Hello, if at 3000 rpm the motor draws at 40V 12A, rated working as motor. And when it works as a generator at 1500 rpm, it will produce electricity with a lower intensity or lower voltage? Does it depend on the resistance of the resistor included in the circuit?

First of all, at 1500 rpm, it will produce less power. And the power is P = UxI The voltage induced by the generator depends on the speed of rotation of the armature. The lower the RPM, the lower the voltage. And the current as you know depends on the voltage - I = U / Robc To sum up - it will provide both lower current and voltage. Obviously, the power transferred from the generator to the load depends on the magnitude of the load. You will get the highest power when the load resistance is equal to the resistance of the motor windings.

The BLDC motor has electronics inside that do not fit the role of a generator. Voltage for the generator U = K * fI * R, where R is the resistance of the motor coil, I - current consumption, f - rotation frequency, K - motor / generator constant. And for the engine U = K * f + I * R (the same K).

What is the relationship that governs this phenomenon? You mean I categorically cannot use this engine as a generator? is it a commutator? what is this constant? what is her name should the frequency of rotation be expressed in [Hz]?

Ohm's law. Read: You can - only that the engine controller must enable the generator to operate. For example, bicycle BLDC motors have controllers equipped with an energy recovery option (i.e. something like KERS) and there the motor can work as a generator. It's exactly called constant of the engine / generator . It is specific to a given machine and results from its design (windings, magnetic guides, etc.). In this case, probably in Hz.

For example, the constant K might be 7.5V / (1000 rpm) - then 'f' will be in rpm. Sometimes they put it on the nameplate.

Though I wonder if it makes any sense to me counting it. Is it not enough just to select the power resistor based on the energy matching? Use the best possible transistor, with high current and maximum voltage?

This is a question of what you actually want to do. The generator does not contain a transistor, and a resistor is not needed for its operation. An AC generator will output from the BLDC motor.

It seems that we are discussing unnecessarily on two identical topics .

BLDC Motor as Generator: Output Voltage & Current at 1500rpm, 40V 12A Ratings, Resistor Impact

Lewandd 8313 8

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#1 16241033 30 Jan 2017 21:47

Lewandd Lewandd

Level 8

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Post #1
16241033 30 Jan 2017 21:47

Hello,
if at 3000 rpm the motor draws at 40V 12A, rated working as motor.
And when it works as a generator at 1500 rpm, it will produce electricity with a lower intensity or lower voltage? Does it depend on the resistance of the resistor included in the circuit?
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#2 16241127 30 Jan 2017 22:16

Xantix Xantix

Level 41

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Post #2
16241127 30 Jan 2017 22:16

Lewandd wrote:
And when it works as a generator at 1500 rpm, it will produce electricity with a lower intensity or lower voltage?

First of all, at 1500 rpm, it will produce less power. And the power is P = UxI
The voltage induced by the generator depends on the speed of rotation of the armature. The lower the RPM, the lower the voltage. And the current as you know depends on the voltage - I = U / Robc
To sum up - it will provide both lower current and voltage.

Lewandd wrote:
Does it depend on the resistance of the resistor included in the circuit?

Obviously, the power transferred from the generator to the load depends on the magnitude of the load. You will get the highest power when the load resistance is equal to the resistance of the motor windings.
#3 16241280 30 Jan 2017 23:12

_jta_ _jta_

Electronics specialist

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Post #3
16241280 30 Jan 2017 23:12

The BLDC motor has electronics inside that do not fit the role of a generator.

Voltage for the generator U = K * fI * R, where R is the resistance of the motor coil, I - current consumption, f - rotation frequency, K - motor / generator constant. And for the engine U = K * f + I * R (the same K).
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#4 16241309 30 Jan 2017 23:29

Lewandd Lewandd

Level 8

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Post #4
16241309 30 Jan 2017 23:29

Xantix wrote:
Obviously, the power transferred from the generator to the load depends on the magnitude of the load. You will get the highest power when the load resistance is equal to the resistance of the motor windings.

What is the relationship that governs this phenomenon?

_jta_ wrote:
The BLDC motor has electronics inside that do not fit the role of a generator.

You mean I categorically cannot use this engine as a generator? is it a commutator?
http://www.dunkermotoren.com/en/products/brushless-dc-motors/detail/885750200101/

_jta_ wrote:
K - engine / generator constant

what is this constant? what is her name should the frequency of rotation be expressed in [Hz]?
#5 16241319 30 Jan 2017 23:38

Xantix Xantix

Level 41

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Post #5
16241319 30 Jan 2017 23:38

Lewandd wrote:
What is the relationship that governs this phenomenon?

Ohm's law. Read:
https://pl.wikipedia.org/wiki/Dopasowanie_energetyczne

Lewandd wrote:
jta_ wrote:
The BLDC motor has electronics inside that do not fit the role of a generator.

You mean I categorically cannot use this engine as a generator?

You can - only that the engine controller must enable the generator to operate. For example, bicycle BLDC motors have controllers equipped with an energy recovery option (i.e. something like KERS) and there the motor can work as a generator.

Lewandd wrote:
what is this constant? what is her name

It's exactly called constant of the engine / generator . It is specific to a given machine and results from its design (windings, magnetic guides, etc.).
Lewandd wrote:
should the frequency of rotation be expressed in [Hz]?

In this case, probably in Hz.
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#6 16241833 31 Jan 2017 10:42

_jta_ _jta_

Electronics specialist

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Post #6
16241833 31 Jan 2017 10:42

For example, the constant K might be 7.5V / (1000 rpm) - then 'f' will be in rpm. Sometimes they put it on the nameplate.
#7 16241896 31 Jan 2017 11:10

Lewandd Lewandd

Level 8

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Post #7
16241896 31 Jan 2017 11:10

Though I wonder if it makes any sense to me counting it. Is it not enough just to select the power resistor based on the energy matching? Use the best possible transistor, with high current and maximum voltage?
#8 16242248 31 Jan 2017 13:35

_jta_ _jta_

Electronics specialist

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Post #8
16242248 31 Jan 2017 13:35

This is a question of what you actually want to do. The generator does not contain a transistor, and a resistor is not needed for its operation. An AC generator will output from the BLDC motor.
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#9 16246020 01 Feb 2017 20:51

Freddy Freddy

Level 43

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Post #9
16246020 01 Feb 2017 20:51

It seems that we are discussing unnecessarily on two identical topics https://www.elektroda.pl/rtvforum/topic3301815.html#16239972 .
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Topic summary

The discussion centers on the performance of a BLDC motor when used as a generator at 1500 RPM, compared to its rated operation as a motor at 3000 RPM drawing 40V and 12A. It is established that the output voltage and current will be lower at reduced RPM due to the relationship defined by Ohm's law and the motor's design characteristics. The induced voltage is directly proportional to the rotational speed, and the current output is influenced by the load resistance. The conversation also touches on the internal electronics of BLDC motors, which may limit their effectiveness as generators unless specifically designed for such use, as seen in bicycle motors with energy recovery systems. The constant K, which relates voltage to RPM, is highlighted as a critical factor in determining generator output.
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BLDC Motor as Generator: Output Voltage & Current at 1500rpm, 40V 12A Ratings, Resistor Impact

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