[TheForge] 15Ton Press

[Ed Fasula]

Hi Steve,
The reason is that a 5hp 3600 rpm motor is a 2-pole and the 3 hp is a 4-pole.

Now I could stop there and maybe sound smart, but I'll go on to say that I 
don't really understand it.   It' what the guy said.  I guess the 4 points 
give you more field for your current but i dunno.  :^)

It sure sounds like gettin' something for nothing to me too, but I talked 
with a good chief electrician and a motor repair shop I've worked with for 
a long time and they both thought there is some truth to it, but they 
weren't really sure how far you could push it.  The guy who wants to sell 
the VFD says they do it all the time with the farmers.  He guarantees it'll 
work or he'll take the VFD back.  Anyway, if I go that way I'll get a VFD 
that can handle a 5hp motor just incase.  If I fry one of the two 3hp 
motors I got for free, I'll chalk it up to cheap tuition.

Ed

At 09:44 PM 1/6/02 -0700, you wrote:
>Ed, I don't see any way that a VFD will convert a 3HP motor into a 5HP motor.
>What you said below is correct; "the motor's output torque will meet or 
>exceed a
>5hp 3600 rpm motor to satisfy the demand of the pump". The problem with it is
>that when you are pulling 5HP out of the motor shaft, you will also be pulling
>5HP worth of current in the windings. The windings are only sized for 3HP, and
>you will fry them pretty quick. Am I missing something here?
>
>VFD's are nice (well, the only way)  if you want to vary the speed of an AC
>motor.
>
>Steve
>
>Ed Fasula wrote:
>
> > Hi Steve,
> >
> > I think it kinda cool that if I start out with an 1800 rpm 3hp motor and
> > use the VFD to double the speed to 3600, the motor's output torque will
> > meet or exceed a 5hp 3600 rpm motor to satisfy the demand of the pump.  (I
> > only need 2.5hp to run at 1800 so 5hp will handle double the hp of the pump
> > at 1800.)  The local motor repair place does it often.  I can get a 5hp VFD
> > factory refurbished for the same price as a new 3hp VFD (about $360).  So
> > I'll start with one of the 3hp motors I got and if that's not kosher for
> > whatever reason I'll scrounge or buy a used 5hp for $80.
> >
> > The other option would be to make a phase converter and run a 3hp motor I
> > have.  Say $80 for the extra motor plus $70 for the phase converter
> > electronics (I think - correct me if I'm wrong).  So I'm paying $210 for
> > the ability to run the wood splitter and tune-in the speed of my press.  I
> > also have thoughts about wiring a switch in that would allow me to use the
> > VFD to run the power hammer motor.  I've always wanted to play with the rpm
> > of that thing.
> >
> > All in all, I don't know if it's wise or not, but it seems worth the
> > experience and possible benefits.  If I don't have to do anything exotic
> > with my cylinder porting I'm getting off pretty cheap on this press so the
> > extra $210 doesn't make me whine to much.
> >
> > Ed
> >
> > >If you double the speed, you also double the HP required out of the motor.
> > >I don't
> > >know if this is a wise idea.
> > >
> > >Steve
> > >
> > >Ed Fasula wrote:
> > >
> > > > Hi Steve,
> > > > I'm thinking that I'd like the variable speed so that I can double 
> speed
> > > > the motor for splitting wood or if I want to go quicker.  Thanks tho.
> > > >
> > > > Ed
> >
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