I had a problem with the relevance of it to the initial question. Converting KW/hr to Amps.
That you see it otherwise is your choice.
And, FWIW, I disagree with response anyway. Not that it matters.
Now can we stick with the original point, please?
Converting KW/hr to amps
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That you see it otherwise is your choice.
And, FWIW, I disagree with response anyway. Not that it matters.
Now can we stick with the original point, please?
drktmplr12
Senior Member
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- South Florida
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- Electrical Engineer
The original premise of converting kw/hr to amps is not possible.
The genset will be required to supply starting current for the largest inductive load while operating all other the equipment that can operate concurrently.
Home owner is cooking on their electric stove, and baking a cake while microwaving some potatoes. They are also running a load of laundry with the electric dryer running, too. the fridge compressor also happens to be running cause they left the fridge door open. The insta-hot heater is running because someone turned on the shower but is sitting on the toilet looking at their phone for the past 20 minutes. All the lights in the house are on for some reason. And for some reason they are doing all of this while the house is powered by the generator. The air conditioner needs to turn on. can the generator start the compressor while running all the other stuff?
perhaps ask the generator manufacturer if they have some type of application that will recommend a size and go from there.
The genset will be required to supply starting current for the largest inductive load while operating all other the equipment that can operate concurrently.
Home owner is cooking on their electric stove, and baking a cake while microwaving some potatoes. They are also running a load of laundry with the electric dryer running, too. the fridge compressor also happens to be running cause they left the fridge door open. The insta-hot heater is running because someone turned on the shower but is sitting on the toilet looking at their phone for the past 20 minutes. All the lights in the house are on for some reason. And for some reason they are doing all of this while the house is powered by the generator. The air conditioner needs to turn on. can the generator start the compressor while running all the other stuff?
perhaps ask the generator manufacturer if they have some type of application that will recommend a size and go from there.
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I agree. I, and several others, have made that point.
drktmplr12
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- South Florida
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- Electrical Engineer
I realize after posting I'm late to the party.
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That does not, in the least, invalidate your point.
gadfly56
Senior Member
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- Professional Engineer, Fire & Life Safety
You did, however, create a narrative that the GC could relate to in trying to make him/her understand the difficulty of determining the correct generator size.
a comment was made why 1800 vs 3600
a response was made that a larger engine was required
I elaborated on that
you disagree that engine torque is directly proportional to displacement, all else being equal?
T = V x Pme / 4Pi
if you know the time, v and pf you can get amps, average amps over the time frame
no useful for sizing unless a load with high duty factor and low variance
not useful for a home
better late than never
just add up the loads
not many in a single family dwelling
and better yet run them thru koehlers free sizing program
gadfly56
Senior Member
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- Professional Engineer, Fire & Life Safety
better late than never
just add up the loads
not many in a single family dwelling
and better yet run them thru koehlers free sizing program
The problem being that you run right into this, from the original post:
You can't get there from here.
Russs57
Senior Member
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Well, if we size the generator to carry what the service is rated at, 225 amps IIRC, we can’t be faulted for anything other than wasting money.
I would argue carrying most of the load for as long as necessary is more important than carrying all of the load for too short a period. So I would start on the fuel side. Natural gas, if available, has the advantage of supplying a larger generator for an unlimited time. But it might not be available during a hurricane. I suggested propane but there are likely limits on what capacity will be allowed. Then we have diesel. Typically this involves lots of compliance matters. Fuel has a limited life span as well. I personally wouldn’t consider gasoline.
As to cost of 1800 vs 3600, 4 pole vs 2 pole will be more copper costs too. Anyone expecting a 3600 rpm gasoline generator to run any appreciable time might look into required oil changes. You might need to do it daily. They do make some capable 3600 rpm diesels. Detroit comes to mind. No idea what they offer in generators.
I mean just stick a chart recorder on it or do a load calculation. Then look at where the lines cross in terms of allowable fuel supply and run time. Make the homeowner make the final decision. If I was asked for a ballpark I’d pick a 30 KW Kohler (Caterpillar or Cummins is better) with twin 1000 gallon propane tanks and some load control devices to keep load side amps under maximum rating.
