Re: Converter or Inverter for 2hp Bridgeport mill - OT?

I don't pretend to be an expert on generators either, but I remember
seeing steam engine plants from the late 1800's whch had a small
generator hooked up to supply EMF to the coils of a much larger
generator (or maybe dynamo, foret whether it was for AC or DC).

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "vavaroutsos" <pete@v...>
wrote:

> Bob, I'm no expert on generators, but I don't think many

generators

> are built like an induction motor. My guess is generator rotors
> either have permanent magnets or coils with slip rings.
>
> While it's true that over speeding an induction motor will

generate

> power, it only works because there is a field in the stator to

induce

> current in the rotor. I don't know how you would start a generator
> like this unless there was enough residual magnetism in the rotor.
>
> ~petev
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bob McKnight"
> <bobmcknight@c...> wrote:
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > From: "vavaroutsos" <pete@v...>
> > Date sent: Mon, 05 Jan 2004 00:42:44 -0000
> > Subject: [CAD_CAM_EDM_DRO] Re: Converter or
> > Inverter for 2hp Bridgeport mill
> > Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
> >
> > petev
> >
> > OK
> > Let me explain where I am coming from and I sure never got this
> > out of a text book. Generators are Motors and Motors are
> Generators.
> >
> > I question this with some of the static motors, but it is from

lack

> of
> > knowledge, not misinformation.
> >
> > I have been told and again never checked it out that if you over
> > speed an induction motor it will become a generator. I kinda
> bought
> > this based on residual magnetism.
> >
> > So your explaination makes sense because I would be operating in
> > the middle of the area between motor and generator which would
> > no current flowing or no energy applied. Except I figured I
> would
> > be supplying a little energy, but I figured I was supplying

energy

> to
> > overcome mainly friction forces, but I can see that is not the
> case.
> >
> > I am at the stage I was many years ago with pumps. I thought

that

> > shutting off the flow of water would make the pump work harder

(true

> > for piston pumps). But in centrifugal pumps.either air or

water,

> > throttling the input reduces current flow. I learned this the

hard

> way.
> > I took a blower unit out of a furnace and ran it just as a vent

fan

> in
> > the shop. It burned up. Fortunately I had more and shut off
> almost
> > all the air on the side opposite the motor to get the current

down

> > where it belonged.
> > Which brings up another question. Most convertors are used to
> > run motors. I am using this to run large a large welding
> transformer.
> > See any problems with the weak leg. The local power company
> > can supply 3 phase for a price and it will have a weak leg.
> >
> > Bob McKnight
> >
> > [ Double-click this line for list subscription options ]
> >
> > Bob, I assume you are using an induction motor? If so, the

magnetic

> > field in the rotor is caused by the slippage. If the rotor is
> turning
> > at the same speed as the stator magnetic field, it does not see a
> > moving field and no currents will be induced. Without a magnetic
> field
> > in the rotor, you won't get any voltage on your generated leg.

If

> you
> > don't beleive me try just spinning the motor with no windings
> > connected. No voltage will be generated because there is no

field in

> > the rotor.
> >
> > When an induction motor is loaded, more slippage occurs. This
> creates
> > more current in the rotor and a stronger magnetic field. This in
> turn
> > balances the force of the load on the rotor.
> >
> > ~petev
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bob McKnight"
> > <bobmcknight@c...> wrote:
> > > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > > From: "vavaroutsos" <pete@v...>
> > > Date sent: Sun, 04 Jan 2004 18:33:33 -0000
> > > Subject: [CAD_CAM_EDM_DRO] Re: Converter or
> > > Inverter for 2hp Bridgeport mill
> > > Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
> > >
> > > Petev
> > >
> > > It started out that way. The motor I am using is a 15 HP unit.
> > > After looking at the voltage differences and the phasing, I

got

> the
> > > idea that some of that may be caused by the slippage from
> > > synchronous. So, since I was going to use a motor to start the
> > > convertor, I decided to try to eliminate the slippage. I have
> asked
> > > around and even my EE friends don't know. I thought somebody

here

> > > might know, if not, I will just plug along.
> > >
> > > Thanks
> > > Bob McKnight
> > > [ Double-click this line for list subscription options ]
> > >
> > > Bob, what are you using the small motor for? Is this just to
> start
> > the
> > > rotary converter? Why don't you just add a start capacitor and
> > > potential relay. If you're building a small unit, you could

use a

> > > Supco SPP-8E hard start available from www.grainger.com

(4MG78).

