[sudev]

Very timely and interesting discussion..not an engineer so getting awed by terms and jargon. But energy efficiency is always understood and is money efficiency both in capital costs and in running costs.

A whole new revolution waiting to happen on our roads and yet MV Act in India is stuck in last to century with few RTO's refusing to give registration to EV's and they cannot specify "Engine CC"

[Sankar]

I found this comparison interesting. Kona has the least output but the highest torque among the three.

Why is that?

[srini1785]

Finally, a thread that discusses electric motors. Takes me back to my college days. I have forgotten most of what i learnt ( am i the only one ? ) and have always wondered what motor goes into these vehicles. For starters , i can tell you this much.

Motor has two parts :

Stator : As name suggests , this does not move , It houses the magnets ( either permanent or electro magnet )

Rotor : As name suggests , this is the shaft that moves, It has the armature which carriers the current.

For physics lovers, simple theory is that when a current carrying conductor ( read rotor ) is introduced in a magnetic field ( read stator ) it experiences a force , don't ask me why. Some english guy named Faraday found this out.

Now for the engineering aspect. Ever since AC ( alternating current lead by Tesla ) won the "current war" over DC ( Direct current lead by Edison ), all the boys toys have been driven by AC. Motors running on AC are easier to construct and speed variation is by changing the frequency of the sine wave.

So much for electrical motor theory.

Electric motors are a staple of almost all industries for constant load applications like say driving a mill or conveyor etc. However, for a car or motorcycle , the speed and torque has to vary depending on conditions. So automotive motors use different design and techniques to achieve this effect. All the books that were mentioned would be a good starting reference for introduction to electric motors.

There was two other topics that were mentioned earlier , the life of permanent magnets. As far as i can understand, with advent of newer materials , they can give you good life. But then again they can also be re magnetized.

The other topic was generating power , this is a newer field of study. A motor can also act as a generator ( now i am getting pretty technical ) imagine that you are driving up a slope, at this point , its the power from batteries that drives the motor and in turn the wheels. Now while driving down , you put the car in neutral its gravity that's driving the car down . In this case , the car wheels drive the motor and the motor pretty much becomes a generator and feeds the batteries and you recover some power that was consumed. The same principle works to generate power from braking , suspension movements etc. Now you can't do that with an IC engine.


Whatever their design would be, i can tell you this much. Electric vehicles are going to be a lot boring than good old petrol since there is nothing much you can put your hands on. They are going to get quieter and less polluting ( read boring ).

[Sankar]

Originally Posted by srini1785

Whatever their design would be, i can tell you this much. Electric vehicles are going to be a lot boring than good old petrol since there is nothing much you can put your hands on. They are going to get quieter and less polluting ( read boring ).

If the future is going to be boring like this I'm ready for it...

Originally Posted by Sankar

I have watched this clip n number of times, far more than I can even remember or count. I coudn't agree more with Hammond when he says "If that is the future I am so ready"; but it looks like there is more to the future with Rimac 2!

https://www.Youtube.com/watch?v=fWrUl3uemb4

I love torque, doesn't matter if its Electric

[Sutripta]

Plenty of points to discuss, but if one goes up the curve from battery powered toys, this

Originally Posted by srini1785

Motor has two parts :

Stator : As name suggests , this does not move , It houses the magnets ( either permanent or electro magnet )

Does not hold. If permanent magnets are used, it is on the rotor.

Regards
Sutripta

[alpha1]

How does one make the electric motor accelerate?

Let us see what happens in internal combustion engine vehicle.
You start the engine, the engine develops minuscule starting torque at idling.
You race the engine a little bit and use a clutch to engage the wheel slowly without stalling the engine. (because engine is not able to develop the desired torque to counter the inertia and friction).

Once the vehicle has reached a steady velocity, you desire to accelerate by pressing the accelerator pedal that opens of the throttle so that higher quantity of fuel and air can go in and produce a higher torque than what is required for constant velocity.
And thus we get acceleration.

So coming back to my question:
What is the analogy in electric motor? How do we make a motor accelerate?

[Sutripta]

^^^
Control the current.

