Re: Converter or Inverter for 2hp Bridgeport mill

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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> http://www.metalworking.com/news_servers.html
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> > http://groups.yahoo.com/group/jobshophomeshop I consider this

to

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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
>
>
>
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