> > >
> > > If you use run caps to both single phase legs and a good motor

you

> > > should get a nice generated leg. My generated leg varies about

10V

> > > from no load to full load and the phase angle is pretty good.
> > >
> > > ~petev
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bob McKnight"
> > > <bobmcknight@c...> wrote:
> > > > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > > > From: "ibewgypsie" <ibewgypsie@h...>
> > > > Date sent: Sun, 04 Jan 2004 06:50:28 -0000
> > > > Subject: [CAD_CAM_EDM_DRO] Re: Converter or
> > > > Inverter for 2hp Bridgeport mill
> > > > Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
> > > >
> > > > Hi
> > > >
> > > > am new to the group, so hope this is appropriate.
> > > > The Home Shop Machinist just completed a series on

rebuilding

> the
> > > > Bridgeport. I am building a rotary converter and wonder if
> anybody
> > > > knows if turning the rotary transformer at synchronous speed
> would
> > > > help even out the current available from each leg. I have a
> small
> > > > motor with a mechanical variable speed drive that I am
> attaching
> > to
> > > > the old motor that is the heart of the machine. Also have
> > > > capacitors to help 'tune' the system.
> > > >
> > > > Bob McKnight
> > > > [ Double-click this line for list subscription options ]
> > > >
> > > > I used a toshiba single phase in, 3 phase out inverter. I

used

> the
> > > > bridgeport relay to turn on with dry contacts, left the
> overload
> > in
> > > > place (overkill since inverter monitors too). I gutted the

cnc

> > > drives
> > > > and upgraded at that time too thou. Inverter works great.
> > > >
> > > > My phase convertor made the head rattle, inverter is much
> > smoother.
> > > > Money well spent. I have my machine on a 30 amp 220 single

phase

> > > > circuit now. Like I said I upgraded the cnc drives too. The

3

> > phase
> > > > cnc drive transformer had to go.
> > > >
> > > > David Cofer
> > > >
> > > >
> > > >
> > > >
> > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "john_glynn57"
> > > > <john_glynn57@y...> wrote:
> > > > > I have just taken delivery of my own Bridgeport mill and

want

> to
> > > > > know which is the best option for powering the machine :

an

> > > inverter
> > > > > or a converter. My research to date suggests that a

Hitachi

> L100
> > > > > inverter is the way to go however I want to question this

as

> > > > > follows: 1. I can run a dedicated 20A or 30A supply to the
> > machine
> > > > > which should be able to handle the startup current demand

of a

> > > > > converter. 2. If I use a converter I can use all the

original

> > > > > Bridgeport systems without mosification ie Bridgeport speed
> > > > > control,forward and reverse,3phase coolant pump and

shaping

> unit
> > > > > which is attached to the machine.
> > > > >
> > > > > My plan is to circumvent the original Bridgeport wiring

and

> > drive
> > > > > the Main motor(s) directly from the hitachi unit and

setting

> the
> > > > > motor speed at the low speed of 1400 and not using the
> valiable
> > > > > speed control of the machine at all. The hitachi will give

me

> > > speed
> > > > > control by varying the frequency however I do intend to

use

> the
> > > > > original forward reverse switch. In addition I plan to
> replace
> > the
> > > > > coolant motor with a single phase model.
> > > > >
> > > > > Am I doing the right thing.
> > > >
> > > >
> > > >
> > > > Addresses:
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> > > > wanliker@a...,
> > > > timg@k... Moderator: pentam@c...
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> > > > OFF Topic POSTS: General Machining
> > > > If you wish to post on unlimited OT subjects goto:
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to

> > > reach
> > > > it if you have trouble.
> > > http://www.metalworking.com/news_servers.html
> > > >
> > > > http://groups.yahoo.com/group/jobshophomeshop I consider

this

> > to
> > > be
> > > > a sister site to the CCED group, as many of the same members

are

> > > > there, for OT subjects, that are not allowed on the CCED

list.

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> > > >
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> > > OFF Topic POSTS: General Machining
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to

> > reach
> > > it if you have trouble.
> > http://www.metalworking.com/news_servers.html
> > >
> > > http://groups.yahoo.com/group/jobshophomeshop I consider

this

> to
> > be
> > > a sister site to the CCED group, as many of the same members

are

> > > there, for OT subjects, that are not allowed on the CCED list.
> > >
> > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC
> > > DOMAIN BY POSTING
> > > THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
> > > EXCEPTIONS........
> > > bill List Mom List Owner
> > >
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > > To visit your group on the web, go to:
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> > >
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> >
> >
> > Addresses:
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> > wanliker@a...,
> > timg@k... Moderator: pentam@c...
> > indigo_red@q... davemucha@j... [Moderators] URL to
> > this
> > group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> > aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> reach
> > it if you have trouble.
> http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this

to

> be
> > a sister site to the CCED group, as many of the same members are
> > there, for OT subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC
> > DOMAIN BY POSTING
> > THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
> > EXCEPTIONS........
> > bill List Mom List Owner
> >
> >
> >
> > Yahoo! Groups Links
> >
> > To visit your group on the web, go to:
> > http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
> >
> > To unsubscribe from this group, send an email to:
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