Regards
Sutripta

[alpha1]

Originally Posted by Sutripta

^^^
Control the current.

Regards
Sutripta

So if I get it right, the motor is designed for certain peak power utilizing peak current (based on internal resistance and heat dissipation allowance).
Now if I add external resistors then I can "reduce" the peak power available.

And my process of desiring an acceleration means progressively reducing this external resistance.
?

[Sutripta]

^^^
Different motors - different ways of controlling it.
Say induction motors - control frequency. Which will also require control of input voltage. Which will change current. Frequency changes expected rpm. Different from actual rpm. So there will be slip. Torque a function of slip.

Don't waste power heating resistances.

Regards
Sutripta

[srini1785]

Originally Posted by Sutripta

^^^
Control the current.

Regards
Sutripta

Forgive me for asking this : I always thought that current controls the torque and not speed. The mechanical load would determine the current that a motor draws from the source(AC/DC).

[Sutripta]

^^^
Correct - torque essentially depends on current.
Without torque in excess of immediate mechanical load one will not accelerate.
To maintain rpm the torque generated must match torque required.

With ICE when one stomps on the accelerator, the engine generates more torque and the vehicle accelerates.

Regards
Sutripta

[Samurai]

Originally Posted by alpha1

What is the analogy in electric motor? How do we make a motor accelerate?

Ok, are you all ready for a crazy analogy? Those who remember the old torque generation and distribution thread, might also remember the crazy analogies that were used, mostly by me. This post is going to be a Déjà vu.

Imagine a dog that is chasing its tail, but with couple difference. The dog is long and elastic. Yeah, like a cartoon dog. If it suddenly takes off, the front part is yards ahead and the rear will take seconds before moving. In this example dog is the motor. The front of the dog is the rotating magnetic field in the stator, and rear of the dog is the rotor that is connected to the load. Sort of...

When you start the car, and first press the accelerator, the current is sent into the motor or the dog. The dog takes off and starts chasing the tail. At first, only the front part moves and rear is stand still. The front is moving because of the current supplied, and the rear is resisting because of the load of the car. This stretch in the dog is the slip. Higher the load, more will be the stretch (slip).

As Sutripta already mentioned, torque is a function of slip. Higher the slip, more torque will be generated. This is why motors generate maximum torque at stand still.

If enough current is sent to overcome the load, the rear eventually starts moving. When the rear reaches the same speed as the front, some stretch (slip) will remain. This slip will generate enough torque to overcome the frictional losses.

Now coming to the question of how to accelerate... send more current. The front of the dog runs faster, leaving the rear in the original speed. The dog stretches again, means more slip, which generates more torque. If the current is maintained, the rear catches up again reducing the slip, keeping just enough to overcome the frictional losses.

If the above is an induction motor, the current is controlled by changing the frequency. The front of the dog is running at the frequency of the AC current.

[Sutripta]

Originally Posted by Samurai

As Sutripta already mentioned, torque is a function of slip. Higher the slip, more torque will be generated.

To prevent hordes of people descending on us like a ton of bricks shouting Gotcha Gotcha, let me quickly add the backside protecting qualifiers - was talking of induction motors operating within their operating envelope. True the operating envelope for an induction motor fed from a controlled power source is very different from that of an induction motor connected to grid (eg stall torque), but we are digressing.

Regards
Sutripta

[Jeroen]

confused about these e-motors? AC, DC, induction? Enter Tesla approach. A bit of everything:

https://cleantechnica.com/2018/03/11...otor-in-depth/

[alpha1]

Got it.

Originally Posted by Samurai

Now coming to the question of how to accelerate... send more current.

If the above is an induction motor, the current is controlled by changing the frequency. The front of the dog is running at the frequency of the AC current.

In DC:
How do I send more current than what is happening right now under various equilibrium (heat dissipation, torque vs friction etc.) - by increasing the voltage across the terminals?

Also in case of AC is it that increasing the frequency increases the slip (momentarily) by rotating the magnetic flux faster thus accelerating the rotor till the torque produced via slip just balances the friction at which point it will settle down to a constant velocity?