[TheForge] 15Ton Press

[Darrell]

You are mixing 2 pole/4 pole motors with power supplies. A 2 pole motor has two
separate windings and that is what causes the motor to run at 3600 RPM.
(60cycles per second times 2 = 120) how many times a second the current changes
direction (120 times 60 seconds = 7200) number of changes per minute (7200 / 2
poles= 3600) speed of a 2 pole motor. (7200 / 4 = 1800) speed of a 4 pole motor.
Certain losses cause the actual speed to be closer to 1725 RPM.
Darrell

http://www.machinemaster.com


----- Original Message -----
From: "Jeff Harding" <jharding@kconline.com>
To: <theforge@mailman.qth.net>
Sent: Monday, January 07, 2002 5:41 AM
Subject: Re: [TheForge] 15Ton Press


> Hi All;
>
>    I can't speak to the VFD, I haven't looked into it and I admit to
> being un-informed, BUT, I can speak to "phase" electricity.
>
>    When you have a three phase or even 220V motor it is set up to take
> current from two or three different sources, at the generating
> facility there is at least three dnynamos if they are producing three
> phase.   Each  phase is from a separate alternator and 220 volt, as
> most of us have in our homes, is just voltage/current supply from two
> separate sources,  stepped down to "110" volts each to enter your
> house. ( actual voltage on my lines runs 121-125 , can't complain
> until it's a 10% over voltage, I checked it out, that means 120 +
> 12... at 132, then I can complain.)
>
>    SO... compare it to one guy pushing a car, "in three pieces", he is
> still applying the same force but in three places on the back of the
> car.   NOW... two other guys join him,   still only one guy pushing on
> each spot, but three times the push... that is how I would analogize
> it.
>
>    Make sense?
>
>    Jeff   ><>
>
>    BTW... the same electricians that call 220v "two pole" , will call
> three phase, "four pole".. .they count the neutral when considering
> three live lines and don't count it when, " It's just 220"... In other
> words...Same thing guys, 220v is two live lines from separate
> alternators and a neutral, three poles...  "three phase" is three
> lines from separate alternators and a neutral, four poles.... why they
> do that is maddening to me..
>
>    I'm sure there is some true 4 phase and maybe even higher in some
> large urban industrial areas, but not enough that many have actually
> touched "4 pole"....
>
> > 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
>
>
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