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bldginsp
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# Posted: 13 Sep 2014 06:45pm
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I'm drilling a well soon, and will have to pick a well pump. There is a great variety of well pumps available, at different capacities. So, I can pick a pump that pumps water at a slower rate, or higher rate. Since I'm pumping to a water tank, I don't need to pump at a certain rate to feed a pressure tank. Slower rate pumps generally cost a bit less, but not much less.
What I'm concerned about is efficient use of my generator, a Briggs +Stratton 5,000 watt. If the generator uses the same amount of gas whether the pump is pulling 750 watts or 1200 watts, then I'd be getting more water per gallon of gas with a larger pump. But, if these generators have governors that regulate gasoline use by load drawn, then perhaps I'm getting the same amount of water pumped per gallon of gas used, with either larger or smaller pump.
The manual for the generator doesn't address this. Anyone know how these typical generators work?
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toyota_mdt_tech
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# Posted: 13 Sep 2014 08:09pm - Edited by: toyota_mdt_tech
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Is it an inverter type generator? If not, then it needs to run at 3600 RPM regardless of load, that is assuming its the lower priced 2 pole units. They do have 4 pole units (more$$$) that run 1800 rpm, usually found under RV's or on diesel gensets. But the rpms must be at 3600, carb is controlled by a governor, which is good as it throttle up under heavier loads and tries to keep the engine target speed at 3600 rpm, very critical for the AC 60Hz (cycles) Means the more wattage, the more fuel usage, even with the constant 3600 RPM.
An inverter type generator can throttle down any where and the inverter maintains a solid 60Hz and steady voltage regardless of engine speeds and if it drops below a critical point, the inverter just shuts off vs giving you low voltage or lower cycles (dangerous to many electronics) These are the best units to get, but cost is higher. Will use less fuel overall, much more efficient.
If you are just filling a container, ie no pressure, a livestock type well may be all you need. Those can be had in 110VAC or even 12, 24, 36, 90 volts ie battery or solar only with no battery in the system at all. If you do an AC system, can you do 110VAC pump? This can allow you to use a much smaller generator, ie the Honda EU2000i, EU3000i etc depending on how many amps are needed. The larger 220VAC units are much heavier, inverter or not. The inverter units add weight.
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razmichael
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# Posted: 13 Sep 2014 08:52pm
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bldginsp
Along with what Toyota_mdt_tech mentioned, here is a quote from the Genric Generator (look at paragraph 5.4 for more details) Generator Info
"Based on experience, a generator at no load typically uses about half of the fuel of a generator at full load. The ratio of output power from a generator to the amount of fuel consumed is almost linear. Consumption on diesel fueled generators is somewhat less than gasoline."
I would then consider that the baseline no load fuel consumption is the major initial cost regardless. From this, figuring out the difference in consumption for two pumps, including considering the different run times, may be more trouble than it is worth given the limited time the pump would be running. If you were planning to buy a new generator then it becomes more important to match it to your needs (a large generator will have a higher no load baseline consumption that would be a waste if you never needed the half/full load. As you already have the generator, not sure if the different pump sizes would make a big difference (I'm assuming we are not talking about a huge difference in GPM).
Agree with T again that you might take a look at 12 volt (or whatever your system is running at, pumps that may take longer to fill but can run "in the background". Solar powered livestock pumps have really come down in cost.
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groingo
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# Posted: 13 Sep 2014 10:34pm
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Simply put if it has an ECO mode it is load sensing and will adjust engine speed to load.
What you want to do is check the generator specs, they typically will tell full load fuel consumption and 1\4 load.
If it"s not an inverter type it will inherently use more fuel as they require more horsepower because they are generating 120 volts or there about, the inverter requires much less horsepower because they put out 12 volts then kick it up to 120 via the inverter.
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razmichael
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# Posted: 13 Sep 2014 11:12pm
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Quoting: groingo the inverter requires much less horsepower because they put out 12 volts then kick it up to 120 via the inverter.
Although not really directly relevant to the question from Bldginsp (I assume he has a regular generator given the power output), this is not strictly true - the inverter generators produce 120, convert to 12, clean this up, then invert back to 120. They do tend to provide better fuel consumption at normal mid range and fluctuating loads as they can adjust engine speed. As the load goes up the comparison is not as easy. Regular generators are also available in a much higher output range (at least at any reasonable cost - although the available output for inverter generators is increasing).
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toyota_mdt_tech
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# Posted: 13 Sep 2014 11:40pm - Edited by: toyota_mdt_tech
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bld insp, if it was me, I'd sell the gennie you have, then find the suitable gennie from Honda to meet your pump needs. The peace you get when its running and you cant even hear it makes it so worth it. You will throw rocks at that old generator as soon as you run that new inverter unit. 
You will never go back to the old non inverter/3600 rpm'rs again. I think the EU2000i or for more power, still 110VAC only, the EU3000i is great too.
I have in addition to the EU2000i, I also have the EU6500is. I see its been replaced with a newer EFI unit, the EU7000is.  for the same cost. I do not take the 6500 to the cabin, to big and heavy and more power than I ever need. But it does have the wheels and fold up handle. Oh, its jsut as quiet as the little EU2000i, same exact noise rating.
However, the EU6500is (electric start) is set up to run my home (residence) during outages. It runs my electric range, electric water heater, electric dryer and does it all in "eco mode" with ease and with no more noise than the little EU2000i. Of course. I cant run 2 of these heavy loads at a time, but one at a time with ease.
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bldginsp
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# Posted: 14 Sep 2014 10:30am
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I need to research exactly what I have. I'll get back on this. thanks for the education
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toyota_mdt_tech
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# Posted: 14 Sep 2014 10:44am
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bldginsp, how deep is your well? And do you know how deep the static water level is?
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skootamattaschmidty
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# Posted: 14 Sep 2014 12:25pm
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Yes I was going to add how deep the well will be and the lift required to fill your water tank wherever it may be. This will be a factor in what size pump you get as well.
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bldginsp
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# Posted: 14 Sep 2014 04:37pm
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Haven't drilled the well yet- that should happen in the next 4 weeks or so- but the depth will probably be about 300 feet with a static level of perhaps 200 feet below grade at well head. Then I need to pump up another 75 feet to get to the water tank. We will see- its always a crap shoot in the area where I am, but I'll probably need at least a 3/4 horsepower pump, maybe 1 horse, and probably pump at 3 or 4 gpm, maybe more.
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