Picking generator to match available piping

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  #1  
Old 03-10-14, 09:35 PM
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Picking generator to match available piping

Hi folks. For a while I've been eyeing getting a small generator to serve as a backup for the house, and occasional (rare) outings.
We don't need much, just enough to run the furnace blower/thermostat, well pump, some lights and a laptop or two. I figure 4500-5500 should be enough, although 6+kW would be great.
The house has natural gas. Turns out there is a great spot to put it behind the back of the house thats away from living quarters... and right on the other side of the wall from a gas dryer and 1/2" pipe service.

Thought it would be cool to T there and run to a disconnect outside, make a little doghouse for it.

I'm looking for some advice, however, on how to find the "best" unit for this size pipe. It's about 35' from the meter. B/c of where the meter is and the line route (through a cement slab) upgrading the line is not an option.

It seems substantially more economical to buy a regular gas unit and ad the tri-fuel adapter. But... gasoline generators are rated in HP and (if lucky) run time for a tank of gas.
The chart here
Natural Gas
suggests the 4kW unit would be about max... not id(not just HP) of the engine? I've read about the Honda's being loved for their efficiency and quiet run (and you pay for it!). Wouldn't that matter?

I guess the question is, how could I really know what unit would yield the most power in this circumstance?
 
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  #2  
Old 03-10-14, 10:41 PM
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From that chart it appears that a 4,000 watt generator is going to be the practical limit using that piping. That MAY, or may not, be large enough to start the well pump, it will certainly handle the other loads. The problem is that electric motors take a huge surge of power to start and if the generator does not have the capability of supplying this surge you will likely stall the engine of the generator.

I would suggest renting a 4,000 watt generator and connecting it to just the well pump and see if it will reliably start the pump. If it does then you should be fine.

I have a Yamaha EF3000iSE (2800-3000 watts) that I converted to gaseous fuel only. I can switch it from natural gas (preferred fuel) to propane by simply closing the maximum fuel (load block) screw about two turns and connecting to a standard 11 inch WC propane regulator on a tank. I personally prefer the gaseous only option over the tri-fuel but I seem to be in the minority on that point. I can power my furnace, refrigerator, entertainment system or computer along with either the microwave oven or a counter-top convection oven along with a few lights. I could also use a counter-top hotplate instead of the microwave or convection oven to heat up some soup. Since I have a municipal water and sewage system I don't have any large loads like a water pump. I can live fairly comfortably with this set-up in case of power outages.

How are you planning on powering the well pump and other loads? The best method in my opinion is with a separate circuit breaker panel via a selector switch from the service (main) panel. Several people here can advise you on that method as well as an all-in-one transfer panel or a service panel interlock.
 
  #3  
Old 07-01-14, 06:03 PM
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Thanks for the input.

I guess what I'm really wondering is - are all engines used for generators really created equal?
For example the implication is that a more efficient motor might get more HP/power per cubic foot of NG. Since I am kind of on the edge between sizes, it might matter.
Everybody seems to love Honda generators... and the price shows... but might that buy me a needed edge here?

FYI - my well pump is only 120v. I'd most likely do the simpler selector switch that auto disconnects main and enables this, not extra circuits and transfer etc.
 
  #4  
Old 07-02-14, 05:10 AM
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Rating engines by horsepower output per unit of fuel used, all small engines are pretty much the same, especially if they are gasoline models. Rating the engine by longevity of service and there are huge differences. The Honda machines are high quality but in my opinion the higher price than similar machines, such as Yamaha, are more name recognition than actual improvements in efficiency, noise level or endurance.

The fact that your well pump is 120 volts actually makes it more likely that you will have a problem with the generator starting the pump as it is amperage that is the deciding factor. As I stated before it would be best to rent a 4,000 watt generator and see if it will reliably start the pump BEFORE actually buying the generator. A generator set up as gaseous fuel only (as opposed to tri-fuel) might be able to squeak by where a tri-fuel would not.
 
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