Re: [CAD_CAM_EDM_DRO] Re: Converter or Inverter for 2hp Bridgeport mill

To: CAD_CAM_EDM_DRO@yahoogroups.com
From: "vavaroutsos" <pete@...>
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:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
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> Addresses:
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> 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
>
>
>
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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



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