Auto Alternators As Motors

Alternators Are Synchronous Motors

Powering the rotor through the slip rings makes the alternator a "synchronous motor" and not an "induction motor".

I think the thought process went like this...

For an automobile there was a desire to improve on the brushed generators they were using and so they went with an alternator that uses the three phase design. This allowed them to remove the permanent magnets and lower the costs. The problem with a pure induction alternator is that it does not produce much power at low rpm and since there is a strong need for autos to be able to recharge while at idle they needed a way to get high charge levels at low loads. It's the low load situation that was the problem. The solution is to "cheat" a little with a slip ring and charge up the rotor so that you get more power even at lower rpm.

Now switch back to the ebikes... what is our thought process?

For a "racing ebike" like I'm trying to make there is no "idle" situation to deal with. You are either at 100% throttle and load or you are off the throttle and braking for a turn. (the rare exception being sweeper turns that use less than full throttle which might be 5% of the time on the road) So for the "racing ebike" we want a 100% induction design because we know that we will be at full throttle and full load most of the time.

Getting back to the auto alternator...

The auto alternator uses slip rings to charge up the rotor and that lowers the efficiency slightly... but the REAL REASON that alternators have low efficiency is that they run at less than full load all the time.

What is needed is to take the auto alternator apart and remove the slip rings and brushes, then short circuit the rotor like in an induction motor so that magnet fields generated on one part of the rotor create counter fields in the other parts. An induction motor's rotor can be nothing but a chunk of iron if you want.

The final product will be an induction motor with fairly low torque at really low rpms, (assuming that your controller limits the currents strictly) but very quickly the torque will rise. Efficiency is always the highest when the load is the largest. The final fully loaded efficiency should be above 80% because many induction motors can get up into the 90% and above when loaded.

It's all about loading... full load good... low load bad....

The "bottom line" is that auto alternators are synchronous and not induction motors so you cannot just plug and play with them. In order to make them of use you need to modify them. That being said, they are still a good foundation to start with and have the potential to deliver the right kind of power.

One of these days we will be able to buy stuff for our ebikes that really deliver what we want out of the box, but it just seems like we are stuck in a loop trying to get what we want. (or figure it out)

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Induction Motors

Class B (IEC Class N) motors are the default motor to use in most applications. With a starting torque of LRT = 150% to 170% of FLT, it can start most loads, without excessive starting current (LRT). Efficiency and power factor are high. It typically drives pumps, fans, and machine tools.

Class A starting torque is the same as class B. Drop out torque and starting current (LRT)are higher. This motor handles transient overloads as encountered in injection molding machines.

Class C (IEC Class H) has higher starting torque than class A and B at LRT = 200% of FLT. This motor is applied to hard-starting loads which need to be driven at constant speed like conveyors, crushers, and reciprocating pumps and compressors.

Class D motors have the highest starting torque (LRT) coupled with low starting current due to high slip ( 5% to 13% at FLT). The high slip results in lower speed. Speed regulation is poor. However, the motor excels at driving highly variable speed loads like those requiring an energy storage flywheel. Applications include punch presses, shears, and elevators.
 
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Auto Alternators As Motors

Forget about Single Phase Induction motors like the Dishwasher motor. The preferred route is to use an Automobile Alternator since it uses a Three Phase motor design.

This thread will deal with "Auto Alternators As Motors For Ebikes".

A good place to start:
I have looked
my response is still I DONT KNOW ................................ OR 2Q + 2Q = 4Q

http://www.rcgroups.com/forums/showthread.php?t=905411

Show Me one you have built and run...




I was going to spell liar here.
I CAN APOLOGIZE IF NECESSARY1111
I WILL GET ON MY KNEES AND KISS YOUR ***.
I will wait!!
2Q + 2q = 4q english to nerd translation $#@^ you
BAN ME IF YOU WANT!
 
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You have to understand this is an "explorative theory" thread. That means that I'm taking it under consideration the possibility of using an automobile alternator as a base for an ebike motor.

I've also looked at Single Phase dishwasher motors as a possibility.

There is no "there there"... so to speak... this is all theory right now.

