Understanding the Capacity of Electric Generators
How to Calculate Generator Load Capacity: Basic Electrical Calculation for Watts, Ohms Law Formulas, I have a 3000 watt generator that I want to use to power a motor.© By: Dave Rongey
Calculating Generator Load Requirements and Load Capacity
Electrical Question: I have a 3000 watt generator that I want to use to power a motor.
- I have a 3000watt generator with one 120v 15 amp duplex outlet.
- One 240v 15 amp duplex outlet. It has 21.7 amps @120v and 10.8 amps @240.
- Is there any way I can use this generator to run this motor continuously.
- I was told the motor is three phase.
- Manufacturer Siemens
- Capacity Speed 3600 RPM
- Estimated Shipping Weight 1750
- Length 45 IN
- Width 30 IN
- Height 25 IN
- Voltage 460 VOLTS
- Frequency 60 HERTZ
- Phase 3
- Frame 445TS
- Horsepower 150 HP
This electrical question came from: Dardanus , a Handyman from Houston, Texas.
Thanks for your electrical question Dardanus.
Calculating Generator Load Requirements
Generator Load Capacity
The motor that is described cannot be connected to the generator that you have because the load is too great and the voltage is not compatible.
Basic Electrical Calculation for Watts
- One way to understand the capacity of the generator is to convert the loads into watts, which is volts times amps such as 30 amps times 240 volts = 7200 watts. This amount does not take into consideration power factor.
- All of the loads to be considered for the generator must be compatible with the voltage as well and in this case the motor voltage is 460 not 240, and the motor is 3 phase not single phase 240 volt.
The nameplate of the generator provides information about the load capacity
- 21.7 amps for 120 volt circuit loads (21.7 amps x 120 volts = 2604 watts at 86.8 % Load).
- 10.8 amps for 240 volt circuit loads (10.8 amps x 240 volts = 2592 watts at 86.4 % load).
- It should be understood that you should never load a circuit up to its maximum potential, 80% is a good rule of thumb, and we see in the above calculations that the generator manufacturer is allowing a maximum load of about 86 %.
- This same formula can be used to determine the load of the proposed circuits as well as the load capacity of the generator.
Ohms Law Formula Examples
- Volts (times) Amps = Watts
- Watts (divided by) Volts = Amps
More about Generators
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- This series covers a wide variety of topics all about home generators including sizing, selecting, connecting and safely operating this all important addition to your home.
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