# Swichover 240V to 120V ???



## frecku (Jun 2, 2012)

I have been shopping around for an air compressor, since the largest portable 120V models give me a max SCFM of 5.5-5.9 I need to step up to the stationary models but they all use 240V.

It will cost me a fortune to upgrade to a dedicated 240V line. So here is my question, if I purchase a 240V upright model will it be possible to simply purchase a 120V motor from HF and call it done. 

I hand cranked the two cylinder one stage pumps at the store, there is little resistance so the 120V motor should have no problem turning it over.

I know I will have to match the RPM not to burn out the pump, it seems so easy, am I missing something ?


----------



## rhenning (Jul 23, 2011)

The reason that 220 is used is 120 motors will not have enough power to run that big of a compressor. Roger


----------



## frecku (Jun 2, 2012)

The compressor pump turns over by hand really easy and there are some compressors that have motors that can be set to either 120V or 240V ?


----------



## rhenning (Jul 23, 2011)

It will not turn over easy when the tank is near full and is pumping air at speed. The dual voltage compressors are generally in the 3 HP range. I have an older SMC 3 HP I run on 120 volts but it takes a 20 amp curcuit to make it work. When wired to run on 220 it only takes 10 amps. Roger


----------



## frecku (Jun 2, 2012)

Now that makes sense, so presumably a 60G tank with a 240V 3.8HP motor that is rated for a max 155PSI will not be able to reach that max PSI using a comparable 120V motor.

Last scenario, what if I were to bump up the HP on the 120V motor, say to 5 or 6 HP, first do they make them that big and second what kind of Amps do they draw ?


----------



## bernietech (Jan 11, 2012)

On a dual voltage motor (120/240vac) the current on the 120 vac configuration will be double the 240 vac rating. Since the current will be doubled the IR loses will be much higher. the HP of the motor will be the same (minus the IR lose). So the question is what current does the present motor draw at 240 vac? If it can be rewired to 120 vac the current will double. The wire size to supply the motor is determind by the current required to run the motor. ( at 120 vac the wire size is much larger than at 240 vac) 

bernie


----------



## cedgo (Sep 29, 2011)

Question. Why will it cost a fortune for the 240 volts?


----------



## rhenning (Jul 23, 2011)

It will be cheaper than having a big enough 120 volt service put in. Call your local electrictions as prices very a great deal with location. What is a fortune by the way? Roger


----------



## frecku (Jun 2, 2012)

Thanks for all the great advice.


----------