I would argue carrying most of the load for as long as necessary is more important than carrying all of the load for too short a period. So I would start on the fuel side. Natural gas, if available, has the advantage of supplying a larger generator for an unlimited time. But it might not be available during a hurricane. I suggested propane but there are likely limits on what capacity will be allowed. Then we have diesel. Typically this involves lots of compliance matters. Fuel has a limited life span as well. I personally wouldn’t consider gasoline.
As to cost of 1800 vs 3600, 4 pole vs 2 pole will be more copper costs too. Anyone expecting a 3600 rpm gasoline generator to run any appreciable time might look into required oil changes. You might need to do it daily. They do make some capable 3600 rpm diesels. Detroit comes to mind. No idea what they offer in generators.
I mean just stick a chart recorder on it or do a load calculation. Then look at where the lines cross in terms of allowable fuel supply and run time. Make the homeowner make the final decision. If I was asked for a ballpark I’d pick a 30 KW Kohler (Caterpillar or Cummins is better) with twin 1000 gallon propane tanks and some load control devices to keep load side amps under maximum rating.
Can we keep on topic please?
that is why I said find the avg and use peaking factor of 4 for estimating purposes
kwired
Electron manager
- Location
- NE Nebraska
I guess I am not a geologist. I have no idea how they can determine if there was a temporary flood that only lasted a day or two or even a week or two several thousand years later. Some major event that had high water for years I can see leaving more evidence behind.Flood plain data is based on modeling, not so much on historical data. My house is on a hill some 80 or 90 feet above the water level in the river that runs through town. I'll bet I'm in a 10,000 year flood plain.
:ashamed1:
I guess generator RPM is much closer to being on topic then flood data
they look at rainfall records
how it correlates to flooding and the freq that you get a give rain
suppose you get 4" rain in 4 hours and it floods to a certain level
the records say that happens every 20 years
that is the 20 year floodplain
they can model this pretty good now
how it correlates to flooding and the freq that you get a give rain
suppose you get 4" rain in 4 hours and it floods to a certain level
the records say that happens every 20 years
that is the 20 year floodplain
they can model this pretty good now
kwired
Electron manager
- Location
- NE Nebraska
So it is just a guesstimate based on what history has been recorded.
Saying they can model it pretty good is sort of giving themselves a pat on the back, thinking they are correct? Chances are good there was that 4 inch rain in 4 hours sometime in the past 10,000 years, but what they don't know is if it was right before we occupied a particular location and someone recorded it in some way (like 200-500 years ago) or if it was actually 9783 years ago.
rainfall records go back aways
plus they have live data now
so they record rainfall and river rise
for all levels of rainfall for all seasons
snowmelt and temp also factor in
with these data points they can build models
and tune based on actualities
they are pretty accurate predicting river rise after a storm
they can a peak and timeframe
they know the river level
they know the projected rise
and they know the ground contours and river bank elevations
it's the best they can do and it is continuously improving
risk accuracy is good
probability not so good
kwired
Electron manager
- Location
- NE Nebraska
But is still just a guesstimate when it comes to what might have happened 1,000 years ago - especially on the American continents. We do have better documentation in the "old world" from what happened that long ago. All that was on the American continents then was native Americans. They passed on stories from generation to generation but didn't make hard copy records of any kind of many of those stories, and you know how stories can change each time they are passed on to another person. Even if they had a record of a heavy rain incident and flooding - not much of a chance they have any method of measuring how much rainfall there was. That kind of precision just wasn't something they were into, they would have been more likely to be concerned that some spirit cursed them with that incident then to be amazed at how many inches (or whatever) of rain had fallen.
gadfly56
Senior Member
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- New Jersey
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- Professional Engineer, Fire & Life Safety
It is not based on rainfall records. It is based on stream flow data. Here is a great introduction by the USGS:
https://water.usgs.gov/edu/100yearflood-basic.html
Includes a discussion of the factors affecting the calculation of the 100- and 500-year flood and how the values may change over time.
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