at moving a car than a starter motor.

Since you are still learning, you probably need to either have someone put together a kit for you, or start with basics and get some experience by trying a small EV build like a tractor or golf cart. And you should take some tutorials and do a lot of studying of basic electrical principles.

I have over 45 years experience and education in electronics and electrical power, and I still have much to learn about motors and controllers. Even before my formal education and industrial experience, I tinkered with electronics and mechanical contraptions.

Here is a friend operating a robot I made in 1960. And it has a motor and battery in it and the wheels make it go forward and reverse as selected by the hand-held control panel. I also built the shack in the background:

And this is me on a "racer" that some of us kids built. No motor, no brakes! We wore work boots and dragged our feet to stop! Later I built a racer out of steel, with an actual steering wheel and linkages to both front wheels. But I don't have any pictures. I gave it away to a friend and he said their father put a motor in it and made a go-cart but then he backed over it in the driveway and destroyed it. But I learned a lot build ing it, and many other projects, by the time I went to high school!

So, I know you are excited to dive into an EV conversion, but you really need some solid grasp of electrical fundamantals and some experience with smaller projects, if you really want to learn and not just have someone do it for you and hand over the keys so you're good to go!

 

[PStechPaul]

PStechPaul, A larger pole count AC induction motor has no advantage over a lower pole count motor other than speed is reduced which means less gearing is required. A typical NEMA design B, 3600 RPM motor and a NEMA design B, 1800 RPM 3-phase motor of the same horsepower, will have identical performance; it is just that the torque of the the 1800 RPM 4-pole motor in this example would have double the torque.

I have found that higher pole count motors of the same frame size have more torque but lower HP. I have three motors, each about the same size, and the 2 pole motor is 2HP, the 4 pole is 1.5HP, and the 8 pole is 1HP. But I think there is less difference for larger motors, such as 20HP and higher. I think this is because there are more slots in the stator and it can be wound more efficiently.

But my point is that, if you want to overclock a motor to get more HP, especially when replacing an existing ICE engine, you don't want to have a shaft speed much above 3600 RPM, which corresponds to a safe and reasonable cruising speed in all gears. Also, motor bearings and other construction aspects are designed for the rated RPM, but I think most bearings will work well up to 3600 RPM. So, you can overclock a 4 pole or 8 pole motor and get higher safe speeds and more HP, and keep the rated torque by following the V/F curve. And without actually rewinding a motor, the best you can do is rewire from star to delta so a 240/480 motor can be about 140/280. So with a 720V DC bus you can get 500 VAC which means you can get a 3.6x boost. A 4 pole motor would run at 6480 RPM, which is still within an ICE redline range, and probably safe. An 8 pole motor would run at 3240 RPM, which may be safe for continuous use. And also remember that you can get an additional 2-3 times rated torque for short bursts, so you might be able to get peak HP of 7x rating for a 3 phase induction motor. But don't count on it for more than a few seconds.

 

[PStechPaul]

AFAIK, many motor bearings, or the rotor or fan, may be rated about 5000-6000 RPM maximum, so 7200 RPM may be problematic and unsafe. If you are replacing an ICE in a vehicle with the usual transmission and differential, 3600 RPM is a pretty comfortable speed for most driving needs, so I think it's better to use a 4 pole motor overclocked to 2x, with twice the torque of a similar size 2 pole motor. You can still overclock it to 3x and even 4x, with field weakening, to get higher top speed. This mostly applies to using industrial 3 phase motors, and not specially designed motors for EVS, which can safely run at 7200 RPM and even much faster. Then you may also need to consider the transmission, which is designed for continuous use at 2000-4000 RPM input.

Ball bearing speed ratings (generally 10,000 RPM or more, up to about 1-1/2" shaft):
http://www.malloyelectric.com/wp-content/uploads/2013/07/Bearing-Handbook-for-Electric-Motors.pdf