However, it does appear that my first assumption about auto alternators was wrong. I had hoped they were induction motors, but they are not and are actually synchronous motors with their own field currents and brushes and slip rings.

What I'm considering is if this is a good place to start or not.

Auto alternators might turn out to be a bad idea... or it might turn out that it's a good idea with the right modifications.

There is no good solution for an induction motor for ebikes "to my knowledge" at this point.

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I've done a lot of work rewinding brushed motors, but they seem to fail because of the commutators, so pushing the limits with them is not looking to be such a great idea. My hope is to get a flatter, more usable, motor powerband with an induction motor... which is another big reason to explore this.

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The main realization I've had about this is that a Three Phase induction motor is pretty much identical to a DC Brushless motor like the RC motors. In fact, in that RC thread they are trying to use RC based ESC controllers to control an auto alternator. It's an interesting thought.
 
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Alternator Slip Rings And Brushes

This information will not contribute to your discussion, but it might help to know what is happening when an alternator is operating as designed.

Automotive alternators have brushes and a revolvig field as the field strength must be controlled to change the amount of output current required by the system. If the battery is fully charged and few accessories are on, then the field current will be very low and the three phase output to the diode bank will be low. If the opposite is true, low battery, AC, lights, etc. on then the field current through the brushed and slip rings will be close to max. All controlled by the regulator, either internal or external.

Old generators had a stationary field and the rotor carried all the output current and as a result the brushes had to do so as well. As the generating windings were rotating through the stationary field, it produced an alternating current, but it was converted to DC by the mechanical action of the commutator. Starters are similar to the old generators. So you can motorize a generator and use a DC motor to generate.

If the revolving field was a permanent magnet, then there would not be any control of the output.

Jim
 
You have to understand this is an "explorative theory" thread. That means that I'm taking it under consideration the possibility of using an automobile alternator as a base for an ebike motor........

While it is an interesting concept, I don't think it is practical. We were all taught that any motor can be turned into a generator, and a generator can be turned into a motor. while this is true, nobody said that a motor would make a good generator or vice versa. While I'm not a motor engineer, it seems to me that an induction motor would not be practical for a motorized bike because of the narrow RPM range. Sure, you can change the speed of the rotating field with a controller, but the induced current in the rotor would be minimal until it got up to its "resonant" design speed. Just look at a washing machine or dryer motor that has a separate "start" winding and mechanical cutoff switch just to get the thing to spin.

Also - brushes in an alternator last a long time. Partly because the maximum current carried is only a few amps to excite the rotor, and partly because it is on a continuous slip ring and not a segmented commutator. If I were to try this, I would keep the rotor energized through the brushes and not have it "self excited" through induction. And power the field with the biggest RC truck brushless controller that I could find. (and even then, it might blow!)

I've seen some interesting electric bar stools made from 24V truck starter motors run at 12 volts. At half their rated voltage (and cooling vents added), they will run continuously without overheating. Don't know about efficiency though......
 
While I'm not a motor engineer, it seems to me that an induction motor would not be practical for a motorized bike because of the narrow RPM range.

This I totally disagree with...

My "Electric Bicycle Road Racer" concept is to build a class of ebikes that work best under racing conditions. Race machines are always either at full throttle (and the rpms are changing rapidly) or they are off. I've already done about 6,500 miles on my first road racer ebike with a permanent magnet motor connected to a six speed transmission and while this works well it would be nice to be able to get what I want with a single gear.

The induction motor has a powerband that is both flatter and wider than the typical permanent magnet motor and it's efficiency is best at full load. Permanent magnet motors have the opposite and their best efficiency is when near their no load speed. (about 90% of max)

Trust me on this one... I'm probably one of the more experienced guys around in high speed ebikes. (my flat land speeds are 50 mph and on a downhill I've hit 60 mph with rides of 30 mph average over 10 miles)

That being said...

The auto alternator is NOT a true induction motor, (it's actually a synchronous motor) so all this dealing with slip rings, brushes and field currents are not helping towards the goal of finding the perfect ebike racing motor.

:rolleyes: Where is there a Three Phase induction motor that could be had for little money and is designed for delivering about 1KW of power?

