Air Compressor Conversion

orezok · Aug 30, 2016

SPYDERLK said:
Sounds like a genny speed problem. Low frequency will cause slow running and will heat a motor up. Compounding that with a sticky start winding switch and youve got a smouldering fuze.

I've checked with my Fluke and both gens were on spec for both voltage and Hz. The centrifugal switch moves freely. For some reason, this motor doesn't like generators.

CobyRupert · Aug 30, 2016

Doesn't the CFM of the blow off valve have to be compared to the (worst case//maximum) CFM of the compressor?

(i.e. otherwise can you have a situation where the compressor can continue to supply more air than the valve can exhaust?)

Deere Dude · Aug 30, 2016

CobyRupert said:
Doesn't the CFM of the blow off valve have to be compared to the (worst case//maximum) CFM of the compressor?

(i.e. otherwise can you have a situation where the compressor can continue to supply more air than the valve can exhaust?)

I think you are correct. But it would take a lot of HP to overcome what a relief valve could dump.

I have an air compressor from an old 8 HP John Deere garden tractor. I needed/wanted a gas operated compressor so I took the setup and put a new 5 HP Briggs motor on it. It just runs and pumps and dumps and repeats. It is noisy with the air dumping now and then, but works well.

Mendonsy · Aug 30, 2016

Soundguy said:
9kw genny should have no problem starting and running that motor...

Not necessarily. That motor should be a bit under 3kw running, but the starting current of that motor will be four to six times that much. A 9kw could be too small to start it.

Soundguy · Aug 30, 2016

Mendonsy said:
Not necessarily. That motor should be a bit under 3kw running, but the starting current of that motor will be four to six times that much. A 9kw could be too small to start it.

My pocket chart says a 2hp motor should take approx 2000 running watts. ( less actual ) If you use actual #, that 9kw genny can fully do 6x running watts theoretical. If using the practical #, then it can do 5x.

Not to mention his genny is 9k running 10K+ starting...

Mendonsy · Aug 30, 2016

Soundguy said:
My pocket chart says a 2hp motor should take approx 2000 running watts. ( less actual ) If you use actual #, that 9kw genny can fully do 6x running watts theoretical. If using the practical #, then it can do 5x.

Not to mention his genny is 9k running 10K+ starting...

He says that his motor is rated at 12 amps, 230 volts. That is 2760 watts or 2.76kw. If the starting current is nominally 5x the running current then it draws 13800 watts to start it. All of that agrees with my handy Square D pocket calculator for a 2 hp, 230 volt motor.

orezok · Aug 30, 2016

Let me clarify some more. The gen "starts" the compressor with just a little bog down and the compressor is running at a good speed. What I don't know is if it is running at full RPM or less than 75% at where the start cap kicks out. Too much noise from both machines to tell. I've got the motor apart right now for inspection, but when I get it back together I'll put the Fluke on it and see what the inrush is and for how long.

Soundguy · Aug 31, 2016

Mendonsy said:
He says that his motor is rated at 12 amps, 230 volts. That is 2760 watts or 2.76kw. If the starting current is nominally 5x the running current then it draws 13800 watts to start it. All of that agrees with my handy Square D pocket calculator for a 2 hp, 230 volt motor.

Lot of iffs.

5x is way on the high side.. "if" it is, I think I get a new motor, you can get better ones, vs horrible power hogs.

We start 2hp motors on jobsites with 9k gennies ( the 6.5k gennies would not start the motors )

Maybee the Genny is overhyped and the 9k # is fake sales speak.. Like stated as a peak#. See that all the time, electrical components advertised with generous peak ratings that mean little.

SPYDERLK · Aug 31, 2016

Mendonsy said:
He says that his motor is rated at 12 amps, 230 volts. That is 2760 watts or 2.76kw. If the starting current is nominally 5x the running current then it draws 13800 watts to start it. All of that agrees with my handy Square D pocket calculator for a 2 hp, 230 volt motor.

If motor SF is above 1 that multiple is applied to motor rating