Generator size to start motor

[Cord]

I have an ejector pump with a 2hp 1/230v motor that draws 13.9 amps and has a recommended breaker size of 20 amps. My 3,000 watt, .8pf generator is rated for 16a/240v. Even with no load on the motor, the generator will not start the motor; it instantly goes to overload and shuts down. I understand the inrush needs to of a motor are greater than it's running amps, but this motor is currently unloaded as we're testing it dry. Assuming the motor is wired correctly, what size generator would be needed to start the motor?

 

[coldsteelva]

Potentially 19.9amps, thus a 20amp breaker - do they make a Kill-A-Watt meter that can plug inline and record the max start pull?

EDIT: Can you post or Google the mfr make model

 

[Soundguy]

If the pump reccomends a 20a breaker, then you can bet that it's max draw is no more than about 25ish amps for a very, very, very short time, otherwise the 20a breaker would pop.

I generally like a generator to be RATED for 2X motor RUN for good starts. Now.. the genny should have a higher 'start' number than it's rated number. For instance.. you see a 6500w rated genny that will do 8500 for starts, etc. That';s on good clean motors.

I've seen some old haggard motors that needed 3X run for starting.. seeing fewer and fewer of those nowadays.

 

[buickanddeere]

Doing a hard start upgrade by making the start capacitor 3 to 5 times larger . Depends if the generator had a real voltage regulator or a peice if crap cheapo bridge rectifier .
7500Watt running maybe able to limp it over but I would go with this.8W/1W Dual Fuel Generator, 459cc - Champion Power Equipment

 

[buickanddeere]

Just because a 2X larger generator usually limps the motor up to speed , after several seconds of wide open governors, dim lights from low voltage and 10 seconds up to speed instead of 2 seconds, doesn't mean you should .
Generators are cheap now compared to the 1999 Y2K prices. Buy what is needed instead of barely enough.
I'll look at the code book but iirc that 20 FLA motor requires a 30 amp breaker and at least 12 gauge wire .

 

[buickanddeere]

Most of the time when something gets broken, burned out or wrecked . The operator was trying to make do with something too small doing too large of a task. 92W/115W Electric Start Portable Generator, 459cc - Champion Power Equipment

 

[Cord]

I attached a cut sheet for the pump. Remember, at this time I'm only trying to start this with no load so I can prove it's functional to the inspector.

The generator that I initially tried to test it on was a MEP-831a. It's a very nice inverter unit, but it's very sensitive to an overload.

For testing, I have a 6,500 cont / 7500 surge generator reserved from a rental house. I wanted a 10k unit, but it wasn't available. I'm concerned the 6.5k won't be enough.

The permanent generator will be a Onan DJB 6k diesel unit.

 

[HarryVanderpool]

We have a 2hp submersible 300' down our well. 230v
In 1994 we bought a bare-bones Generac 5000 watt generator.
When we have extended power outages, which we have had many,sometimes 3 and 4 days, we run the generator 3 hours in the morning and 4 in the evening.
When the well kicks on, the generator lets out a momentary bark and runs very smoothly.
No problems with this set-up in 23 years. Never even changed the spark plug.
Yearly filled with stabilized gas and always turn the valve off and run the carb dry prior to storage.
ALWAYS starts on the first pull.
We never run it unless a power outage.

 

[buickanddeere]

Depends what other loads the 6Kw diesel is carrying when the 2HP pump starts . I have started a 3/4HP 240V deep well pump with a 5000 watt Honda and it's plenty for that generator. A 2HP deep well start on 5000watt will be very slow and at brownout voltage if it starts at all. Sure that isn't a 1/2HP instead of 2HP ?

 

[HarryVanderpool]

1/2hp 300' down would be a very bad idea; don't you think?

 

[Soundguy]

Just because a 2X larger generator usually limps the motor up to speed , after several seconds of wide open governors, dim lights from low voltage and 10 seconds up to speed instead of 2 seconds, doesn't mean you should .
Generators are cheap now compared to the 1999 Y2K prices. Buy what is needed instead of barely enough.
I'll look at the code book but iirc that 20 FLA motor requires a 30 amp breaker and at least 12 gauge wire .

I think you are making a blanket assumption. A 2x rated genny doesn't automatically mean a motor is going to limp up to speed and cause dim lights etc.

Size the genny to correctly HANDLE the starting load of the motor you want to use and be done with it.

Not every motor load is the same, not all motors are created equal.. We have a 5500/6500 genny at work that won't start a 2hp submersable pump, but will start and run a 2hp belted motor that is running some industrial equipment without even a thought.

 

[buickanddeere]

Low flow , just wondering how he is managing to get a 2HP pump rolling with a 5000watt generator. Just the 3/4HP pump bogs my Honda 5000 with low voltage and low frequency for approx 3 seconds even when the governor has the throttle blade wide open.

