# Forums

## Increasing RPM

Hi! I'm new here. I would like to ask, what are the ways to increase the RPM of a 3 phase AC Induction Motor? Tesla Roadster has maximum RPM of 14,000. Is it because of the Drive Inverter and VFD? Thank You.

DTsea | 9 ottobre 2014

you cant.

bfactor17 | 9 ottobre 2014

I read in some article that with the use of VFD, it can increase the motor RPM of 50% to 150%. Is it true?

Anemometer | 9 ottobre 2014

You could ask me but I'd get confused trying to explain. After studying electrical and electronic enginering over 20 years ago I wish I'd stuck with it instead of moving to software, as we are about to hit the electrical drive renaissance.

My question is do you want to increase revs? To increase top speed of the car or to get more power from the motor? Or both, he he ;) Or are tou asking how telsa managed to get the rpm to 14,000?

The basic problem youll hit is that for a given motor as it spins faster it starts to become a generator, at some point it will reach equilibrium and you cant make it go any faster or get any more torque out of it. so you can change the gearing and get higher max speed and better cruising efficiency but lower acceleration.

Older 3 phase drives were stuck at the mains frequency so they could spin up to some multiple of 50/60hz but with inverter technology you can move the magnetic field around the motor and take power and speed beyond what is possible with fixed frequency.

Lots of googling will get you more answers. Im just starting to read more and more as these motors didn't exist when I was a student. :)

nikolateslas88 | 9 ottobre 2014

one part is the poles of the motor. poles in a motor are the coil windings that are tied together to make the rotating field. adding more poles usually reduces speed, and as you move to fewer poles this makes it faster because the poles can reverse faster over the phase. one video said the tesla induction motor is a 4 pole motor so its probably at the lowest pole number so this probably wont help on a tesla. going to different phase numbers might actually increase your motor speed, even using parts of the pole field to cancel the phase in the coil before, obviously wasting energy but reducing the interference of the magnetized field and giving you faster speeds. you would probabaly need to build a motor from scratch for that.... tesla two phase might spin faster as well becauase its 90 degrees out of phase between phases(different winding from three phase motors) giving faster shifting vs three phase which is 120 degrees or a closer phase shift of the rotor....

flip flop, data flip flop(shift register configuration), or "ring" oscillator circuits will be able to artificially push your 3 phase motor to its limits from a DC source like a battery. resonant feedback circuits like this can get you well into radio frequencies so you would have a very large range of frequencies, however things might fail going that high with a large current carrying motor lol.. it would seem this would be technology used on a tesla control circuit on lower frequencies for acceleration control.

a RING OSCILLATOR CIRCUIT can be controlled with solid state frequency pulses(555 chip or simple transistor feedback loop) hitting a control input pin. as the pulse hits the first ring oscillator circuit, it will push one phase, as soon as the phase is pushed, the next portion of the circuit turns on pushing the next phase winding, and then finally the last part turns on pushing the third phase winding. thus a DC voltage is turned into a false "3 phase" and the cycle repeats as long as the control frequency is comming in on the control pin. its like 1,2,3... 1,2,3... 1,2,3 making a phase shift and rotation.

almost as if your controlling the 3 phase with 3 bits of information in a shift register lol.

Anemometer | 9 ottobre 2014

This post does make me realise the whole world has a lot of learning to do. In the old days it was suck squash bang blow, but now its... erm... something about your pointy first finger, thumb and middle finger at right angles to each other. Index finger I is the current in amps, First finger is the magnetic Field, and thuMb is the Motion, Or soemthing, Thats a visual memory from my physics class teacher, Mr Phillips er, 27 years ago.

How many winding phases and windings do you need to get 360bhp? And how thick do the wires need to be? Is the AC induction true AC or a digital square wave made to look sinusoidal? Can you increase the frequency of the field? What about ....

Scary innit. Electic motors just work. We all know a 4 litre ICE will do about 20-25 mpg and stick out about 300-400 bhp it has a crank and pistons and valves to let air and fuel in and out, and ignition circuit to release a spark as the piston compresses the fuel air mix, But EV motors... WTF? Something the size of a waste paper basket with 360hp, or 420 if you use the "performance" inverter. What does the perfromance inverter do that the standard inverter doesnt have?

I'm someone who studied electrical engineering at degree level, so what chance has anyone else got... I have a rough knowledge of what could be done, but interested to find out what actually is happening in those boxes. Solid state power electrocnics. aaaah.

bfactor17 | 10 ottobre 2014

Thank you to all of your input. I'm thinking of fabricating the AC Induction Motor based on the Tesla Patent that they have released and connect it to a VFD/ Inverter. But based on my computation, I will only reach 4,500 rpm. Tesla Motors mentioned that the based speed is at 7,200 rpm, at this point the torque will went down as the speed progresses. I'm also thinking experimenting different winding, 2 poles maybe. I'll post an update here if I will be able to come near at the Maximum RPM of a Tesla Roadster. I still have a lot of things to learn here. If ever anyone of you manage to have an answer on how the TESLA Roadster reach its maximum RPM, please message me anytime this is my email address: bfactor17@gmail.com

Thank you!

nikolateslas88 | 13 ottobre 2014

yo be careful going too fast things tend to fly apart from materials limits, tesla had trouble with the full functions of the "tesla turbines" because they could spin so fast that the materials couldnt handle the strain, could happen with the motor.

DonS | 14 ottobre 2014

Once up a time, motors were built with armatures that had the tendency to fly apart in an over speed event. My college had giant industrial AC and DC motors in the basement lab. There was one station that had metal pieces embedded in the concrete ceiling, which I was told was the result of a large DC motor letting loose. Motors today can still damage themselves from over speed, but the designs generally have an outer case strong enough to contain the pieces.

milesbb | 14 ottobre 2014

The speed of an induction motor is directly related to the frequency of the supplied power. If you want to raise the speed of the motor you need to raise the frequency of the supplied power. A four pole induction motor such as supplied by tesla will have a synchronous speed of one complete revolution for every two cycles of the ac system. At 60 hz the four pole motor will have a synchronous speed of 30 revolutions per second, or more commonly known as 1800 revolutions per minute (rpm). A synchronous speed of 14,000 rpm requires a supplied frequency of 467 hz for a four pole motor. An induction motor generally runs a bit slower then synchronous speed however. Motor torque is zero at synchronous speed but rises quickly if the motor is turning below synchronous speed. The speed the motor turns below synchronous speed is known as slip. A motor generally develops rated torque when slip is less then 5%. The torque of a motor is related to the slip as well as the supplied voltage, higher voltage more torque, larger slip more torque.

The key to making an induction motor turn faster is raising the voltage as well as ther frequency of the supply source. These parameters are adjusted by the motor inverter to get the right motor responce

guruymca | 8 aprile 2019

Hi bfactor17
The RPM for Induction motor is determined by 120F/P. So the number of poles are constant. The only way to multiply/increase the output RPM is to increase frequency. If you use a VFD, the frequency can be multiplied. Also we can increase the RPM upto 14000 by using a propulsion gear after motor output.