Most of the industrial motors are designed to be triple the needed size because bigger motors work better than smaller ones. But for an ebike you can't sacrifice the weight. (so we need something unique)
 
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Ruling Out PMA's

On the RC thread they stumbled upon a Permanent Magnet Alternator (PMA) that does not need slip rings, brushes or field currents:

http://www.rcgroups.com/forums/showthread.php?t=905411&page=11

http://cgi.ebay.com/HighAmp-PMA-Per...in_0?hash=item3ca4d0d20e&_trksid=p3286.c0.m14

...but from my perspective they've missed the point of this exercise. For me the goal is to get away from permanent magnets and go towards the induction motor design. Dishwashers use Single Phase induction motors and while that's tempting they are not self starting. Three Phase induction motors are self starting and the increased number of poles actually lowers the effective rpm. Three Phase seems the best standard to go with.

The guys at Electric Motorsport seem to have the right idea:

http://www.electricmotorsport.com/store/ems_ev_parts_motors_ac-induction.php

motor_ac_induction_curve.jpg


...however, for ebikes the needs are much lower.

A 1KW motor is enough, 14KW is complete overkill for an ebike. (18 hp)
 
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Motor Controllers

Pardon my ignorance, but I have very little experience playing with motor controllers for bikes and scooters. (Rebuilt one for a friend that he blew some switching transistors by connecting the 24 volt battery in reverse. It is a controller made up of separate components and powering a 500 watt brush motor with a PM field.) As I recall all the motors seem to have only two leads and I guessed the controller used pulse width modulation to control speed and had a PM rotating field? That would be the motive current from the controller, not a field control. So an alternator being three phase would require a controller that energized each phase in sequence, 120 degrees apart. 3 phase can be produced with capacitors and inductors, but all would require an AC input, not DC. I am not seeing anything here that would make the alternator turn using a 24 or 48 volt battery pack? It would seem you would need a triple output motor controller which would power each phase in order, if you were to run it on DC.

Open to input to fill in my lack of knowledge?

Jim
 
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You are correct.

Many of the ebikes out there now are using brushed motors with PWM controllers. (myself included)

Some are experimenting with RC motors that are brushless and have three phases much like the AC motors. The RC motors use a special controller called an ESC that does not require sensors in the motor itself and can "sense" the backEMF automatically

Other people are riding brushless hub motors that have sensors and their own controllers.

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A full blown induction motor would require some controller much like the RC motors ESC or something homebuilt.

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From my vantage point the "ideal" ebike induction motor would have many poles so that the rpm is lower. Something like 16 poles could drive the motor efficiently at around 500 rpm.

I'm just having a hard time finding things that are going to work.

You almost have to build a custom motor and controller if you want to get anywhere near what the laws of physics say is possible.

(so we're kind of wallowing in ad hoc and extreme modifications these days)

It would be great if the "ideal" motor was out there somewhere, but the auto alternator has a pretty good chance of being modified to work well enough for a first generation of testing. They are solidly built and should be able to handle some serious stress.
 
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......The induction motor has a powerband that is both flatter and wider than the typical permanent magnet motor and it's efficiency is best at full load. Permanent magnet motors have the opposite and their best efficiency is when near their no load speed. (about 90% of max)

Trust me on this one... I'm probably one of the more experienced guys around in high speed ebikes. (my flat land speeds are 50 mph and on a downhill I've hit 60 mph with rides of 30 mph average over 10 miles)

Like I said, I am not a motor engineer. I am heavily into radio controlled hobbies, and have modified conventional brushed ESC's and brushless PMDC motor controllers.

From my understanding, and induction motor IS a synchronous motor as its RPM is synchronized with the "rotating" field. If the rotor gets out of synchronization with the field, torque and power go down the tubes. An example would be a sensorless brushless motor losing sync. and "cogging" on acceleration.

Induction motors are designed for single speed, single frequency operation. If you take an induction motor designed for 60Hz operation and plug it into a 50hz power source, it will run slower because of the lower frequency )of course) but won't it overheat or put out less power because the inductance of the windings and the rotor are engineered for 60 cycle operation?

Brushed PMDC motors have high starting torque, and produce a lot of power for their size whan compared to AC induction motors. Varying speed is as easy as varying voltage. Downsides are brush and commutator maintenance.
 
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