 

[Soundguy]

I think alot of it has to do with the motor and stored kinetic energy, and HP available.

Ideally, a generator head should be matched to an engine that can drive the generator head at it's full overload rating, with -0- hit on the engine... But that's not the case. Builders today put an engine on a genny head that is just barely able to make rated power, and really takes an rpm hit on the overload rating.

Some years back I was over at a buddies farm doing some cleanup mowing on some fields he let go. He was trying to sell the place and needed to do some fence work and mow down the weeds. He had a small ford tractor that was basically just a big lawnmower. He had an 8KW pto generator.

I was mowing with my old ford 5000 and afterwards, we drove around to do some fencing. he had a pancake compressor and an air nailer and a stick welder all strapped to a palate on a carryall that his pto generator was hooked to. The pancake compressor would kick on as needed as we nailed. circular saw didn't seem to do much either. Come to a point and we need to do some gate welding, and that tractor just would not carry that generator while I was striking an arc. We pull my 5000 over and hook it up, and I could strike and weld to my hearts content. engine sound didn't even change striking an arc.

What was the difference? about 50 horse power...

The kinetic rotation mass of the larger tractors engine and pto drivetrain dwarfed the smaller tractors setup. When a big electrical load was applied to the genny, it applied a large kinetic load to the tractor. The tractor / engine didn't have enough mass to push thru, and the governor had to kick in and build the rpms back up. vs having so much flywheel power built up in the form of big rotating parts, that the kinetic load from the genny was absorbed before the governor had to do very much.

Now.. using a 70 hp tractor on a 8kw generator is total overkill and not needed... but.. it illustrates the point well. an old tired 20 hp tractor had a hard time with 8kw.. and old tired 70 hp tractor that weighed 4x as muchg didn't.

I've seen some small generators these days that are basically using weed eater engines. what kinetic reserve do these engines the size of a grapefruit have? ( none )

 

[CobyRupert]

Can this genny start this motor?

It's a complex question.
- Are there other loads being run on genny, if so starting order can be important. (i.e. you may have to start motor before others)
- Characteristics of genny's coil come into play. How easily saturated?
- Starting characteristics of electric motor come into play (Is inrush 3 x full load amps (FLA), 6 times, 8 times, 13 times?). High efficiency motor? Torque speed characteristics?
-Load characteristics come into play. Is load variable torque load like a fan or a pump, where it take almost zero torque to start, or does it require a greater starting torque from the get go like a crusher?
-Genny's engine & motor's combined flywheel effect?
-Genny engine's governor response characteristics (fast/slow?) come into play, as combined with:
-Genny's engine's speed -torque characteristics (powerband) come into play. Many factors, including fuel type (e.g. gas, diesel, or natural gas motor) will alter how a (say) 20 hp motor responds to a sharp increase in load.

 

[HarryVanderpool]

Low flow , just wondering how he is managing to get a 2HP pump rolling with a 5000watt generator. Just the 3/4HP pump bogs my Honda 5000 with low voltage and low frequency for approx 3 seconds even when the governor has the throttle blade wide open.

First of all, my generator is not a Honda.
It is a bare bones Generac with a 10hp Tecumseh.
Got it on sale at Home Depot in 1994 for under $500
It not only starts and runs the pump, but appears to do so easily.
When the well kicks on there is an about 1/2 second grunt and then it runs much the same. When the pump turns off there is a tiny change in tone.
No big deal.

 

[HarryVanderpool]

One thing I often think about in these discussions is having only as much generator as one needs.
We run our generator for 3 hours in the morning and 4 in the evening.
It takes care of all of our needs.
Still, you are looking at about 4 gallons or more each day.
The longest we have ever been out of power was 4 days.
What if it was 2 or 3 weeks? How much fuel does one have on hand?
Then add to that, people want their generator to run 24 hours daily!!????
YIKES!!!

Along with owning a generator, We have a procedure.
First, we burn wood in the winter so heat is not an issue.
When there is an outage and it appears to be serious, we place 2, 4 gallon buckets of water in each bathroom for flushing toilets.
So when the generator is off, our system holds pressure for all of our uses until the next run.
We shower when the generator is running.

Also, there is always talk about generators that provide clean power for electronics.
I can guarantee you that mine is not one of them!!
Yet, we always watch TV in the evening and have never had a problem.
Our computer is on a UPS so it doesn't matter how dirty the juice is.

So, I'm not just blabbing away. I have 23 years of experience with this set-up and have no complaints.

 

[bigdeano]

My 10kw generator would start and run my 3hp submersible pump where I used to live. It won't even budge the 5hp motor on my air compressor even though there's no load at startup.