Re: Converter or Inverter for 2hp Bridgeport mill

Most VFD's have a parameter for setting the drives profile to
constant torque. This setting can draw up to 80% of full motor load
and provides 100% rated torque down to about 10 RPM.The problem now
is that at 10 RPM the motors fans do not provide the cooling required
by an 80% full load condition. Even though this has never caused me
any problems or even any motor heating for brief operation, extended
operation points to a problem. Bridgeport's also have the low range
back gear to handle severe loads at low RPM so a single belt speed of
about 2000 RPM @ 50HZ is what I prefer. This allows for the higher
top end speeds you will wish you had.

Jeff

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "john_glynn57"
<john_glynn57@y...> wrote:

> Thanks Vavaroutsos and Lee,
> My Understanding, at the moment, is this and I should proceed as
> follows:
> 1. The inverter route is the way to go.
> 2. I should setup the inverter to control the forward reverse
> control.
> 3. I should setup the inverter and the Bridgeport to run at the low
> speed of 1400 RPM and the inverter to deliver 1400 RPM at 50Hz.
> 4. I sholud increase the motor speed by increasing the frequency of
> the inverter to >50 to simulate the higher speed of the Bridgeport
> and use the pulleys to actually gain the desired spindle speed at
> the toolcutter end.
> 5. By Carrying out 3&4 I should maintain the normal speed\torque
> curce for the Motor.
>
> Please tell me if I am wrong.
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "vavaroutsos" <pete@v...>
> wrote:
> > If you don't use the variable speed pulley, you are going to

loose

> > spindle power at low RPM. The pulley provides about a 9:1 ratio
> > between slowest/fastest settings. The motor is 4 pole 1800RPM so
> you
> > could probably drive it safely to 3600RPM or a bit more. This

only

> > gives you a 2:1 ratio in the constant HP area of the curve. This
> > means the lower RPM will have to come at lower than 1800RPM which
> > will be in the constant torque area of the curve with diminishing
> HP.
> >
> > ~petev
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lee Studley"
> > <indigo_red@q...> wrote:
> > > In parallel to John's question, I'd like to know about setting
> the
> > > spindle/motor ratio on my varispeed BP also, so that I can
> control
> > > the speed via the VFD. Does anyone have experience doing this?
> Any
> > > caveats?
> > > -Lee
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lee Studley"
> > > <indigo_red@q...> wrote:
> > > > VFD's are great!!
> > > > I think most VFD's have reversing builtin(?). Having a switch
> > > break
> > > > connections from the VFD to the motor doens't sound good to
> me. If
> > > > you want to keep the mechanics of the original Fwd/Rev

switch,

> I
> > > > would suggest wiring it as a switch to control the VFD's
> external
> > > > fwd/rev option if it can be done as an external control.
> > > >
> > > > -Lee JMO-ICBW:-)
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > --- 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.