Auto Alternators As Motors

safe

Active Member
Joined
Mar 28, 2009
Messages
1,329
Likes
2
#1
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:

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


safe

Active Member
Joined
Mar 28, 2009
Messages
1,329
Likes
2
#2
Past Auto Alternator examples include the "somewhat infamous" Randy Draper ebike:



...many people seem to have problems with this guy, but he just seems really excited about what he's into. Since he was already ahead of the curve back in 2003 with Three Phase power for an ebike we ought to give him some credit for being right. (you may not like him, but give him the respect he deserves)

Induction motors seem the better option in the "big picture" compared to permanent magnets because you can push the rotors as hard as you want to get more power. With permanent magnets you literally have a "speed limit" built into the motor. Induction motors actually work best at full throttle, so that's another plus. Permanent magnets only work well in a narrow rpm range and light loads. Because of all this it's more realistic to get better overall efficiency with the Induction motor than the Permanent Magent motor because in a racing situation you are always under load.
 
Last edited:

bluegoatwoods

Well-Known Member
Joined
Mar 23, 2008
Messages
3,021
Likes
71
#4
I'm anything but an authority in this field, but if you could get an alternator to work at all, then wouldn't it require AC current to do the job?
 

safe

Active Member
Joined
Mar 28, 2009
Messages
1,329
Likes
2
#5
You might check the rc group thread:

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

...they came to the conclusion that you can use an RC motor ESC to achieve the control over the motor and it's a simple plug in task to complete.

All brushless motors use AC current, so this is not really that different than using an ebike with a brushless motor. The big difference is that an Induction motor has a solid rotor that is not magnetic. You literally "induce" the magnetic field in the rotor as opposed to relying on permanent magnets to attain a magnetic field.

The big advantage is that when it comes to the power-to-weight ratio it should be possible to get incredibly high power levels from an induction motor.

The auto alternator is a good idea... I've basically destroyed too many brushed motors to want to bother with them much any more, so I'm looking for "big power" in a light weight package.

The Tesla Roadster is built with an Induction motor.

--------------------------

Note: Technically speaking the RC motor ESC is a PWM signal and not a true analog Sine wave. They slice up the pulses in such a way as to trick the motor into thinking that it's analog.
 
Last edited:
T

Tinker1980

Guest
#7
Feel free to shoot me down, but don't some alternators have brushes in them?

I'd love to see an alternator powered bike... you wouldn't even need a new alternator. The part that usually fails on them is the diode, which is something you're going to toss out if you want to make a motor.

One should poke around a junkyard... the GMT 400 chevrolet trucks (1988-1998) typically had a 105-amp alternator. Some older caddy's had them even bigger.

-Mark
 

safe

Active Member
Joined
Mar 28, 2009
Messages
1,329
Likes
2
#8
The really old cars used to use generators with brushes.

I looked it up on the internet and have forgotten the link, but the date that the cars started to use true alternators was about 1970. So the pre-1970 or so alternators used brushes and then pretty much everything afterwards is without them.

Since a brand new alternator can be purchased for $40 it seems like it would be better to go to the auto parts store and look through all your options and find the best match. However, if you already have an alternator laying around it would be worth checking it out.

I would prefer to buy the smallest and lowest amp alternator because then when you flip it around and use it as a motor it will drain your battery more slowly.

Remember that the MAIN reasons for switching would be:

:D No brushes means less to fail.

:D Induction as opposed to Permanent Magnet means that the powerband is wider and flatter. As long as you have the throttle wide open you will get good efficiency... the moment you let off the throttle is when the efficiency drops. It's better to run the motor full on or full off. (race mode)

...of those two the brushes part is what got me started on the idea, but it's the Inductance part that really serves the need for my Electric Bicycle Road Racer concept. The idea being that the "perfect" motor will run with maximum torque at a constant input power level. If the racing class is defined as "Formula 1K" then you are allowed a maximum of 1000 Watts of input power. A Permanent Magnet would not work as well under the fixed input power concept. (this all fits together in something much larger that I'm working on) If I ran the alternator at 48 volts and 40 amps that translates to 1920 watts of input power. (which is too much) So in order to satisfy my own "restrictor plate" racing I might go:

48 volts * 20 amps = 960 watts (effectively 1000 watts)

24 volts * 40 amps = 960 watts (effectively 1000 watts)

The sort of amazing thing is that I've had it set in the back of my mind that the Induction motor would be the "Holy Grail" of racing ebikes, but I somehow "never got the memo" that auto alternators were Three Phase Induction motors. That was a "wow" realization for me. :unsure:
 
Last edited:

safe

Active Member
Joined
Mar 28, 2009
Messages
1,329
Likes
2
#9
Slip Rings?

(after returning from the Auto Parts store having discovered that auto alternators all use brushes)

Auto Alternators have Slip Rings and Brushes that are used to charge up the field current of the stator. In a generator this is necessary because at low rpm the rotor is barely going to produce any response in the coils and no current will be produced. The addition of a small "exciter" current in the coils is a trick that creates a much bigger field on the output side.

But when you reverse things... and create a motor out of the alternator... is there any reason to keep the Slip Rings and the Brushes?

When you want motor power you simply send the currents through the coils as a motor and I don't see the need for the field current anymore unless you want really, really high starting torque. (like a dragster)

Remove the Slip Rings and brushes that go with them?

Or find a way to keep them?
 
Last edited:

arceeguy

Active Member
Joined
May 20, 2008
Messages
1,162
Likes
3
#10
You will still need to power the rotor through the slip rings, otherwise the rotor won't turn when the stator is energized by the motor controller. I've seen some auto alternators turned into PM generators by mounting rare earth magnets in the rotor. Usually used in low RPM windmills. If you did that, then you would have a large PM brushless DC motor.

As far as converting a car alternator to a motor, remember that a car alternator is not very efficient in converting mechanical energy into electricity - so it might stand to reason that it won't be very efficient converting electrical energy to mechanical energy without significant modification.
 
Top