How to calculate HP for motors (alternators)

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Discussion Overview

The discussion revolves around calculating the horsepower (HP) required for motors to drive a 30 kW alternator operating at 300 RPM. Participants explore various motor types, energy conversion, and the feasibility of using different power sources, including solar energy.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant calculates that 30 kW is equivalent to approximately 40.25 HP, using the conversion factor of 1 HP = 745.7 watts.
  • Another participant suggests that a motor capable of 300 RPM may require gear reduction to effectively drive the alternator.
  • Some participants express skepticism about the feasibility of using a low HP motor to achieve a 30 kW output, citing conservation of energy principles.
  • There is mention of alternative motor types, including diesel and gasoline, as well as the possibility of using a single-phase motor or solar panels to power the alternator.
  • One participant emphasizes the importance of labeling power inputs and outputs to ensure they match, highlighting concerns about energy conservation and the concept of perpetual motion.

Areas of Agreement / Disagreement

Participants generally disagree on the feasibility of using a low HP motor to drive the alternator for a 30 kW load, with some asserting it is impossible due to energy conservation laws, while others propose alternative setups without reaching a consensus.

Contextual Notes

There are unresolved assumptions regarding the specific configurations of motors and alternators, as well as the definitions of energy inputs and outputs in the proposed scenarios.

rizwan25
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Hi,
I want to purchase a alternators that have 300 rpm and 20kw three phase can any body guide to me that which motor is best to spin this alternator means in HP.
Thanks
 
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Welcome to PF.

20 kW = 26.82 HP
What type of motor?
The 300 RPM will be a problem as you will probably need a gear reduction.
Can you please give us a link to the 300 RPM, 3PH alternator.
 
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Its from AliExpress
 

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Sorry its 30kw
 
rizwan25 said:
Sorry its 30kw
1 HP = 745.7 watt
30 / 0.7457 = 40.25 HP

There are better 3PH alternators for faster motors.
500 RPM is for wind turbines.
What type of motor, diesel, gasoline?
 
Baluncore said:
1 HP = 745.7 watt
30 / 0.7457 = 40.25 HP

There are better 3PH alternators for faster motors.
500 RPM is for wind turbines.
What type of motor, diesel, gasoline?
Actually i want to run with a single phase motor.
Or with solar panels that runs the motor then solar motor runs the alternator.

Is it possible to run alternator with low hp motor to get 30kw laod.
 
rizwan25 said:
Is it possible to run alternator with low hp motor to get 30kw laod.
No.
Conservation of energy says you cannot get more energy out than you put in.
Power is the rate of flow of energy.

The electric energy you can take from the alternator, will be less than the energy the electric motor is consuming while it turns the alternator. The missing energy is lost as heat.

There is no such thing as a free lunch.
We do not discuss mythical free energy, or perpetual motion, on this forum.
 
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Thank you for your guide.but in this scenario source of motor is different.mean i just take energy for 3 or 4 HP motor from an electric company that runs alternator.the production of alternator consumes the energy separately it's doesn't provide energy to single phase motor.
 
16825906273101694762257769938455.jpg
 
  • #10
rizwan25 said:
Thank you for your guide.but in this scenario source of motor is different.mean i just take energy for 3 or 4 HP motor from an electric company that runs alternator.the production of alternator consumes the energy separately it's doesn't provide energy to single phase motor.
"Perpetual motion machine" doesn't literally just mean self powered, it is an overall category of devices that violates conservation of energy. Label the power inputs and outputs (both mechanical and electrical) on your diagram and you will see they don't match. They have to match.
 
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  • #11
@rizwan25 Can you please just tell us what are you trying to do?

Do you wish to convert solar panel output to 3 phase AC?
Or do you want to convert 1 phase AC to 3 phase AC?
 
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