How to calculate HP for motors (alternators)

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In summary, the conversation discusses the purchase of an alternator with specific RPM and power requirements. It is mentioned that a motor with 40.25 HP is needed to spin the alternator, and there are better alternators available for faster motors. The possibility of running the alternator with a low HP motor or solar panels is also explored, but it is determined that this would not be feasible due to the conservation of energy and the concept of perpetual motion. The conversation concludes with a request for clarification on the purpose of the alternator.
  • #1
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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  • #2
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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  • #3
Its from AliExpress
 

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  • #4
Sorry its 30kw
 
  • #5
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?
 
  • #6
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.
 
  • #7
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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  • #8
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.
 
  • #9
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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1. How do I calculate the horsepower (HP) of a motor or alternator?

To calculate the horsepower of a motor or alternator, you will need to know the torque and speed of the motor or alternator. The formula for calculating horsepower is HP = (Torque x Speed) / 5252. Make sure to use consistent units for torque and speed, such as foot-pounds (ft-lb) and revolutions per minute (RPM).

2. What is the difference between mechanical horsepower and electrical horsepower?

Mechanical horsepower (mhp) is a unit of power that measures the amount of work a motor or engine can do. Electrical horsepower (ehp) is a unit of power that measures the electrical power output of a motor or alternator. To convert between the two, you can use the formula ehp = mhp x 746.

3. How does the efficiency of a motor or alternator affect its horsepower?

The efficiency of a motor or alternator is the ratio of its output power to its input power. This means that the more efficient the motor or alternator is, the higher its horsepower will be. To calculate the horsepower of an efficient motor or alternator, you can use the formula HP = (Torque x Speed x Efficiency) / 5252.

4. Can I calculate the horsepower of a motor or alternator using only voltage and current?

No, voltage and current alone cannot be used to calculate the horsepower of a motor or alternator. The power (in watts) of a motor or alternator is equal to the product of its voltage and current, but this does not take into account the speed and torque of the motor or alternator. Horsepower takes into account all of these factors and is a more accurate measure of the motor or alternator's power.

5. How can I determine the horsepower of a motor or alternator if I don't have access to its torque and speed information?

If you do not have access to the torque and speed information of a motor or alternator, you can use a dynamometer to measure its power output. A dynamometer is a device that measures the power output of an engine or motor. Once you have the power output in watts, you can convert it to horsepower using the formula HP = Power (Watts) / 746.

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