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Arizona_928's Avatar
 
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Generator size, is it possible to go too big (kw question)

I need a 3 phase, 480v generator to run a deep well pump. The the pump looks like it needs 15 kw ish peak...
So I'm looking at generators. Diesel type. Only thing remotely close to my price range is a 40kw unit.
So the question is; would it be safe to assume with less load the generator will run more efficient (less fuel) then say a smaller 25 kw unit? Also, I would hate to use this generator only to power a pump.

Thanks Guys

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Old 04-22-2018, 09:01 PM
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Yes, but with a diesel youíll get glazing of the cylinders ( I think thatís the issue)if you donít run it hard on a regular basis. I only run the one at work when it has a load on it and every few years the service company brings out the load bank and runs it hard.
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Old 04-23-2018, 01:46 AM
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If you run a Diesel engine under 60% of its capacity for prolonged periods you could experience wet stacking, which is unburned fuel leaking past the cylinders.

Short periods of wet stacking is not too damaging but repeatedly and for prolonged periods your maintenance costs will skyrocket.
Old 04-23-2018, 02:45 AM
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Standby generators regularly run in the 30% region. They are sized for in rush current.

Gen size = voltage * inrush current(s) * (100 - allowable voltage say in %).

Typical allowable voltage sag is 20-30% depending on the device.

In rush is 3-5 times the operating current, unless you use a soft starter or VFD.
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Old 04-23-2018, 02:54 AM
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Quote:
Originally Posted by Crowbob View Post
If you run a Diesel engine under 60% of its capacity for prolonged periods you could experience wet stacking, which is unburned fuel leaking past the cylinders.

Short periods of wet stacking is not too damaging but repeatedly and for prolonged periods your maintenance costs will skyrocket.
Most diesel engines do not run at 60% load.
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Old 04-23-2018, 02:55 AM
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Quote:
Originally Posted by AZ_porschekid View Post
I need a 3 phase, 480v generator to run a deep well pump. The the pump looks like it needs 15 kw ish peak...
So I'm looking at generators. Diesel type. Only thing remotely close to my price range is a 40kw unit.
So the question is; would it be safe to assume with less load the generator will run more efficient (less fuel) then say a smaller 25 kw unit? Also, I would hate to use this generator only to power a pump.

Thanks Guys
Is this backup power, or will it run the pump all the time?
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Old 04-23-2018, 02:57 AM
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Quote:
Originally Posted by red-beard View Post
Is this backup power, or will it run the pump all the time?
It will run the pump only, probably a total of 15 hrs a week.

I guess worst case I'll get wet stacking, and have to change the oil more often... Not bad.
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Last edited by Arizona_928; 04-23-2018 at 06:54 AM..
Old 04-23-2018, 06:50 AM
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That must be one bad mama jama pump. Wow.

My pump is just a 220 1.5 HP pump but it only produces 18 GPM. Enough to water the yard, which is why I put in the well. 3 phase and 480 volt is a serious pump.
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Old 04-23-2018, 09:55 AM
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What is the HP of the pump? A Lima Mac generator is good for starting 1HP WITH 1KW.
Other generators need to be over-sized to get the same motor starting. I do this everyday day with the ag market. A 40KW wouldn't break in properly. Once broken in it would be just fine. Most engines use fuel based on HP load which is 1.5HP to generate 1KW electricity. I have big engines with the same load a smaller one and use about the same amount of fuel
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Last edited by 88-diamondblue; 04-23-2018 at 11:17 AM..
Old 04-23-2018, 11:12 AM
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Quote:
Originally Posted by 88-diamondblue View Post
What is the HP of the pump? A Lima Mac generator is good for starting 1HP WITH 1KW.
Other generators need to be over-sized to get the same motor starting. I do this everyday day with the ag market. A 40KW wouldn't break in properly. Once broken in it would be just fine. Most engines use fuel based on HP load which is 1.5HP to generate 1KW electricity. I have big engines with the same load a smaller one and use about the same amount of fuel
He said it is 3 phase, 480VAC 15kW, so a 20HP pump.
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Old 04-23-2018, 02:09 PM
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Wet stacking comes from not running the engine up to operating temperature. You can run it at 40% capacity if you do it long enough to get it hot.
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Old 04-23-2018, 05:49 PM
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Anyone make anything of this?
The unit produces 480v and assuming 3 phase (even my abb friends want to agree to 3 phase) deawoo engine that is practically new. Zero blow by at 220 hours.
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Last edited by Arizona_928; 04-23-2018 at 05:54 PM..
Old 04-23-2018, 05:50 PM
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Here's the one from the engine
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Old 04-23-2018, 05:53 PM
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The 40kW generator will work fine, assuming you're running all the time. You might be able to go smaller if you install a soft starter on the water pump motor. That generator is only 32kW PRIME, so it might have a soft starter already.
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Old 04-23-2018, 06:04 PM
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well that one is bought and paid for. the seller claimed it was a 40kw.... so 32kw and a soft start and everything will work. I hope! it was only a few grand so nothing too much was invested.
Its starting system is interesting. it has one of these.
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Last edited by Arizona_928; 04-23-2018 at 08:08 PM..
Old 04-23-2018, 08:02 PM
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I didnít know Lucas made generators!
Old 04-24-2018, 12:23 AM
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we have a 100kw on the radar site here at work. the site only loads it down about 20% so the load bank comes on and loads it down to about 60%, about another 40kw.

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Old 04-24-2018, 03:47 AM
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