Supercharge an electric motor?

Question

I drive a 2004 Toyota Prius, and I was struck by a sudden thought recently. I know that if you increase the magnetic field around an electric motor, the rotor will spin faster, even with the same electric current provided. (I assume that anyone who would answer this question is familiar with the equation F=ILBsin(theta) ). So, theoretically, I should be able to make an electromagnet (powered by a different battery that I would purchase) to go around the Prius's electric motor and increase its output, right? First of all, let me know if that would even work, or if my reasoning is wrong. Second, would that work if I actually did it, or would it mess up something else in the car? I haven't tried it yet; I was just brainstorming.

Answer 1

Add a series of insanely large capacitors on a switch...it would be the Hybrid equivalent to Nitrous.

Answer 2

smart idea. but would the stock prius motor be able to take the abuse?

i would suggest switching to a brushless motor.

there powering huge electric rc aircraft that weigh close to 50 lbs.

look into it, you seem smart enough to convert something like that.

look into some motors from companys like

neu

Hacker

etc.

didnt really answer your question but thought id share.

Adam.

Answer 3

Your reasoning is incorrect.  A motor under load looks like a resistance to the power supply.  To increase the power out, you must increase the power in.  

To give it more detail, your force does indeed increase with a larger magnetic field.  But force (or torque, in a rotary motor) is not the same as work, or energy, which is what you want.  As the rotor coil turns within your bigger magnetic field, it also acts as a generator.  The voltage produced by this generator bucks the voltage of your power supply, meaning that to maintain your current you must increase your power supply voltage.  Then both voltage and current increase, which means that your power input has increased.  

Motors are optimized within an inch of their little lives.  You won't be able to make any improvements there.  But keep thinking; this is how everyone who is at all curious learns electrical engineering.

Answer 4

I believe you are confusing current and power:

"I know that if you increase the magnetic field around an electric motor, the rotor will spin faster, even with the same electric current provided"

If you increase the magnetic field you will have to increase the voltage to maintain the same current, therefore you increase the power (current x voltage) being provided.

I'm pretty sure Toyota has designed the most efficient motor they could. I doubt adding an external magnet would have much effect at all, much less a beneficial effect, though there is a possibility of "mess[ing] up something else"

[EDIT] RE "additional information" you say:

"I know for a fact that if I bring a permanent magnet closer to a motor, the rotor spins faster or slower depending on which pole is closer to the motor--I've used small electric motors and even when I am using a power outlet that puts out a constant 12V, the speed will vary when I introduce a magnet"

Were those unloaded or very lightly loaded, motors? it is possible that the external magnet was partially canceling the original magnetic field, thus reducing the back EMF at a given speed and allowing the motor to go faster for a given input voltage. While the _unloaded_ speed could be higher, with any significant load the torque would be less and the speed would probably fall to less than it was before the external magnet was introduced.

Answer 5

As mentioned earlier, the Prius uses a brushless, permanent magnet motor (Synchronous AC). This means that the rotor (rotating bit) has permanent magnets and the stator (outside casing) has windings that require an electric current to create a magnetic field.  This motor requires a variable speed drive (VSD) to operate it.  The VSD delivers an alternating current (AC) to each of the 3 windings in the stator. The AC frequency, phase and amplitude is finely adjusted to suit the the prevailing requirements (eg constant speed, acceleration, etc) and requires accurate information on the position of the rotor.  Any attempt to introduce a magnetic field near the motor is likely to interfere with the field generated by the stator and reduce performance.

The only real way to increase performance is to modify the VSD to provide more voltage/current.  If you did this you will likely also need to improve the cooling of the electric motor.