Help understanding genreator spec sheet?

  • Thread starter Frangelo
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In summary: The attached spec is for a drive-shaft powered AC generator to be used to power a 2500 square foot home in a remote location. The application is for a stand-by system because the power is not reliable. The house has a 100amp panel and no unusual power requirements save for central air conditioning. The real question is though is how powerful a motor (in HP) I'm likely to need to run this generator. The chart below talks about "Code H" and "Code F" and talks about "motor starting", so I don't know if that only means "on startup" if that the continuous HP/torque required to power it to 90%. It seems like it's either 1/2 or 2/3
  • #1
Frangelo
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Hi,

If somebody could help me interpret the attached spec for this drive-shaft powered AC generator I'd be very grateful. The application is to power a 2500 square foot home in WA state in a remote location. This is a stand by system because the power is not reliable. The house has a 100amp panel, and no unusual power requirements save for central a/c.

From reading about typical home power consumption, it seems like a 20kw model should handle peak load. Does that sound right?

The real question is though is how powerful a motor (in HP) I'm likely to need to run this generator.
The chart below talks about "Code H" and "Code F" and talks about "motor starting", so I don't know if that only means "on startup" if that the continuous HP/torque required to power it to 90%.

It seems like it's either 1/2 or 2/3 hp per kw produced, but that's a meanigful difference. Also this thing will be running nearly continuously so I don't think I will starting and stopping it frequently, so wondering what the "continuos" power requirement might be, or does tha tnot matte.r
 

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  • #2
I quote from;
http://www.reliance.com/prodserv/motgen/b9652new/b9652.htm

INRUSH CURRENT
When started with full line voltage, AC motors draw line currents substantially greater than their full load running current rating. The actual magnitude of this current is called "inrush current." It is a function of the motor horsepower and design characteristics. It is also called Locked Rotor Current.
A letter used to indicate the "Design Code Rating" on the nameplate is referred to as the "Code Letter." The Code letter of the motor is an indication of the locked rotor KVA per horsepower. It is a function of the motor's design. Code letter ratings indicate the starting current motor will draw. Code letters below F indicates a low starting current; beyond F indicates a high starting current.
The motor's Code Letter is helpful in determining the maximum rating of the motor's electrical circuit protection. A replacement motor should have the same rating as its predecessor.
 
  • #3
Could you be more specific about the power requirements of the house? Is the heat from fuel/electric resistance/heat pump? Is the stove electric? The dryer? Water heater?
 
  • #4
The motor that is required is an internal combustion motor, which will need to be about 10 horse power, just as the spec sheet suggests.
These motors are pretty cheap if gasoline is acceptable and fuel storage is not an issue. If they are diesel, the price goes up but the engine is more efficient and robust, plus the fuel is less volatile, also big plus.
The buyer has to decide whether it is worth installing an automatic backup, where the engine kicks in by itself when the power drops out, or whether a manual start is acceptable. Also, the duration of the backup power needed is a big factor.
Note that these setups need to have code approval. For one, it is essential to disconnect the backup from the grid, lest it electrocute the repair crews.
That said, a 20kW backup is a good size. Washington state is not the tropics, there is no need for a gigawatt A/C, pumps usually need about 5kW for the starting surge, fridge needs are in the kilowatt range and lighting etc is just rounding errors.
 
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  • #5
A 20kW output alternator with an efficiency of about 80% will need 25kW drive.
There are 746W per HP, so 25kW is equivalent to 33.5 HP.

A contactor should isolate the mains and connect the alternator to the house only once the engine is up to speed. Starting the IC engine should not therefore be a problem.

The 1800 RPM requirement suggests a direct coupled diesel would be appropriate.
 
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1. What is a generator spec sheet?

A generator spec sheet is a document that contains all of the technical specifications and details about a specific generator. It typically includes information such as the power output, fuel type, dimensions, and other key features of the generator.

2. Why is it important to understand a generator spec sheet?

Understanding a generator spec sheet is important because it allows you to make an informed decision when purchasing or using a generator. It provides crucial information about the capabilities and limitations of the generator, which can help you determine if it is suitable for your needs.

3. What are some key terms to look for on a generator spec sheet?

Some key terms to look for on a generator spec sheet include power output, voltage, current, fuel consumption, and noise level. These terms can give you a better understanding of the generator's performance and how it will meet your power needs.

4. How do I interpret the information on a generator spec sheet?

The information on a generator spec sheet can be interpreted by comparing the values to your specific power needs. For example, if you need a generator for backup power during a blackout, you will want to look for a high power output and long run time. It is also important to consider the fuel type and noise level based on your preferences and location.

5. Are there any red flags to watch out for on a generator spec sheet?

Yes, there are some red flags to watch out for on a generator spec sheet. These can include significantly lower power output than advertised, high fuel consumption, and excessive noise levels. It is important to carefully review the spec sheet and compare it to your needs to avoid any potential issues with the generator.

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