Generator

[backyardsugarer]

How big of a generator (watts) will I need to run a 3 horse electric Motor. The motor says 17.5 amps and 35 amps. I am assuming that is 17.5 amps if wired 220 or is that start up amps and running amps? I am an electrical infant and would appreciate any help. From what I have read a 5000 watt generator should be ok? Thanks

Chris

[mapleman3]

Chris if it says LRA 35amps... thats locked rotor amps(startup from a dead stop)

RLA is run load amps.. normal running.... then they may have Full load amps... as it runs under a full load.

I would think the 17.5 is 220v a 5000w gen should run that no problem just start without a load on it.

[Acer]

edited post for content

[brookledge]

5000 watts/240Volts=20.83 Amps
5000 watts/120volts=41.66Amps
I doubt that your generator has a 120V 35 Amp outlet so you will need to use the 240 20Amp plug.
Keith

[maplehound]

My 5000watt generator has a hard time starting a 3 hp pump even though it is wired 220. I have had to stay with a 1 1/2 hp pump.

[Homestead Maple]

Generator sizing becomes more difficult when electric motors are involved, due to their large starting demand. Typically, there are two motor styles: CODE G requires 3 times running watts to start, and CODE L requires 5 to 6 times running watts to start. Check your efficiency number on the motor tag. Could be 75%, 80%, or even higher and this needs to be factored in when sizing your generator. Some charts show that you may need an 8,000 watt generator to start a 3hp motor.

Sizing a generator for single phase motor starting LRA : The formula is: Motor HP x KVA per HP x (1000 / Motor Voltage) = LRA.

Example: A 3/4 HP, Code L motor connected to 240 Volts, requires what LRA? Always use the largest KVA/HP number, so select 9.9. The formula becomes: .75 x 9.9 x (1000/240) = 7.425x4.167 = 30.9 = 31 LRA. The generator must produce 31 Amps at 240 Volts, to safely start this motor. Multiply 31 amps x 240 Volts = 7400 Watts or 7.5 KW generator size.
What code is your motor, what is the efficiency, single phase operation or three phase, 110v, or 220v operation?

[backyardsugarer]

WOW, I will check that and get back to you tomorrow. I was hoping to get away with 5500 watts or so but this could be worse than I thought.

[white mt]

Thats alot of good information bill. I have had the same questions.thanks

[Jim Brown]

Gentlemen; I have a 5000watt we us in the small bush to run our vac pumps.It is turning a 3hp motor. I think the key is (and I stress) I'm No ELECTRICIAN. That you need a start capasitor(spelling) to start the larger motors. Ours spins right over. Last season the pump motor would not start would just kick out the 20 amp breaker on the gen. A friend said we needed a new start capasitor(spelling again). Found a new one put it on and away she went. no problems
Just our two cents!

Jim

[backyardsugarer]

RPM 1730 Phase 1 Class B Code K Volts 115/230 Amps 35 17.5
Type cs 60 HZ.

So what does all that mean?

Thanks,

Chris