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Old 10th September 2019, 12:22   #31
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Default Re: Electric vehicles - Types of motors?

With possibilities of getting corrected/trolled:

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Originally Posted by alpha1 View Post
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?
For that you need a power management circuit.

For a small hobby kit motor rated at say 12-36V, you can get variable DC supplies and can vary both voltage and current. However, the important point is that any motor is rated for a certain Voltage and current. You need to be careful as anything more than the rated voltage or current, the motor is fried.

For a industrial grade motor, similar such setup is also possible.

The point here is that for any motor, generally speaking , the current is never controlled and usually left floating and the motor would draw a current depending on mechanical load. In other words, motor voltage need not be adjusted in order to maintain a constant speed ( rpm ). The motor would automatically adjust to varying mechanical load conditions.

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Originally Posted by alpha1 View Post
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?
Yes. VFD's ( variable frequency drives ) are used for this purpose.
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Old 10th September 2019, 12:59   #32
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Default Re: Electric vehicles - Types of motors?

Quote:
Originally Posted by srini1785 View Post
For a industrial grade motor, similar such setup is also possible.

The point here is that for any motor, generally speaking , the current is never controlled and usually left floating and the motor would draw a current depending on mechanical load. In other words, motor voltage need not be adjusted in order to maintain a constant speed ( rpm ). The motor would automatically adjust to varying mechanical load conditions.
Since we are talking about DC motors for EVs, how can we depend on load to control the speed? What if the driver wants to go faster? Reducing load is not answer.

Since BLDC motors work on the principle of magnetic push and pull force, I thought varying the voltage will let us select the speed under a give load, using closed loop control circuit. So I am not able to follow your logic.
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Old 10th September 2019, 13:58   #33
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Default Re: Electric vehicles - Types of motors?

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Originally Posted by Samurai View Post
Since we are talking about DC motors for EVs, how can we depend on load to control the speed? What if the driver wants to go faster? Reducing load is not answer.

Since BLDC motors work on the principle of magnetic push and pull force, I thought varying the voltage will let us select the speed under a give load, using closed loop control circuit. So I am not able to follow your logic.
My earlier post was about PMSM motor and not EV motors.

Now for EV motors:

From what i understand, EV motors are of two types either DC stepper motors or AC induction motors. The article which Jeroen refered to, mentions that newer tesla models uses a switched reluctance motor. A switched reluctance motor is essentially a DC stepper motor. Steppers are controlled by pulsing from a controller which is attached to a power supply (battery). A stepper takes a fixed number of pulses per rotation. Say in full step mode , it would be around 360 pulses ( 5V DC ).

When pressing the pedal, we either increase or decrease the pulses thereby varying the speed. However, what is important is that even here, the current that the stepper draws from the controller would depend on the mechanical load. The controller has a inbuilt power management circuit. Simple DC circuitry logic is that both the terminal voltages of the controller and motor would be same and current drawn depends on load.

The older TESLA motor was a 3 phase AC induction motor. For such a motor, to run it from a battery ( DC) , you first convert DC to AC using a SCR firing circuit and then use a bridge circuit to vary the frequency. So in effect you control the frequency and the motor again would take a current depending on load.

Last edited by srini1785 : 10th September 2019 at 14:07.
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