# What size generator would I need to run a 10HP electric motor?



## MrEd (Dec 8, 2009)

Anyone here have any idea what size generator I would need to have installed in order to run a 10HP electric motor ? It only will need to run for a few minutes every hour, one day per week, and the cost of bringing in lines is too expensive so we are looking into the generator route.


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## MrEd (Dec 8, 2009)

Bondo said:
			
		

> Ayuh,...  What are the electrical Requirements for the 10hp motor,..??



I guess that is my question...wouldn't all 10HP motors have the same requirements? This is what I am trying to figure out...


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## stee6043 (Dec 8, 2009)

You could have single phase, three phase, 220V, 480V, etc and so on.  There should be a tag on the motor that tells you what it's setup for.  I'd start there...


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## kenny chaos (Dec 8, 2009)

Probably 2 1/2 - 3 times the size of the motor or 25-30hp generator.


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## dave11 (Dec 8, 2009)

Need to size the voltage and amperage requirements of the motor to the generator. Then decide if the generator can handle the service required in terms of cycle times, etc.


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## pastera (Dec 8, 2009)

10hp is approximately 7500 watts

you will need to oversize to handle startup current  - probably a 15kW minimum if you need to start under load.

look at a variable frequency drive to ramp up/down the speed - this will lower the oversize requirements.

How about using hydraulics instead of electric? 

Aaron


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## MrEd (Dec 8, 2009)

SOunds like I need to get better specs on the motor before I can get a better answer. I know it is single phase, but thats all.


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## TMonter (Dec 8, 2009)

Single phase motors have very high startup current requirements, so be aware of that when sizing.


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## Danno77 (Dec 8, 2009)

the cost of a generator that big rivals the cost to have electrical run. is electric motor your only option? what's it running?


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## Highbeam (Dec 8, 2009)

You can directly convert HP into watts. My HP calculator tells me that 10HP=7456.9987 watts. That's running watts and the startup current will be the bugger.

Note that folks using little tiny 1 HP well pumps report needing no less than a 5000 watt genset even though 1HP = 745.6999 watts. 

A single phase 10HP motor is pretty rare. That motor will suck major amps at startup. You'll be looking at a genset that is typically used to provide backup power to large commercial buildings like schools, chicken farms, dairies, and police stations. Not quite as big as the hospital gensets. Expect it to be powered by a 6 cylinder diesel engine. You'll also need to keep it running all day to provide the few minutes per hour of use. May as well power the plant with it on those days.

The good thing about going that big is that very few crappy gensets are made since they are usually critical equipment. The huge gensets are usually run on a schedule to stay fresh and are maintained by professionals on a schedule. Look for a used genset.


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## EatenByLimestone (Dec 8, 2009)

Can you replace the electric motor with a gas one?  You can probably pull it from a snow blower for horizontal shaft or a riding lawn mower for vertical shaft.  Even if you had to buy new it would be much less expensive.  Since you are only looking at running it for short periods you wouldn't even have to worry about fuel tank capacity.

Matt


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## MrEd (Dec 8, 2009)

It is a motor for a large trash compactor. 

What would be the biggest single-phase electric motor that one could run off of regular residential power service, if nothing else was running?

It'll only run a few times a day, for a few minutes.


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## JustWood (Dec 8, 2009)

The biggest single phase motor you can get I believe is 10 HP. I have never seen one bigger.


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## Highbeam (Dec 8, 2009)

Your normal modern residential power service is 200 amps. I believe that it is 200 amps from each 110 volt leg for 44000 available watts. 

Straight running HP, you could run 59 HP but you need to consider startup surge at 3-5x running wattage so divided by 5 is about a 12HP motor. 

See, this is crap though because my 5HP air compressor motor runs off of a 15 amp 110volt  circuit. Is there a plate on the motor that lists current requirement?


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## peakbagger (Dec 8, 2009)

The starting inrush current is what will do you in. One trick is to switch to a 3 phase motor and run it off a variable speed drive. A 460 volt 3 phase motor is a lot easier to find in that size range and the physical size is smaller as the wires dont need to be as large as the current is lower. If you specify the variable speed drive correctly, you can feed it with 220 volt single phase and have it output 460 volt 3 phase, then set it up to ramp up the current when starting rather than across the line start. The compactor is probably a hydrauilc unit so it wont mind a slow ramp up. This will cut your inrush current way down, so your generator doesnt need to be as large.


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## GVA (Dec 9, 2009)

peakbagger said:
			
		

> The starting inrush current is what will do you in. One trick is to switch to a 3 phase motor and run it off a variable speed drive. A 460 volt 3 phase motor is a lot easier to find in that size range and the physical size is smaller as the wires dont need to be as large as the current is lower. If you specify the variable speed drive correctly, you can feed it with 220 volt single phase and have it output 460 volt 3 phase, then set it up to ramp up the current when starting rather than across the line start. The compactor is probably a hydrauilc unit so it wont mind a slow ramp up. This will cut your inrush current way down, so your generator doesnt need to be as large.


I would agree this is the best route, And have used these before.....
But however, A single to three phase 10hp VFD would be *at least *$400 now add a generator?
IMHO run the lines from the home direct.
Or as someone stated earlier try to put a gas motor on there..


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## seige101 (Dec 9, 2009)

Highbeam said:
			
		

> See, this is crap though because my 5HP air compressor motor runs off of a 15 amp 110volt  circuit. Is there a plate on the motor that lists current requirement?



In the teeny tiny fine print it probably states peak HP. Shop vacs love to pull that little stunt too.


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## EatenByLimestone (Dec 9, 2009)

Maybe I'm off here, but if it's hydraulic, you could run a smaller motor hooked to the pump and have a slower cycle time... 

Matt


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## Gooserider (Dec 9, 2009)

EatenByLimestone said:
			
		

> Maybe I'm off here, but if it's hydraulic, you could run a smaller motor hooked to the pump and have a slower cycle time...
> 
> Matt



In theory, yes, but generally pumps and motors are matched by the manufacturer - so it would take that much of a motor to drive the existing pump...  OTOH, if you replaced BOTH the pump and motor, then you could get a lower gpm pump, and drive it with a smaller motor, at the cost of longer cycle times as you suggested...

Gooserider


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## d.n.f. (Dec 9, 2009)

Standard single phase?
Capacitor-start split phase?
Dual capacitor (capacitor start, capacitor run)?
Permanent capacitor?

All the info will be on the motor name plate.

I know nothing about motors, but I think you want a capacitor start split phase motor due to higher torque loads required in a trash compactor (I think that is what you said it was for).  Torques up to 450% of full load torque and improved power factor during starting.


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